Local Yield Surfaces in Model Amorphous Solids

It has been the aim of much recent work to connect concepts regarding the physics of plasticity in glassy and amorphous materials to plastic constitutive theories. In doing so, many "plastic descriptors" have emerged to predict irreversible response to shear in atomistic models; almost all of these are inherently scalar. The scalar nature of these predictors mirrors the state variables that have been incorporated into many rate-and-state based theories of amorphous plasticity: concepts like "free volume," "effective temperature," and "softness". However there are strong reasons to believe that scalar measures are insufficient for describing the response of the glass structure. Here we discuss our investigations of both 2D and 3D simulated glasses from which we extracted the local yield stress throughout the simulated system. The shape of the resulting yield surface and the statistics of the yield events reveal interesting aspects of the underlying physics. We will use this data as a jumping off point to discuss what should supersede scalar order parameters in next-generation constitutive theories of amorphous plasticity.