PLASTIC INSTABILITIES AND THEIR RELATION TO FRACTURE

When plastic instabilities occur the plastic deformation ahead of a cr ack tip is heterogeneous. This heterogeneity changes the rate of plast ic dissipation ahead of a crack. Thus, depending on the nature of the instability (steady as persistant slip bands, propagative as Portevin- Le Chatelier bands) the toughness K is influenced by plastic instabili ties. In parallel, plastic localization is known to produce enhanced d amage, very localized, influencing the ductility. As an example of suc h effect, we will show that the Coffin-Manson law for fatigue can be d erived from the localized nature of plastic flow and its relation to m icrocrack nucleation. This contribution will present theoretical appro aches for those two aspects with experimental evidence mainly from alu minium alloys and steels.