Dynamics of shear-transformation zones in amorphous plasticity: Formulation in terms of an effective disorder temperature

This investigation extends earlier studies of a shear-transformation-zone (STZ) theory of plastic deformation in amorphous solids. The main purpose is to explore the possibility that the configurational degrees of freedom of such systems fall out of thermodynamic equilibrium with the heat bath during persistent mechanical deformation and that the resulting state of configurational disorder may be characterized by an effective temperature. The further assumption that the population of STZ's equilibrates with the effective temperature allows the theory to be compared directly with experimentally measured properties of metallic glasses, including their calorimetric behavior. The coupling between the effective temperature and mechanical deformation suggests an explanation of shear-banding instabilities.