Comparison of several closure approximations for evaluating the thermoelastic properties of an injection molded short-fiber composite

The accurate prediction of both the elastic properties and the thermal expansion coefficients is very important for the precise simulation of such processes as injection molding of short-fiber polymer-matrix composites. In this work, a two-step homogenization procedure is applied and compared with experimental values obtained on a polyarylamide/glass fiber composite for a broad range of temperatures. It is observed that the stiffness averaging version of the model surpasses the compliance averaging variant, especially when it is combined with a precise evaluation of the fourth-order orientation tensor. It is also demonstrated that the orthotropic closure approximations are significantly better than previous ones (linear, quadratic, and hybrid) and than a very recent one. Among the orthotropic closure approximations, the fitted ones lead to acceptable results, which are very close to those obtained with the experimentally measured fourth-order orientation tensor.