A PHYSICAL APPROACH TO THE TOUGHNESS PROBLEM - FROM THERMODYNAMICS TO KINETICS .1. 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.