In most mathematical problems considering voids, why does the equation of balance of Equilibrated force not include any thermal relaxation parameter considering Green-Lindsay theory or any higher order of thermoelasticity?
If we consider piezoelectricity, the extra equation arising due to the presence of an electric field (gauss law) has a thermal relaxation parameter. By the same logic, shouldn't the equation of balance of Equilibrated force also involve a thermal relaxation parameter?
A literature survey reveals that most papers haven't considered any. Can someone please provide some justification?