Composition effect in the thermomechanical behavior of glasses, and its modelization

We employed molecular-dynamics simulations to explore comparatively the thermomechanical behavior of two glass materials---an oxide silica glass (${\mathrm{SiO}}_{2}$) and a binary Cu-Zr-based metallic alloy (${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$)---during shear and elongation deformation cycles. By calculating the energy balance and tracking the temperature evolution of both glasses under deformation cycles, we are able to propose, for each of them, a constitutive law that accurately reproduces the self-heating process due to plastic deformation. These relatively simple constitutive laws involve strain rate sensitivity and a nonlinear temperature dependence of the thermal dilatancy coefficients, as well as strain gradient plasticity. To identify the right parameters, both glasses are equilibrated at very low temperature (10 K), and two independent deformation rates were applied to each sample for each type of deformation. Thermal attenuation is greatly amplified in silica compared to the metallic glass. Moreover, using a precise atomic description of the instantaneous deformation, combined with an exact coarse-graining procedure, we show, in silica, that self-heating is mainly supported by inhomogeneous strain gradient plasticity with nanometric characteristic lengthscales.