New contributions to the effective surface energy of cleavage

We propose two new contributions to the effective surface energy of cleavage, those of ligaments and ledges. Although these undergo plastic deformation and thus contribute to fracture surface plasticity, this is not plastic energy dissipation in the classic sense. Much of the plastic work occurs after the crack has passed and the true effect on the crack extension force is an elastic one based upon how the restraining force lowers the crack-tip stress intensity. Another way of looking at this is that such an elastic restraining force increases the effective stress intensity or surface energy for continued crack extension. It is suggested that such a mechanism may have similar implications to composites, two-phase microstructures and stress-corrosion cracking occurring in "cleavage" modes.