A Thermomechanically Coupled Visco-Elasto-Plastic Model with Nonlocal Damage for Semi-Crystalline Thermoplastics
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Thermoplastic materials are increasingly employed in high-performance structural applications across automotive, aerospace, and energy sectors due to their favorable manufacturability, recyclability, and damage tolerance. Nevertheless, their mechanical response and failure behavior are strongly influenced by coupled thermo-mechanical effects, rate-dependent nonlinear deformation mechanisms, and process-induced material morphology, particularly crystallinity. These interactions span multiple spatial and temporal scales and remain insufficiently understood, often limiting the predictive capability required for reliable structural design. This contribution is part of an ongoing NSF–DFG collaborative research project aimed at developing predictive material models for thermoplastics that establish quantitative links between process-induced morphology, mechanical performance, and failure behavior. In the present work, we develop a constitutive material model for semi-crystalline thermoplastics that integrates viscoelastic and elastoplastic mechanisms to describe the nonlinear, time-dependent thermo-mechanical response of thermoplastic polymers. A bidirectional coupling between deformation and temperature is incorporated to account for self-heating effects during mechanical loading, while crystallinity is prescribed and enters the constitutive law in a unidirectional manner to represent morphology-dependent material behavior. Nonlinear inelastic deformation and failure are described within a unified framework by extending the constitutive model with a nonlocal damage formulation. This regularized approach ensures mesh objectivity, mitigates pathological strain localization, and enables the prediction of distributed damage zones and progressive failure processes that are strongly influenced by thermally activated deformation mechanisms and crystallinity variations. The resulting coupled thermo-visco-elasto-plastic–damage model allows for the prediction of the spatiotemporal evolution of stress, temperature, heat generation, and damage under varying loading rates, thermal conditions, and crystallinity levels. Please let me know if you agree with the proposed submission or if you would suggest any changes.
