TY - JOUR A1 - Müller, Jan Peter A1 - Dell'Avvocato, G. A1 - Krankenhagen, Rainer T1 - Assessing overload-induced delaminations in glass fiber reinforced polymers by its geometry and thermal resistance N2 - The one-dimensional thermal quadrupole method is used to evaluate a pulsed thermography measurement at delaminations in a glass-fiber reinforced plastic plate quantitatively. The large-scale delaminations have been induced by tension overload and are air-filled and are usually located at the same depth as the notch bottom of a notch on the rear side. While classical evaluation methods like pulsed phase thermography and thermal Signal reconstruction are focused on the delamination depth only, the thermal quadrupole method determines spatially resolved two parameters for delaminations, delamination depth and local thermal resistance. Interestingly, lateral heat flows do not disturb this kind of depth evaluation. KW - Pulsed thermography KW - Delamination KW - Debond KW - Composite materials PY - 2020 DO - https://doi.org/10.1016/j.ndteint.2020.102309 VL - 116 SP - 102309 PB - Elsevier Ltd. AN - OPUS4-50937 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ahmadi, Samim A1 - Burgholzer, P. A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias T1 - Super resolution laser line scanning thermography N2 - In this paper we propose super resolution measurement and post-processing strategies that can be applied in thermography using laser line scanning. The implementation of these techniques facilitates the separation of two closely spaced defects and avoids the expected deterioration of spatial resolution due to heat diffusion. The experimental studies were performed using a high-power laser as heat source in combination with pulsed thermography measurements (step scanning) or with continuous heating measurements (continuous scanning). Our work shows that laser line step scanning as well as continuous scanning both can be used within our developed super resolution (SR) techniques. Our SR techniques make use of a compressed sensing based algorithm in post- processing, the so-called iterative joint sparsity (IJOSP) approach. The IJOSP method benefits from both - the sparse nature of defects in space as well as from the similarity of each measurement. In addition, we show further methods to improve the reconstruction quality e.g. by simple manipulations in thermal image processing such as by considering the effect of the scanning motion or by using different optimization algorithms within the IJOSP approach. These super resolution image processing methods are discussed so that the advantages and disadvantages of each method can be extracted. Our contribution thus provides new approaches for the implementation of super resolution techniques in laser line scanning thermography and informs about which experimental and post-processing parameters should be chosen to better separate two closely spaced defects. KW - Super resolution KW - Laser thermography KW - Compressed sensing KW - Laser scanning KW - Joint sparsity PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-509796 DO - https://doi.org/10.1016/j.optlaseng.2020.106279 SN - 0143-8166 VL - 134 SP - 106279 PB - Elsevier Ltd. AN - OPUS4-50979 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Thummerer, G. A1 - Mayr, G. A1 - Hirsch, Philipp Daniel A1 - Ziegler, Mathias A1 - Burgholzer, P. T1 - Photothermal Image Reconstruction in Opaque Media with Virtual Wave Backpropagation N2 - Thermographic reconstruction of defects that lie in the bulk of a sample is a difficult task because entropy production during heat diffusion leads to information loss. To reconstruct defects one has to solve an inverse heat conduction problem. The quality of the reconstruction is closely related to the information content of the observed data set that is reflected by the decreasing ability to spatially resolve a defect with growing defect depth. In this work we show a 2D reconstruction of rectangular slots with different width-to-depth ratios in a metallic sample. For this purpose, we apply the virtual wave concept and incorporate positivity and sparsity as prior information to overcome the diffusion-based information loss partially. The reconstruction is based on simulated and experimental pulse thermography data. In the first reconstruction step, we compute a virtual wave field from the surface temperature data. This allows us, in the second step, to use ultrasonic backpropagation methods for image reconstruction. KW - Virtual wave concept KW - Thermography KW - Photothermal Technique KW - Image reconstruction PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-506166 DO - https://doi.org/10.1016/j.ndteint.2020.102239 VL - 112 SP - 102239 PB - Elsevier Ltd. CY - Netherlands AN - OPUS4-50616 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ahmadi, Samim A1 - Burgholzer, P. A1 - Mayr, G. A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias T1 - Photothermal super resolution imaging: A comparison of different thermographic reconstruction techniques N2 - This paper presents different super resolution reconstruction techniques to overcome the spatial resolution limits in thermography. Pseudo-random blind structured illumination from a onedimensional laser array is used as heat source for super resolution thermography. Pulsed thermography measurements using an infrared camera with a high frame rate sampling lead to a huge amount of data. To handle this large data set, thermographic reconstruction techniques are an essential step of the overall reconstruction process. Four different thermographic reconstruction techniques are analyzed based on the Fourier transform amplitude, principal component analysis, virtual wave reconstruction and the maximum thermogram. The application of those methods results in a sparse basis representation of the measured data and serves as input for a compressed sensing based algorithm called iterative joint sparsity (IJOSP). Since the thermographic reconstruction techniques have a high influence on the result of the IJOSP algorithm, this paper Highlights their Advantages and disadvantages. KW - Super resolution KW - Compressed sensing KW - Laser thermography KW - Virtual wave KW - Defect reconstruction PY - 2020 DO - https://doi.org/10.1016/j.ndteint.2020.102228 VL - 111 SP - 2228 PB - Elsevier Ltd. CY - Netherlands AN - OPUS4-50419 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ahmadi, Samim A1 - Hirsch, Philipp Daniel A1 - Lecompagnon, Julien A1 - Hassenstein, Christian A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias T1 - New techniques in super resolution photothermal imaging for nondestructive testing N2 - In this work we focus on our most recent studies to super resolution (SR) laser thermography. The goal of SR nondestructive testing methods is to facilitate the separation of closely spaced defects. We explain how to combine laser scanning with SR techniques. It can be shown that stepwise as well as continuous scanning techniques are applicable. Finally, we discuss the effect of experimental parameters and im-age processing techniques to find the optimal SR technique which leads to the highest reconstruction quality within laser thermography. T2 - SMSI 2020 Conference CY - Online meeting DA - 22.06.2020 KW - Super resolution KW - Laser thermography KW - Nondestructive testing KW - Laser scanning KW - Photothermal imaging PY - 2020 DO - https://doi.org/10.5162/SMSI2020/C4.1 SP - 169 EP - 170 AN - OPUS4-50895 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ziegler, Mathias A1 - Ahmadi, Samim A1 - Hirsch, Philipp Daniel A1 - Lecompagnon, Julien A1 - Hassenstein, Christian A1 - Thiel, Erik A1 - Pech May, Nelson Wilbur T1 - Using spatial and temporal shaping of laser-induced diffuse thermal wave fields in thermography N2 - The diffuse nature of thermal waves is a fun-damental limitation in thermographic nonde-structive testing. In our studies we investigated different approaches by shaping the thermal wave fields which result from heating. We have used high-power laser sources to heat metallic samples. Using these spatial and temporal shaping techniques leads to a higher detection sensitivity in our measurements with the infra-red camera. In this contribution we show our implementation of shaping laser-induced diffuse thermal wave fields and the effect on the defect reconstruction quality. T2 - SMSI 2020 Conference CY - Online meeting DA - 22.06.2020 KW - Thermal wave KW - Diffusion KW - High-power laser KW - Thermography KW - Spatiotemporal shaping PY - 2020 DO - https://doi.org/10.5162/SMSI2020/C5.1 SP - 179 EP - 180 AN - OPUS4-50897 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Puthiyaveettil, N. A1 - Thomas, K. R. A1 - Myrach, Philipp A1 - Ziegler, Mathias A1 - Rajagopal, P. A1 - Balasubramaniamam, K. T1 - Defect detection in steel bars up to 600 °C using laser line thermography N2 - Crack detection in steel bars at high surface temperatures is a critical problem in any manufacturing industry. Surface breaking cracks are the major problems during the billet casting. Many NDT techniques are proven its capability in crack detection at room temperature. Here, we are demonstrating the possibility of exposure of cracks using laser line thermography at higher surface temperatures (up to 600 °C). A continuous-wave (CW) laser is used to excite the sample kept at higher surface temperatures. The temperature distribution over the sample due to the laser line scanning is captured using a temperature calibrated infrared (IR) thermal camera. The response of the sample temperature in crack detection is investigated using a validated FE model. The impact of the oxide layer in crack detection is investigated by using two types of samples; one without any oxide layer and the second is with the oxide layer. The influence of laser power in the detection of defects at high temperatures is studied. 3D numerical models were developed for the cases; when the sample is with oxide layer and without any oxide layer for a better understanding of physics. The surface temperature rise due to laser heating is higher for the scaled sample compared to the no-scale sample. The presence of the oxide layer above the parent metal will reduce the reflectivity of the surface. Lower reflectivity will lead to increased absorption of incident energy so that the surface temperature rise will be higher than the surface with no scale. Thermal contrast linearly depends on laser power, which means higher laser power will increase the defect detectability even at a higher surface temperature. KW - Laser thermography KW - High temperature KW - Modeling KW - Surface cracks KW - Non-destructive testing PY - 2020 DO - https://doi.org/10.1016/j.infrared.2020.103565 SN - 1350-4495 VL - 111 SP - 103565 PB - Elsevier B.V. AN - OPUS4-51573 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Oster, Simon A1 - Mann, S. A1 - Sharma, R. A1 - Reisgen, U. T1 - In-situ Identifikation der Schweißnahtgeometrie bei der Anwendung von MSG-Schweißprozessen N2 - Lichtbogenbasierte Schweißverfahren wie das Metallschutzgasschweißen (MSG) zählen zu den Standardverfahren der Fügetechnik und werden in vielen Industriebereichen automatisiert unter Verwendung von Industrierobotern eingesetzt. Dabei können Schweißnahtabweichungen auftreten, die aus Änderungen der Prozessrandbedingungen und der hohen Prozessdynamik resultieren. Hier ist die Kontrolle von Schmelzbad- und Schweißnahtgeometrie für die Sicherung der Nahtqualität bedeutsam. Durch den Einsatz optischer Sensorsysteme können mit hoher zeitlicher Auflösung in-situ Informationen des Prozesszustands ermittelt werden. Dabei stellen die rauen Prozessbedingungen und die hohe Strahlungsintensität des Lichtbogens eine Herausforderung für die optischen Komponenten dar. Forschungsarbeiten am Institut für Schweißtechnik und Fügetechnik der RWTH Aachen haben gezeigt, dass durch den Einsatz einer HDR-Kamera in Kombination mit einer strukturierten Laserbelichtung gezielt geometrische Informationen des Lichtbogens und des Schmelzbads aus den Prozessaufnahmen gewonnen werden können. In dieser Arbeit wird eine parallele Schweißnaht- und Schmelzbadbeobachtung durchgeführt, wobei geometrische Informationen durch die Anwendung von Bildverarbeitungsalgorithmen extrahiert werden. Dabei wird ein nachlaufendes Sensorsystem eingesetzt, welches aus einer HDR-Kamera und einer Laserbeleuchtung besteht. Es werden diffraktive optische Elemente (DOE) zur Erzeugung von verschiedenen Laserprojektionsmustern verwendet, um sowohl eine unidirektionale als auch eine multidirektionale Prozessbeobachtung durchführen zu können. Aus den geometrischen Informationen werden Kenngrößen berechnet, anhand derer der Prozesszustand beurteilt werden kann. Es zeigt sich, dass anhand der Kenngrößenverläufe Abweichungen in der Schweiß- und Schmelzbadgeometrie und Positionierungsfehler des Roboters identifiziert werden können. T2 - Große Schweißtechnische Tagung - DVS CAMPUS CY - Online meeting DA - 14.09.2020 KW - Schweißnahtgeometrie KW - MSG-Schweißen KW - In-situ Monitoring KW - Schmelzbadbeobachtung PY - 2020 SN - 978-3-96144-098-6 VL - 365 SP - 41 EP - 47 PB - DVS Media GmbH CY - Düsseldorf AN - OPUS4-51576 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Oster, Simon T1 - In-situ Identifikation der Schweißnahtgeometrie bei der Anwendung von MSG-Schweißprozessen N2 - Lichtbogenbasierte Schweißverfahren wie das Metallschutzgasschweißen (MSG) zählen zu den Standardverfahren der Fügetechnik und werden in vielen Industriebereichen automatisiert unter Verwendung von Industrierobotern eingesetzt. Dabei können Schweißnahtabweichungen auftreten, die aus Änderungen der Prozessrandbedingungen und der hohen Prozessdynamik resultieren. Hier ist die Kontrolle von Schmelzbad- und Schweißnahtgeometrie für die Sicherung der Nahtqualität bedeutsam. Durch den Einsatz optischer Sensorsysteme können mit hoher zeitlicher Auflösung in-situ Informationen des Prozesszustands ermittelt werden. Dabei stellen die rauen Prozessbedingungen und die hohe Strahlungsintensität des Lichtbogens eine Herausforderung für die optischen Komponenten dar. Forschungsarbeiten am Institut für Schweißtechnik und Fügetechnik der RWTH Aachen haben gezeigt, dass durch den Einsatz einer HDR-Kamera in Kombination mit einer strukturierten Laserbelichtung gezielt geometrische Informationen des Lichtbogens und des Schmelzbads aus den Prozessaufnahmen gewonnen werden können. In dieser Arbeit wird eine parallele Schweißnaht- und Schmelzbadbeobachtung durchgeführt, wobei geometrische Informationen durch die Anwendung von Bildverarbeitungsalgorithmen extrahiert werden. Dabei wird ein nachlaufendes Sensorsystem eingesetzt, welches aus einer HDR-Kamera und einer Laserbeleuchtung besteht. Es werden diffraktive optische Elemente (DOE) zur Erzeugung von verschiedenen Laserprojektionsmustern verwendet, um sowohl eine unidirektionale als auch eine multidirektionale Prozessbeobachtung durchführen zu können. Aus den geometrischen Informationen werden Kenngrößen berechnet, anhand derer der Prozesszustand beurteilt werden kann. Es zeigt sich, dass anhand der Kenngrößenverläufe Abweichungen in der Schweiß- und Schmelzbadgeometrie und Positionierungsfehler des Roboters identifiziert werden können. T2 - Große Schweißtechnische Tagung - DVS CAMPUS CY - Online meeting DA - 14.09.2020 KW - Schweißnahtgeometrie KW - MSG-Schweißen KW - In-situ Monitoring KW - Schmelzbadbeobachtung PY - 2020 AN - OPUS4-51579 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Moskovchenko, A. I. A1 - Vavilov, V. P. A1 - Bernegger, Raphael A1 - Maierhofer, Christiane A1 - Chulkov, A. O. T1 - Detecting Delaminations in Semitransparent Glass Fiber Composite by Using Pulsed Infrared Thermography N2 - Thanks to its good strength/mass ratio, a glass fibre reinforced plastic (GFRP) composite is a common material widely used in aviation, power production, automotive and other industries. In its turn, active infrared (IR) nondestructive testing (NDT) is a common inspection technique for detecting and characterizing structural defects in GFRP. Materials to be tested are typically subjected to optical heating which is supposed to occur on the material surface. However, GFRP composite is semitransparent for optical radiation of both visual and IR spectral bands. Correspondingly, the inspection process represents a certain combination of both optical and thermal phenomena. Therefore, the known characterization algorithms based on pure heat diffusion cannot be applied to semi-transparent materials. In this study, the phenomenon of GFRP semi-transparency has been investigated numerically and experimentally in application to thermal NDT. Both Xenon flash tubes and a laser have been used for thermal stimulation of opaque and semi-transparent test objects. It has been shown that the Penetration of optical heating radiation into composite reduces detectability of shallower defects, and the signal-to-noise ratio can be enhanced by applying the technique of thermographic signal reconstruction (TSR). In the inspection of the semi-transparent GFRP composite, the most efficient has been the laser heating followed by the TSR data processing. The perspectives of defect characterization of semi-transparent materials by using laser heating are discussed. A neural network has been used as a candidate tool for evaluating defect depth in composite materials, but its training should be performed in identical with testing conditions. KW - Infrared thermography KW - Thermal testing KW - GFRP KW - Semi-transparent composite KW - Laser heating PY - 2020 DO - https://doi.org/10.1007/s10921-020-00717-x VL - 39 SP - 69 PB - Springer Science+Business Media, LLC, part of Springer Nature 2020 AN - OPUS4-51179 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ahmadi, Samim A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Burgholzer, P. A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias T1 - Laser excited super resolution thermal imaging for nondestructive inspection of internal defects N2 - A photothermal super resolution technique is proposed for an improved inspection of internal defects. To evaluate the potential of the laser-based thermographic technique, an additively manufactured stainless steel specimen with closely spaced internal cavities is used. Four different experimental configurations in transmission, reflection, stepwise and continuous scanning are investigated. The applied image post-processing method is based on compressed sensing and makes use of the block sparsity from multiple measurement events. This concerted approach of experimental measurement strategy and numerical optimization enables the resolution of internal defects and outperforms conventional thermographic inspection techniques. KW - Super Resolution KW - Laser Thermography KW - Non Destructive Testing KW - Comressed Sensing KW - Inverse Problem KW - Thermography PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-519016 DO - https://doi.org/10.1038/s41598-020-77979-y VL - 10 IS - 1 SP - 22357 PB - Springer Nature AN - OPUS4-51901 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - INPR A1 - Ahmadi, Samim A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Burgholzer, P. A1 - Jung, P. A1 - Caire, G. T1 - Laser excited super resolution thermal imaging for nondestructive inspection of internal defects N2 - A photothermal super resolution technique is proposed for an improved inspection of internal defects. To evaluate the potential of the laser-based thermographic technique, an additively manufactured stainless steel specimen with closely spaced internal cavities is used. Four different experimental configurations in transmission, reflection, stepwise and continuous scanning are investigated. The applied image post-processing method is based on compressed sensing and makes use of the block sparsity from multiple measurement events. This concerted approach of experimental measurement strategy and numerical optimization enables the resolution of internal defects and outperforms conventional thermographic inspection techniques. KW - Super resolution KW - Photothermal KW - Imaging KW - Compressed sensing KW - Internal defects KW - Nondestructive testing PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-518866 DO - https://doi.org/10.48550/arXiv.2007.03341 SN - 2331-8422 SP - 1 EP - 9 PB - Cornell University CY - Ithaca, NY AN - OPUS4-51886 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pech May, Nelson Wilbur A1 - Lauster, T. A1 - Retsch, M. T1 - Design of Multimodal Absorption in the Mid-IR: A Metal Dielectric Metal Approach N2 - Specific control on the mid-infrared (mid-IR) Emission properties is attracting increasing attention for thermal camouflage and passive cooling applications. Metal−dielectric−metal (MDM) structures are well known to support strong magnetic polariton resonances in the optical and near-infrared range. We extend the current understanding of such an MDM structure by specifically designing Au disc arrays on top of ZnS−Au−Si substrates and pushing their resonances to the mid-IR regime. Therefore, we combine fabrication via lift-off photolithography with the finite element method and an inductance−capacitance model. With this combination of techniques, we demonstrate that the magnetic polariton resonance of the first order strongly depends on the individual disc diameter. Furthermore, the fabrication of multiple discs within one unit cell allows a linear combination of the fundamental resonances to conceive broadband absorptance. Quite importantly, even in mixed resonator cases, the absorptance spectra can be fully described by a superposition of the individual disc properties. Our contribution provides rational guidance to deterministically design mid-IR emitting materials with specific narrow- or broadband properties. KW - Mid-IR absorption KW - Thermal emission PY - 2021 DO - https://doi.org/10.1021/acsami.0c18160 VL - 13 IS - 1 SP - 1921 EP - 1929 PB - ACS Publications AN - OPUS4-52070 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pech May, Nelson Wilbur A1 - Paul, A. A1 - Ziegler, Mathias T1 - Pulse-compression laser thermography using a modified Barker code: Enhanced detection of subsurface defects N2 - Pulse-compression thermography is an emerging technique that has shown versatility by combination of pulsed and lock-in thermography. Accordingly, several aspects of this technique are still unexplored, and some others not fully developed yet. Barker codes were widely used in radar applications due to their simplicity and their optimum autocorrelation function. Nevertheless, applications were limited by the amplitude of the sidelobes present in the autocorrelation function and therefore, several filters have been developed which aim to reduce the sidelobes. However, the filters usually depend on empirical parameters which must be determined for each application. A better alternative would improve the applicability of the Barker codes. In this work, we further develop the pulse-compression thermography technique by introducing a 13-bit modified Barker code (mBC): This allows to drastically reduce the sidelobes characteristic of the 13-bit Barker code (BC). Consequently, the thermographic impulse response, obtained by cross-correlation, is almost free of such sidelobes. Deeper defects become easier to detect in comparison with using a 13-bit Barker code. Numerical simulations using the finite element method are used for comparison and experimental measurements are performed in a sample of steel grade St 37 with machined notches of three different depths: 2 mm, 4 mm and 6 mm. T2 - SPIE Defense + Commercial Sensing 2021 CY - Online meeting DA - 13.04.2021 KW - Pulse-compression laser thermography KW - Barker codes KW - Non-destructive testing PY - 2021 DO - https://doi.org/10.1117/12.2586078 SN - 0277-786X VL - 11743 SP - 1 EP - 11 PB - SPIE CY - Bellingham, Wash. AN - OPUS4-53247 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pech May, Nelson Wilbur A1 - Paul, A. A1 - Ziegler, Mathias T1 - Pulse-compression laser thermography using a modified Barker code: Enhanced detection of subsurface defects N2 - Pulse-compression thermography is an emerging technique that has shown versatility by combination of pulsed and lock-in thermography. Accordingly, several aspects of this technique are still unexplored, and some others not fully developed yet. Barker codes were widely used in radar applications due to their simplicity and their optimum autocorrelation function. Nevertheless, applications were limited by the amplitude of the sidelobes present in the autocorrelation function and therefore, several filters have been developed which aim to reduce the sidelobes. However, the filters usually depend on empirical parameters which must be determined for each application. A better alternative would improve the applicability of the Barker codes. In this work, we further develop the pulse-compression thermography technique by introducing a 13-bit modified Barker code (mBC): This allows to drastically reduce the sidelobes characteristic of the 13-bit Barker code (BC). Consequently, the thermographic impulse response, obtained by cross-correlation, is almost free of such sidelobes. Deeper defects become easier to detect in comparison with using a 13-bit Barker code. Numerical simulations using the finite element method are used for comparison and experimental measurements are performed in a sample of steel grade St 37 with machined notches of three different depths: 2 mm, 4 mm and 6 mm. T2 - SPIE Defense + Commercial Sensing 2021 CY - Online meeting DA - 13.04.2021 KW - Pulse-compression laser thermography KW - Barker codes KW - Non-destructive testing PY - 2021 AN - OPUS4-53249 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pech May, Nelson Wilbur A1 - Ziegler, Mathias T1 - Surface breaking crack detection algorithm for flying spot and line thermography based on the Canny approach N2 - In this work we introduce an algorithm based on the well-known Canny approach for effectual crack detection in thermographic films obtained using flying spot thermography (FST) or flying line thermography (FLT). The proposed algorithm performs faster than another algorithm, for crack detection, based on the application of two Sobel filters (one in x and another one in y directions). For FLT it is shown that processing 10-25 % of the thermograms of a thermographic film required to scan a whole sample is enough to obtain good results. In contrast, using the Sobel filter approach requires the processing of twice the thermographic film length. Experimental measurements are performed on a metallic component of complex shape which contains real defects, that is, surface breaking cracks due to industrial use. The specimen is tested using flying line thermography. Three different scanning speeds are tested: 10, 30 and 60 mms-1 with laser powers of 50, 60 and 120 W respectively. The sample and an infrared camera are aligned and fixed on a motorized linear stage. The diode laser LDM500 (500 W max power) is fixed on an optical bench separately from the linear stage. The results obtained with the proposed algorithm are additionally compared with a previously established algorithm for flying spot thermography based on the Sobel filter. It is shown that the proposed algorithm based on the Canny approach, can be used in automated systems for thermographic non-destructive testing. T2 - SPIE Future Sensing Technologies 2021 CY - Online meeting DA - 14.11.2021 KW - Flying line thermography KW - Flying spot thermography KW - Canny approach KW - automated thermographic nondestructive testing PY - 2021 DO - https://doi.org/10.1117/12.2603913 SP - 119140M-1 EP - 119140M-6 AN - OPUS4-53961 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pech May, Nelson Wilbur A1 - Ziegler, Mathias T1 - Detection of surface breaking cracks using flying line laser thermography: A Canny-based algorithm N2 - In this work, we introduce a new algorithm for effectual crack detection using flying line laser thermography, based on the well-known Canny approach. The algorithm transforms the input thermographic sequence into an edge map. Experimental measurements are performed on a metallic component that contains surface breaking cracks due to industrial use. The specimen is tested using flying line thermography at different scanning speeds and laser input powers. Results obtained with the proposed algorithm are additionally compared with a previously established algorithm for flying spot thermography. The proposed Canny-based algorithm can be used in automated systems for thermographic non-destructive testing. T2 - Advanced Infrared Technology and Applications 2021 CY - Online meeting DA - 26.10.2021 KW - Canny approach KW - Flying line thermography KW - Crack detection PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-539628 DO - https://doi.org/10.3390/engproc2021008022 SN - 2673-4591 VL - 8 IS - 1 SP - 1 EP - 4 PB - MDPI CY - Basel AN - OPUS4-53962 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stamm, Michael T1 - EvalTherm - Evaluation of passive Thermography for the inspection of wind turbine blades N2 - The EvalTherm project is presented. The concept of passive thermography on rotor blades as well as first results of field measurements are discussed. As this is an industry-related conference, the focus in this paper is on practical aspects that are of interest for industrial applications. T2 - AMI Wind Turbine Blade Manufacture conference 2021 CY - Cologne, Germany DA - 15.11.2021 KW - Windenergy KW - Thermography KW - Inspection KW - NDT PY - 2021 AN - OPUS4-53928 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Herrmann, K. A1 - Pech May, Nelson Wilbur A1 - Retsch, M. T1 - Photoacoustic thermal characterization of low thermal diffusivity thin films N2 - The photoacoustic measurement technique is a powerful yet underrepresented method to characterize the thermal transport properties of thin films. For the case of isotropic low thermal diffusivity samples, such as glasses or polymers, we demonstrate a general approach to extract the thermal conductivity with a high degree of significance. We discuss in particular the influence of thermal effusivity, thermal diffusivity, and sample layer thickness on the significance and accuracy of this measurement technique. These fundamental thermal properties guide sample and substrate selection to allow for a feasible thermal transport characterization. Furthermore, our data evaluation allows us to directly extract the thermal conductivity from this transient technique, without separate determination of the volumetric heat capacity, when appropriate boundary conditions are fulfilled. Using silica, poly(methyl methacrylate) (PMMA) thin films, and various substrates (quartz, steel, and silicon), we verify the quantitative correctness of our analytical approach. KW - Thermal conductivity KW - Photoacoustic characterization KW - Thin film characterization PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-528743 DO - https://doi.org/10.1016/j.pacs.2021.100246 SN - 2213-5979 VL - 22 SP - 100246 PB - Elsevier AN - OPUS4-52874 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ahmadi, Samim A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Burgholzer, Peter A1 - Jung, Peter A1 - Caire, Giuseppe A1 - Ziegler, Mathias T1 - Laser excited super resolution thermal imaging for nondestructive testing N2 - The work to be presented focuses on our most recent studies to laser excited super resolution (SR) thermography. The goal of nondestructive testing with SR is to facilitate the separation of closely spaced defects. Photothermal SR can be realized by performing structured illumination measurements in com-bination with the use of deconvolution algorithms in post-processing. We explain that stepwise as well as continuous scanning techniques are applicable to generate structured illumination measurements. Finally, we discuss the effect of experimental parameters and image processing techniques to find the optimal SR technique which leads to the highest reconstruction quality within laser thermography. T2 - Sensor and Measurement Science International Conference SMSI 2021 CY - Online meeting DA - 03.05.2021 KW - Super resolution KW - Laser thermography KW - Nondestructive testing KW - Laser scanning KW - Photothermal imaging PY - 2021 SP - 181 EP - 182 AN - OPUS4-52780 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ahmadi, Samim T1 - Laser excited super resolution thermal imaging for nondestructive testing N2 - The work to be presented focuses on our most recent studies to laser excited super resolution (SR) thermography. The goal of nondestructive testing with SR is to facilitate the separation of closely spaced defects. Photothermal SR can be realized by performing structured illumination measurements in com-bination with the use of deconvolution algorithms in post-processing. We explain that stepwise as well as continuous scanning techniques are applicable to generate structured illumination measurements. Finally, we discuss the effect of experimental parameters and image processing techniques to find the optimal SR technique which leads to the highest reconstruction quality within laser thermography. T2 - Sensor and Measurement Science International Conference SMSI 2021 CY - Online meeting DA - 03.05.2021 KW - Super resolution KW - Laser thermography KW - Nondestructive testing KW - Laser scanning KW - Photothermal imaging PY - 2021 AN - OPUS4-52781 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ahmadi, Samim T1 - Neue Verfahren der thermografischen Super Resolution mit strukturierter 1D-Lasererwärmung N2 - Die thermografische ZfP basiert auf der Wechselwirkung von thermischen Wellen mit Inhomogenitäten. Die Ausbreitung von thermischen Wellen von der Wärmequelle zur Inhomogenität und zur Detektionsoberfläche entsprechend der thermischen Diffusionsgleichung führt dazu, dass zwei eng beieinander liegende Defekte fälschlicherweise als ein Defekt im gemessenen Thermogramm erkannt werden können. Um diese räumliche Auflösungsgrenze zu durchbrechen, also eine Super Resolution zu realisieren, kann die Kombination von räumlich strukturierter Erwärmung und numerischen Verfahren des Compressed Sensings verwendet werden. Für unsere Arbeiten benutzen wir Hochleistungs-Laser im Kilowatt-Bereich um die Probe entweder hochaufgelöst entlang einer Linie (1D) abzurastern oder strukturiert zu erwärmen. Die Verbesserung des räumlichen Auflösungsvermögens zur Defekterkennung hängt dann im klassischen Sinne direkt von der Anzahl der Messungen ab. Mithilfe des Compressed Sensings und Vorkenntnissen über das System ist es jedoch möglich die Anzahl der Messungen zu reduzieren und trotzdem Super Resolution zu erzielen. Wie viele Messungen notwendig sind und wie groß der Auflösungsgewinn gegenüber der konventionellen thermografischen Prüfung mit flächiger Erwärmung ist, hängt von einer Reihe von Messparametern, der Messstrategie, Probeneigenschaften und den verwendeten Rekonstruktionsalgorithmen ab. Unsere Studien befassen sich mit dem Einfluss der experimentellen Parameter, wie z.B. der Pulslänge der Laserbeleuchtung und der Größe des Laserspots. Weiterhin haben wir uns mit der Wahl der Parameter in der Rekonstruktion auseinandergesetzt, die einen Einfluss auf das im Compressed Sensing zugrundeliegende Minimierungsproblem haben. Für jeden getesteten Parametersatz wurde eine Rekonstruktionsqualität berechnet. Schließlich wurden die Defektrekonstruktionen basierend auf den Parameternsätzen verglichen, sodass eine Parameterwahl für hohe Rekonstruktionsqualitäten mit thermografischer Super Resolution empfohlen werden kann. T2 - DGZfP-Jahrestagung 2021 CY - Online meeting DA - 10.05.2021 KW - Super resolution KW - Thermografie KW - Strukturiert KW - Photothermisch PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-527820 AN - OPUS4-52782 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ahmadi, Samim T1 - Neue Verfahren der thermografischen Super Resolution mit strukturierter 1D-Lasererwärmung N2 - Die thermografische ZfP basiert auf der Wechselwirkung von thermischen Wellen mit Inhomogenitäten. Die Ausbreitung von thermischen Wellen von der Wärmequelle zur Inhomogenität und zur Detektionsoberfläche entsprechend der thermischen Diffusionsgleichung führt dazu, dass zwei eng beieinander liegende Defekte fälschlicherweise als ein Defekt im gemessenen Thermogramm erkannt werden können. Um diese räumliche Auflösungsgrenze zu durchbrechen, also eine Super Resolution zu realisieren, kann die Kombination von räumlich strukturierter Erwärmung und numerischen Verfahren des Compressed Sensings verwendet werden. Für unsere Arbeiten benutzen wir Hochleistungs-Laser im Kilowatt-Bereich um die Probe entweder hochaufgelöst entlang einer Linie (1D) abzurastern oder strukturiert zu erwärmen. Die Verbesserung des räumlichen Auflösungsvermögens zur Defekterkennung hängt dann im klassischen Sinne direkt von der Anzahl der Messungen ab. Mithilfe des Compressed Sensings und Vorkenntnissen über das System ist es jedoch möglich die Anzahl der Messungen zu reduzieren und trotzdem Super Resolution zu erzielen. Wie viele Messungen notwendig sind und wie groß der Auflösungsgewinn gegenüber der konventionellen thermografischen Prüfung mit flächiger Erwärmung ist, hängt von einer Reihe von Messparametern, der Messstrategie, Probeneigenschaften und den verwendeten Rekonstruktionsalgorithmen ab. Unsere Studien befassen sich mit dem Einfluss der experimentellen Parameter, wie z.B. der Pulslänge der Laserbeleuchtung und der Größe des Laserspots. Weiterhin haben wir uns mit der Wahl der Parameter in der Rekonstruktion auseinandergesetzt, die einen Einfluss auf das im Compressed Sensing zugrundeliegende Minimierungsproblem haben. Für jeden getesteten Parametersatz wurde eine Rekonstruktionsqualität berechnet. Schließlich wurden die Defektrekonstruktionen basierend auf den Parameternsätzen verglichen, sodass eine Parameterwahl für hohe Rekonstruktionsqualitäten mit thermografischer Super Resolution empfohlen werden kann. T2 - DGZfP-Jahrestagung 2021 CY - Online meeting DA - 10.05.2021 KW - Super resolution KW - Laserthermografie KW - Strukturiertes Heizen KW - Photothermisch PY - 2021 AN - OPUS4-52783 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Forero-Sandoval, I. A1 - Cervantes-Alvarez, F. A1 - Ramirez-Rincon, J. A1 - Macias, J. A1 - Pech May, Nelson Wilbur A1 - Ordonez-Miranda, J. A1 - Alvarado-Gil, J. T1 - Percolation Threshold of the Thermal, Electrical and Optical Properties of Carbonyl-Iron Microcomposites N2 - Composites made up of microparticles embedded in a polymeric matrix have attracted increasing attention due to the possibility of tailoring their physical properties by adding the adequate quantity of fillers. As the concentration of these fillers increases, their connectivity changes drastically at a given threshold and therefore the electrical, thermal and optical properties of these composites are expected to exhibit a percolation effect. In this work, the thermal and electrical conductivities along with the emissivity of Composites composed of carbonyl-iron microparticles randomly distributed in a polyester resin matrix are measured, for volume fractions ranging from 0 to 0.55. It is shown that both the thermal and electrical conductivities increase with the particles’ concentration, such that their percolation threshold appears at volume fractions of 0.46 and 0.38, respectively. The emissivity, on the other hand, decreases as the fillers’ concentration increases, such that it exhibits a substantial decay at a volume fraction of 0.41. The percolation threshold of the emissivity is thus higher than that of the thermal conductivity, but lower than the electrical conductivity one. This dispersion on the percolation concentration is justified by the different physical mechanisms required to activate the electrical, thermal, and optical responses of the considered composites. The obtained results thus show that the percolation phenomenon can efficiently be used to enhance or reduce the physical properties of particulate composites. KW - Thermal conductivity KW - Emissivity KW - Thermal percolation threshold PY - 2021 DO - https://doi.org/10.1007/s10443-021-09869-z VL - 28 IS - 2 SP - 447 EP - 463 PB - Springer AN - OPUS4-52355 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kästner, L. A1 - Ahmadi, Samim A1 - Jonietz, Florian A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias A1 - Lambrecht, J. T1 - Classification of Spot-Welded Joints in Laser Thermography Data Using Convolutional Neural Networks N2 - Spot welding is a crucial process step in various industries. However, classification of spot welding quality is still a tedious process due to the complexity and sensitivity of the test material, which drain conventional approaches to its limits. In this article, we propose an approach for quality inspection of spot weldings using images from laser thermography data. We propose data preparation approaches based on the underlying physics of spot-welded joints, heated with pulsed laser thermography by analyzing the intensity over time and derive dedicated data filters to generate training datasets. Subsequently, we utilize convolutional neural networks to classify weld quality and compare the performance of different models against each other. We achieve competitive results in terms of classifying the different welding quality classes compared to traditional approaches, reaching an accuracy of more than 95 percent. Finally, we explore the effect of different augmentation methods. KW - Active thermal imaging KW - Laser thermography KW - Spot-welded joints KW - Convolutional neural network KW - Classification KW - Data processing PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-524216 DO - https://doi.org/10.1109/ACCESS.2021.3063672 VL - 9 SP - 48303 EP - 48312 AN - OPUS4-52421 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ahmadi, Samim A1 - Thummerer, G. A1 - Breitwieser, S. A1 - Mayr, G. A1 - Lecompagnon, Julien A1 - Burgholzer, P. A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias T1 - Multi-dimensional reconstruction of internal defects in additively manufactured steel using photothermal super resolution combined with virtual wave based image processing N2 - We combine three different approaches to greatly enhance the defect reconstruction ability of active thermographic testing. As experimental approach, laser-based structured illumination is performed in a step-wise manner. As an intermediate signal processing step, the virtual wave concept is used in order to effectively convert the notoriously difficult to solve diffusion-based inverse problem into a somewhat milder wavebased inverse problem. As a final step, a compressed-sensing based optimization procedure is applied which efficiently solves the inverse problem by making advantage of the joint sparsity of multiple blind measurements. To evaluate our proposed processing technique, we investigate an additively manufactured stainless steel sample with eight internal defects. The concerted super resolution approach is compared to conventional thermographic reconstruction techniques and shows an at least four times better spatial resolution. KW - Active thermography KW - Additive manufacturing KW - Stainless steel KW - ADMM KW - Block regularization KW - Internal defects KW - Joint sparsity KW - Laser excitation KW - Multi-dimensional reconstruction KW - Photothermal super resolution KW - Virtual waves PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-525330 DO - https://doi.org/10.1109/tii.2021.3054411 SN - 1551-3203 SN - 1941-0050 VL - 17 IS - 11 SP - 7368 EP - 7378 PB - IEEE CY - New York, NY AN - OPUS4-52533 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - INPR A1 - Ahmadi, Samim A1 - Hauffen, Jan Christian A1 - Kästner, L. A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias T1 - Learned block iterative shrinkage thresholding algorithm for photothermal super resolution imaging N2 - Block-sparse regularization is already well-known in active thermal imaging and is used for multiple measurement based inverse problems. The main