Correlating toughness and roughness in ductile fracture

TL;DR

This study uses 3D simulations to explore how ductile fracture toughness correlates with fracture surface roughness, revealing a linear relationship between correlation length and toughness across different microstructures.

Contribution

It provides the first quantitative correlation between fracture surface roughness and toughness in ductile fracture through detailed 3D microstructure simulations.

Findings

Fracture surfaces are self-affine over two orders of magnitude.

Roughness exponent is approximately 0.54.

Correlation length of fracture surface scales linearly with toughness.

Abstract

Three dimensional calculations of ductile crack growth under mode I plane strain, small scale yielding conditions are carried out using an elastic-viscoplastic constitutive relation for a progres- sively cavitating plastic solid with two populations of void nucleating second phase particles. Full field solutions are obtained for three dimensional material microstructures characterized by ran- dom distributions of void nucleating particles. Crack growth resistance curves and fracture surface roughness statistics are calculated using standard procedures. The range of void nucleating particle volume fractions considered give rise to values of toughness, JIC, that vary by a factor of four. For all volume fractions considered, the computed fracture surfaces are self-affine over a size range of about two orders of magnitude with a roughness exponent of 0.54 $\pm$ 0.03. For small void nucleating particle volume fractions, the mean large particle spacing serves as a single dominant length scale. In this regime, the correlation length of the fracture surface corresponding to the cut-off of the self-affine behavior is found to be linearly related to JIC thus quantitatively correlating toughness and fracture surface roughness.