TY - CONF A1 - Müller, Jan P. A1 - Götschel, S. A1 - Maierhofer, Christiane A1 - Weiser, M. T1 - Determining the material parameters for the reconstruction of CFRP specimens measured by flash thermography N2 - CFRP materials are progressively used in areas where the weight as well as the strength of materials matter. Since they are used in safety relevant environments, like aircrafts and cars, an assessment of the components for defects is mandatory. Flash thermography has proven to be a valuable tool to resolve defects. However, a quantitative evaluation of the defect extent and depth within the specimen is extremely challenging, since the commonly used analytical models do not incorporate lateral heat flow around the defect areas. Hence a reconstruction of the samples by numerical simulations is a path to improve the results. This finally enables pass and fail tests for specimens based on quantitative results. The properties of the anisotropic CFRP materials vary dependent on the matrix and fibre chosen. In addition the fabrication processes are distinct, hence it is strongly desirable to measure the properties of a sound sample in a fast and reliable way. The knowledge of diffusivity and heat capacity in three dimensions finally enables the simulation to improve modelling the specimen geometry. The in-plane diffusivity is determined by heating the sample with a laser line (a flat top profiled focused in one dimension) and monitoring the transient temperature at the front surface of the sample. This method is compared to measurements of the diffusivity using a Gaussian laser spot. The results are compared to results obtained by flash thermography in transmission. In addition the heating process of the sample on its surface as well the heat conduction is monitored using an IR-microscopic objective. Hence the transparency of the sample as well as the temperature conduction of the two components in microscopic scale can be studied. Finally the results are applied to provide precise parameters in the simulation of defects in a CFRP sample. It is gratefully acknowledged that the present work is funded by the DFG within the framework of the project WE 2937/6-1. T2 - QNDE, Review of Progress in Quantitative Nondestructive Evaluation CY - Atlanta, GA, USA DA - 17.07.2016 KW - Flash thermography KW - Reconstruction KW - Thermography KW - Quantitative nondestructive evaluation PY - 2016 AN - OPUS4-36977 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Götschel, S. A1 - Maierhofer, Christiane A1 - Müller, Jan P. A1 - Rothbart, Nick A1 - Weiser, M. T1 - Quantitative defect reconstruction in active thermography for fiber-reinforced composites N2 - Carbon-fiber reinforced composites are becoming more and more important in the production of light-weight structures, e.g. in the automotive and aerospace industry. Thermography is often used for non-destructive testing of these products, especially to detect delaminations between different layers of the composite. In this presentation, we aim at methods for defect reconstruction from thermographic measurements of such carbon-fiber reinforced composites. The reconstruction results shall not only allow locating defects, but also give a quantitative characterization of the geometric properties of the defect. We discuss the simulation of the measurement process using finite element methods, as well as the experimental validation. In order to take anisotropic heat transport due to the fibers into account, we compare describing layers separately by individual diffusion tensors with using an averaged diffusion tensor. Especially in pulse thermography, thin boundary layers with steep temperature gradients occurring at the heated surface need to be resolved. Here we consider the combination of a 1D analytical solution combined with numerical solution of the remaining defect equation. Moreover, we discuss the mathematical modelling of various defects like delaminations and undulations, as well as the description of inhomogeneous heating by geometric optics. Finally, we will describe PDE-based methods for the solution of the inverse problem as well as ideas for fast heuristic methods to avoid expensive computations. T2 - 19th World Conference on Non-Destructive Testing CY - Munich, Germany DA - 13.06.2016 KW - Active thermography KW - Reconstruction KW - Quantitative nondestructive evaluation KW - Finite-element simulation KW - Transient thermogram PY - 2016 AN - OPUS4-37503 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -