Effect of crystallinity on the interlaminar fracture toughness of continuous glass fiber-polyamide composites

Using a thermoplastic matrix in continuous fiber reinforced composite laminates results in higher interlaminar fracture toughnesses compared to those with conventional, untoughened thermosetting matrices. In this paper the effect of crystallinity of a semicrystalline thermoplastic matrix on the interlaminar fracture behavior is investigated by microstructural characterization (density, SEM, WAXS and polarized light microscopy) and under mode I (DCB) and mode II (ENF) loading conditions. For these purposes specimens were produced out of a commercially available FIT® material (fiber impregnated thermoplastic) which consists of E-glass fibers surrounded by a solid Polyamide 12 powder and sheath matrix. The results reflect an overall high interlaminar fracture toughness which, however, slightly decreases with increasing crystallinity.