Viscoelastically prestressed polymeric matrix composites – Potential for useful life and impact protection

A viscoelastically prestressed polymeric matrix composite (VPPMC) is produced by applying tension to polymeric fibres, the tensile load being released prior to moulding the fibres into a matrix. Following matrix solidification, compressive stresses imparted by the viscoelastically strained fibres improve composite tensile, flexural and impact properties. This study focuses on the potential for useful life and impact protection capability by performing Charpy impact tests on nylon 6,6 fibre–polyester resin samples subjected to accelerated ageing. Prior to testing, time–temperature superposition principles were used, the samples being aged by heating to 60 °C for periods representing a 10-fold increase over previous work. The results demonstrated no deterioration in impact performance over a duration equivalent to 40 °C for ∼20 years. Combining these data with previous work showed that VPPMC samples absorbed, on average, ∼30% more impact energy than control (unstressed) counterparts. Four mechanisms are highlighted, which should enable VPPMCs to contribute towards high velocity (blast fragment) impact protection and crashworthiness applications, especially for situations requiring low mass components with complex geometries.