Accelerated Measurement of the Long-Term Creep Behaviour of Plastics
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 dur
- PDF / 641,031 Bytes
- 14 Pages / 439.37 x 666.142 pts Page_size
- 22 Downloads / 160 Views
Accelerated Measurement of the Long-Term Creep Behaviour of Plastics F. Achereiner, K. Engelsing and M. Bastian
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.
27.1
Introduction
Plastic parts are increasingly used in engineering applications with high demands on long-term mechanical behaviour. Therefore, this behaviour needs to be considered in the early stages of product development in order to meet the requirements, particularly for products relevant to security or difficult to replace where the minimum guaranteed service life is often significantly longer than 10 years and may reach up to 50 or 100 years (e.g. for pipes and geomembranes for landfills). The service life of products permanently exposed to mechanical load is mostly limited by failure or excessive deformation. Plastic pipes laid in the ground must be for example designed against the increasing deformation of the cross section to ensure full functionality. However, polymers are viscoelastic materials and their F. Achereiner (&) K. Engelsing M. Bastian SKZ – German Plastics Center, Würzburg, Germany © Springer International Publishing AG 2017 W. Grellmann and B. Langer (eds.), Deformation and Fracture Behaviour of Polymer Materials, Springer Series in Materials Science 247, DOI 10.1007/978-3-319-41879-7_27
389
390
F. Achereiner et al.
mechanical behaviour strongly depends on time. A straightforward extrapolation of short-term creep experiments over more than one decade (log scale) is mostly impossible. Estimating the long-term deformation under static load would thus require conventional creep experiments over a long period of 5–10 years in order to account for product lifetimes of 50–100 years. Therefore, tight product development schedules necessitate a way to accelerate the strongly time-dependent creep response with adequate accelerated testing methods. Increasing the temperature is a common way to accelerate the time-dependent creep response [1]. Based on
Data Loading...
