Physics of toughness. A kinetic approach of the brittle–ductile transition and of the role of plastic instabilities

The thermodynamical stability of a crack is analyzed in terms of plastic dissipation due to dislocation motion in the plastic zone, and of reduction of the stress intensity factor due to crack tip blunting. The stability criterion thus obtained provides a simple diption of the brittle–ductile transition, and of the influence of yield stress, work hardening coefficient, and strain‐rate sensitivity on toughness. Furthermore, the blunting approximation is shown to be valid in most cases, and is conveniently applied to the treatment of toughness in the case of plastic instabilities, as slip bands, Lüders bands, or Portevin le Chǎtelier plastic waves.