Interaction of void spacing and material size effect on inter-void flow localisation

TL;DR

This study investigates how void spacing and material size effects influence void coalescence in porous metals, revealing that strain gradient effects can alter the impact of void ligament size on fracture behavior.

Contribution

It introduces a finite element model incorporating strain gradient effects to analyze the interaction between void spacing and material size on void coalescence.

Findings

Decreasing inter-void ligament size increases coalescence propensity without strain gradient effects.

Strain gradient effects harden the material and reduce the influence of ligament size on coalescence.

Strain gradients can mitigate the effect of void spacing on fracture in porous metals.

Abstract

The ductile fracture process in porous metals due to growth and coalescence of micron scale voids is not only affected by the imposed stress state but also by the distribution of the voids and the material size effect. The objective of this work is to understand the interaction of the inter-void spacing (or ligaments) and the resultant gradient induced material size effect on void coalescence for a range of imposed stress states. To this end, three dimensional finite element calculations of unit cell models with a discrete void embedded in a strain gradient enhanced material matrix are performed. The calculations are carried out for a range of initial inter-void ligament sizes and imposed stress states characterised by fixed values of the stress triaxiality and the Lode parameter. Our results show that in the absence of strain gradient effects on the material response, decreasing the inter-void ligament size results in an increase in the propensity for void coalescence. However, in a strain gradient enhanced material matrix, the strain gradients harden the material in the inter-void ligament and decrease the effect of inter-void ligament size on the propensity for void coalescence.