A Comprehensive Review of Continuum Constitutive Models for Thermoplastic Polymers

Thermoplastic polymers exhibit complex mechanical behavior characterized by nonlinear visco-elasticity, visco-plasticity, 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. To contextualize these models, an overview of continuum, micro-mechanical, and multi-scale modeling frameworks is provided. Emphasis is placed on continuum models, highlighting in particular their interpretation based on rheological elements originating from linear viscoelasticity, and adaptability through the selection of appropriate nonlinear functions for the different elements. 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 optimization techniques for parameter identification are briefly discussed, with a focus on Bayesian optimization strategies that enhance efficiency while reducing experimental costs.