We propose a methodology to determine the thermal diffusivity of both isotropic and anisotropic samples when they move at constant speed, using laser spot thermography with continuous illumination. In the case of anisotropic samples, the method does not require knowledge of the thermal principal directions and is able to provide the orientation the principal axes with respect to the direction of motion. We show analytically that, once the steady state has been reached, the natural logarithm of the temperature along any temperature profile crossing the center of the laser spot features a linear dependence with the distance. The slopes of these straight lines are related with the speed of the sample, the principal thermal diffusivities and the orientation of the principal directions. We present experimental data taken on both, isotropic and anisotropic reference materials moving at constant speed. From the fitting of the slopes of the radial profiles in multiple directions, we are able to assess the values of the principal thermal diffusivities as well as the orientation of the principal axes with high accuracy. These results are promising regarding the quality control of industrial products in a production chain as, for instance, for fiber orientation monitoring of carbon fiber reinforced composites.
|