bottleneck of this method is the choice of regularization parameters which differs for each experiment. To avoid time-consuming manually selected regularization parameters, we propose a learned block-sparse optimization approach using an iterative algorithm unfolded into a deep neural network. More precisely, we show the benefits of using a learned block iterative shrinkage thresholding algorithm that is able to learn the choice of regularization parameters. In addition, this algorithm enables the determination of a suitable weight matrix to solve the underlying inverse problem. Therefore, in this paper we present the algorithm and compare it with state of the art block iterative shrinkage thresholding using synthetically generated test data and experimental test data from active thermography for defect reconstruction. Our results show that the use of the learned block-sparse optimization approach provides smaller normalized mean square errors for a small fixed number of iterations than without learning. Thus, this new approach allows to improve the convergence speed and only needs a few iterations to generate accurate defect reconstruction in photothermal super resolution imaging. KW - Iterative shrinkage thresholding algorithm KW - Neural network KW - Deep learning KW - Active thermography KW - Photothermal super resolution PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-525364 DO - https://doi.org/10.48550/arXiv.2012.03547 SN - 2331-8422 SP - 1 EP - 11 PB - Cornell University CY - Ithaca, NY AN - OPUS4-52536 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - INPR A1 - Ahmadi, Samim A1 - Kästner, L. A1 - Hauffen, Jan Christian A1 - Jung, P. A1 - Ziegler, Mathias T1 - Photothermal-SR-Net: A customized deep unfolding neural network for photothermal super resolution imaging N2 - This paper presents deep unfolding neural networks to handle inverse problems in photothermal radiometry enabling super resolution (SR) imaging. Photothermal imaging is a well-known technique in active thermography for nondestructive inspection of defects in materials such as metals or composites. A grand challenge of active thermography is to overcome the spatial resolution limitation imposed by heat diffusion in order to accurately resolve each defect. The photothermal SR approach enables to extract high-frequency spatial components based on the deconvolution with the thermal point spread function. However, stable deconvolution can only be achieved by using the sparse structure of defect patterns, which often requires tedious, hand-crafted tuning of hyperparameters and results in computationally intensive algorithms. On this account, Photothermal-SR-Net is proposed in this paper, which performs deconvolution by deep unfolding considering the underlying physics. This enables to super resolve 2D thermal images for nondestructive testing with a substantially improved convergence rate. Since defects appear sparsely in materials, Photothermal-SR-Net applies trained blocksparsity thresholding to the acquired thermal images in each convolutional layer. The performance of the proposed approach is evaluated and discussed using various deep unfolding and thresholding approaches applied to 2D thermal images. Subsequently, studies are conducted on how to increase the reconstruction quality and the computational performance of Photothermal-SR-Net is evaluated. Thereby, it was found that the computing time for creating high-resolution images could be significantly reduced without decreasing the reconstruction quality by using pixel binning as a preprocessing step. KW - Photothermal super resolution KW - Nondestructive testing KW - Deep unfolding KW - Deep learning KW - Deep imaging KW - Physics-based deep learning KW - Laser thermography KW - Elastic net KW - Iterative shrinkage thresholding algorithm PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-525371 DO - https://doi.org/10.48550/arXiv.2104.10563 SN - 2331-8422 SP - 1 EP - 10 PB - Cornell University CY - Ithaca, NY AN - OPUS4-52537 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien A1 - Ahmadi, Samim A1 - Hirsch, Philipp Daniel A1 - Ziegler, Mathias ED - Zalameda, J. N. ED - Mendioroz, A. T1 - Full-frame thermographic super-resolution with 2D-structured laser heating N2 - Thermographic super-resolution techniques allow the resolution of defects/inhomogeneities beyond the classical limit, which is governed by the diffusion properties of thermal wave propagation. Photothermal super-resolution is based on a combination of an experimental scanning strategy and a numerical optimization which has been proven to be superior to standard thermographic methods in the case of 1D linear defects. In this contribution, we report on the extension of this approach towards a full frame 2D photothermal super-resolution technique. The experimental approach is based on a repeated spatially structured heating using high power lasers. In a second post-processing step, several measurements are coherently combined using mathematical optimization and taking advantage of the (joint) sparsity of the defects in the sample. In our work we extend the possibilities of the method to efficiently detect and resolve defect cross sections with a fully 2D-structured blind illumination. T2 - Thermosense: Thermal Infrared Applications XLIII CY - Online meeting DA - 12.04.2021 KW - Thermography KW - super-resolution KW - NDT KW - Inspection KW - Image resolution PY - 2021 DO - https://doi.org/10.1117/12.2586093 VL - 11743 SP - 11743-26, 10 PB - SPIE AN - OPUS4-52524 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Full-frame thermographic super-resolution with 2D-structured laser heating N2 - Thermographic super-resolution techniques allow the resolution of defects/inhomogeneities beyond the classical limit, which is governed by the diffusion properties of thermal wave propagation. Photothermal super-resolution is based on a combination of an experimental scanning strategy and a numerical optimization which has been proven to be superior to standard thermographic methods in the case of 1D linear defects. In this contribution, we report on the extension of this approach towards a full frame 2D photothermal super-resolution technique. The experimental approach is based on a repeated spatially structured heating using high power lasers. In a second post-processing step, several measurements are coherently combined using mathematical optimization and taking advantage of the (joint) sparsity of the defects in the sample. In our work we extend the possibilities of the method to efficiently detect and resolve defect cross sections with a fully 2D-structured blind illumination. T2 - Thermosense: Thermal Infrared Applications XLIII CY - Online meeting DA - 12.04.2021 KW - Thermography KW - Super-resolution KW - NDT KW - Inspection KW - Image resolution PY - 2021 UR - https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11743/117430T/Full-frame-thermographic-super-resolution-with-2D-structured-laser-heating/10.1117/12.2586093.full AN - OPUS4-52526 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - 2D-Photothermal super-resolution with sparse matrix stacking N2 - Thermographic super resolution techniques allow the spatial resolution of defects/inhomogeneities below the classical limit, which is governed by the diffusion properties of thermal wave propagation. In this work, we re-port on the extension of this approach towards a full frame 2D super resolution technique. The approach is based on a repeated spatially structured heating using high power lasers. In a second post-processing step, several measurements are coherently combined using mathematical optimization and taking advantage of the (joint) sparsity of the defects in the sample. T2 - Sensor and Measurement Science International Conference SMSI 2021 CY - Online meeting DA - 03.05.2021 KW - Thermography KW - Super-resolution KW - NDT KW - Inspection KW - Image resolution PY - 2021 AN - OPUS4-52579 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien A1 - Ahmadi, Samim A1 - Hirsch, Philipp Daniel A1 - Ziegler, Mathias T1 - 2D-Photothermal Super Resolution with Sparse Matrix Stacking N2 - Thermographic super resolution techniques allow the spatial resolution of defects/inhomogeneities below the classical limit, which is governed by the diffusion properties of thermal wave propagation. In this work, we report on the extension of this approach towards a full frame 2D super resolution technique. The approach is based on a repeated spatially structured heating using high power lasers. In a second post-processing step, several measurements are coherently combined using mathematical optimization and taking advantage of the (joint) sparsity of the defects in the sample T2 - Sensor and Measurement Science International Conference SMSI 2021 CY - Online meeting DA - 03.05.2021 KW - Thermography KW - Super-resolution KW - NDT KW - Inspection KW - Image resolution PY - 2021 SN - 978-3-9819376-4-0 DO - https://doi.org/10.5162/SMSI2021/C2.2 VL - SMSI 2021 - Sensors and Instrumentation SP - 183 EP - 184 AN - OPUS4-52589 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Thermografische Super Resolution mit 2D-strukturierter Erwärmung N2 - Thermografische Super Resolution ermöglicht die Auflösung von Defekten/Inhomogenitäten unterhalb des klassischen Limits, welches durch die Diffusionseigenschaften der thermischen Wellenausbreitung bestimmt wird. Basierend auf einer Kombination aus der Anwendung spezieller Abtaststrategien und einer anschließenden numerischen Optimierungsschritt bei der Datenauswertung hat sich die thermografische Super Resolution bereits bei der Detektion von 1D-Defekten gegenüber den Standard-Thermografieverfahren als überlegen erwiesen. In unserer Arbeit erweitern wir die Möglichkeiten der Methode zur effizienten Detektion und Auflösung von Defektquerschnitten mit einer vollständig 2D-strukturierten Erwärmung. Der experimentelle Ansatz basiert auf einer wiederholten räumlich strukturierten Erwärmung durch einen Hochleistungslaser. In einem zweiten Nachbearbeitungsschritt werden mehrere kohärente Messungen mittels mathematischer Optimierung und unter Ausnutzung der (Joint-) Sparsity der Defekte innerhalb des Prüfkörpers kombiniert. Als Ergebnis kann eine 2D-sparse Defekt-/ Inhomogenitätskarte erhalten werden. Da die Kombination von räumlich strukturierter Erwärmung und anschließender numerischer Kombination mehrerer kohärenter Messungen nicht nur die Auflösung verbessert, sondern auch die Messkomplexität drastisch erhöht, werden verschiedene Scanstrategien untersucht. Abschließend werden die erhaltenen Ergebnisse mit denen konventioneller thermografischer Prüfverfahren verglichen. T2 - DGZfP-Jahrestagung 2021 CY - Online meeting DA - 10.05.2021 KW - Thermography KW - Super-resolution KW - NDT KW - Inspection KW - Image resolution PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-526396 UR - https://jahrestagung.dgzfp.de/Programm#P45 AN - OPUS4-52639 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krankenhagen, Rainer T1 - Thermische Kontraste - der Blick hinter die Fassade N2 - Die Thermografie beruht auf der bildlichen Darstellung von Temperaturunterschieden oder auch thermischen Kontrasten an der Oberfläche eines Untersuchungsobjektes. Diese bilden sich nur her-aus, wenn sich das Untersuchungsobjekt gerade erwärmt oder abkühlt. Der Beitrag erklärt mittels eines stark vereinfachten Modells die Entstehung solcher Kontraste als dynamischen Effekt ver-schiedener Abkühlgeschwindigkeiten. Neben Laborergebnissen werden beispielhaft einige Ergeb-nisse von einem mittelalterlichen Baudenkmal präsentiert, um das Verständnis für die thermografi-sche Inspektion von Fassaden zu vertiefen. T2 - 14. Konservierungswissenschaftliches Kolloquium Berlin Brandenburg CY - Berlin, Germany DA - 12.11.2021 KW - Aktive Thermografie KW - Bauthermografie KW - Ablösungen KW - Metallanker PY - 2021 AN - OPUS4-53757 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien A1 - Ahmadi, Samim A1 - Hirsch, Philipp Daniel A1 - Rupprecht, C. A1 - Ziegler, Mathias ED - Kimata, M. ED - Shaw, J. A. ED - Valenta, C. R. T1 - Investigations on photothermal super resolution reconstruction using 2D-structured illumination patterns N2 - Active thermography as a nondestructive testing modality suffers greatly from the limitations imposed by the diffusive nature of heat conduction in solids. As a rule of thumb, the detection and resolution of internal defects/inhomogeneities is limited to a defect depth to defect size ratio greater than or equal to one. Earlier, we demonstrated that this classical limit can be overcome for 1D and 2D defect geometries by using photothermal laser-scanning super resolution. In this work we report a new experimental approach using 2D spatially structured illumination patterns in conjunction with compressed sensing and computational imaging methods to significantly decrease the experimental complexity and make the method viable for investigating larger regions of interest. T2 - Future Sensing Technologies Conference 2021 CY - Online meeting DA - 15.11.2021 KW - Thermography KW - Super resolution KW - NDT KW - Inspection KW - Image resolution PY - 2021 DO - https://doi.org/10.1117/12.2603838 VL - 11914 SP - 124 EP - 131 PB - International Society for Optics and Photonics. SPIE AN - OPUS4-53745 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Investigations on photothermal super resolution reconstruction using 2D-structured illumination patterns N2 - Active thermography as a nondestructive testing modality suffers greatly from the limitations imposed by the diffusive nature of heat conduction in solids. As a rule of thumb, the detection and resolution of internal defects/inhomogeneities is limited to a defect depth to defect size ratio greater than or equal to one. Earlier, we demonstrated that this classical limit can be overcome for 1D and 2D defect geometries by using photothermal laser-scanning super resolution. In this work we report a new experimental approach using 2D spatially structured illumination patterns in conjunction with compressed sensing and computational imaging methods to significantly decrease the experimental complexity and make the method viable for investigating larger regions of interest. T2 - Future Sensing Technologies Conference 2021 CY - Online meeting DA - 15.11.2021 KW - Thermography KW - Super resolution KW - NDT KW - Inspection KW - Image resolution PY - 2021 UR - https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11914/2603838/Investigations-on-photothermal-super-resolution-reconstruction-using-2D-structured-illumination/10.1117/12.2603838.full AN - OPUS4-53747 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pech May, Nelson Wilbur T1 - Photothermal characterization of polyester composites loaded with parallelly arranged graphite rods N2 - One of the biggest challenges in the measurement of thermal properties is to measure inhomogeneous materials This work focuses on measuring the thermal properties of cylindrical polyester resin composite materials loaded with graphite rods oriented in the direction of the resin thickness, varying the graphite concentrations starting from zero to 8 75 of volumetric fraction and changing the distribution of graphite rods inside the polyester matrix. T2 - International Conference in Photoacoustics and Photothermal Phenomena (ICPPP21) CY - Bled, Slovenia DA - 19.06.2022 KW - Heat diffusion KW - Heterogeneous materials PY - 2022 AN - OPUS4-55384 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pech May, Nelson Wilbur T1 - Automatic inspection of surface breaking cracks using laser scanning thermography N2 - In this work, we report on a method for automatic inspection of components using laser scanning thermography, in which the relative motion is performed by a robot to fully inspect complex test objects such as turbine blades. We demonstrate our evaluation algorithms with the aim of automatically detecting surface defects on calibrated specimens. We show the influence of the excitation laser, which can be varied in terms of spot geometry, wavelength, and scan scheme. Additionally, we show some advantages, versatility, and current challenges of using a programmed robot for non-destructive evaluation in thermography. T2 - International Conference in Photoacoustics and Photothermal Phenomena (ICPPP21) CY - Bled, Slovenia DA - 19.06.2022 KW - Flying line thermography KW - Surface breaking defects KW - Canny approach PY - 2022 AN - OPUS4-55386 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Rupprecht, C. A1 - Ziegler, Mathias ED - Mendioroz, A. ED - Avdelidis, N. P. T1 - Thermographic testing using 2D pseudo-random illumination and photothermal super resolution reconstruction N2 - Due to the diffusive nature of heat propagation in solids, the detection and resolution of internal defects with active thermography based non-destructive testing is commonly limited to a defect-depth-to-defect-size ratio greater than or equal to one. In the more recent past, we have already demonstrated that this limitation can be overcome by using a spatially modulated illumination source and photothermal super resolution-based reconstruction. Furthermore, by relying on compressed sensing and computational imaging methods we were able to significantly reduce the experimental complexity to make the method viable for investigating larger regions of interest. In this work we share our progress on improving the defect/inhomogeneity characterization using fully 2D spatially structured illumination patterns instead of scanning with a single laser spot. The experimental approach is based on the repeated blind pseudo-random illumination using modern projector technology and a high-power laser. In the subsequent post-processing, several measurements are then combined by taking advantage of the joint sparsity of the defects within the sample applying 2D-photothermal super resolution reconstruction. Here, enhanced nonlinear convex optimization techniques are utilized for solving the underlying ill-determined inverse problem for typical simple defect geometries. As a result, a higher resolution defect/inhomogeneity map can be obtained at a fraction of the measurement time previously needed. T2 - Thermosense: Thermal Infrared Applications XLIV CY - Orlando, Florida, USA DA - 05.04.2022 KW - Thermography KW - Super resolution KW - NDT KW - Material testing KW - Internal defects KW - DMD KW - DLP PY - 2022 DO - https://doi.org/10.1117/12.2618562 SN - 0277-786X VL - 12109 SP - 1 EP - 10 PB - SPIE AN - OPUS4-54909 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krankenhagen, Rainer A1 - Zirker, Stefan A1 - Joniertz, Florian T1 - Determination of thermal parameters of concrete by active thermographic measurements N2 - The knowledge of the thermal parameters of a particular concrete is essential for thermal design of a building, but also could help to identify and assess the state of a concrete structure. Active thermography has the potential to be applied onsite and to provide a fast investigation of thermal properties. In this work, three different concrete samples were investigated by active thermography in reflection and in transmission setup. It was found that this method yields the same results without direct contact as the Transient Plane Source (TPS) method as an established inspection tool. KW - Concrete KW - Effusivity KW - Thermal diffusivity KW - Photothermal KW - Thermography KW - Hot disc method KW - Parker method KW - Onsite inspection PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-543781 DO - https://doi.org/10.1007/s10921-022-00861-6 SN - 0195-9298 SN - 1573-4862 VL - 41 IS - 1 SP - 1 EP - 20 PB - Springer AN - OPUS4-54378 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Thermographic testing using 2D pseudo-random illumination and photothermal super resolution reconstruction N2 - Due to the diffusive nature of heat propagation in solids, the detection and resolution of internal defects with active thermography based non-destructive testing is commonly limited to a defect-depth-to-defect-size ratio greater than or equal to one. In the more recent past, we have already demonstrated that this limitation can be overcome by using a spatially modulated illumination source and photothermal super resolution-based reconstruction. Furthermore, by relying on compressed sensing and computational imaging methods we were able to significantly reduce the experimental complexity to make the method viable for investigating larger regions of interest. In this work we share our progress on improving the defect/inhomogeneity characterization using fully 2D spatially structured illumination patterns instead of scanning with a single laser spot. The experimental approach is based on the repeated blind pseudo-random illumination using modern projector technology and a high-power laser. In the subsequent post-processing, several measurements are then combined by taking advantage of the joint sparsity of the defects within the sample applying 2D-photothermal super resolution reconstruction. Here, enhanced nonlinear convex optimization techniques are utilized for solving the underlying ill-determined inverse problem for typical simple defect geometries. As a result, a higher resolution defect/inhomogeneity map can be obtained at a fraction of the measurement time previously needed. T2 - Thermosense: Thermal Infrared Applications XLIV CY - Orlando, FL, USA DA - 05.04.2022 KW - Thermography KW - Super resolution KW - NDT KW - Material testing KW - Internal defects KW - DMD KW - DLP PY - 2022 AN - OPUS4-54667 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ahmadi, Samim A1 - Kästner, L. A1 - Hauffen, Jan Christian A1 - Jung, P. A1 - Ziegler, Mathias T1 - Photothermal-SR-Net: A customized deep unfolding neural network for photothermal super resolution imaging N2 - This article presents deep unfolding neural networks to handle inverse problems in photothermal radiometry enabling super-resolution (SR) imaging. The photothermal SR approach is a well-known technique to overcome the spatial resolution limitation