Internal Thermodynamic Variables and Failure of Microcracked Materials

Thermodynamic stability of materials is investigated in the presence of internal variables. The possibility of phase boundaries in nonequilibrium solid materials is considered which suggests the concept of phase breaking similar to the phase transitions in case of fluid and gaseous systems. Two particular models of damage mechanics are proposed and investigated in more detail as illustrative examples. Both models are direct thermodynamic generalizations of well known damage mechanical models considering general loading conditions. According to these thermodynamic suggestions a new failure criterion is suggested for microcracked materials and compared with experiments and other criteria.