Effect of thermo- oxidative aging on elastic- viscoplastic behavior of polyethylene pipe: experiments, constitutive modeling, parametric study

Current research on pressure-bearing polyethylene (PE) pipes often neglects environmentally induced degradation of mechanical properties, resulting in overly conservative safety assessments based on numerical simulations. Investigating the effects of thermo-oxidative aging on their elastic- viscoplastic behavior is essential for advancing structural modeling and safety evaluations under multi-factor coupling conditions. In this study, long-term thermo-oxidative aging tests were first conducted on PE pipes to characterize the material’s physicochemical degradation process. Changes in crystallinity were measured using differential scanning calorimetry (DSC), with the evolution of crystallinity over exposure time- compared to the original material- serving as an indicator of material degradation. An elastic- viscoplastic constitutive model suitable for describing the mechanical behavior of PE pipes was then developed within a finite deformation framework. Based on experimental observations, evolution functions for key material properties were introduced to incorporate the influence of thermo-oxidative aging. A parameter identification methodology was proposed, and the effects of material parameters were computationally investigated through numerical implementation. The proposed model accurately captures characteristics of stress–strain behavior under monotonic, cyclic, and large-strain conditions. It also enables the prediction of ratcheting strain evolution and reflects microstructural changes, outperforming established models such as the Bergström- Boyce (B-B) model and the Three Network model (TNM). With improved accuracy and explicit consideration of thermo-oxidative aging effects on material parameters, the presented model offers enhanced micromechanical interpretability and provides a reliable basis for safety assessments of in-service PE pipes under multi-field coupling conditions.