A universal creep model for polymers considering void evolution

Creep behavior in polymers has posed a significant challenge across various industries, yet no theoretical model exists to fully describe their complete three-stage creep process. This paper, for the first time, develops a universal model capable of describing three stages of polymer creep. The model's development is made possible considering void nucleation and evolution during polymer creep, supported by molecular-scale modelling and observations. It provides a precise definition of the start and end times for each creep stage, a milestone not previously achieved. Validation of the model was conducted through creep tests on epoxy resin under different stress levels and temperatures, supplemented by comparisons with experimental data from the literature. The findings show that creep properties, such as creep failure time and minimum creep rate, exhibit an exponential relationship with stress. The model identifies the maximum creep damage (measured by the area fraction of the void in a cross section) for epoxy as 0.15, independent of temperature, with ∼90 % of damage occurring in the tertiary stage. Additionally, the ASTM D 2990 formula tends to overestimate creep failure time, with greater overestimations at lower stress levels—approximately 10 % for a 10-year failure time. This model represents a major advancement, offering the ability to predict the complete three-stage creep failure of any polymer under varying stress and temperature conditions. It provides a critical tool for engineers to reliably predict polymer creep behavior and prevent failure, addressing a long-standing challenge in polymer research and applications.