Nonlinearly coupled thermo-visco-elasticity

The d-dimensional thermo-visco-elasticity system for Kelvin-Voigt-type materials at small strains with a general nonlinear coupling is considered. Thermodynamical consistency leads to a heat capacity dependent both on temperature and on the strain. Using higher-gradient theory, namely the concept of so-called second-grade non-simple materials (or of hyper-stresses), existence of a weak solution to a system arising after an enthalpy-type transformation is proved by a suitably regularized Rothe method, fine a-priori estimates for the temperature gradient performed for the coupled system, and a subsequent limit passage.