Polymers are becoming more common in construction, for example as polymeric pipes and polymer composite reinforcements for concrete. Polymeric structural elements are often subject to complex, time-dependent loading, e.g, pipelines installed using trenchless technologies. Behaviour under these loads and long-term strength and failure modes linked with environmental stress cracking (ESC) are of great practical interest. In this paper, experimental tensile creep tests are used for defining material properties of polyethylene to be used in constitutive equations. Prony's series and associated multi-Kelvin modelling are used to find material factors. The Modified Superposition Principle is applied to predict the behaviour of polyethylene under variable stress conditions over time. The model considers time-dependent and nonlinear behaviour of the material. The theoretical and experimental results on polyethylene subjected to various load histories are compared and discussed.
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