Measurement of 3D thermal diffusivity distribution with lock-in thermography and application for high thermal conductivity CFRPs

Abstract

This paper presents a new technique for measuring detailed three-dimensional thermal diffusivity by the laser-spot-periodic-heating-method using lock-in thermography. Using lock-in thermography, the in-plane thermal diffusivity distribution and out-of-plane thermal diffusivity distribution could be obtained. First, the validity of the measurement method and principle were confirmed using pure metal, isotropic graphite, and a ceramic as reference materials. As a result, the in- and out-of-plane thermal diffusivities coincided with the recommended value, respectively. Next, the three-dimensional thermal diffusivity measurement was applied for high thermal conductivity carbon-fiber-reinforced plastic (CFRP) samples. The two types of CFRP sample, unidirectional (UD) with unidirectional carbon fibers and cross-ply (CP) with orthogonal two-directional carbon fibers, were measured. As a result, it was revealed that UD sample had extremely high thermal diffusivity in the fiber direction only. On the other hand, it was inferred by measurement and by thermal analysis that the result of CP sample had a high, isotropic, in-plane thermal diffusivity distribution.