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 -