Proposal of fiber orientation identification method for discontinuous fiber CFRP based on thermal diffusivity distribution measurement using lock-in thermography and demonstration of its effectiveness by mechanical properties

Abstract

In this study, a novel nondestructive evaluation method is proposed to investigate the fiber orientation distribution of discontinuous Carbon Fiber Reinforced Plastic (CFRP). The main concept is based on measuring thermal diffusivity distribution since it is related to the orientation of the fibers. The elliptical shape of the measured distribution is then analyzed by fitting. The slope and the eccentricity of the fitted ellipse are extracted and quantified as evaluation parameters. The experimental setup consists of a laser, a microscope and lock-in thermography system. The surface of the specimen is periodically heated by the laser spot and the thermal response at the backside of the specimen, which represents the in-plane thermal diffusivity distribution, is observed with the lock-in thermography camera. 64 points of four discontinuous CFRP of unknown orientation, manufactured with the same molding method, are evaluated. Furthermore, the local mechanical properties around the measurement points are measured. The results show positive correlation between the local mechanical properties and the fiber orientation. The effectiveness of the proposed method in predicting the mechanical property distribution of CFRP is also demonstrated.