MODE-I INTERLAMINAR FRACTURE OF COMINGLED YARN BASED GLASS POLYPROPYLENE COMPOSITES

A 50:50%wt mixture of co-mingled glass/polypropylene fibers was selected to study the correlations between morphological details, mode I interlaminar fracture toughness and failure mechanisms. Unidirectional 'prepreg' sheets and laminates subjected to different thermal histories were manufactured in a steel mold in a hot press. Mode I interlaminar fracture tests were performed by using the DCB (double cantilever beam) test procedure. A simple model was established for identifying the energy contributions of various failure mechanisms to the interlaminar fracture toughness. Extensive fiber peeling and breakage events were observed for these co-mingled yarn based composites, which were consolidated at temperatures above the melting point of the polymer fibers, followed by different thermal cooling histories. When the composites were subjected to low cooling rates or an isothermal crystallization process, large voids and coarse spherulites existed in the resin-rich areas. These resulted in the presence of inter-spherulitic fracture paths between the debonded fiber-rich regions, so that the interlaminar fracture toughness was much lower than in the case where a rapid cooling condition was applied.