Plastic instabilities and their relation to fracture

When plastic instabilities occur the plastic deformation ahead of a crack tip is heterogeneous. This heterogeneity changes the rate of plastic dissipation ahead of a crack. Thus, depending on the nature of the instability (steady as persistant slip bands, propagative as Portevin-Le Châtelier bands) the toughness K is influenced by plastic instabilities. In parallel, plastic localization is known to produce enhanced damage, very localized, influencing the ductility. As an example of such effect, we will show that the Coffin-Manson law for fatigue can be derived from the localized nature of plastic flow and its relation to microcrack nucleation. This contribution will present theoretical approaches for those two aspects with experimental evidence mainly from aluminium alloys and steels.