in photothermal imaging by extracting high-frequency spatial components based on the deconvolution with the thermal point spread function (PSF). However, stable deconvolution can only be achieved by using the sparse structure of defect patterns, which often requires tedious, handcrafted tuning of hyperparameters and results in computationally intensive algorithms. On this account, this article proposes Photothermal-SR-Net, which performs deconvolution by deep unfolding considering the underlying physics. Since defects appear sparsely in materials, our approach includes trained block-sparsity thresholding in each convolutional layer. This enables to super-resolve 2-D thermal images for nondestructive testing (NDT) with a substantially improved convergence rate compared to classic approaches. The performance of the proposed approach is evaluated on various deep unfolding and thresholding approaches. Furthermore, we explored how to increase the reconstruction quality and the computational performance. Thereby, it was found that the computing time for creating high-resolution images could be significantly reduced without decreasing the reconstruction quality by using pixel binning as a preprocessing step. KW - Deep unfolding KW - Defect reconstruction KW - Elastic net KW - Inverse problems KW - Iterative shrinkage thresholding KW - Neural network KW - Nondestructive testing (NDT) KW - Photothermal imaging KW - Super resolution (SR) KW - Thermography PY - 2022 DO - https://doi.org/10.1109/tim.2022.3154803 SN - 1557-9662 VL - 71 SP - 1 EP - 9 PB - IEEE AN - OPUS4-54678 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stamm, Michael A1 - Krankenhagen, Rainer T1 - Weather-dependent passive thermography of unheated wind turbine blades N2 - Up to now, the inspection of wind turbines with industrial climbers has been considered ”state of the art”. However, ever-larger wind turbines and advancing digitization make modern and automated inspection methods indispensable. Passive thermography can serve as such a digital and atomized method while it is well known for its applications in the inspection of buildings or electrical circuits. However, its application relies on thermal gradients in the inspected object such that a temperature contrast exists between damaged and sound areas. This also holds for unheated structures like rotor blades of wind turbines which show no intrinsic temperature gradient and can hardly be heated. Under certain weather conditions with sufficient solar loading and diurnal temperature variations, passive thermography is suitable for the in-service inspection of rotor blades. However, for a reliable use of passive thermography on ”thermal passive” components, the incorporation of these environmental conditions in the planning and evaluation of thermal inspections is crucial. Additionally, the complex inner structure of wind turbine blades in comparison to other objects and buildings require a specific method referencing the individual rotor blades to each other. This allows the distinction between the thermal response of design-specific structural features and damages or irregularities between the three blades. We show thermal signatures of damage in rotor blades and contrast them with structural characteristics by comparing the three blades. In addition to measurements in industrial environments, laboratory measurements are shown and compared to simulations. The long-term goal is to simulate the influence of different weather parameters and thus gain a better understanding of measurements in the field. The results shown here can be seen as one step towards industrial application. T2 - SPIE Defense + Commercial Sensing CY - Orlando, Florida, USA DA - 03.04.2022 KW - Passive thermography KW - Wind energy KW - FEM simulations PY - 2022 DO - https://doi.org/10.1117/12.2618740 VL - 12109 SP - 1 EP - 8 PB - Society of Photo-Optical Instrumentation Engineers (SPIE) AN - OPUS4-54943 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stamm, Michael T1 - Weather-dependent passive thermography of unheated wind turbine blades N2 - Up to now, the inspection of wind turbines with industrial climbers has been considered ”state of the art”. However, ever-larger wind turbines and advancing digitization make modern and automated inspection methods indispensable. Passive thermography can serve as such a digital and atomized method while it is well known for its applications in the inspection of buildings or electrical circuits. However, its application relies on thermal gradients in the inspected object such that a temperature contrast exists between damaged and sound areas. This also holds for unheated structures like rotor blades of wind turbines which show no intrinsic temperature gradient and can hardly be heated. Under certain weather conditions with sufficient solar loading and diurnal temperature variations, passive thermography is suitable for the in-service inspection of rotor blades. However, for a reliable use of passive thermography on ”thermal passive” components, the incorporation of these environmental conditions in the planning and evaluation of thermal inspections is crucial. Additionally, the complex inner structure of wind turbine blades in comparison to other objects and buildings require a specific method referencing the individual rotor blades to each other. This allows the distinction between the thermal response of design-specific structural features and damages or irregularities between the three blades. We show thermal signatures of damage in rotor blades and contrast them with structural characteristics by comparing the three blades. In addition to measurements in industrial environments, laboratory measurements are shown and compared to simulations. The long-term goal is to simulate the influence of different weather parameters and thus gain a better understanding of measurements in the field. The results shown here can be seen as one step towards industrial application. T2 - Defense + Commercial Sensing 2022 CY - Orlando, Florida, USA DA - 3.4.2022 KW - Passive thermography KW - Wind energy KW - FEM simulations PY - 2022 UR - https://spie.org/defense-commercial-sensing/presentation/Weather-dependent-passive-thermography-of-unheated-wind-turbine-blades/12109-19?SSO=1 AN - OPUS4-54944 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stamm, Michael T1 - Towards automated passive thermography of wind turbine blades N2 - Up to now, the inspection of wind turbines by industrial climbers has been considered "state of the art". However, many aspects like ever-larger wind turbines, minimizing the risk for man and machine and the advancing digitalization make modern and automated inspection methods indispensable. A particular interest here is contactless and remote methods that can be used with drones instead of climbing robots. The work presented here contributes to the long-term goal of making autonomous and advanced inspections of wind turbine rotor blades using drones ready for industrial use. Besides visual inspection, only a few inspection methods are capable of non-contact inspection on an industrial scale. Passive thermography can serve as such a contactless and digital inspection method and is well known for its applications in the inspection of buildings or electrical circuits. It can even sense both near-surface and subsurface defects. The sensitivity to subsurface defects makes one advantage of thermography over visual inspections. As a digital inspection method, it is generally also more objective and offers more comparability. For example, defects and their extent can be easily monitored and compared over time. However, its industrial application relies on thermal gradients in the inspected object such that a temperature contrast exists between damaged and sound areas. This also applies to large unheated structures such as wind turbine rotor blades, which do not have an intrinsic temperature gradient and at the same time cannot be easily heated externally. Under certain weather conditions, a change of the environmental temperature or the solar loading conditions can provide the necessary thermal gradients to make passive thermography viable for the in-service inspection of rotor blades. For a reliable use of passive thermography on "thermal passive" components, the incorporation of these environmental conditions in the planning and evaluation of thermal inspections is crucial. Compared to many other objects and buildings, wind turbine blades have varying and often unknown complex internal structures depending on the model. A special method is therefore required, that can be used independently of the internal structure of the blades and that relates the individual thermograms of the three rotor blades to each other. This allows the distinction between the thermal response of design-specific structural features and damages or irregularities between the three blades. In this work we present thermal signatures of rotating in-service rotor blades taken under industrial relevant conditions. These thermograms show surface and subsurface damages and irregularities which we contrast with structural design features by referencing the three blades to each other. In addition, we examine the strong influence of different weather conditions on the inspection results. A direct comparison of measured results with inspection reports from industrial climbers serves as a benchmark. T2 - EERA DeepWind conference CY - Trondheim, Norway DA - 19.01.2022 KW - Thermography KW - Wind energy KW - Passve IR KW - Rotor blades KW - Maintenance PY - 2022 AN - OPUS4-55818 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stamm, Michael T1 - Towards the in-service blade inspection by ground-based passive thermography N2 - Until today, the optical inspection of rotor blades by industrial climbers is considered state of the art. However, both more and larger rotor blades and the increasing digitalization of maintenance work make modern inspection methods increasingly necessary. In this context, passive thermography can serve as a useful digital technique for in-service inspection of wind turbine blades. Unlike active thermography, this inspection method does not require an active heat source but takes advantage of heating by the sun and diurnal temperature fluctuations. This allows inspections from the ground during operation and does not require shutting down the wind turbine. However, an inspection with passive thermography is highly weather dependent. Thus, the already weak thermal signatures formed due to internal structures and possible internal damage are only strong enough under certain weather conditions. To obtain meaningful inspection results despite the relatively small thermal differences between intact and defective components, three aspects are crucial: 1. Measurements should be taken at the time of optimum weather conditions. It must be kept in mind that different internal damage will be revealed by thermal signatures under different weather conditions. 2. The thermal signature of the rotor blades, including possible damages, must be simulated with FEM simulations. In this way, the influence of different weather conditions can be predicted but also understood in the aftermath. 3. The temperature differences between identically designed and assembled rotor blades must be considered to analyze variations between blades. This work will address all these aspects and show, based on field measurements under industrial conditions (exemplarily shown in figure 1), laboratory measurements and FEM simulations, which steps must be taken to establish passive thermography as an industrial inspection method. T2 - EERA SP7 Rotor Blade workshop CY - Roskilde, Denmark DA - 23.06.2022 KW - Thermography KW - Wind energy KW - Maintenance KW - Rotor blades KW - Passive IRT PY - 2022 AN - OPUS4-55819 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stamm, Michael T1 - In situ Charakterisierung von Reparaturen in GFK Schalenstrukturen mittels Lockin Thermografie und Felddehnungsmessungen N2 - Die tiefgreifende Reparatur von Faserverbundwerkstoffen stellt durch deren inneren Aufbau eine besondere Herausforderung dar, die unter anderem bei der Instandhaltung von Rotorblättern von Windkraftanlagen zum Tragen kommt. Um die Reparaturen von Rotorblattschalen zu untersuchen und zu optimieren, wurden an der BAM Sandwich-Schalenprüfkörper aus Glasfaserkunststoff (GFK) entwickelt. Nachdem in diese Schalenprüfkörper Modell-Reparaturen eingebracht wurden, werden zyklische mechanische Ermüdungsversuche bis zum Bruch durchgeführt. Vorrangiges Ziel ist es, den Einfluss verschiedener Reparaturvariablen auf die Ermüdungslebensdauer der Struktur zu verstehen, sowie die stabilste Reparaturmethode zu bestimmen. Während der zyklischen Lastversuche wurden regelmäßig in-situ Messungen mit einer Thermografie Kamera und einem optischen Felddehnungsmesssystem durchgeführt. Durch beide Messmethoden lassen sich Eigenschaften der Probekörper zeitlich und räumlich aufgelöst darstellen. Während die Felddehnungsmessungen Aufschluss über die Verformung an der Oberfläche geben, erfasst die thermische Inspektion Temperaturänderungen an der Oberfläche. Besonders die thermografischen Messwerte bilden hier das oberflächennahe Volumen ab, in dem sich Temperaturänderungen an der Oberfläche abzeichnen. Die Messergebnisse beider Systeme stellen also verschiede aber korrelierte Parameter dar. Denn die zyklische Belastung (Bewegung) ruft eine periodische Temperaturänderung im Bauteil hervor. Dieser so genannte Thermoeleastische Effekt kann durch eine Lockin-Analyse der Temperaturtransienten (Temperaturverläufe) nachgewiesen werden. Die räumliche Darstellung der thermischen Effekte lässt Rückschlüsse auf die tatsächliche Lastverteilung im Probekörpervolumen zu. Darüber hinaus führen nichtelastische Verformungen zu einer zusätzlichen Wärmefreisetzung, die durch geeignete Auswerteverfahren ebenfalls nachgewiesen werden können. Entsprechende Hot-Spots in der räumlichen Verteilung erlauben eine frühzeitige Erkennung besonders belasteter Bereiche lange vor dem eigentlichen Bauteil-Versagen. Das gestattet die Lokalisierung des Initial-Schadens, was mit der numerischen Spannungsanalyse korreliert werden kann und die Entwicklung und Bewertung verschiedener Reparaturstrategien. T2 - DGZfP Jahrestagung 2022 CY - Kassel, Germany DA - 23.05.2022 KW - Lockin Thermografie KW - GFK KW - NDT KW - ZfP PY - 2022 AN - OPUS4-55823 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hauffen, J. C. A1 - Kästner, L. A1 - Ahmadi, Samim A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias T1 - Learned block iterative shrinkage thresholding algorithm for photothermal super resolution imaging N2 - Block-sparse regularization is already well known in active thermal imaging and is used for multiple-measurement-based inverse problems. The main bottleneck of this method is the choice of regularization parameters which differs for each experiment. We show the benefits of using a learned block iterative shrinkage thresholding algorithm (LBISTA) that is able to learn the choice of regularization parameters, without the need to manually select them. In addition, LBISTA enables the determination of a suitable weight matrix to solve the underlying inverse problem. Therefore, in this paper we present LBISTA and compare it with state-of-the-art block iterative shrinkage thresholding using synthetically generated and experimental test data from active thermography for defect reconstruction. Our results show that the use of the learned block-sparse optimization approach provides smaller normalized mean square errors for a small fixed number of iterations. Thus, this allows us to improve the convergence speed and only needs a few iterations to generate accurate defect reconstruction in photothermal super-resolution imaging. KW - Thermography KW - Laser KW - Machine learning KW - Optimization KW - Non-destructive testing KW - NDT KW - Neural network KW - Defect reconstruction KW - Block-sparsity KW - Active thermal imaging KW - Regularization KW - Laser thermography PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-554598 DO - https://doi.org/10.3390/s22155533 SN - 1424-8220 VL - 22 IS - 15 SP - 1 EP - 15 PB - MDPI CY - Basel AN - OPUS4-55459 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krankenhagen, Rainer A1 - Maierhofer, Christiane ED - Drachenberg, T. T1 - Thermische Kontraste - Der Blick hinter die Fassade N2 - Die Thermografie beruht auf der bildlichen Darstellung von Temperaturunterschieden oder auch thermischen Kontrasten an der Oberfläche eines Untersuchungsobjektes. Diese bilden sich nur her-aus, wenn sich das Untersuchungsobjekt gerade erwärmt oder abkühlt. Der Beitrag erklärt mittels eines stark vereinfachten Modells die Entstehung solcher Kontraste als dynamischen Effekt verschiedener Abkühlgeschwindigkeiten. Neben Laborergebnissen werden beispielhaft einige Ergeb-nisse von einem mittelalterlichen Baudenkmal präsentiert, um das Verständnis für die thermografische Inspektion von Fassaden zu vertiefen. T2 - 14. Konservierungswissenschaftliches Kolloquium Berlin Brandenburg CY - Berlin, Germany DA - 12.11.2021 KW - Ablösungen KW - Aktive Thermografie KW - Bauthermografie KW - Metallanker PY - 2021 SN - 978-3-945880-90-6 VL - 61 SP - 104 EP - 119 PB - Hendrik Bäßler CY - Berlin AN - OPUS4-55475 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ziegler, Mathias T1 - Thermographic super resolution reconstruction using 2D pseudo-random pattern illumination N2 - Thermographic non-destructive testing is based on the interaction of thermal waves with inhomogeneities. The propagation of thermal waves from the heat source to the inhomogeneity and to the detection surface according to the thermal diffusion equation leads to the fact that two closely spaced defects can be incorrectly detected as one defect in the measured thermogram. In order to break this spatial resolution limit (super resolution), the combination of spatially structured heating and numerical methods of compressed sensing can be used. The improvement of the spatial resolution for defect detection then depends in the classical sense directly on the number of measurements. Current practical implementations of this super resolution detection still suffer from long measurement times, since not only the achievable resolution depends on performing multiple measurements, but due to the use of single spot laser sources or laser arrays with low pixel count, also the scanning process itself is quite slow. With the application of most recent high-power digital micromirror device (DMD) based laser projector technology this issue can now be overcome. T2 - ICPPP21: International Conference on Photoacoustic and Photothermal Phenomena CY - Bled, Slovenia DA - 19.06.2022 KW - Thermography KW - Super resolution KW - NDT KW - Inspection KW - Internal defects KW - DMD KW - DLP PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-551224 UR - https://indico.ung.si/event/5/contributions/237/ AN - OPUS4-55122 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lecompagnon, Julien A1 - Ahmadi, Samim A1 - Hirsch, Philipp Daniel A1 - Rupprecht, C. A1 - Ziegler, Mathias T1 - Thermographic detection of internal defects using 2D photothermal super resolution reconstruction with sequential laser heating N2 - Thermographic photothermal super resolution reconstruction enables the resolution of internal defects/inhomogeneities below the classical limit, which is governed by the diffusion properties of thermal wave propagation. Based on a combination of the application of special sampling strategies and a subsequent numerical optimization step in post-processing, thermographic super resolution has already proven to be superior to standard thermographic methods in the detection of one-dimensional defect/inhomogeneity structures. In our work, we report an extension of the capabilities of the method for efficient detection and resolution of defect cross sections with fully two-dimensional structured laser-based heating. The reconstruction is carried out using one of two different algorithms that are proposed within this work. Both algorithms utilize the combination of several coherent measurements using convex optimization and exploit the sparse nature of defects/inhomogeneities as is typical for most nondestructive testing scenarios. Finally, the performance of each algorithm is rated on reconstruction quality and algorithmic complexity. The presented experimental approach is based on repeated spatially structured heating by a high power laser. As a result, a two-dimensional sparse defect/inhomogeneity map can be obtained. In addition, the obtained results are compared with those of conventional thermographic inspection methods that make use of homogeneous illumination. Due to the sparse nature of the reconstructed defect/inhomogeneity map, this comparison is performed qualitatively. KW - Thermography KW - Super resolution KW - NDT KW - Inspection KW - Internal defects PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-548351 DO - https://doi.org/10.1063/5.0088102 SN - 1089-7550 VL - 131 IS - 18 SP - 1 EP - 12 PB - AIP Publishing AN - OPUS4-54835 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Scheuschner, Nils T1 - In-situ Prozessüberwachung in der additiven Fertigung von Metallen (PBF-LB /M) mittels TT und ET N2 - Durch die additive Fertigung ergeben sich durch die nun mögliche wirtschaftliche Fertigung hochgradig individueller und komplexer metallischer Bauteile in kleinen Stückzahlen bis hinunter zum Einzelstück für viele Industriebereiche ganz neue Möglichkeiten. Gleichzeitig entstehen jedoch neue Herausforderungen im Bereich der Qualitätssicherung, da sich auf statistischen Methoden beruhende Ansätze nicht anwenden lassen, ohne wiederum die Vorteile der Fertigung massiv einzuschränken. Eine mögliche Lösung für dieses Problem liegt in der Anwendung verschiedener In-situ-Überwachungstechniken während des Bauprozesses. Jedoch sind nur wenige dieser Techniken kommerziell verfügbar und noch nicht so weit erforscht, dass die Einhaltung strenger