Crack bridging and fibre pull-out in polyethylene fibre reinforced epoxy resins

An investigation has been undertaken of the stress distributions in high-pe rformance polyethylene fibres bridging cracks in model epoxy composites. Th e axial fibre stress has been determined from stress-induced Raman band shi fts and the effect of fibre surface treatment has been followed using untre ated and plasma-treated polyethylene fibres. It is found that when the spec imen is cracked, the fibres do not break and stress is transmitted from the matrix to the fibre across the fibre/matrix interface. A debond propagates along the fibre/matrix interface accompanied by friction along the debonde d interface. The axial stress distributions in the fibres can be analysed u sing a partial-debonding model based upon shear-lag theory and it is found that the maximum interfacial shear stress at the bond/debond transition is a function of the debond length. The debonding process has been modelled su ccessfully in terms of the interfacial fracture energy-based criterion deve loped by Hsueh for the propagation of a debond along a fibre/matrix interfa ce accompanied by constant friction along the interface. (C) 1998 Kluwer Ac ademic Publishers.