Novel fiber orientation evaluation method for CFRP/CFRTP based on measurement of anisotropic in-plane thermal diffusivity distribution

This study proposes a new method for evaluating fiber orientation of sheet-like fiber reinforced materials based on thermal diffusivity measurements. The experimental apparatus comprises a laser, function generator, microscope, and thermographic camera. The surface of a sample is heated periodically by a laser spot, and the thermal response on the rear side of the sample is measured by a lock-in thermographic camera to obtain in-plane thermal diffusivity distribution. This thermal diffusivity angular distribution is directly related to the fiber orientation distribution (FOD). In this study, FOD density function can be obtained to fit the thermal diffusivity angular distribution. At first, the feasibility of this method was verified using a unidirectional (UD) carbon fiber reinforced plastic with a known FOD. The FOD of the UD sample can be estimated within 0.3° at the maximum. The method was then applied to a carbon fiber reinforced thermoplastic (CFRTP) sample having discontinuous fibers. The thermal diffusivity angular distributions were measured, and the FOD fitting method was applied to the results. The FOD can be evaluated from the fiber orientation angle and strength. Finally, mapping measurements were conducted using a CFRTP sheet molded by the long fiber thermoplastic-direct method. The mapping measurement is valid for the measurement of large scale samples.