Abstract
A method for improving impact resistance is reported. Polymeric fibres are stretched under a load which is released prior to moulding them into a matrix. On solidification of the matrix, compressive stresses imparted by the viscoelastically strained fibres impede crack propagation. The prestressing principle is illustrated through a polariscope study of nylon 6,6 monofilament embedded in transparent resin. Previous work demonstrated the method through Charpy tests on nylon 6,6 fibre-polyester resin composites: prestressed samples absorbed 25% more impact energy than their control (unstressed) counterparts. Further impact studies are reported in the present work to evaluate probable service life. Batches are tested from 12 to 96 hours after moulding 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.
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