A physical approach to the toughness problem: from thermodynamics to kinetics-I. The homogeneous case

The classical equilibrium equation of a crack under stress is reconsidered, introducing the deformation kinetics through a blunting correction to the elastic energy storage term, and a recalculation of the energy dissipation in the plastic zone. Both are expressed in terms of yield stress, strain hardening rate and strain rate sensitivity. The resulting instability criterion exhibits a ductile-brittle transition, and shows the influence of the above physical parameters on the critical stress intensity factor K_C. In addition, the blunting approximation, which neglects the energy dissipation in the plastic zone, is shown to be valid in most cases.