Drop weight impact behaviour of viscoelastically prestressed composites

Viscoelastically prestressed polymeric matrix composites (VPPMCs) are produced by subjecting fibres to tensile creep, the creep load being released prior to fibre moulding. Following matrix curing, the viscoelastically recovering fibres generate compressive stresses within the matrix which, from previous studies, can improve mechanical properties by up to 50%. This paper reports on the first study of thin flat-plate VPPMCs, using nylon 6,6 fibre-polyester resin to form cross-fibre composite plates (CCPs) with 0°/90° fibre layers and randomly distributed discontinuous fibre plates (RCPs). Drop-weight impact testing was performed on CCPs with impact velocities of 1.9 – 5.8 m/s and, compared with (unstressed) control samples, VPPMC damage depth was reduced by up to 29%; however, this difference decreased with impact velocity, indicating little improvement above 7.7 m/s. RCPs, tested at 3.0 m/s, showed a ~30% reduction in VPPMC damage depth, compared with ~20% for CCPs, but with no changes in debonded area