Evaluation of anisotropic thermal conductivity for unidirectional FRP in laser machining

Abstract

Due to the significant thermal anisotropy and the high-ablation temperature of carbon fiber, thermal damage can be produced during the thermal processing of carbon fiber-reinforced plastics by laser. It leads to poor assembly tolerance and long-term performance deterioration. The current study investigates the grooving of unidirectional Carbon/Epoxy in several representative directions relative to the fiber axis. Two methods, the Eigenvalue Method and the Isotherm Method, have been used to evaluate the general anisotropic thermal conductivities from the principal thermal conductivities. A finite-difference analysis, incorporating the Conductivity Ellipsoid Model due to Jaeger and the developed thermal conductivity models, is adopted to determine the extent of heat affected zone (HAZ). Simulations using either thermal conductivity model show a reasonable agreement with experimental results, i.e. the Eigenvalue Method and Isotherm Method for determining the thermal conductivity in generic direction are equally effective in the subsequent prediction of HAZ of an unidirectional FRP.