An effective model for fiber breakage prediction of injection-molded long fiber reinforced thermoplastics

Abstract

Fiber length is an important factor affecting the mechanical properties of long fiber reinforced thermoplastic (LFRT). When LFRT is processed by injection molding, the strong shear flow usually leads to severe fiber breakage. Therefore, it is a crucial issue to reduce the loss of fiber length as much as possible during composite molding. Current work focused on constructing an effective model for predicting fiber breaking caused by shear stress during melt filling. Based on the Oseen formula, the disturbance of liquid flow caused by a single external force was studied, and the force acceptance formula of fiber immersed in flow field was derived. A mechanical model for characterizing the degree of fibers buckling and breaking and the shear stress was constructed by the Euler buckling criterion. To verify the model, glass fiber reinforced polypropylene (GF/PP) composites with initial fiber length of 3 mm and 6 mm was subjected to shear at the specific shear rate by using a rotating rheometer. The length of GF after sheared was measured by fiber length distribution analyser. The breaking ratio of fibers was predicted using the new model, and the predicted results were in good agreement with experiment, although more comparisons with experiments are necessary.