FRACTURE-BEHAVIOR OF LONG-FIBER REINFORCED THERMOPLASTICS

This paper deals with the fracture performance of injection moulded lo ng glass fibre composites based on polybutylene terephthalate (PBT) an d polypropylene (PP) matrices. The tensile behaviour of these composit es is analysed using the shear lag theory taking into consideration th e interfacial shear strength, fibre length distribution and fibre orie ntation in the mouldings. The fracture performance is investigated usi ng the post yield fracture mechanics approach. The crack growth resist ance of the PP and PBT long fibre composite was found to increase with increasing fibre volume content up to 35%. Above 35% a plateau in the fracture performance was observed. A combination of high fibre degrad ation and a change in the fibre orientation pattern of the moulded pie ces is found to be responsible for the plateau region in the performan ce of the high concentration system. In fact, the dependence of the ma ximum crack growth resistance of the composites on fibre length and fi bre orientation is also controlled by testing temperature. The competi tion between fibre-induced matrix deformation and the fibre pull-out d etermines the ability of the composites to resist crack propagation.