Influence of microstructure-driven strain localization on the ductile fracture of metallic alloys

Abstract

Most models in the literature that are used to understand and predict ductile failure, ductility or fracture toughness implicitly consider that the plastic response of the material is homogeneous at the level of the microstructure. However, in a number of situations, plasticity is intrinsically localized, because the microstructure is spatially heterogeneous, or because the loading leads to strain localization on the microscale, such as in fatigue loading, or because the dynamics of plastic flow are unstable, such as in Portevin–Le Chatelier instabilities. This paper presents, from analysing various examples, the influence of these strain localization phenomena on the ductile fracture behaviour of metallic alloys. Examples to illustrate these effects will be chosen from, firstly, internal necking between cavities growing to ductile fracture, secondly, damage mechanisms from fatigue persistent slip bands, thirdly, the effect of Portevin–Le Chatelier bands on toughness and, fourthly, damage mechanisms in alloys with precipitate-free zones at grain boundaries.

Acknowledgements

This paper gives us the opportunity to thank the colleagues and friends who have collaborated on the different topics discussed in this paper: D. Dumont, A. Deschamps, D. Embury, J.W. Hutchinson, T. Magnin, P. Gomiero, F. Louchet and D. Sornette. Some of the work presented in this paper was carried out in the framework of the PAI 5-1-9 project ‘From microstructure towards plastic behaviour of single-phase and multiphase materials’ supported by the Federal Office for Scientific, Technical and Cultural Affairs (OSTC), Belgium.

Notes

† Note also that, on the other hand, microshear bands can sometimes be thinner than the void spacing or even the void size and not interact with the damaging process. This is the case in some aluminium alloys in which microshear bands of less than 50 nm are observed (M. Gasperini, 2002, private communication). In other instances microshear bands in the 1–10 µm range are observed and interact with the damage process.