Abstract
A 45:55 weight% mixture of commingled glass/polyethylene terephthalate (PET) fabric was selected to study the relationships between material microstructure, Mode I and Mode II interlaminar fracture toughnesses and failure mechanisms. Composite laminates subjected to different cooling histories were manufactured within a steel mould using a laboratory heat press. Mode I and Mode II interlaminar fracture tests were performed using double cantilever beam and end-notched flexure specimens. PET matrix morphology appeared to be sensitive to the thermal histories, although this occurred on a subspherulitic scale (in contrast to observations made with polypropylene-based composites). The spherulitic textures were generally very fine and no evidence of interspherulitic fracture paths could be identified. When the composites were subjected to low cooling rates or an isothermal crystallization process, many small matrix cracks developed between fibres within the reinforcing bundles. The lower the cooling rate, the higher the density of matrix cracks per unit volume of material. The interlaminar fracture toughness in the laminates with slow cooling rates was much lower than in the case where a quasi-quenched condition was applied.