Vol4 num4-15 X-ray tomography investigation of the use of veils to improve the impact tolerance of thin-ply composite laminates

Abstract

Interleaving high fibre areal weight veils, typically used to improve the interlaminar fracture toughness and impact tolerance of composite laminates, impairs their tensile and compressive properties. We characterized the mechanical response of a thin-ply quasi-isotropic baseline laminate and laminates interleaved with two types of light (4 g/m2) co-polyamide veil: tension, compression, mode-I interlaminar fracture toughness, impact and compression after impact. X-ray tomography provided comprehensive understanding into the effect interleaving has on the microstructure, impact resistance and fracture process zone of double cantilever beam specimens. The veil fibre diameter was the key-parameter controlling the tensile properties (the veil with thinner fibres avoided resin accumulation at the interfaces and left the baseline tensile properties unaffected). The adhesion between veil fibres and resin controlled mode-I interlaminar fracture toughness (the veil with a suspected higher adhesion deflected crack propagation to the surrounding 0° plies, which enhanced mode-I interlaminar fracture toughness by 43%). Both veils reduced pristine compressive strength by up to 9%; however, the veil with thinner fibres improved CAI strength by up to 28% for impact at 14 J.