| I examine two possible mechanisms for shear localization in the shear-transformation zone model as developed by Falk and Langer. The first method uses the elasticity of the surrounding material as medium for interaction between zones. Unfortunately, the model as currently written does not handle energy balance properly and for any physically reasonable set of parameters cannot cause shear bands without violating the second law of thermodynamics. The second method entails including an effective temperature to describe the configurational degrees of freedom. Such a model, does successfully produce shear bands as a steady state for certain ranges of strain rates. More importantly, this model is especially unstable during the initial transients of loading, and can produce shear bands for strain rates above a critical value that though temporary, last longer than typical experimental durations. |
