Ju l 1 99 8 A molecular - dynamics study of ductile and brittle fracture in model noncrystalline solids

A molecular-dynamics study of ductile and brittle fracture in model noncrystalline solids Abstract Molecular-dynamics simulations of fracture in model amorphous solids are shown to exhibit brittle or ductile behavior depending on small changes in interatomic potential. Yet, simulations of these two model solids under pure shear reveal no significant difference in their ultimate yield stress. To understand this change in failure mode we consider the relationship between crack dynamics, rate-dependent plasticity, and molecular-level structures in the glassy solid. In particular these simulations can be understood in the context of Freund and Hutchinson's theory of brittle fracture and the theory of viscoplasticity proposed by Falk and Langer. We also consider a simplified model of the microscopics of plastic deformation as a first-step toward the construction of first-principles models of dynamic plasticity and the brittle ductile transition in noncrystalline materials.