A comparative study of fracture in Al: quantum mechanical vs. empirical atomistic description

TL;DR

This study compares quantum mechanical and empirical atomistic models of fracture in aluminum, revealing significant differences in crack behavior, dislocation activity, and charge density distribution.

Contribution

It provides a detailed comparison of fracture predictions in Al using DFT-based QCDFT and empirical EAM-QC methods, highlighting qualitative and quantitative differences.

Findings

EAM-QC predicts a straight crack front and micro-twinning.

QCDFT finds a rounded crack profile without twinning.

Dislocation emission differs between methods, with fewer dislocations in QCDFT.

Abstract

A comparative study of fracture in Al is carried out by using quantum mechanical and empirical atomistic description of atomic interaction at crack tip. The former is accomplished with the density functional theory (DFT) based Quasicontinuum method (QCDFT) and the latter with the original Quasicontinuum method (EAM-QC). Aside from quantitative differences, the two descriptions also yield qualitatively distinctive fracture behavior. While EAM-QC predicts a straight crack front and a micro-twinning at the crack tip, QCDFT finds a more rounded crack profile and the absence of twinning. Although many dislocations are emitted from the crack tip in EAM-QC, they all glide on a single slip plane. In contrast, only two dislocations are nucleated under the maximum load applied in QCDFT, and they glide on two adjacent slip planes. The electron charge density develops sharp corners at the crack tip in EAM-QC, while it is smoother in QCDFT. The physics underlying these differences is discussed.