Qualitäts- und Sicherheitsstandards gewährleistet werden kann. In diesem Beitrag stellen wir die Ergebnisse einer Studie über mittels L-PBF gefertigte Probekörper aus der Nickelbasis-Superlegierung Haynes 282 vor, bei denen die Bildung von Defekten durch lokale Variationen der Prozessparameter wie der Laserleistung provoziert wurde. Die Proben wurden in-situ mittels Thermographie, optischer Tomographie, Schmelzbadüberwachung und Wirbelstromprüfung sowie ex-situ mittels Computertomographie (CT) überwacht, mit dem Ziel, die Machbarkeit und die Aussichten der einzelnen Methoden für die zuverlässige Erkennung der Bildung relevanter Defekte zu bewerten. T2 - DGZfP Jahrestagung 2022 CY - Kassel, Germany DA - 23.05.2022 KW - Additive Manufacturing KW - Thermografie KW - Additive Fertigung KW - Thermography PY - 2022 AN - OPUS4-55851 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Scheuschner, Nils T1 - In-situ Monitoring of PBF-LB/M by thermography, optical tomography, melt-pool-monitoring and eddy current N2 - The formation of defects such as keyhole pores is a major challenge for the production of metal parts by Laser Powder Bed Fusion (LPBF). The LPBF process is characterized by a large number of influencing factors which can be hard to quantify. Machine Learning (ML) is a prominent tool to predict the outcome of complex processes on the basis of different sensor data. In this study, a ML model for defect prediction is created using thermographic image features as input data. As a reference, the porosity information calculated from an x-ray Micro Computed Tomography (µCT) scan of the produced specimen is used. Physical knowledge about the keyhole pore formation is incorporated into the model to increase the prediction accuracy. From the prediction result, the quality of the input data is evaluated and future demands on in-situ monitoring of LPBF processes are formulated. T2 - AM Bench 2022 CY - Bethesda, Washingthon DC, USA DA - 15.08.2022 KW - Additive Manufacturing KW - Thermography KW - Additive Fertigung KW - Thermografie PY - 2022 AN - OPUS4-55854 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pech May, Nelson Wilbur T1 - Robot-assisted laser thermography for surface breaking crack detection on complex shaped components N2 - Laser thermography using a focused (spot or line) beam has proved to be effective for detection of surface breaking cracks on planar samples. In this work, we use the same principle, but applied to complex shaped components, like a rail cross-section, a gear, and a gas turbine blade. We use a six-axis robot to move the sample in-front of our thermographic setup. Several scanning-path and thermographic parameters are explored: scanning speed, density of points in each scanning slice, laser power, camera framerate. Additionally, we explore semi-automatic evaluation algorithms for crack detection, as well as 2D-to-3D registration of the found indications. T2 - SPIE Future Sensing Technologies 2023 CY - Yokohama, Japan DA - 18.04.2023 KW - Flying line thermography KW - Crack-detection algorithms PY - 2023 UR - https://www.spiedigitallibrary.org/conference-proceedings-of-spie/12327/1232715/Robot-assisted-infrared-thermography-for-surface-breaking-crack-detection-on/10.1117/12.2666757.short AN - OPUS4-57594 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Scheuschner, Nils T1 - In-situ monitoring of the laser powder bed fusion process by thermography, optical tomography and melt pool monitoring for defect detection N2 - For the wide acceptance of the use of additive manufacturing (AM), it is required to provide reliable testing methods to ensure the safety of the additively manufactured parts. A possible solution could be the deployment of in-situ monitoring during the build process. However, for laser powder bed fusion using metal powders (PBF-LB/M ) only a few in-situ monitoring techniques are commercially available (optical tomography, melt pool monitoring) but not researched to an extent that allows to guarantee the adherence to strict quality and safety standards. In this contribution, we present results of a study of PBF-LB/M printed parts made of the nickel-based superalloy Haynes 282. The formation of defects was provoked by local variations of the process parameters and monitored by thermography, optical tomography and melt pool monitoring. Afterwards, the defects were characterized by computed tomography (CT) to identify the detection limits of the used in-situ techniques. T2 - LiM Conference 2023 - Lasers in Manufacturing CY - Munich, Germany DA - 26.06.2023 KW - Thermography KW - High temperature alloys KW - Additive Manufacturing KW - PBF-LB/M PY - 2023 AN - OPUS4-57947 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Thermographic Detection of Internal Defects using Photothermal Super Resolution Reconstruction and 2D structured Illumination Patterns N2 - For a long time, the rule of thumb for active thermography as a non-destructive testing method was that the resolution of internal defects/inhomogeneities is limited to a ratio of defect depth/defect size ≤ 1. This is due to the diffusive nature of thermal conduction in solids. So-called super resolution approaches have recently allowed this physical limit to be overcome many times over. This offers the attractive possibility of developing thermography from a purely near surface-sensitive testing method to one with improved depth range. How far this development can be pushed is the subject of current research. We have already been able to show that this classical limitation for one- and two-dimensional defect geometries can be overcome by illuminating the test object sequentially in a structured manner with individual laser spots and thus subsequently calculating a defect map from the resulting measurement data by applying photothermal super resolution reconstruction, which allows significantly improved separation of individual closely spaced defects. As a result, this method benefits strongly from the combination of sequential spatially structured illumination and modern numerical optimization methods, which come at the expense of higher experimental complexity. This leads to long measurement times, large data sets, and tedious numerical analysis, in contrast to the application of established standard thermographic methods with homogeneous illumination. In this work, we report on the application of full-area spatially structured two-dimensional illumination patterns, which, by applying state-of-the-art laser projector technology in conjunction with a high-power laser, makes it possible to achieve an efficient implementation of photothermal super-resolution reconstruction even for larger test areas in the first place. T2 - 13th European Conference on Non-destructive Testing CY - Lisbon, Portugal DA - 03.07.2023 KW - Thermography KW - Super resolution KW - Digital light processing KW - Material testing KW - Internal defects KW - DMD PY - 2023 AN - OPUS4-57909 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Detection of internal defects applying photothermal super resolution reconstruction utilizing two-dimensional high-power random pixel patterns N2 - In this work, we report on our progress for investigating a new experimental approach for thermographic detection of internal defects by performing 2D photothermal super resolution reconstruction. We use modern high-power laser projector technology to repeatedly excite the sample surface photothermally with varying spatially structured 2D pixel patterns. In the subsequent (blind) numerical reconstruction, multiple measurements are combined by exploiting the joint-sparse nature of the defects within the specimen using nonlinear convex optimization methods. As a result, a 2D-sparse defect/inhomogeneity map can be obtained. Using such spatially structured heating combined with compressed sensing and computational imaging methods allows to significantly reduce the experimental complexity and to study larger test surfaces as compared to the one-dimensional approach reported earlier. T2 - Quantitative Infrared Thermography 2022 CY - Paris, France DA - 04.07.2022 KW - Thermography KW - Super resolution KW - NDT KW - Inspection KW - Internal defects KW - DMD KW - DLP PY - 2022 AN - OPUS4-55262 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Rupprecht, C. A1 - Ziegler, Mathias T1 - Hochaufgelöste thermografische Detektion eingeschlossener Defekte mit Hilfe von 2Dstrukturierten Beleuchtungsmustern N2 - Für die aktive Thermografie als zerstörungsfreie Prüfmethode galt lange Zeit die Faustformel, dass die Auflösung interner Defekte/Inhomogenitäten auf ein Verhältnis von Defekttiefe/Defektgröße ≤ 1 beschränkt ist. Die Ursache hierfür liegt in der diffusiven Natur der Wärmeleitung in Festkörpern. Sogenannte Super-Resolution-Ansätze erlauben seit Kurzem die Überwindung dieser physikalischen Grenze um ein Vielfaches. Damit ergibt sich die attraktive Möglichkeit die Thermografie von einem rein oberflächensensitiven Prüfverfahren hin zu einem Verfahren mit verbesserter Tiefenreichweite zu entwickeln. Wie weit diese Entwicklung getrieben werden kann, ist Gegenstand aktueller Forschung. Wir konnten bereits zeigen, dass diese klassische Grenze für 1D- und 2D Defektgeometrien mit Hilfe des Abscannens des Prüfkörpers mittels einzelner Laserspots und der anschließenden Anwendung von photothermischer Super-Resolution-Rekonstruktion überwunden werden kann. Bei dieser Methode wird eine Kombination aus sequenzieller räumlich strukturierter Beleuchtung und numerischen Optimierungsmethoden eingesetzt. Dies geschieht allerdings auf Kosten der experimentellen Komplexität, die zu einer langen Messdauer, großen Datensätzen und langwieriger numerischer Auswertung führt. In dieser Arbeit berichten wir über einen neuen experimentellen Ansatz, bei dem räumlich strukturierte 2D-Beleuchtungsmuster in Verbindung mit Compressed-Sensing und Computational-Imaging-Methoden verwendet werden, um die experimentelle Komplexität deutlich zu verringern und die Methode für die Untersuchung größerer Prüfflächen nutzbar zu machen. Der experimentelle Ansatz basiert dabei auf der wiederholten (blinden) photothermischen Anregung mit räumlich strukturierten 2D-Mustern unter Verwendung moderner Projektortechnik und eines Hochleistungslasers. In der anschließenden numerischen Rekonstruktion werden mehrere Messungen unter Ausnutzung der Joint-Sparsity der Defekte innerhalb des Prüfkörpers mittels nichtlinearer konvexer Optimierungsmethoden kombiniert. Als Ergebnis kann eine 2D-sparse Defekt-/Inhomogenitätskarte erstellt werden. T2 - DGZfP-Jahrestagung 2022 CY - Kassel, Germany DA - 23.05.2022 KW - Thermografie KW - Super resolution KW - NDT KW - ZfP KW - Eingeschlossene Defekte KW - Projektor PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-548945 SN - 978-3-947971-25-1 VL - 177 SP - 1 EP - 16 PB - Deutsche Gesellschaft für Zerstörungsfreie Prüfung AN - OPUS4-54894 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Hochaufgelöste thermografische Detektion eingeschlossener Defekte mit Hilfe von 2Dstrukturierten Beleuchtungsmustern N2 - Für die aktive Thermografie als zerstörungsfreie Prüfmethode galt lange Zeit die Faustformel, dass die Auflösung interner Defekte/Inhomogenitäten auf ein Verhältnis von Defekttiefe/Defektgröße ≤ 1 beschränkt ist. Die Ursache hierfür liegt in der diffusiven Natur der Wärmeleitung in Festkörpern. Sogenannte Super-Resolution-Ansätze erlauben seit Kurzem die Überwindung dieser physikalischen Grenze um ein Vielfaches. Damit ergibt sich die attraktive Möglichkeit die Thermografie von einem rein oberflächensensitiven Prüfverfahren hin zu einem Verfahren mit verbesserter Tiefenreichweite zu entwickeln. Wie weit diese Entwicklung getrieben werden kann, ist Gegenstand aktueller Forschung. Wir konnten bereits zeigen, dass diese klassische Grenze für 1D- und 2D-Defektgeometrien mit Hilfe des Abscannens des Prüfkörpers mittels einzelner Laserspots und der anschließenden Anwendung von photothermischer Super-Resolution-Rekonstruktion überwunden werden kann. Bei dieser Methode wird eine Kombination aus sequenzieller räumlich strukturierter Beleuchtung und numerischen Optimierungsmethoden eingesetzt. Dies geschieht allerdings auf Kosten der experimentellen Komplexität, die zu einer langen Messdauer, großen Datensätzen und langwieriger numerischer Auswertung führt. In dieser Arbeit berichten wir über einen neuen experimentellen Ansatz, bei dem räumlich strukturierte 2D-Beleuchtungsmuster in Verbindung mit Compressed-Sensing und Computational-Imaging-Methoden verwendet werden, um die experimentelle Komplexität deutlich zu verringern und die Methode für die Untersuchung größerer Prüfflächen nutzbar zu machen. Der experimentelle Ansatz basiert dabei auf der wiederholten (blinden) photothermischen Anregung mit räumlich strukturierten 2D-Mustern unter Verwendung moderner Projektortechnik und eines Hochleistungslasers. In der anschließenden numerischen Rekonstruktion werden mehrere Messungen unter Ausnutzung der Joint-Sparsity der Defekte innerhalb des Prüfkörpers mittels nichtlinearer konvexer Optimierungsmethoden kombiniert. Als Ergebnis kann eine 2D-sparse Defekt-/Inhomogenitätskarte erstellt werden. T2 - DGZfP-Jahrestagung 2022 CY - Kassel, Germany DA - 23.05.2022 KW - Thermografie KW - Super resolution KW - NDT KW - ZfP KW - Eingeschlossene Defekte KW - Projektor PY - 2022 AN - OPUS4-54895 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pech May, Nelson Wilbur T1 - Robot-assisted laser thermography - Towards automatic characterization of surface defects N2 - By means of laser thermography, surface defects, in particular surface breaking cracks, can be detected with high sensitivity. Basically, this requires a focused heat source (high-power laser), a thermographic camera and a relative movement between laser and test object, as well as a suitable evaluation algorithm to distinguish between surface defects and defect-free areas. In this paper we report on a method in which the relative motion is realised by a robot to fully inspect large and non-planar test objects such as rail sections, turbine blades, gears, etc. We show the influence of the excitation laser, which can be varied in terms of spot geometry, wavelength, and scan scheme, and we demonstrate our evaluation algorithms with the aim of automatically detecting surface defects. T2 - 16th Quantitative Infrared Thermography Conference CY - Paris, France DA - 04.07.2022 KW - Flying line thermography KW - Surface breaking defects KW - Robot-assisted thermography PY - 2022 AN - OPUS4-55560 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krankenhagen, Rainer T1 - Obituary of Christiane Maierhofer N2 - Obituary for Christiane Maierhofer, the head of the department "Thermographic Methods" at BAM (2015-2022). KW - Obituary KW - In Memoriam PY - 2022 DO - https://doi.org/10.1080/17686733.2022.2105019 SN - 1768-6733 SN - 2116-7176 VL - 19 IS - 4 SP - 221 EP - 222 PB - Taylor & Francis CY - London AN - OPUS4-55603 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Tran, T. A1 - Kodisch, C. A1 - Schöttle, M. A1 - Pech May, Nelson Wilbur A1 - Retsch, M. T1 - Characterizing the thermal diffusivity of single, micrometer-sized fibers via high-resolution lock-in thermography N2 - Many advanced materials consist of fibers. They are used as nonwovens, fabrics, or in composite materials. Characterization of individual fibers allows us to predict resulting material properties. We present a measurement setup and analysis software to characterize individual, micrometer-sized fibers fast and reliably. The setup is based on the lock-in thermography principle. Thermal diffusivity values of seven reference samples agree very well with previously reported values. We use our setup to investigate critical measurement parameters like excitation frequency, excitation power, pixel size, and fiber orientation. Our results show that fibers with subpixel diameters can be measured even if they are not aligned. However, special care has to be taken to choose an adequate excitation power. Measurements at high intensities can underestimate thermal diffusivity even though the raw data looks reasonable. By automatically measuring at different excitation powers, our setup solves this issue. KW - Surfaces, coatings and films KW - Physical and theoretical chemistry KW - General energy KW - Electronic, optical and magnetic materials PY - 2022 DO - https://doi.org/10.1021/acs.jpcc.2c04254 SN - 1932-7455 VL - 126 IS - 32 SP - 14003 EP - 14010 PB - American Chemical Society (ACS) CY - Washington, DC AN - OPUS4-58128 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Rupprecht, C. A1 - Ziegler, Mathias T1 - Influence of the number of measurements on detecting internal defects using photothermal super resolution reconstruction with random pixel patterns N2 - In this work, the limits of using spatially structured heating combined with subsequent photothermal super resolution reconstruction for the thermographic detection and resolution of internal defects are investigated. The approach is based on the application of modern high-power laser projector technology, which is used to repeatedly project varying spatially structured 2D pixel patterns to photothermally heat the object under test. After processing the generated thermographic data using nonlinear convex optimisation in conjunction with exploiting the joint-sparse nature of the defect signals within the individual measurements, a high-resolution 2D-sparse defect/inhomogeneity map is obtained. The main focus of the investigation is set on the influence of the number of individual measurements on the achievable reconstruction quality. Using numerical simulations based on an analytical representation of the forward solution to the underlying inverse problem, the convergence rate over performed measurements of the achievable reconstruction quality is determined. Finally, all findings are experimentally validated by reconstructing a set of internal defects in an additively manufactured sample. In this work, it is shown that for a variety of different defect separation distances, the projection of 50 different pixel patterns allows for a good trade-off between experimental complexity and reconstruction quality. KW - Super resolution KW - Digital micromirror device KW - Digital light processing KW - Internal defects PY - 2023 DO - https://doi.org/10.1080/17686733.2023.2223392 SN - 2116-7176 SP - 1 EP - 11 PB - Taylor & Francis AN - OPUS4-57778 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Rupprecht, C. A1 - Ziegler, Mathias ED - Maldague, X. T1 - Detection of internal defects applying photothermal super resolution reconstruction utilizing two-dimensional high-power random pixel patterns N2 - In this work, we report on our progress for investigating a new experimental approach for thermographic detection of internal defects by performing 2D photothermal super resolution reconstruction. We use modern high-power laser projector technology to repeatedly excite the sample surface photothermally with varying spatially structured 2D pixel patterns. In the subsequent (blind) numerical reconstruction, multiple measurements are combined by exploiting the joint-sparse nature of the defects within the specimen using nonlinear convex optimization methods. As a result, a 2D-sparse defect/inhomogeneity map can be obtained. Using such spatially structured heating combined with compressed sensing and computational imaging methods allows to significantly reduce the experimental complexity and to study larger test surfaces as compared to the one-dimensional approach reported earlier. T2 - Quantitative Infrared Thermography 2022 CY - Paris, France DA - 04.07.2022 KW - Thermography KW - Super resolution KW - NDT KW - inspection KW - Internal defects KW - DMD KW - DLP PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-577795 DO - https://doi.org/10.21611/qirt.2022.1005 SN - 2371-4085 SP - 1 EP - 7 PB - QIRT Council AN - OPUS4-57779 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krankenhagen, Rainer T1 - Photothermal determination of thermal properties of concrete – a method evaluation N2 - The evaluation of thermal properties is probably an underrated tool for the onsite health monitoring of concrete structures. The photothermal approach offers a possibility to realize a real onsite measurement. This contribution presents the application of the photothermal approach under lab conditions on three different concrete types. The obtained results were compared with those of a commercial device based on the Transient Plane Source (TPS) method. Both agreed well within the estimated uncertainty ranges and therefore demonstrate the applicability of the photothermal method for this kind of investigations. First results of a concrete sample with different water contents support the potential of this method for the characterization of concrete in general. T2 - NDTCE 2022 CY - Zurich, Switzerland DA - 16.8.2022 KW - Thermal effusivity KW - Thermal conductivity KW - Moisture PY - 2022 AN - OPUS4-56063 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krankenhagen, Rainer T1 - Quantitative Bewertung von Randeffekten bei einer einfachen thermografischen Transmissionsmessung mittels FEM N2 - Der Einsatz von Simulationen mit FEM (Finite Element Method) ermöglicht die die quantitative Beschreibung von Wärmeleitungsprozessen in komplexen Geometrien, bei denen analytische Ansätze nicht angewandt werden können, weil die zugrunde liegenden Vereinfachungen nicht gelten. Bei der genauen Modellierung eines kompletten thermografischen Experiments sieht sich der Modellierer einer ganzen Reihe von technischen und physikalischen Parametern gegenüber, die nicht immer bekannt sind und daher geschätzt werden müssen. Im konkreten Fall wurde ein relativ einfaches Experiment mit einfachen Geometrien betrachtet: ein durch Additive Manufacturing gefertigter Metallblock wurde mit einem Laserpuls homogen erwärmt. Aus dem Zeitverlauf der Oberflächentemperatur an der nicht erwärmten Rückseite des gleichmäßig dicken Blocks sollte die thermische Diffusivität des Volumenmaterials