Yielding of FCC crystals at zero deformation rate: evidence for hidden transition

Despite much effort, no theory, consistent with all rigorous thermodynamic constraints, has been derived that can predict the yield point of a real solid. An exact result states that the free energy of any material, made up of entities interacting with short ranged forces, cannot depend on the shape of the boundary. This implies that crystalline solids are guaranteed to yield at infinitesimal stresses when deformed at vanishing rates. Here we present our work on yielding of an ideal FCC solid in the strictly zero strain rate limit. In this limit, the yield point vanishes for infinitely large systems. Earlier, we showed, for an ideal 2d triangular crystal that the yielding phenomena is a dynamic consequence of a hidden first order phase transition. Our calculations of the free energy of such solids also show that the solid phase is always metastable at any finite temperature and infinitesimal deformation. Our prediction for the dynamical yield points agree with MD simulations for a wide range of deformation rates. We describe, here, our extension of this previous work to the initially defect-free FCC crystal. We discuss about commensuration, finite-size effects and consequences of systematically introduced disorders as random interactions of varying strength in such solids.