RHEOLOGY OF SHORT-FIBER COMPOSITES - A SYSTEMATIC-APPROACH

A systematic study of the transient and steady-state theological behav ior of model fiber suspensions under simple shear flow is presented. I ncreasing gradually the complexity of the system, the effects of diffe rent parameters are analyzed at each step. First a fiber suspension in a Newtonian fluid is studied, taking only into account the fiber cont ribution to the theological behavior, analyzing the influence of shear rate, aspect ratio (L/D), length and concentration of fibers for mono dispersed and bimodal in fiber length suspensions with different initi al fiber orientation distributions. The effect of fiber-fiber interact ions is also considered through a study of flow reversibility. Finally , the influence of the viscoelasticity of different matrices is consid ered by testing the rheological behavior of fiber suspensions in non-N ewtonian fluids (second-order and 'shear thinning' fluids). The method ology presented in this study can be used to analyze the processabilit y of short-fiber polymeric matrix composites in high speed injection t echnologies where the theological behavior of the compound is dominate d by its transient response.