UHMWPE fibre-based composites: Prestress-induced enhancement of impact properties

The impact properties of continuous unidirectional UHMWPE fibre-reinforced polyester resin composites have been investigated, to elucidate the effects of prestress on energy absorption characteristics. Prestress within composite samples was produced by subjecting the UHMWPE fibres to a creep load, which was then released prior to moulding. From Charpy impact tests, these viscoelastically prestressed samples absorbed ∼20% more energy than their control (unstressed) counterparts, with some batches reaching 30-40%. Generally, whether prestress is created through elastic or viscoelastic means, fibre-matrix debonding is regarded as being a major energy absorption mechanism in this type of composite, but this was not evident in the current study. Instead, evidence of debonding at the skin-core interface within the UHMWPE fibres was found, the skin regions possessing lower stiffness and longer term viscoelastic activity. Skin-core debonding appears to have a significant energy absorbing role within the prestressed samples and we believe it is a previously unrecognised mechanism.