Comparison of short and long term creep testing in high performance polymers

The creep behaviour of thermoplastics plays an important role in engineering design and especially the failure and lifetime prediction of structural components in a variety of industries. Often this mechanical property is determined with long-term creep tests. In order to reduce the development time of components made from such materials used in applications with conditions over 100 °C for long times, we propose the use of dynamic-mechanical analysis to predict long-term creep deformation through the stepped isothermal (SIM) and the stepped isostress methods (SSM). The present study aims to determine whether SIM and SSM can be generalised to material characterisation of advanced polymers at high temperature. Both methods are evaluated and verified by long-term measurements. Both amorphous and semi-crystalline polymers are studied and the influence of the glass transition temperature (Tg) on the accelerated test results is examined with tests conducted above and below the Tg region for PEEK. The results of our analysis show accelerated testing is an effective tool in predicting long term behaviour and comparing the creep response of thermoplastics. PAI exhibits a far superior creep response when compared to PEEK and PEI over 100 °C. •Accelerated creep tests can be used to compare the relative creep response of different materials at elevated temperatures.•We predicted the creep behaviour for amorphous polyetherimide with a Tg of 217 °C, at temperatures of 120 °C and 150 °C.•We produced an approximation for the creep response of PEEK with a Tg of 143 °C, both above and below Tg.•The stepped isostress method is a useful technique comparing polymers of complex and simple rheology at high temperatures.•For both semi-crystalline and amorphous plastics, we predicted the creep response to over 70 times the test time.•Amorphous PAI with a Tg of 275 °C has very high creep resistance at 120 °C and 150 °C, compared to PEEK and PEI.