Accelerated Measurement of the Long-Term Creep Behaviour of Plastics

Abstract

Plastic parts are increasingly used in engineering applications with high demands on long-term mechanical behaviour. Therefore, suitable accelerated test methods are strongly required. The Stepped Isothermal Method (SIM), a short-term creep experiment during which the temperature is elevated stepwise, was originally developed for product testing of geosynthetics. This method was successfully applied to characterise the long-term creep behaviour of polypropylene tensile specimens. The measured strain can be rescaled and subsequently shifted according to the time–temperature superposition principle (TTSP) to build a master curve out of a single experiment. SIM master curves matched the results of the classical TTSP procedure while reducing the experimental effort to a minimum. This offers a useful tool, e.g. for a quick screening of material formulations during the early development stages or the at-line assessment of resins as part of quality assurance. Furthermore, SIM experiments can be performed until creep failure and, thus, accelerate the determination of the creep strength and the construction of creep rupture curves.