Analytical Modeling of Flash Thermography: Results for a Layered Sample

摘要

For a long time quantitative data analysis for nondestructive evaluation of material properties with flash ther-mography meant a simple comparison of the measured temperature to a standard at a fixed time after excitation. With the advent of modern infrared camera technology a few improved concepts for extracting measurement data were developed, but no testing technique used for industrial applications took advantage of the physical properties of thermal diffusion. We present an analytical 1-dimensional model for a multi-layer sample that predicts the time evolution of the surface temperature after excitation. Based on an experimentally confirmed model for thermography with periodic excitation, this calculation tool permits to determine parameters like layer thickness or heat conductivity taking into account the complete data set instead of a single image. For samples with a geometry and thermal properties specified before measuring, an unknown parameter could be extracted from experimental data without further calibration standards. The model is also capable of accommodating arbitrary excitation and semitransparent layers. We present calculations of different test scenarios like layer thickness measurement. Finally, we compare the model calculation to test samples with known characteristics.