Prestressed polymeric composites produced by viscoelastically strained nylon 6,6 fibre reinforcement

A method for improving impact resistance is reported. Polymeric fibres are stretched under a load which is released prior to moulding them into a matr ix. On solidification of the matrix, compressive stresses imparted by the v iscoelastically strained fibres impede crack propagation The prestressing p rinciple is illustrated through a polariscope study of nylon 6,6 monofilame nt embedded in transparent resin. Previous work demonstrated the method thr ough Charpy tests on nylon 6,6 fibre-polyester resin composites: prestresse d samples absorbed 25% more impact energy than their control (unstressed) c ounterparts. Further impact studies are reported in the present work to eva luate probable service life. Batches are tested from 12 to 96 hours after m oulding and (through heat treatment to accelerate ageing) at estimated ages of one to 10 years. They show no discernible change in impact performance with age.