ermittelt werden. Bei dem Versuch, die experimentellen Daten durch eine passende Simulation zu beschreiben, ergab sich zunächst eine deutliche Abweichung: die gemessenen Temperaturen waren generell zu niedrig, was auf einen zusätzlichen Wärmeverlustmechanismus hinwies. Es erwies sich, dass die freie Auflage des Materialblocks auf einem flachen Bolzen zur Probenfixierung bei der Simulation des Experiments zu berücksichtigen ist, um eine gute Übereinstimmung zwischen Experiment und thermischer Simulation zu erzielen. Der Beitrag illustriert damit die Möglichkeiten und Potentiale von FEM-Simulationen bei der quantitativen Bewertung von thermografischen Inspektionen zur zerstörungsfreien Prüfung. T2 - Thermografie-Kolloquium der DGZfP CY - Saarbrücken, Germany DA - 28.9.2022 KW - Thermische Simulation KW - Aktive Thermografie KW - Thermischer Kontakt PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-560641 UR - https://www.ndt.net/search/docs.php3?id=27487 PB - NDT.net CY - Bad Breisig AN - OPUS4-56064 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ziegler, Mathias T1 - Stand der Normierung in der Thermografie N2 - Die Thermografie ist trotz ihrer ausgereiften wissenschaftlichen und technologischen Grundlagen ein noch relativ junges Mitglied in der Familie der zerstörungsfreien Prüfverfahren. Sie erschließt sich aufgrund einer Reihe von Vorzügen eine wachsende Anwenderschaft. Für eine weitere Verbreitung insbesondere im industriellen Kontext spielen Normen, Standards und Richtlinien eine wichtige Rolle. In diesem Beitrag wird der aktuelle Stand der Normierung vorgestellt. Wir werden zeigen, welche Grundlagennormen und Anwendungsnormen es für die Thermografie in Deutschland und international gibt und wir wagen einen Blick in die Zukunft. Darüber hinaus lebt auch die Normierungsarbeit von der Beteiligung durch interessierte Kreise. Dies können industrielle und akademische Anwender*innen, Hersteller*innen von Geräten, Forschungseinrichtungen oder Dienstleistungsunternehmen sein. Sie können gern Ihre Bedarfe bezüglich Normierungsprojekten mitbringen und/oder direkt an die Autoren senden. T2 - Thermographie-Kolloquium 2022 CY - Saarbrücken, Germany DA - 27.09.2022 KW - Thermografie KW - Normung KW - Normierung KW - Standardisierung KW - Zerstörungsfreie Prüfung PY - 2022 AN - OPUS4-55972 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Chaudhuri, Somsubhro T1 - EvalTherm - Weather-dependent passive thermography and thermal simulation of in-service wind turbine blades N2 - To cope with the increase in the manufacturing and operation of wind turbines, wind farm operators need inspection tools that are able to provide reliable information while keeping the downtime low. Current inspection techniques require to stop the wind turbine. This work presents the current progress in the project EvalTherm, in which passive thermography is evaluated as a possible non-destructive inspection tool for operational wind turbine blades (WTBs). A methodology to obtain thermal images of rotating WTBs has been established in this project. However, the quality of the results is heavily dependent on various aspects such as weather conditions, information on the inspected WTB, damage history, etc. In this work, a section of a used WTB is simulated using finite-element modelling (FEM) as well as experimentally tested for evaluating the accuracy of the model. Such a model will provide insight into the potential thermal response of a certain structure (with specific material properties) in given weather (boundary) conditions. The model is able to provide satisfactory predictions of the thermal response of the structure, as well as indicate what thermal contrast(s) result from artificial defects introduced in the structure. T2 - WindEurope Annual Event 2023 CY - Copenhagen, Denmark DA - 25.04.2023 KW - FEM KW - Thermografie KW - Wind turbine rotor blades KW - Windenergie anlage rotorblätter PY - 2023 AN - OPUS4-58274 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Lasers: A versatile Heat Source for Modern Active Thermographic Testing N2 - The properties of laser radiation result in a wide range of applications, making laser technologies indispensable in areas such as industry, science and medicine. The possible areas of application for thermography in this context are just as diverse. Thermography is used in laser applications when permanent monitoring and control of thermal development is necessary. Among others, this is the case in additive manufacturing, laser-based measuring devices and non-destructive testing. Furthermore, thermography is ideally suited as a testing method when it comes to ensuring the quality of the laser itself. In this talk it is outlined, how lasers can be used as a heat source in active thermographic testing. Furthermore, two special variants (spatial & temporal structured heating) are described, for which lasers are highly suitable. T2 - Webinar: Laser Technologies Benefiting from Infrared Thermography CY - Online meeting DA - 24.04.2024 KW - Thermography KW - Laser KW - NDT PY - 2024 UR - https://www.infratec.eu/press/press-releases/details/2024-03-04-laser-technologies-benefiting-from-infrared-thermography/ AN - OPUS4-59934 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pech May, Nelson Wilbur A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Ziegler, Mathias T1 - Robot-assisted infrared thermography for surface breaking crack detection on complex shaped components N2 - Infrared thermography using a focused (spot or line) beam has proved to be effective for detection of surface breaking cracks on planar samples. In this work, we use the same principle, but applied to complex shaped components, like a rail section, a gear, and a gas turbine blade. We use a six-axis robot arm to move the sample in front of our thermographic setup. Several scanning paths and thermographic parameters are explored: scanning speed, density of points in each scanning slice, laser power and camera frame-rate. Additionally, we explore semi-automatic evaluation algorithms for crack detection, as well as 2D-to-3D registration of the found indications. T2 - SPIE Future Sensing Technologies, 2023 CY - Yokohama, Japan DA - 18.04.2023 KW - Complex shaped component testing KW - Flying line thermography KW - Robot-assisted thermography KW - Crack detection KW - Robot path planning KW - 2D/3D thermographic registration PY - 2023 DO - https://doi.org/10.1117/12.2666757 VL - 12327 SP - 1 EP - 3 PB - SPIE Future Sensing Technologies AN - OPUS4-59867 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krankenhagen, Rainer A1 - Dell'Avvocato, Giuseppe A1 - Gohlke, Dirk A1 - Palumbo, Davide A1 - Galietti, Umberto T1 - Quantitative evaluation of the welded area in Resistance Projection Welded (RPW) thin joints by pulsed laser thermography N2 - A semi-automatic thermographic procedure for the assessment of the welded area of resistance projection welded joints has been developed. Currently, to assess the quality of RPW joints destructive tests are used and the more commonly used non-destructive technique is the ultrasonic one. The possibility for a quantitative evaluation of the welded area by thermographic technique has been proved by means of an innovative procedure applied on steel RPW joints with ‘as it’ surface conditions. Measurements obtained by thermography and ultrasound have been compared, to verify the developed procedure. T2 - Thermosense: Thermal Infrared Applications XLIV, CY - Orlando, USA DA - 03.04.2022 KW - Nondestructive evaluation KW - Ultrasonics KW - Contact area PY - 2022 DO - https://doi.org/10.1117/12.2618806 VL - 12109 SP - 1 EP - 14 PB - SPIE AN - OPUS4-59380 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Automatisierte aktive thermografische Prüfung N2 - Aktive thermografische Prüfung ist ein vielseitiges Instrument in der Familie der zerstörungsfreien Prüfverfahren. Der Einzug moderner Lasertechnologie hat hier bedeutende neue Anwendungsfelder eröffnet. In Kombination mit Industrierobotik können nun beispielsweise beliebig komplex geformte Bauteile großflächig vollautomatisiert auf Oberflächenrisse überprüft werden. Der hier vorliegende Vortrag gibt einen Überblick über die Grundlagen der Laserthermografie, zeigt unsere Anstrengungen am Fachbereich im Bereich der automatisierten thermografischen Detektion von Oberflächenrissen und gibt ein Ausblick über neue moderne Thermografieverfahren aus der Forschung. T2 - VATH Frühjahrssymposium CY - Lingen, Germany DA - 26.04.2024 KW - Thermografie KW - Laser KW - ZfP PY - 2024 AN - OPUS4-59965 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Lecompagnon, Julien T1 - Nondestructive defect characterization using full-frame spatially structured super resolution laser thermography N2 - Laser-based active thermography is a contactless non-destructive testing method to detect material defects by heating the object and measuring its temperature increase with an infrared camera. Systematic deviations from predicted behavior provide insight into the inner structure of the object. However, its resolution in resolving internal structures is limited due to the diffusive nature of heat diffusion. Thermographic super resolution (SR) methods aim to overcome this limitation by combining multiple thermographic measurements and mathematical optimization algorithms to improve the defect reconstruction. Thermographic SR reconstruction methods involve measuring the temperature change in an object under test (OuT) heated with multiple different spatially structured illuminations. Subsequently, these measurements are inputted into a severely ill-posed and heavily regularized inverse problem, producing a sparse map of the OuT’s internal defect structure. Solving this inverse problem relies on limited priors, such as defect-sparsity, and iterative numerical minimization techniques. Previously mostly experimentally limited to one-dimensional regions of interest (ROIs), this thesis aims to extend the method to the reconstruction of two-dimensionalROIs with arbitrary defect distributions while maintaining reasonable experimental complexity. Ultimately, the goal of this thesis is to make the method suitable for a technology transfer to industrial applications by advancing its technology readiness level (TRL). In order to achieve the aforementioned goal, this thesis discusses the numerical expansion of a thermographic SR reconstruction method and introduces two novel algorithms to invert the underlying inverse problem. Furthermore, a forward solution to the inverse problem in terms of the applied SR reconstruction model is set up. In conjunction with an additionally proposed algorithm for the automated determination of a set of (optimal) regularization parameters, both create the possibility to conduct analytical simulations to characterize the influence of the experimental parameters on the achievable reconstruction quality. On the experimental side, the method is upgraded to deal with two-dimensional ROIs, and multiple measurement campaigns are performed to validate the proposed inversion algorithms, forward solution and two exemplary analytical studies. For the experimental implementation of the method, the use of a laser-coupled DLP-projector is introduced, which allows projecting binary pixel patterns that cover the whole ROI, reducing the number of necessary measurements per ROI significantly (up to 20x). Finally, the achieved reconstruction of the internal defect structure of a purpose-made OuT is qualitatively and qualitatively benchmarked against well-established thermographic testing methods based on homogeneous illumination of the ROI. Here, the background-noise-free two-dimensional photothermal SR reconstruction results show to outclass all defect reconstructions by the considered reference methods. N2 - Die laserbasierte aktive thermografische Prüfung als berührungslose Methode der zerstörungsfreien Werkstoffprüfung (NDT) basiert auf der aktiven Erwärmung des Testobjekts (OuT) und Messung des resultierenden Temperaturanstiegs mit einer Infrarotkamera. Dadurch bedingt können systematische Abweichungen vom vorhergesagten Erwärmungsverhalten Aufschluss über dessen innere Struktur geben. Jedoch ist das Auflösungsvermögen für innenliegende Defekte durch die diffusive Natur der Wärmeleitung in Festkörpern begrenzt. Thermografische Super-Resolution (SR)-Methoden zielen darauf ab, diese Limitation durch die Kombination mehrerer Messungen mit jeweils unterschiedlicher strukturierter Erwärmung und mathematischer Optimierungsmethoden zu überwinden. Zur Rekonstruktion innerer Defekte mithilfe thermografischer SR-Rekonstruktionsmethodik wird für die Gesamtheit mehrerer Messungen ein schlecht gestelltes und stark regularisiertes inverses mathematisches Problem gelöst, was in einer dünnbesetzten Karte der internen Defektstruktur des OuTs resultiert. Die Inversion mittels iterativer numerischer Minimierungsverfahren profitiert dabei von einzelnen Annahmen wie der vergleichsweisen Seltenheit von Materialdefekten. Nachdem die Methode bisher experimentell fast ausschließlich auf eindimensionale Messbereiche (ROIs) beschränkt war, zielt diese Arbeit auf eine Erweiterung zur Prüfung zweidimensionaler ROIs mit arbiträren Defektverteilungen bei erträglicher experimenteller Komplexität ab. Ziel ist es, durch die Weiterentwicklung des Technologie-Reifegrades (TRL) den Technologietransfer zur industriellen Anwendung zu ermöglichen. Hierzu werden erst die numerische Erweiterung der SR-Rekonstruktionsmethodik für zweidimensionale ROIs erörtert und zwei neue Algorithmen zur Invertierung des zugrunde liegenden inversen Problems vorgestellt, sowie eine Vorwärtslösung des inversen Problems entwickelt. In Verbindung mit einem neuartigen Algorithmus zur automatisierten Bestimmung der (optimalen) Regularisierungsparameter wird erstmals die Möglichkeit geschaffen, analytische Simulationen zum Einfluss einzelner Parameter auf die erreichbare Rekonstruktionsqualität durchzuführen. Weiterhin wird der experimentelle Ansatz zur Prüfung zweidimensionaler ROIs erweitert. Mehrere Messkampagnen validieren die eingeführten Inversionsalgorithmen, die Vorwärtslösung und zwei exemplarische analytische Studien. Für die experimentelle Umsetzung wird erstmals die Verwendung lasergekoppelter DLP-Technologie für die makroskopische thermografische Prüfung nutzbar gemacht, welche die Projektion großflächiger binärer Pixelmuster ermöglicht. Dadurch kann die Anzahl der erforderlichen Messungen pro ROI ohne Qualitätseinbußen erheblich reduziert werden (bis zu 20x). Abschließend werden die erzielten Rekonstruktionsergebnisse der internen Defektstruktur eines speziell angefertigten OuTs qualitativ und quantitativ mit auf homogener Erwärmung basierenden etablierten Methoden der thermografischen Prüfung verglichen. Hier zeigt sich, dass die weitgehend rauschfreien SR-Rekonstruktionsergebnisse alle Defektrekonstruktionen der betrachteten Referenzmethoden deutlich übertreffen. KW - Nondestructive testing KW - Zerstörungsfreie Prüfung KW - Thermography KW - Thermografie KW - Super resolution KW - Structured illumination KW - Strukturierte Beleuchtung KW - Defect characterization KW - Defektcharakterisierung KW - DMD KW - DLP PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-588296 DO - https://doi.org/10.14279/depositonce-19271 SP - 1 EP - 154 PB - Technische Universität Berlin CY - Berlin AN - OPUS4-58829 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Nondestructive defect characterization using full frame spatially structured super resolution laser thermography N2 - Laser-based active thermography is a contactless non-destructive testing method to detect material defects by heating the object and measuring its temperature increase with an infrared camera. Systematic deviations from predicted behavior provide insight into the inner structure of the object. However, its resolution in resolving internal structures is limited due to the diffusive nature of heat diffusion. Thermographic super resolution (SR) methods aim to overcome this limitation by combining multiple thermographic measurements and mathematical optimization algorithms to improve the defect reconstruction. Thermographic SR reconstruction methods involve measuring the temperature change in an object under test (OuT) heated with multiple different spatially structured illuminations. Subsequently, these measurements are inputted into a severely ill-posed and heavily regularized inverse problem, producing a sparse map of the OuT’s internal defect structure. Solving this inverse problem relies on limited priors, such as defect-sparsity, and iterative numerical minimization techniques. Previously mostly experimentally limited to one-dimensional regions of interest (ROIs), this thesis aims to extend the method to the reconstruction of twodimensional ROIs with arbitrary defect distributions while maintaining reasonable experimental complexity. Ultimately, the goal of this thesis is to make the method suitable for a technology transfer to industrial applications by advancing its technology readiness level (TRL). In order to achieve the aforementioned goal, this thesis discusses the numerical expansion of a thermographic SR reconstruction method and introduces two novel algorithms to invert the underlying inverse problem. Furthermore, a forward solution to the inverse problem in terms of the applied SR reconstruction model is set up. In conjunction with an additionally proposed algorithm for the automated determination of a set of (optimal) regularization parameters, both create the possibility to conduct analytical simulations to characterize the influence of the experimental parameters on the achievable reconstruction quality. On the experimental side, the method is upgraded to deal with two-dimensional ROIs, and multiple measurement campaigns are performed to validate the proposed inversion algorithms, forward solution and two exemplary analytical studies. For the experimental implementation of the method, the use of a laser-coupled DLP-projector is introduced, which allows projecting binary pixel patterns that cover the whole ROI, reducing the number of necessary measurements per ROI significantly (up to 20x). Finally, the achieved reconstruction of the internal defect structure of a purpose-made OuT is qualitatively and qualitatively benchmarked against well-established thermographic testing methods based on homogeneous illumination of the ROI. Here, the background-noise-free twodimensional photothermal SR reconstruction results show to outclass all defect reconstructions by the considered reference methods. T2 - Öffentliche wissenschaftliche Aussprache an der Technischen Universität Berlin CY - Berlin, Germany DA - 31.10.2023 KW - Thermography KW - Super resolution KW - NDT KW - Material testing KW - Internal defects KW - DMD KW - DLP PY - 2023 AN - OPUS4-58771 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Overcoming the Spatial Resolution Limits imposed by the Thermal MTF with Thermographic Photothermal Super Resolution Reconstruction N2 - The achievable spatial resolution of active thermographic testing is inherently limited by the diffusive nature of heat conduction in solids. This degradation of the achievable spatial resolution for a semi-infinite body acting on a defect signal can be approximated by spatial convolution with the Green’s function of the heat PDE. As the degradation in spatial resolution is dependent on the depth 𝐿, a common rule of thumb specifies that for proper detection, any defect should feature a spatial extension greater or equal to the depth it is located at. However, as the exact shape of a defect can have a large impact on its severity, at best a proper reconstruction of the defect shape should be performed, which therefore must also deal with the aforementioned adverse effects of heat conduction. One recent method to overcome the spatial resolution limit of thermographic testing is the photothermal super resolution reconstruction method. It is based on performing multiple active thermographic measurements on the same region of interest (ROI) with varying spatially structured heating and subsequent numerical reconstruction of the measured defect signals by solving a severely ill-posed inverse reconstruction problem relying on heavy regularization. By extending the experimental implementation of the method to make use of random-pixel patterns projected onto the ROI using a laser-coupled DLP-projector, defect reconstructions can now be performed within a reasonable time frame (~15 min per ROI) at high accuracy. Compared to conventional thermographic testing methods, the photothermal super resolution reconstruction stands out by resulting in a sparse representation of the defect structure of the ROI, making it especially well-suited to further automatic defect classification and quality assurance measures in an Industry 4.0 context. T2 - INTERNATIONAL SCHOOL OF QUANTUM ELECTRONICS: 67th Course: Progress in Photoacoustic & Photothermal Phenomena CY - Erice, Italy DA - 24.09.2023 KW - Thermography KW - Super resolution KW - NDT KW - Internal defects KW - DLP PY - 2023 AN - OPUS4-58472 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Chaudhuri, Somsubhro T1 - Weather-dependent passive thermography and thermal simulation of in-service wind turbine blades N2 - The thermographic methods NDT division of BAM is aiming to develop a wind turbine blade (WTB) inspection tool using infrared thermographic scanning of operational wind turbines in the project EvalTherm. T2 - WindEurope Annual Event 2023 CY - Copenhagen, Denmark DA - 25.04.2023 KW - FEM KW - Thermografie KW - Wind turbine rotor blades KW - Windenergie anlage rotorblätte PY - 2023 AN - OPUS4-58275 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Chaudhuri, Somsubhro A1 - Stamm, Michael A1 - Krankenhagen, Rainer T1 - Weather-dependent passive thermography and thermal simulation of in-service wind turbine blades N2 - . To cope with the increase in the manufacturing and operation of wind turbines, wind farm operators need inspection tools that are able to provide reliable information