A comprehensive review of continuum constitutive models for thermoplastic polymers

Thermoplastic polymers exhibit complex mechanical behavior characterized by nonlinear viscoelasticity, viscoplasticity, strain-rate sensitivity, temperature dependence, and distinct deformation mechanisms such as shear yielding, crazing, and internal particle cavitation. Understanding and accurately modeling their response is crucial for various engineering applications. Within this setting, this contribution provides a comprehensive review of continuum constitutive modeling approaches for thermoplastic polymers. The review adopts a modular standpoint: each model is treated as an arrangement of springs and dashpots inherited from linear viscoelasticity, into which nonlinear flow rules, yield criteria and free energies are inserted in place of the linear elements. Separating the arrangement from the elements makes explicit what models proposed independently have in common, and allows them to be compared on a single footing. The increasing complexity of these models often results in a high number of material parameters, necessitating extensive experimental characterization. To address this challenge, recent advancements in constitutive parameter identification techniques are briefly mentioned, highlighting the role of optimization techniques in improving efficiency and reducing experimental effort.