A micromechanical fracture criterion accounting for in-plane and out-of-plane constraint

This paper presents the results of a finite element micromechanical simulation of the interaction between a matrix of voids and a crack for combinations of in-plane and out-of-plane constraint for an elastic–plastic material. Attention has been paid to the effects of out-of-plane constraint since previously this has rarely been investigated. It is known that in-plane and out-of-plane constraint have essentially the same influence on fracture and therefore a parameter should exist that quantifies their combined effect, although despite the efforts of researchers no unique measure of constraint has yet been found. In this paper it is argued that if the equivalent plastic strain upon fracture is used to rank the experimental data, a unique trend can be obtained. By using this trend, a new micromechanical fracture criterion is suggested for aluminium alloy 2024 that accounts for any level of in-plane and out-of-plane constraint. Finally, the findings are verified by comparison with three different sets of earlier experiments performed by the authors or extracted from the literature.

► A finite element micromechanical simulation is performed of the interaction between a matrix of voids and a crack with varying constraint.
► It is shown that the stress triaxiality factor is unable to characterise the effect of in-plane and out-of-plane constraint on fracture.
► The paper presents a new micromechanical fracture criterion that is able to account for the effect of both in-plane and out-of-plane constraint.
► The findings of the micromechanical model are verified by comparison with three different sets of experiments.