| Though commonly used, high-density polyethylene (HDPE) is a complex material with mechanical properties hard to model. As the majority of plastics, it exhibits a strong viscoelastic behavior resulting in a large creep. Due to its semicrystalline structure, this polymer is indeed subject to physical aging. Therefore, the definition of the thermal history is essential before using an extrapolating method. The objective of this project is to develop a predicting method able to shorten testing time for a complex thermal history of a biomedical device (an endovascular stent).; First, a new way of modeling creep based on dual kriging is presented. It enables to accurately describe short-term experiments. Then, short-term data at different stress levels lead to the construction of a master curve using time-stress superposition principle. Afterwards, the aging effects are determined from creep tests after different thermal histories. The prediction can finally be corrected by the use of effective time theory. Two limiting cases are thus studied to understand the influence of the storage time on polyethylene properties. (Abstract shortened by UMI.)... |
