Dependence on fibre type of interlaminar fracture toughness enhancement in interleaved polymer composites

A systematic investigation into the influence on the Interlaminar Fracture Toughness (IFT) of carbon/epoxy composites interleaved with nonwoven veils formed with a range of fibre types is presented. For veils with a range of areal densities and coverage, both mode I and mode II IFT were found to increase to a plateau above a mean coverage of about 3. The dependence of IFT on the fibre type of microfibre veils was found to differ depending on the mode of loading. For mode I, the increase in IFT with coverage was dependent on veil fibre type, with polymer fibres showing higher increases than inorganic fibres; for mode II, the increase in IFT was broadly insensitive to fibre type. For the polymer veil interleaves that significantly increased IFT, SEM fractography revealed highly curled veil fibres that were absent from the original veil, revealing a significant energy absorbing mechanism.