THERMOMECHANICS AND NONLINEAR VISCOELASTICITY AS APPLIED TO ROCK MECHANICS

High hydrostatic pressure complicates rock constitutive modeling, putting into question mechanical testing conducted under ambient conditions. This work defines strain energy density such that distortional deformation is separated from axial dilatation along the principal directions. The framework effectively captures time and temperature dependent strain induced orthotropy. We show how the first and second laws of thermodynamics naturally lead to a generalized Maxwell model in Mechanics. The Maxwell spring deformations constitute a set of Schapery’s internal state variables (ISVs). Nonlinear springs provide a loading history agnostic failure criterion. Grounded in thermodynamics, the framework naturally accommodates temperature and pressure effects.