Predictive models for the creep behaviour of PMMA

Two models of the creep behaviour of polymers were investigated. Both of these models are relatively simple and so have potential as predictive design tools. One was the θ concept model which has been used successfully with metals and ceramics. The other was derived from the universal formula and effective time theories that were developed from physical aging models. The creep behaviour of PMMA was measured under a wide range of conditions, including various (in some cases unknown) aging times, high stresses and temperatures higher than the aging temperature. Both approaches were then used to model these creep data. It was found that the θ concept was not completely successful since it does not account for the viscoelastic response of polymers very well and takes no account of physical aging. The universal formula and effective time theories showed much more promise, although more work is needed to fully develop this.