Elastic properties of injection molded short glass fiber reinforced thermoplastic composites

Depending on fiber size and volume fraction, polymer matrix type, processing temperature, injection speed, etc., short fiber reinforced composites produced by injection molding may exhibit complex fiber concentration, orientation and length distributions at different locations, causing large variations in their mechanical properties. In this work, a representative volume element (RVE) scheme is developed to describe the elastic properties of short glass fiber reinforced PA6,6 composites produced by injection molding. In the RVE formulation, fiber length is assumed to follow a two-parameter Weibull distribution, and a new concept, namely preferential angle, is introduced to account for the preferential alignment of fibers at different locations of injection molded composites. A random sequential insertion algorithm is developed to implement the fiber length distribution and fiber preferential alignment, and finite element method (FEM) is employed to analyze the relations of the elastic properties of RVE with three parameters, that is, the mean length, volume fraction and preferential angle of the fibers. Based on the FEM results, quantitative formulas for these relations are obtained. It is found that the variations in the mean length, volume fraction, and preferential angle of the fibers can cause large variations in elastic moduli and elastic anisotropy of the RVE.