Role of stress triaxiality on ductile versus brittle fracture in pre-cracked FCC single crystals: an atomistic study

Abstract

The ductile versus brittle fracture in crystalline materials depends on the relative values of KIc and KIe as defined by well-known Rice theory, where KIc and KIe are the critical values of stress intensity factor corresponding to cleavage and dislocation emission, respectively. For KIc < KIe, the brittle fracture (or cleavage) takes place in atomically sharp pre-cracked crystal subjected to Mode I loading. For KIe < KIC, the dislocations are emitted from the crack front resulting in ductile fracture. To this end, molecular static simulations are used to explain the crystal orientation dependent fracture behaviour of FCC single crystal and its contradiction with respect to Rice theory based on stress triaxiality at the crack front. The stress triaxiality at crack front changes with crystal orientation due to transformation of stiffness tensor Cijkl. It is shown that high stress triaxiality suppressed the dislocation initiation leading to cleavage failure even for the case when KIe < KIc.