Interfacial properties in commingled yarn thermoplastic composites. Part II: Influence on crack initiation and propagation

The second paper in this series aims to identify the relationship between fiber/ matrix interface and cracking phenomena occurring in commingled yam glass fiber/ polypropylene (GF/PP) composites. For this purpose, different interfacial qualities were obtained by a modification of the fiber reinforcement sizing and the matrix coupling. In addition to transverse tensile stress-strain relationships (Part 1 (17)), mode I interlaminar resistance relationships have been recorded while monitoring acoustic emissions. A mode I mechanical analysis points out the influences of the sizing on the mechanisms contributing to energy absorption, which are protection of fibers against break, creation of an interphase and control of adhesion at the glass fiber surface. Sizing appears as a key parameter governing crack initiation and propagation for these commingled thermoplastic composites. Owing to the relationship between global fiber/matiix adhesion and cracking mechanisms, mode I fracture mechanics is a powerful characterization technique of the interfacial quality of GF/PP composites. (C) 2004 Society of Plastics Engineers.