RHEOLOGY OF SHORT-FIBER COMPOSITES - A SYSTEMATIC-APPROACH

A systematic study of the transient and steady-state theological behavior of model fiber suspensions under simple shear flow is presented. Increasing gradually the complexity of the system, the effects of different parameters are analyzed at each step. First a fiber suspension in a Newtonian fluid is studied, taking only into account the fiber contribution to the theological behavior, analyzing the influence of shear rate, aspect ratio (L/D), length and concentration of fibers for monodispersed and bimodal in fiber length suspensions with different initial fiber orientation distributions. The effect of fiber-fiber interactions is also considered through a study of flow reversibility. Finally, the influence of the viscoelasticity of different matrices is considered by testing the rheological behavior of fiber suspensions in non-Newtonian fluids (second-order and 'shear thinning' fluids). The methodology presented in this study can be used to analyze the processability of short-fiber polymeric matrix composites in high speed injection technologies where the theological behavior of the compound is dominated by its transient response.