INFLUENCE OF UNIFORMITY OF INTERLEAVED VEILS ON INTERLAMINAR FRACTURE TOUGHNESS IN LAMINATED COMPOSITES OF CARBON FABRICS

Abstract

This study assesses the effect of fibre distribution of interleaved nonwovens veils on the mode I and mode II interlaminar fracture toughness (IFT) of reinforced laminated composites. Polyphenylene Sulfide (PPS) handsheet fibre samples with different fibre distributions were manufactured following the standard TAPPI T205 for manufacturing handsheet nonwoven samples. The key parameters of the process were iterated to obtain an empirical manufacturing procedure for achieving three main types of fibre distribution on handsheets, which were qualitatively defined as good, medium and bad fibre distribution. These handsheet samples were subsequently interleaved into carbon fibre-epoxy laminated composites and tested for mode I and mode II IFT according to standard ISO 15027 and the protocol for 4 End Notched Flexure (4ENF) respectively. The results show that there is no significant effect of fibre distribution on mode I IFT, whereas the mode II IFT showed a notable dependence on fibre distribution. A fractographic analysis shows the fibre bridging mechanism with no significant difference among the three types for the samples tested for mode I IFT, but a significant number of cusps, fibre clusters and ribbons in the samples tested for mode II IFT that contributed to the absorption of fracture energy according to their amount, size and distribution. Key words: Interlaminar fracture toughness mode I, interlaminar fracture toughness mode II, nonwovens, fibre distribution, handsheets, wet-laid process, interleaved composites, composites.