while keeping the downtime low. Current inspection techniques require to stop the wind turbine. This work presents the current progress in the project EvalTherm, in which passive thermography is evaluated as a possible non-destructive inspection tool for operational wind turbine blades (WTBs). A methodology to obtain thermal images of rotating WTBs has been established in this project. However, the quality of the results is heavily dependent on various aspects such as weather conditions, information on the inspected WTB, damage history, etc. In this work, a section of a used WTB is simulated using finite-element modelling (FEM) as well as experimentally tested for evaluating the accuracy of the model. Such a model will provide insight into the potential thermal response of a certain structure (with specific material properties) in given weather (boundary) conditions. The model is able to provide satisfactory predictions of the thermal response of the structure, as well as indicate what thermal contrast(s) result from artificial defects introduced in the structure. T2 - WindEurope Annual Event 2023 CY - Copenhagen, Denmark DA - 25.04.2023 KW - FEM KW - Thermografie KW - Wind turbine rotor blades KW - Windenergie Anlage Rotorblätter PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-582777 DO - https://doi.org/10.1088/1742-6596/2507/1/012025 VL - 2507 SP - 1 EP - 12 PB - IOP Publishing Ltd. AN - OPUS4-58277 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Chaudhuri, Somsubhro T1 - EvalTherm - Detectability of internal defects in wind turbine rotor blades using passive infrared thermography N2 - A steady increase of wind energy infrastructure brings along a challenge of maintaining and operating wind turbines (WT) with its multiple components. Inspection of wind turbine rotor blades (WTB) is an important part of maintaining the overall health and safety of a WT. It involves visually or mechanically examining the blades for signs of damage or wear that could affect their performance and structural integrity of the entire WT. A WTB is a complex structure due to its ever-increasing scale (going beyond 100 m for a 16 MW WT) as well as multi-material construction. Passive infrared thermography offers an alternative to contact- or proximity-based inspection techniques currently in use such as visual inspection performed by technical personnel (using a lift or a drone) and involves looking for signs of damage on the surface of the blades, and ultrasonic testing to detect internal defects. In contrast to active thermography, passive thermography uses the sun as source of heat, instead of conventional heat lamps, flash, or laser. An inspection technique to (semi-autonomously) inspect the WTBs of an operating WT from the ground has been developed. Given the optimum thermal contrast (weather conditions for field measurements), external as well as internal features of the WTB can be visualised with appropriate post-processing. The work presented here is part of an ongoing multi-partner project titled “EvalTherm”: the evaluation of passive thermography as a non-destructive inspection tool of WTBs in operation. In this work, artificial defects representative of realistic defects in glass fibre reinforced plastic (GFRP) WTBs are introduced in out-of-service WTB pieces. These are scanned using X-ray computed tomography to obtain a three-dimensional reconstruction to be used as input for finite-element based thermal simulation using COMSOL Multiphysics. The simulation data is compared with infrared thermal inspection of the same WTB section, in order to compare the effect of thermal contrast caused in certain weather conditions. In addition, the influence of defect characteristics such as defect size, morphology, and location on detectability is investigated. Validated simulation models are used to predict thermal signatures of defects along with the optimal thermal contrast. Such simulation models in combination with weather forecast data can assist operators of wind turbine infrastructure to plan passive thermography inspection without the need of dangerous inspection procedures and associated shutdown of energy production. T2 - Wind Energy Science Conference (WESC) 2023 CY - Glasgow, Scotland DA - 23.05.2023 KW - FEM KW - Thermografie KW - Wind turbine rotor blades KW - Windenergie anlage rotorblätter KW - Thermography PY - 2023 AN - OPUS4-58283 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mehri Sofiani, F A1 - Chaudhuri, Somsubhro A1 - Elahi, S.A. A1 - Hectors, K. A1 - De Waele, W. T1 - Quantitative Analysis of the Correlation between Geometric Parameters of Pits and Stress Concentration Factors for a Plate Subject to Uniaxial Tensile Stress N2 - The offshore environment is inherently corrosive. Consequently, pits may nucleate on exposed steel surfaces. Corrosion pits can be a source of crack initiation when the structure is subject to fatigue loading. The criticality of a corrosion pit with respect to the structural integrity depends on its shape and size and can be quantified using a stress concentration factor (𝐾𝑡). In this work, a parametric 3D finite element model is developed to perform stress analysis of a pitted plate subjected to uniaxial tensile stress. The model is used for an extensive parameter study in which 𝐾𝑡 is determined for various pit configurations. It is demonstrated that each one of the geometrical parameters holds a substantial influence on the location of the Most Critical Region (MCR). It is shown that 𝐾𝑡 increases as the pit gets narrower. Pits with an elliptical mouth yield higher 𝐾𝑡 values when the angle between the load direction and the pit mouth major axis increases. Moreover, 𝐾𝑡 increases with the increase in the localized thickness loss which is more pronounced for relatively wider pits. Finally, a regression model is presented for estimating 𝐾𝑡 based on the geometric parameters of a pit. KW - FEM KW - Corrosion KW - SCF KW - Pitting corrosion PY - 2023 DO - https://doi.org/10.1016/j.tafmec.2023.104081 SN - 0167-8442 VL - 127 SP - 1 EP - 27 PB - Elsevier Ltd. AN - OPUS4-58284 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stamm, Michael T1 - Semi-automated detection of rain erosion damages on turbine blades with passive thermography and AI image processing N2 - The European Green Deal and the global fight against climate change call for more and larger wind turbines in Europe and around the world. To meet the increasing demand for maintenance and inspection, partly autonomous methods of remote inspection are increasingly being developed in addition to industrial climbers performing the inspection. Rotor blades are exposed to extreme weather conditions throughout their lifetime of 20 years, and the leading edge erodes over time. These erosion damages change the aerodynamic features of blades and can cause structural damages. The estimated annual energy production (AEP) losses caused by erosion damages are between 0.5% and 2% per year. The classification of the severity of a rain erosion damage and the quantification of the resulting AEP losses for cost efficient repair and maintenance efforts and improved power production of wind turbines are subject of scientific research. For the inspection of wind turbine rotor blades, passive thermography is an option that has been used to detect both internal damage [3, 4] as well as erosion on the surface [5, 6]. The advantage is that, given suitable boundary conditions, not only the rain erosion damage itself but also temperature differences caused by the resulting turbulences can be observed on the surface of the blade. Turbulences reduce the efficiency of the rotor blades and result in AEP losses. Optimised thermography inspections can contribute to detect and to evaluate rain erosion damages. The thermal inspection lasts 10 minutes per turbine and is performed while the turbine is in full operation, avoiding downtime and lost opportunities for the turbine owner which are usually caused by conventional blade inspections. The timely inspection procedure is complemented by an automatic data evaluation and results in a considerable number of inspected wind turbines in a certain period of time. A fully convolutional network (FCN) is implemented for the automated evaluation of thermal images. In the presented study, more than 1000 thermographic images of blades were annotated, augmented and used to train and test the FCN. The aim is the precise marking of thermal signatures caused by erosion damage at the leading edge. The area size of the detected temperature difference caused by turbulences was used to identify and categorise damages. Certain strategies were adopted to group small individual indications as one large damage, in order to develop simplification rules based on realistic thermal imaging resolution. T2 - Wind Energy Science Conference (WESC) 2023 CY - Glasgow, Scotland DA - 23.05.2023 KW - Non-destructive testing KW - Thermography KW - Wind turbine blade PY - 2023 AN - OPUS4-58498 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stamm, Michael T1 - In situ characterisation of GFRP shell structures of wind turbine rotor blades under test using lock-in thermography N2 - The work shown demonstrates the possibility of measuring the load distribution of complex components such as rotor blades in cyclic tests using thermography. This is confirmed in the experiments presented by comparison with DIC measurements. The advantage of thermography is that it does not require any treatment of the test specimens in the setup shown and the measurement procedure can in principle be scaled to large components. In addition, compared to other imaging methods, the actual loads and not the deformation are measured. With a suitable data evaluation by means of Lockin analysis, small loads can be verified in a formative manner. Using the example of model repairs in shell test specimens made of sandwich glass fibre composite material, it is shown that inhomogeneous load distribution due to internal structures can be detected using thermography. T2 - WindEurope Annual Event 2023 CY - Copenhagen, Denmark DA - 25.04.2023 KW - Thermography KW - TSA PY - 2023 AN - OPUS4-58500 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stamm, Michael T1 - Infrared Thermography of wind turbine rotor blades: 3 use cases N2 - Thermography is a widely accepted non-invasive measurement method and is generally used in various areas of the life cycle of infrastructure and machinery. This includes design, production and maintenance. Thermography is particularly suitable for remote inspection of large areas that are difficult to reach. In this presentation, applications of thermography in the field of wind energy will be shown, touching on three explicit examples from rotor blade inspection. Experimental testing and validation: Thermography can measure and visualise the stress distribution on the surface during cyclic tests of rotor blades and rotor blade sections. The so-called thermoelastic stress analysis makes use of special evaluation algorithms (Lockin analysis) of the measurement data and the cyclic loading of components. An advantage of the measurement methods compared to other measurement methods such as strain gauges or digital image correlation is that it does not require any extra treatment or sensoring of the components. In the work shown here, repair methods are optimised and evaluated in cyclic tests on shell test specimens. Operation and maintenance: Rotor blades can be inspected from the ground during operation using passive thermography. Here, the integration of weather forecasts and conditions as input for simulations is crucial and will be demonstrated with some examples from the field. The goal of the ongoing research is to obtain detailed insights into the internal structure of the inspected rotor blades with individual measurements. A specially developed automated measuring system is able to measure a wind turbine (one-sided) within 5 minutes without impacting its operation. Environmental impact: In cases where less strict time and economic constraints apply than in the maintenance of rotor blades in operation, thermography can also be used to realise other inspection processes that take more time. Examples of this are quality control or the characterisation of rotor blades during dismantling. In the latter case, for example, it can be crucial to know which components such as foam, balsa, belt and spar are present in which parts of the blade when dismantling the rotor blades. Long-term measurements (~1-2 h) under suitable weather conditions can provide good insights into the inner structure of the rotor blades, both during disassembly and during quality control before installation. For this purpose, the sun is used as a heat source, which induces a thermal response of the rotor blades. The thermal behaviour of the rotor blades then allows conclusions to be drawn about the internal structure. T2 - EERA DeepWind conference 2023 CY - Trondheim, Norway DA - 18.01.2023 KW - Thermography KW - Wind turbine blade KW - Inspection PY - 2023 AN - OPUS4-58501 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Scheuschner, Nils A1 - Heinrichsdorff, F. A1 - Oster, Simon A1 - Uhlmann, E. A1 - Polte, J. A1 - Gordei, A. A1 - Hilgenberg, Kai T1 - In-situ monitoring of the laser powder bed fusion process by thermography, optical tomography and melt pool monitoring for defect detection N2 - For the wide acceptance of the use of additive manufacturing (AM), it is required to provide reliable testing methods to ensure the safety of the additively manufactured parts. A possible solution could be the deployment of in-situ monitoring during the build process. However, for laser powder bed fusion using metal powders (PBF-LB/M) only a few in-situ monitoring techniques are commercially available (optical tomography, melt pool monitoring), which have not been researched to an extent that allows to guarantee the adherence to strict quality and safety standards. In this contribution, we present results of a study of PBF-LB/M printed parts made of the nickel-based superalloy Haynes 282. The formation of defects was provoked by local variations of the process parameters and monitored by thermography, optical tomography and melt pool monitoring. Afterwards, the defects were characterized by computed tomography (CT) to identify the detection limits of the used in-situ techniques. T2 - Lasers in Manufacturing Conference 2023 CY - Munich, Germany DA - 26.06.2023 KW - Thermography KW - Optical tomography KW - Melt-pool-monitoring KW - Laser powder bed fusion KW - Haynes 282 KW - Additive Manufacturing PY - 2023 UR - https://www.wlt.de/lim2023-proceedings/system-engineering-and-process-control SP - 1 EP - 10 AN - OPUS4-58466 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pech May, Nelson Wilbur A1 - Tabasco-Novelo, Carolina A1 - Quintana, Patricia A1 - Rodriguez-Gattorno, Geonel A1 - Alvarado-Gil, Juan J. T1 - Evidence of a Thermal Diffusivity Gap in Sintered Li–Co–Sb–O Solid Solutions N2 - In this work, the thermal properties of ternary Li₃ₓCo₇₋₄ₓSb₂₊ₓO₁₂ solid solutions are studied for different concentrations in the range 0 ≤ x ≤ 0.7. Samples are elaborated at four different sintering temperatures: 1100, 1150, 1200 and 1250 °C. The effect of increasing the content of Li⁺ and Sb⁵⁺, accompanied by the reduction of Co²⁺, on the thermal properties is studied. It is shown that a thermal diffusivity gap, which is more pronounced for low values of x, can be triggered at a certain threshold sintering temperature (around 1150 °C in this study). This effect is explained by the increase of contact area between adjacent grains. Nevertheless, this effect is found to be less pronounced in the thermal conductivity. Moreover, a new framework for heat diffusion in solids is presented that establishes that both the heat flux and the thermal energy (or heat) satisfy a diffusion equation and therefore highlights the importance of thermal diffusivity in transient heat conduction phenomena. KW - General Chemical Engineering KW - General Chemistry PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-593248 DO - https://doi.org/10.1021/acsomega.2c07557 SN - 2470-1343 VL - 8 IS - 8 SP - 7808 EP - 7815 PB - American Chemical Society (ACS) CY - Washington, DC AN - OPUS4-59324 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ziegler, Mathias T1 - Aktueller Stand der Normung in der Thermografie N2 - Die Thermografie ist trotz ihrer ausgereiften wissenschaftlichen und technologischen Grundlagen ein noch relativ junges Mitglied in der Familie der zerstörungsfreien Prüfverfahren. Sie erschließt sich aufgrund einer Reihe von Vorzügen eine wachsende Anwendungsgemeinde. Für eine weitere Verbreitung insbesondere im industriellen Kontext spielen Normen, Standards und technische Regeln eine wichtige Rolle. In diesem Beitrag wird der aktuelle Stand der Normung in Deutschland vorgestellt. Wir zeigen, welche Normen und technischen Regeln es für die Thermografie in Deutschland und international gibt und wir wagen einen Blick in die Zukunft. Darüber hinaus lebt auch die Normierungsarbeit von der Beteiligung durch interessierte Kreise. Dies können industrielle und akademische Anwender*innen, Hersteller*innen von Geräten, Forschungseinrichtungen oder Dienstleistungsunternehmen sein. Sie können gern Ihre Bedarfe bezüglich Normierungsprojekten mitbringen und/oder direkt an die Autoren senden. T2 - DACH-Jahrestagung 2023 CY - Friedrichshafen, Germany DA - 15.05.2023 KW - Thermografie KW - Zerstörungsfreie Prüfung KW - Normung KW - Standardisierung PY - 2023 AN - OPUS4-59250 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ziegler, Mathias T1 - Aktueller Stand der Normung in der Thermografie N2 - Die Thermografie ist trotz ihrer ausgereiften wissenschaftlichen und technologischen Grundlagen ein noch relativ junges Mitglied in der Familie der zerstörungsfreien Prüfverfahren. Sie erschließt sich aufgrund einer Reihe von Vorzügen eine wachsende Anwendungsgemeinde. Für eine weitere Verbreitung insbesondere im industriellen Kontext spielen Normen, Standards und technische Regeln eine wichtige Rolle. In diesem Beitrag wird der aktuelle Stand der Normung in Deutschland vorgestellt. Wir zeigen, welche Normen und technischen Regeln es für die Thermografie in Deutschland und international gibt und wir wagen einen Blick in die Zukunft. Darüber hinaus lebt auch die Normierungsarbeit von der Beteiligung durch interessierte Kreise. Dies können industrielle und akademische Anwender*innen, Hersteller*innen von Geräten, Forschungseinrichtungen oder Dienstleistungsunternehmen sein. Sie können gern Ihre Bedarfe bezüglich Normierungsprojekten mitbringen und/oder direkt an die Autoren senden. T2 - DACH-Jahrestagung 2023 CY - Friedrichshafen, Germany DA - 15.05.2023 KW - Thermografie KW - Zerstörungsfreie Prüfung KW - Normung KW - Standardisierung PY - 2023 AN - OPUS4-59251 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stamm, Michael A1 - Krankenhagen, Rainer T1 - EvalTherm - Weather-dependent passive thermography of unheated wind turbine blades N2 - Evaluation of passive Thermography for the inspection of wind turbine blades. Comparison of passive thermography from the ground with drone-supported images and active thermography. Better understand the influence of weather conditions through field measurements. Development of an inspection planning tool that incorporates weather forecasts. Use FEM simulations to predict thermal contrasts of different damages under different environmental conditions. T2 - Kolloquium CY - Saarbrücken, Germany DA - 28.09.2022 KW - Thermography KW - Wind turbine rotor blades KW - FEM PY - 2022 AN - OPUS4-56913 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Rupprecht, C. A1 - Ziegler, Mathias T1 - Nondestructive thermographic detection of internal defects using pixel-pattern based laser excitation and photothermal super resolution reconstruction N2 - In this work, we present a novel approach to photothermal super resolution based thermographic resolution of internal defects using two-dimensional pixel pattern-based active photothermal laser heating in conjunction with subsequent numerical reconstruction to achieve a high-resolution reconstruction of internal defect structures. With the proposed adoption of pixelated patterns generated using laser coupled high-power DLP projector technology the complexity for achieving true two-dimensional super resolution can be dramatically reduced taking a crucial step forward towards widespread practical viability. Furthermore, based on the latest developments in high-power DLP projectors, we present their first application for structured pulsed thermographic inspection of macroscopic metal samples. In addition, a forward solution to the underlying inverse problem is proposed along with an appropriate heuristic to find the regularization parameters necessary for the numerical inversion in a laboratory setting. This allows the generation of synthetic measurement data, opening the door for the application of machine learning based methods for future improvements towards full automation of the method. Finally, the proposed method is experimentally validated and shown to outperform several established conventional thermographic testing techniques while conservatively improving the required measurement times by a factor of 8 compared to currently available photothermal super resolution techniques. KW - Thermography KW - Super resolution KW - NDT KW - Inspection KW - Internal defects KW - DMD KW - DLP PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-570551 DO - https://doi.org/10.1038/s41598-023-30494-2 SN - 2045-2322 VL - 13 SP - 1 EP - 13 PB - Nature Research AN - OPUS4-57055 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krankenhagen, Rainer T1 - Influence of Moisture in Concrete on the Photothermal Response—A New Approach for a Measurement Method? N2 - Recently, the photothermal determination of the thermophysical properties of concrete under lab conditions was reported. Their values are mainly needed to look at the energy consumption of