TY - JOUR A1 - Schlichting, Joachim A1 - Ziegler, Mathias A1 - Dey, Anika A1 - Maierhofer, Christiane A1 - Kreutzbruck, Marc T1 - Efficient data evaluation for thermographic crack detection N2 - We present an all-purpose crack detection algorithm for flying spot thermography which is directly applicable to a thermogram sequence without the need of any additional information about the experimental setup. A single image containing distinct crack signatures is derived in two steps. Firstly, the spatial derivative is calculated for each frame of the sequence and, secondly, the resulting data set is sorted pixel wise along the time axis. The feasibility of the proposed procedure is proven by testing a piece of rail that comprises roll contact fatigue cracks and by comparing the results with magnetic particle testing. KW - Active thermography KW - Laser scanner KW - Railway KW - Roll contact fatigue KW - Open surface cracks PY - 2011 SN - 1768-6733 VL - 8 IS - 1 SP - 119 EP - 123 PB - Lavoisier CY - Cachan Cedex AN - OPUS4-24255 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Maierhofer, Christiane A1 - Röllig, Mathias A1 - Steinfurth, Henrik A1 - Ziegler, Mathias A1 - Kreutzbruck, Marc A1 - Scheuerlein, C. A1 - Heck, S. T1 - Non-destructive testing of Cu solder connections using active thermography N2 - Impulse and lock-in thermography have been applied to detect delaminations of prototype solder joints, similar to those to be produced between Cu shunts and Cu busbar stabilisers at the Large Hadron Collider (LHC) at CERN. Two infrared cameras with different detector materials and with different spectral ranges and two excitation techniques have been tested and compared for their ability to detect delaminations behind 2 and 3 mm thick Cu shunts. We have analyzed the signal to noise ratio (SNR) for each detected defect and are able to detect defects down to a nominal edge length of 4 mm behind 2 mm thick Cu shunts by using fast impulse thermography and a camera with a microbolometer array. For the 3 mm thick Cu shunt, on the other hand, the nominal 4 mm defect is only visible in the lock-in thermography phase images and the highest SNR has been achieved with a cooled InSb-based camera. In addition, numerical simulations show the influence of the minimum detectable defect size on the shunt thickness and that the developed on-site testing technique is sufficient to find all defects that are detectable theoretically. KW - Active thermography KW - Solder joint KW - Copper KW - FFT KW - Signal-to-noise-ratio PY - 2012 DO - https://doi.org/10.1016/j.ndteint.2012.07.010 SN - 0963-8695 VL - 52 SP - 103 EP - 111 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-27575 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jonietz, Florian A1 - Myrach, Philipp A1 - Suwala, H. A1 - Ziegler, Mathias T1 - Examination of Spot Welded Joints with Active Thermography N2 - The method described here allows to determine the size of the thermal contact between two metal sheets joined by spot welding. This size is a measure for the size of the weld nugget, i.e. the zone melted during the welding process, and thus the quality of the welded joint. The method applies active thermography in transmission or reflection setup. Especially the reflection setup offers an attractive possibility for non-destructive testing when components can be accessed from one side only. The spot weld region is optically heated by laser or flash light radiation. The weld nugget provides the mechanical joint, but also constitutes a thermal bridge between the two welded sheets. The latter will be exploited in this method. The better thermal contact at the weld Nugget contrasts with the surrounding material, where the heat transfer between the two sheets is comparatively low. A major advantage of the described method is the applicability on sheets without any surface treatment. This is achieved by a proper normalization of the data, allowing for a correction of the varying surface emissivity. KW - Active thermography KW - Spot weld KW - Automotive industry PY - 2016 UR - http://link.springer.com/article/10.1007/s10921-015-0318-4?wt_mc=internal.event.1.SEM.ArticleAuthorIncrementalIssue DO - https://doi.org/10.1007/s10921-015-0318-4 VL - 35:1 SP - 1 EP - 14 PB - Springer CY - New York AN - OPUS4-35480 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Thiel, Erik A1 - Kreutzbruck, M. A1 - Ziegler, Mathias T1 - Laser-projected photothermal thermography using thermal wave field interference for subsurface defect characterization N2 - The coherent superposition of two anti-phased thermal wave fields creates a zone of destructive interference which is extremely sensitive to the presence of defects without any reference measurements. Combining a high power laser with a spatial light modulator allows modulating phase and amplitude of an illuminated surface that induces spatially and temporally controlled thermal wave fields. The position and depth of defects are reconstructed from analysis of the Amplitude and Phase of the resulting photothermal signal. The proposed concept is experimentally validated and supported by numerical modeling. KW - Thermal waves KW - Active thermography KW - DMD KW - Spatial light modulator KW - Subsurface defects PY - 2016 UR - http://scitation.aip.org/search?value1=laser+projected+photothermal&option1=all&option912=resultCategory&value912=ResearchPublicationContent&operator8=AND&option8=pub_serialIdent&value8=aip%2Fjournal%2Fapl&qs=true DO - https://doi.org/10.1063/1.4963139 SN - 0003-6951 VL - 109 IS - 12 SP - 123504-1 EP - 123504-4 PB - AIP Publishing CY - Melville, New York AN - OPUS4-37590 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Thiel, Erik A1 - Ziegler, Mathias T1 - Subsurface defect localization by structured heating using laser projected photothermal thermography N2 - The presented method is used to locate subsurface defects oriented perpendicularly to the surface. To achieve this, we create destructively interfering thermal wave fields that are disturbed by the defect. This effect is measured and used to locate the defect. We form the destructively interfering wave fields by using a modified projector. The original light engine of the projector is replaced with a fiber-coupled high-power Diode laser. Its beam is shaped and aligned to the projector's spatial light modulator and optimized for optimal optical throughput and homogeneous projection by first characterizing the beam profile, and, second, correcting it mechanically and numerically. A high-performance infrared (IR) camera is set up according to the tight geometrical situation (including corrections of the geometrical image distortions) and the requirement to detect weak temperature oscillations at the sample surface. Data acquisition can be performed once a synchronization between the individual thermal wave field sources, the scanning stage, and the IR camera is established by using a dedicated experimental setup which needs to be tuned to the specific material being investigated. During data post-processing, the relevant information on the presence of a defect below the surface of the sample is extracted. It is retrieved from the oscillating part of the acquired thermal radiation coming from the so-called depletion line of the sample surface. The exact location of the defect is deduced from the analysis of the spatial-temporal shape of these oscillations in a final step. The method is reference-free and very sensitive to changes within the thermal wave field. So far, the method has been tested with steel samples but is applicable to different materials as well, in particular to temperature sensitive materials. KW - Active thermography KW - Structured heating KW - Digital micromirror device KW - Thermal wave field KW - Photothermal PY - 2017 UR - https://www.jove.com/video/55733 DO - https://doi.org/10.3791/55733 SN - 1940-087X IS - 123 SP - e55733-1 EP - e55733-13 PB - MyJoVE Corp. AN - OPUS4-40281 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 -