Effect of preliminary loading on the deformation and strength properties of high-strength fibres

Abstract

High-strength, high-modulus polyethylene fibres fabricated with gel technology is similar to low-modulus fibres of the olefin and amide series (Capron, polypropylene) with respect to the character of the correlation of the stress—strain diagrams and curve of accumulation of the residual component of deformation. The residual deformation component is relatively large both for high-strength PE fibre and for p-polyamide fibres. The differences in the character of accumulation of the plastic component in these fibres are due to the fact that the residual strains arising in high-strength PE fibre, as in other flexible-chain polymer fibres (polypropylene, Capron) is initiated by breaking of bonds in the main chain. In p-polyamide fibres (Armos, SVM, Terlon, Kevlar), plastic strains arise due to highly elastic deformation “frozen≓ by hydrogen bonds and orientation of molecular chains. Preliminary deformation affects the strength properties of high-modulus fibres differently: in PE fibres, the strength decreases, it increases for Armos and SVM fibres, and remains unchanged for Terlon fibre. This difference is to a great degree due to the difference in the types of intermolecular interaction in fibres of the olefin and amide series. For all fibres investigated, the character of accumulation of the residual deformation component can be correlated with the type of stress—strain diagram, which will allow creating simpler methods of evaluating residual strains.