TY - CONF A1 - Lecompagnon, Julien A1 - Hirsch, Philipp A1 - Ahmadi, Samim A1 - Pech-May, Nelson W. A1 - Hauffen, Jan Christian A1 - Thiel, Erik A1 - Ziegler, Mathias T1 - New options for finding defects on and below the surface using structured laser thermography N2 - In infrared thermography, the interaction of the heat flow with the internal geometry or inhomogeneities in a sample and their effect on the transient temperature distribution is used, e.g., to detect defects non-destructively. An equivalent way of describing this is the propagation of thermal waves inside the sample. Although thermography is suitable for a wide range of inhomogeneities and materials, the fundamental limitation is the diffuse nature of thermal waves and the need to measure their effect radiometrically at the sample surface only. The crucial difference between diffuse thermal waves and propagating waves, as they occur, e.g., in ultrasound, is the rapid degradation of spatial resolution with increasing defect depth. This degradation usually limits the applicability of thermography for finding small defects on and below the surface. A promising approach to improve the spatial resolution and thus the detection sensitivity and reconstruction quality of the thermographic technique lies in the shaping of these diffuse thermal wave fields using structured laser thermography. Some examples are: • Narrow crack-like defects below the surface can be detected with high sensitivity by superimposing several interfering thermal wave fields, • Defects very close to each other can be separated by multiple measurements with varying heating structures, • Defects at different depths can be distinguished by an optimized temporal shaping of the thermal excitation function, • Narrow cracks on the surface can be found by robotic scanning with focused laser spots. We present the latest results of this technology obtained with high-power laser systems and modern numerical methods. T2 - 20th World Conference on Non-Destructive Testing (WCNDT) CY - Incheon, Korea DA - 27.05.2024 KW - Thermography KW - Laser KW - NDT KW - Super-Resolution KW - DLP KW - DMD PY - 2024 AN - OPUS4-60172 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lecompagnon, Julien A1 - Ahmadi, Samim A1 - Hirsch, Philipp A1 - Rupprecht, C. A1 - Ziegler, Mathias T1 - New methods of thermographic super resolution with structured laser heating N2 - Thermographic NDT 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. Our studies deal with the application of fully 2D-structured DMD-based excitation and subsequent super-resolution-based defect reconstruction. We analyze the influence of different testing parameters, like the number of measurements or the white content of the excitation pattern. Furthermore, we have dealt with the choice of parameters in the reconstruction that have an influence on the underlying minimization problem in terms of compressed sensing. Finally, the results of the super resolution reconstruction are compared with the results based on conventional thermographic testing methods. T2 - 20th World Conference on Non-Destructive Testing (WCNDT) CY - Incheon, Korea DA - 27.05.2024 KW - Thermography KW - Laser KW - NDT KW - Super-Resolution KW - DLP KW - DMD PY - 2024 AN - OPUS4-60171 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 -