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Abstract
Ultra-high molecular weight polyethylene (UHMWPE) fibres have high tensile strength
(approaching 4 GPa), high elastic modulus (about 130 GPa), and low density (970 kg/m3), which provide enhanced capacity to absorb energy and resist penetration under impact loading. For protection against impact threats, these fibres are most commonly used in the form of non-woven composite laminates comprising unidirectional plies of collimated fibres embedded in polyurethane or rubber matrices. However, there is a paucity of data on the impact behaviour of woven fabrics and fabric-reinforced composite laminates made of these fibres. Therefore, this thesis aims to investigate the penetration and failure mechanisms of UHMWPE woven fabrics and fabric-reinforced composite laminates and identify the effects of several important factors.
The tensile properties of UHMWPE single yarns were tested at various strain rates from
3.3×10-5 to 400 s-1. A transition from ductile to brittle failure of yarns was observed as
the strain rate increased. It was found that the tensile strength and Young’s modulus
increased while the failure strain and toughness decreased with strain rate at low strain
rates (below 0.33 s-1). However, these tensile properties were almost insensitive to strain rate at higher strain rates. The strength of yarns followed the 2-parameter Weibull
distribution at all strain rates studied.
The impact behaviour of multi-ply woven fabrics was studied by means of impact testing
and finite element modelling. The effect of fabric folding was investigated for the first
time by comparing the impact performance of unfolded fabrics, accordion-fold fabrics,
and roll-fold fabrics. The results showed that the perforation resistance and energy
absorption capacity were significantly improved by folding a fabric into multiple plies
compared to the unfolded counterparts, and the roll-fold fabrics performed best.
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The impact behaviour of woven fabric-reinforced composite laminates with four different
resins was experimentally investigated. The laminates having flexible matrices performed better in perforation resistance and energy absorption, but had a larger extent of deformation and damage than the counterparts made of rigid matrices. The matrix rigidity played a crucial role in controlling the propagation of transverse deformation, and thereby the local strain and perforation resistance of the laminates.