A physical approach to the toughness problem: from thermodynamics to kinetics-II. The heterogeneous case

The quasistatic evolution of the stress intensity factor at a crack tip during loading is discussed in the frame of the blunting approximation. This approach allows a very simple treatment of the influence of strain localization and plastic instabilities on toughness of an homogeneous crystal. The evolution with time of the effective stress intensity factor is computed for 3 types of strain heterogeneities: slip bands, Lüders bands and Portevin Le Châtelier instabilities. The first type of localization is shown to improve systematically toughness, whereas the other two types improve toughness only for the most brittle materials, but are deleterious for the less brittle ones.