A study of nonlinear viscoelasticity of an unsaturated polyester resin. Part 1. Uniaxial model

Abstract

A nonlinear viscoelastic theory is proposed to model the creep behaviour of an unsaturated polyester resin. The theory is based on Schapery's single-integral model, modified by an exponential kernel function. Further Struik's theory of physical ageing has been included to describe long-term behaviour. A series of tests has been carried out in order to characterize the model parameters and verify the established theory. The model which contains only two nonlinearizing parameters accurately describes the creep-recovery behaviour of the resin over a tensile stress range up to 40 MPa. The model has been verified for various cyclic loading conditions. Under these loading conditions, the strains predicted with the model correspond within an error band of 1% with the measured strains. Although the model parameters are obtained by simple creep tests, the successful prediction of the cyclic loading cases and long term creep deformation demonstrates the wider applicability of the model.