Constitutive model calibration for the thermal viscoelastic-viscoplastic behavior of high density polyethylene under monotonic and cyclic loading

High density polyethylene (HDPE) can show viscoelastic-viscoplastic behaviors under monotonic loads and a stress softening after reloading under cyclic ones. This sets a challenge in simultaneously representing such response in material constitutive models. In addition, due to the adoption of novel accelerated tests at higher temperatures, e.g., 95 °C, the need for a higher temperature calibration is motivated. Therefore, the objective of this study is threefold: (i) to investigate the capability of the three network viscoplastic (TNV) model in capturing HDPE thermo-viscoplasticity under monotonic and cyclic loads, (ii) to report observations on HDPE at various strain-rates and temperatures from 23 °C to 95 °C including the α-relaxation region (iii) to explore the ratcheting behavior of HDPE, i.e., cyclic creep. The FEA analysis based on the calibrated TNV model was successfully able to predict the HDPE behavior under static, quasi-static and dynamic loads. The predicted strain range Δε and mid-range strain ε_s of the cyclic creep showed good agreements. This implies that the TNV model can be a reliable candidate for HDPE engineering assessments. Findings of this work will have many industrial applications, e.g., products manufacturers or resin producers, in which HDPE is used under complex loads. Similar procedures can be followed for other thermoplastics which lays the basis for establishing a standard calibration guideline.