buildings. Additionally, changes in their values in relation to the initial state might also be a good indicator for material quality or for moisture. The present contribution explains the photothermal method in a more general way to indicate the potential for on-site application. Secondly, a special application case is regarded: the detection of moisture in concrete. Two concrete samples were soaked with water, followed by a drying period, to obtain different levels of water penetration. The water contents were determined by weighing, and the photothermal response was measured. The results show a large influence on the measured temperature transients, which is larger than expected from the original simple model. They clearly provide two points: the photothermal method is suited to detect moisture in concrete, but the magnitude of the actual measurement effect is not yet understood. KW - Thermal effusivity KW - Thermal conductivity KW - Moisture KW - Reflectivity PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-570439 DO - https://doi.org/10.3390/app13052768 VL - 13 IS - 5 SP - 1 EP - 18 PB - MDPI CY - Basel, Switzerland AN - OPUS4-57043 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Detektion innenliegender Defekte mittels photothermischer Super-Resolution-Rekonstruktion und 2D-Beleuchtungsmustern N2 - Für die aktive Thermografie als zerstörungsfreie Prüfmethode galt lange Zeit die Faustformel, dass die Auflösung interner Defekte/Inhomogenitäten auf ein Verhältnis von Defekttiefe/Defektgröße ≤ 1 beschränkt ist. Die Ursache hierfür liegt in der diffusiven Natur der Wärmeleitung in Festkörpern. Sogenannte Super-Resolution-Ansätze erlauben seit Kurzem die Überwindung dieser physikalischen Grenze um ein Vielfaches. Damit ergibt sich die attraktive Möglichkeit die Thermografie von einem rein oberflächensensitiven Prüfverfahren hin zu einem Verfahren mit verbesserter Tiefenreichweite zu entwickeln. Wie weit diese Entwicklung getrieben werden kann, ist Gegenstand aktueller Forschung. Wir konnten bereits zeigen, dass diese klassische Einschränkung für ein- und zweidimensionale Defektgeometrien überwunden werden kann, indem das Prüfobjekt mit einzelnen Laserspots sequenziell strukturiert beleuchtet wird und damit anschließend aus den resultierenden Messdaten durch Anwendung photothermischer Super-ResolutionRekonstruktion eine Defektkarte berechnet werden kann, welche eine deutlich verbesserte Trennung einzelner naheliegender Defekte erlaubt. Dieses Verfahren profitiert dabei im Ergebnis stark von der Kombination von sequenzieller räumlich strukturierter Beleuchtung und modernen numerischen Optimierungsverfahren, was jedoch in Summe stark auf Kosten der experimentellen Komplexität geht. Dies führt im Gegensatz zur Anwendung von etablierten thermografischen Standardverfahren mit vollflächiger Beleuchtung zu langen Messzeiten, großen Datensätzen und langwieriger numerischer Auswertung. In dieser Arbeit berichten wir über die Anwendung vollflächig räumlichstrukturierter zweidimensionaler Beleuchtungsmuster, welche es durch den Einsatz modernster Laserprojektortechnik in Verbindung mit einem Hochleistungslaser überhaupt erst erlaubt, eine effiziente Umsetzung von photothermischer Super-ResolutionRekonstruktion auch für größere Prüfflächen zu erreichen. T2 - Thermographie-Kolloquium 2022 CY - Saarbrücken, Germany DA - 28.09.2022 KW - Thermografie KW - Super resolution KW - Eingeschlossene Defekte KW - ZfP KW - DLP KW - Projektor KW - DMD PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-565222 UR - https://www.dgzfp.de/Portals/thermo2022/BB178/Inhalt/13.pdf AN - OPUS4-56522 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Hirsch, Philipp Daniel T1 - Roboterunterstütze Inspektion von stark gekrümmten Oberflächen mit Laserthermografie N2 - Zur Gewährleistung der Dauerhaftigkeit von Bauteilen sind regelmäßige Prüfungen notwendig. Für oberflächennahe Risse wurde bereits das Potenzial von Flying-Spot-Untersuchungen gezeigt, bei denen das Messfeld mit einem Laserpunkt, z.B. mittels eines Laserscanners, abgerastert wird. Eine Beschleunigung der Messung durch die Verwendung von Laserlinien ist möglich, wobei die Detektierbarkeit von Rissen u.a. von ihrer Ausrichtung zur Scanrichtung abhängt. Zudem können bei stark gekrümmten Oberflächen, wie z.B. denen von Turbinenschaufeln oder Maschinenteilen mit einem einzelnen stationären Messaufbau nur ein Teil der Oberfläche mit aktiver Thermografie auf Risse untersucht werden da die begrenzte Tiefenschärfe der optischen Systeme (Laser und Kamera)die mechanischen Nachführung innerhalb des Schärfentiefe-Bereichs erforderlich macht. Um eine vollständige Untersuchung der Oberfläche durchzuführen, sind daher mehrere Perspektiven notwendig. Die hier angewandte Laserthermografie erzeugt dabei die Relativbewegung durch die Manipulation des Prüfobjektes mit einem Roboterarm, welcher es erlaubt, komplexe Oberflächen abzuscannen. Es erfolgt ein systematisches Abfahren mit einer Laserlinie entlang zuvor geplanter Bahnen der gesamten erreichbaren Oberfläche. Da der Roboterarm das Prüfobjekt trägt, sind die eingesetzten Messsysteme unbeeinflusst. Die Bewegung des Prüfobjektes ist dabei mit vielen Freiheitsgraden möglich, was eine Optimierung für das Messproblem erlaubt. Es können unter anderem die Scangeschwindigkeit, Laserleistung, Laserspotgeometrie, Laserwellenlänge, Scanschema und Kamerabildrate variiert werden. Mithilfe der Positionsdaten des Roboterarms kann jedem Punkt auf dem Prüfkörper ein Temperaturverlauf zugeordnet werden, um einen ortsaufgelösten Temperaturverlauf zu erzeugen. Das Ziel ist es, die oberflächennahen Defekte zu detektieren und deren Position auf der Oberfläche des 3D Models positionsgenau darstellen zu können. In diesem Vortrag werden die Ergebnisse zur robotergestützten Thermografie an unterschiedlichsten Prüfkörpern vorgestellt. Vorteile gegenüber herkömmlichen Methoden werden erläutert und aktuelle Herausforderungen auf der Hard- und Softwareseite für den praktischen Einsatz diskutiert. T2 - Thermographie-Kolloquium 2022 CY - Saarbrücken, Germany DA - 28.09.2022 KW - Laserthermografie KW - Roboter KW - Risserkennung KW - Canny approach KW - Flying line thermography PY - 2022 AN - OPUS4-56545 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Maillard, S. T1 - Development of Active Thermography for NDT applications through standardization N2 - Many laboratories have been working about Active Thermography as a Non Destructive Testing method for many years. This method can be applied on metallic or composites materials for surface or subsurface defects. Thus, many different configurations can be encountered to measure the heat distribution and generate heat flow into the part. Signal processing is also widely used to improve the performance of detection. After encouraging results, aerospace, automotive and energy industries are now involved into industrialization of the technology to apply it for production or maintenance applications. Good practices and common wording are often required by end-user to qualify the process. Since the beginning of the 2000s, a working group was founded within CEN/TC138 'Non-destructive Testing' to define standards in thermography, in the European Committee for Standardization (CEN). Some other actors have also produced standards (ISO, IEC, ASTM...). This paper aims to list the standards currently available about thermography and the associatd vocabulary. It describes the generic terms to be used in active and passive thermography (operating modes, reference blocks, reporting…) and also more specific elements about laser and induction thermography for example. It will also put in perspective the further works to be done in the next few years to take into account the new trends in active thermography and how to qualify for industrial applications. T2 - 17th Quantitative InfraRed Thermography Conference - QIRT 2024 CY - Zagreb, Croatia DA - 01.07.2024 KW - Infrared Thermography KW - Non-destructive testing KW - Standardization PY - 2024 AN - OPUS4-60931 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Maillard, S. T1 - Development of Active Thermography for NDT applications through standardization N2 - Many laboratories have been working about Active Thermography as a Non Destructive Testing method for many years. This method can be applied on metallic or composites materials for surface or subsurface defects. Thus, many different configurations can be encountered to measure the heat distribution and generate heat flow into the part. Signal processing is also widely used to improve the performance of detection. After encouraging results, aerospace, automotive and energy industries are now involved into industrialization of the technology to apply it for production or maintenance applications. Good practices and common wording are often required by end-user to qualify the process. Since the beginning of the 2000s, European Committee for Standardization (CEN) has launched a Working Group within CEN/TC138 to define standards in thermography. Some other actors have also produced standards (ISO, IEC, ASTM,..). This goal of this presentation is to present a status of the standard currently available about thermography and the associated vocabulary. It describes the generic terms to be used in active and passive thermography (operating modes, reference blocks, reporting,…) and also more specific elements about laser and induction thermography for example. It will also put in perspective the further works to be done in the next few years to take into account the new trends in active thermography and how to qualify for industrial applications. T2 - 20th World Conference on Non-Destructive Testing (20th WCNDT) CY - Incheon, South Korea DA - 27.05.2024 KW - Infrared Thermography KW - Non-destructive testing KW - Standardization PY - 2024 AN - OPUS4-60913 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien T1 - Practical study on the thermographic detectability of internal defects using temporally structured laser heating N2 - Modern laser systems have proven to be versatile heat sources for active thermographic testing applications. Compared to more traditional light sources, e.g. flash or halogen lamps, their output power can be easily modulated at high rates, allowing a wide variety of complex excitations to be realized. Although their total optical output power can be theoretically scaled to arbitrary values, the maximum output power is practically limited by many factors: the maximum power that the sample under test can absorb without altering the lighted surface itself, the trade-off between power density and inspected area, the cost of the laser system, etc. Furthermore, when working with spatial modulator systems, the output power could be limited to avoid provoking any damages on such devices. Nevertheless, to guarantee sufficient heating even for highly thermally conductive materials and/or deeply buried defects, the heating times can be extended, e.g., either by using step heating, long pulse thermography, or by lock-in thermography with a continuously modulated heating. However, for all these approaches, the ranging capabilities of the thermographic defect detection are reduced due to the limited frequency content of the excitation. To tackle this problem, i.e. to increase the excitation energy while preserving its frequency content, new approaches have been developed in the last two decades, among which the use of coded excitations combined with pulse-compression, and the use of multiple lock-in analysis or of a frequency modulated excitation signal. The challenges of such temporally structured heating techniques are manifold, for example, the DC component inherent in optical heating must be taken into account. In general, a wider frequency bandwidth or greater variability of the frequency components also means greater complexity for signal generation and data processing. In this paper, temporal structured excitation schemes with different degrees of complexity are compared on a high power laser system. T2 - 17th Quantitative InfraRed Thermography Conference (QIRT) CY - Zagreb, Croatia DA - 01.07.2024 KW - Thermography KW - Laser KW - NDT KW - Temporal structuring KW - Pulse-compression PY - 2024 AN - OPUS4-60563 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krankenhagen, Rainer T1 - Thermographic Investigation of the Anisotropic Behaviour of Additively Manufactured AISI 316 Steel using DED-arc N2 - Additive manufacturing is one of the most promising techniques for industrial production and maintenance, but the specifics of the layered structure must be considered. The Direct Energy Deposition-Arc process enables relatively high deposition rates, which is favourable for larger components. For this study, specimens with different orientations were prepared from one AISI316 steel block – parallel and orthogonal to the deposition plane. Quasistatic tensile loading tests were carried out, monitored by an infrared camera. The obtained surface temperature maps revealed structural differences between both orientations. The consideration of surface temperature transients yields more details about the behaviour of the material under tensile loading than the conventional stress-strain-curve. These preliminary investigations were supplemented by thermographic fatigue trials. Although the anisotropy was also observed during fatigue loading the fatigue behaviour in general was the same, at least for both inspected specimens. The presented results demonstrate the abilities and the potential of thermographic techniques for tensile tests. T2 - 17th Quantitative Infrared Thermography Conference CY - Zagreb, Croatia DA - 01.07.2024 KW - Thermoelastic effect KW - Thermoplastic effect KW - Thermal stress analysis PY - 2024 AN - OPUS4-60574 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Chaudhuri, Somsubhro A1 - Stamm, Michael T1 - Infrared thermography of turbulence patterns of operational wind turbine rotor blades supported with high-resolution photography: KI-VISIR Dataset N2 - With increasing wind energy capacity and installation of wind turbines, new inspection techniques are being explored to examine wind turbine rotor blades, especially during operation. A common result of surface damage phenomena (such as leading-edge erosion) is the premature transition of laminar to turbulent flow on the surface of rotor blades. In the KI-VISIR (Künstliche Intelligenz Visuell und Infrarot Thermografie – Artificial Intelligence-Visual and Infrared Thermography) project, infrared thermography is used as an inspection tool to capture so-called thermal turbulence patterns (TTP) that result from such surface contamination or damage. To compliment the thermographic inspections, high-resolution photography is performed to visualise, in detail, the sites where these turbulence patterns initiate. A convolutional neural network (CNN) was developed and used to detect and localise the turbulence patterns. A unique dataset combining the thermograms and visual images of operational wind turbine rotor blades has been provided, along with the simplified annotations for the turbulence patterns. Additional tools are available to allow users to use the data requiring only basic Python programming skills. KW - Reference Data KW - Infrared Thermography KW - Wind energy KW - Dataset PY - 2024 DO - https://doi.org/10.5281/zenodo.13771899 PB - Zenodo CY - Geneva AN - OPUS4-61102 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krankenhagen, Rainer T1 - Comment on "Sizing the depth and width of ideal delaminations using modulated photothermal radiometry" [J. Appl. Phys. 131, 085106 (2022)] N2 - Comment on the article "Sizing the depth and width of ideal delaminations using modulated photothermal radiometry" by Agustín Salazar and Arantza Mendioroz, Journal of Applied Physics 131, 085106 (2022, https://doi.org/10.1063/5.0085178). KW - Ideal delamination KW - Modulated photothermal radiometry KW - Delamination depth KW - Delamination width PY - 2022 DO - https://doi.org/10.1063/5.0107603 VL - 132 SP - 1 PB - AIP CY - Melville, NY AN - OPUS4-56261 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yagdjian, H. A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Ziegler, Mathias A1 - Gurka, M. T1 - Application of the thermal shock response spectrum (TSRS) methodology to various forms of heat sources by pulse thermography and comparison by using a rotating line scan contour search algorithm N2 - In this paper, we propose a novel contour search algorithm (CSA) for image processing. Its efficacy is evaluated through a comparative analysis with established techniques such as Canny Edge and Snakes: Active contour models, utilizing infrared thermography (IRT) images. Based on the new CSA, we investigate the influence of different pulse shapes on the IRT post-processing methodology, particularly focusing on the thermal shock response spectrum (TSRS), using two different heat sources: xenon flash lamps and a laser. Moreover, this allows for a more precise quantitative comparison of the TSRS with existing IRT post-processing techniques, including pulse phase thermography and thermal signal reconstruction, concerning the detection of defects in composite materials, particularly in carbon fiber-reinforced polymer. A quantitative comparison was performed using the Tanimoto criterion and signal-to-noise ratio. A more detailed analysis is conducted to identify inherent limitations and potential benefits of the new TSRS methodology. We further investigate and experimentally confirm our previous finding on the qualitative correlation between the one-dimensional thermal N-layer model and test data from the TSRS optimization process for defect determination. This correlation can eliminate the time-consuming optimization step, making TSRS a more attractive alternative to common IRT methods and enhancing the quantitative description of defects. KW - Thermography KW - Non-destructive testing KW - NDT KW - Defect identification KW - Laser KW - Contour search PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-615056 DO - https://doi.org/10.1063/5.0232015 SN - 1089-7550 VL - 136 IS - 175101 SP - 1 EP - 20 PB - AIP Publishing AN - OPUS4-61505 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Chaudhuri, Somsubhro A1 - Stamm, Michael A1 - Lapšanská, Ivana A1 - Lançon, Thibault A1 - Osterbrink, Lars A1 - Driebe, Thomas A1 - Hein, Daniel A1 - Harendt, René T1 - Infrared Thermography of Turbulence Patterns of Operational Wind Turbine Rotor Blades Supported With High‐Resolution Photography: KI‐VISIR Dataset N2 - With increasing wind energy capacity and installation of wind turbines, new inspection techniques are being explored to examine wind turbine rotor blades, especially during operation. A common result of surface damage phenomena (such as leading edge erosion) is the premature transition of laminar to turbulent flow on the surface of rotor blades. In the KI-VISIR (Künstliche Intelligenz Visuell und Infrarot Thermografie—Artificial Intelligence-Visual and Infrared Thermography) project, infrared thermography is used as an inspection tool to capture so-called thermal turbulence patterns (TTPs) that result from such surface contamination or damage. To complement the thermographic inspections, high-resolution photography is performed to visualise, in detail, the sites where these turbulence patterns initiate. A convolutional neural network (CNN) was developed and used to detect and localise turbulence patterns. A unique dataset combining the thermograms and visual images of operational wind turbine rotor blades has been provided, along with the simplified annotations for the turbulence patterns. Additional tools are available to allow users to use the data requiring only basic Python programming skills. KW - Thermography KW - Thermografie KW - Wind energy KW - Leading edge erosion KW - KI PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-615772 DO - https://doi.org/10.1002/we.2958 IS - e2958 SP - 1 EP - 9 PB - Wiley AN - OPUS4-61577 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yagdjian, H. A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Gurka, M. T1 - Optimization of thermal shock response spectrum as infrared thermography post-processing methodology using Latin hypercube sampling and analytical thermal N-layer model N2 - In this work, we continue to develop and investigate the Thermal Shock Response Spectrum (TSRS) method as an alternative data processing method for infrared thermography (IRT). We focus on improving the current TSRS algorithm and present an optimization methodology for finding the optimal thermal Q-factor and characteristic frequency pair, which is based on the widely applied random sampling method. We show the qualitative relationship between the determined optimal characteristic frequency and the corresponding maximum difference in diffusion length between reference and defective models, as calculated by selecting a specific one-dimensional thermal N-layer model. The investigations were performed on an inhomogeneous plate made of carbon fiber reinforced polymer (CFRP) with artificial square defects at different depths. Furthermore, two different heat sources were used: a xenon flash lamp and a laser. These sources are not only distinct by their underlying physics but also generate inherently different pulse shapes. To quantitatively estimate the contrast between defect and non-defect areas, and to compare these results with commonly used infrared thermography (IRT) data postprocessing methods such as Pulse Phase Thermography (PPT) and Thermographic Signal Reconstruction (TSR), the Tanimoto criterion (TC) and signal-to-noise ratio (SNR) were used. KW - infrared thermography KW - Composite materials KW - TSRS optimization KW - Defect identification KW - Heat source shape KW - N-layers model KW - Latin Hypercube Sampling PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-614283 DO - https://doi.org/10.1016/j.infrared.2024.105582 SN - 1350-4495 VL - 143 SP - 1 EP - 15 PB - Elsevier B.V. AN - OPUS4-61428 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -