Effective thermal conductivity of misoriented short-fiber reinforced thermoplastics

Abstract

Abstract This paper deals with the effective thermal conductivity of composites containing misoriented fibers. Statistical distribution functions such as Weilbull can be used to represent this kind of distribution. The orientation distribution of fibers in FRTP (fiber-reinforced thermoplastics) can be characterized by a single parameter exponential function F(θ) = 1 - e−λθ A large λ indicates a highly oriented material whereas a small λ represents a quasi-isotropic material. A method based on the idea of Mori-Tanala's mean field theory in conjunction with the Eshelby's equivalent inclusion method for steady-state heat conduction in composite including the effects of fiber length and orientation to predict thermal conductivity of FRTP is presented. The effective thermal conductivity of planar orientation distribution and transversely isotropic distribution of fibers are studied. For planar orientation case, we have examined the thermal conductivity constants of injection-molded tensile bars of poly (pheylene sulfide) reinforced with 30 and 40% by weight of carbon or glass fibers which have been measured by Choy et al. (1992). For transversely isotropic orientation case, the thermal conductivity constants of a transversely isotropic composite are explicitly derived. These thermal conductivity constants are given in terms of the length-diameter aspect ratio, the volume fraction, and the orientation-distribution parameter of the short fibers. Numerical results are presented to demonstrate the effects of the fiber thermal property, aspect ratio, volume fraction and orientation distribution function on composite thermal conductivity. The fiber orientation distribution and aspect ratio have a more significant effect on composite longitudinal thermal conductivity than does the fiber volume fraction within the range examined.