Is ab initio fracture toughness evaluation appropriate?

A verification with molecular dynamics

Abstract

First-principles calculation approaches have long been attempted to evaluate fundamental materials properties of fracture, such as ideal strength. Recently, Li and Snyder proposed the integral stress-displacement method (ISDM) and claimed that one can evaluate fracture toughness by first-principles calculations, showing good agreement with experimental evaluations. However, there doesn’t seem to be consensus about the validity of using such calculation methods for the evaluation of fracture toughness. In this study, we compared ISDM and crack propagation molecular dynamics simulation for Si using an identical empirical interatomic potential. It was found that ISDM is by design dependent on the simulation cell size, requiring a predetermined length parameter to calculate the fracture toughness. In our simulation of crack propagation along (111) plane, we found nearly two-fold discrepancy between the ISDM evaluation and the molecular dynamics result. This may indicate the need of further investigation at the nanometer scale about the size of the process zone even in brittle fracture.