Service Performance of Polymeric Materials: Prediction from Short-term Tests

Abstract

Service performance seems to be the ultimate test of successful synthesis, processing, characterization and testing of polymeric materials. Viscoelasticity and the time dependence of mechanical properties can be considered as a nuisance, but in fact they provide us with the capability of prediction of long-term performance in service on the basis of short-term tests. The material characteristics and their influence on long-term life prediction are evaluated using two concepts, the cooperative response of the material and the chain relaxation capability (CRC). We show quantitative predictions using the time-temperature correspondence, time-strain correspondence, frequency-temperature correspondence, stress-time correspondence and the slow crack propagation on the basis of these concepts. The predictions include the use of a generalized temperature shift factor aT formula. Our formula includes the W-L-F equation of 1955 as a special case and has a much larger range of applications. Our stress shift factor a [sgrave] equation provides a prediction tool for a phenomenon demonstrated experimentally already in 1948.