Determining the thermal diffusivity and the principal directions on anisotropic moving samples with laser-spot thermography

Abstract

We propose a method to measure the thermal diffusivity of (an)isotropic samples moving at constant speed using laser-spot thermography with continuous illumination. The method does not require previous knowledge of the principal directions and can be applied whichever their orientation with respect to the direction of motion. We demonstrate analytically that any radial temperature profile crossing the center of the laser spot fulfills a linear relation with the distance to the laser spot, whose slope depends on the thermal diffusivity, on the sample speed and on the angle of the profile with respect the sample motion. A multi-linear fitting of the temperature profiles at several angles provides a reliable method to obtain the thermal diffusivity. Experiments performed on reference samples, both isotropic and anisotropic, con- firm the validity of the method to provide accurate and precise thermal diffusivity values and to identify the thermal principal directions.