Characterization of short glass fiber filled polystyrene by fiber orientation and mechanical properties

A quasi-steady state, non-isothermal, compressible, inelastic, and creeping flow of polymer melt into a thin cavity is analyzed to predict fiber orien tation states. Modified Cross model and Tait's state equation are adopted t o consider shear-thinning behavior and compressibility of the polymer melt. Second order tensors are introduced to describe 3-dimensional fiber orient ation. Flow-induced fiber orientation can be predicted by solving the equat ions of change for the orientation tensor with a suitable closure approxima tion. The orthotropic closure is applied except for the case of low interac tion coefficient. Fiber orientation develops mainly due to shear flow in th e skin layer and due to stretching effect in the core layer. It turns out t hat the compressibility, which induces additional velocity gradients during packing, reduces development of the fiber orientation, Results are depende nt upon the magnitude of the interaction coefficient. The larger the intera ction coefficient, the smaller the orientation development and the effect o f compressibility. To predict orientation dependent mechanical properties, the orientation averaging for an arbitrary orientation is carried out from the properties of a transversely isotropic unit cell. The compressibility r educes the axial modulus and increases the transverse modulus. Opposite tre nds are observed for thermal expansion coefficients. It is also observed th at the consideration of compressibility reduces the overall anisotropy of t he molded product. Effects of compressibility on mechanical properties of t he parts are reduced as the interaction coefficient becomes larger.