Thermomechanically coupled visco–hyperelastic–plastic model with self-heating for thermoplastics

Thermoplastic polymers exhibit strongly coupled finite-strain behavior involving rate dependence, crystallinity-dependent mechanical resistance, thermal softening, and mechanically induced self-heating. This work presents a rotation-free finite-strain computational formulation for thermomechanically coupled visco–hyperelastic–plastic semi-crystalline thermoplastics. The formulation is built in a corotational intermediate configuration, where plastic, hardening, and viscoelastic updates are expressed through symmetric stretch variables. This casts the time-discrete local constitutive update as a rotation-free finite-dimensional nonlinear residual at each Gauss point, compatible with automatic differentiation of consistent stress and heat-source tangent blocks without branch-specific objective-rate linearizations. Processing-informed crystallinity is prescribed as a field that modulates stiffness, yield resistance, and hardening, while a reversible/irreversible heat-source decomposition separates thermoelastic, plastic, and viscous thermal contributions. The local map is batchable over integration points and is evaluated with JAX/XLA for GPU-vectorized Gauss-point computations within a monolithic finite element setting. Comparisons with PA6 tensile experiments show that the formulation reproduces the pre-peak mechanical response and the measured temperature evolution, including the transition from initial thermoelastic cooling to dissipative self-heating without empirical cooling terms. The post-peak localization regime is retained only as a structural demonstration of the local coupled formulation and is explicitly scoped as non-mesh-objective without additional regularization.