Long-term open-hole tensile creep properties of self-reinforced PET composites measured by digital image correlation

Abstract

This study utilizes digital image correlation (DIC) method to study the open-hole tensile creep behavior of hole drilled self-reinforced polyethylene terephthalate (srPET) composites and compare it with results obtained by conventional mechanical tensile systems (MTS). The short-term tensile creep behavior obtained by DIC and MTS at elevated temperatures was analyzed using Findley's viscoelastic models. For srPET composites without a hole drilled, the short-term creep results obtained by MTS and DIC are similar. However, for hole-drilled srPET composites, DIC determined the strain field including the maximum strain (DIC-M) at the edge of the hole, while MTS only obtained the average strain, which does not represent the maximum strain caused by the strain concentration, resulting in a lower strain estimate. The long-term creep behavior of srPET composites was described successfully by an Arrhenius-type time–temperature superposition principle (TTSP). The DIC creep master curve increased exponentially with time, while the MTS curve remained linear. The master curve obtained by MTS underestimates the creep strain and fails to predict the failure time and thus only applicable to samples without holes, but not to hole-drilled samples or materials with local stress/strain concentrations. An onset point of 107.2 s was determined from the DIC creep master curve and was regarded as the failure time. The creep strain increased with hole size increased and lead to the failure time decreased. An MR value of 70% may serve as an indication of creep failure for the lifetime prediction of srPET composites.ϖ.