DETERMINATION OF CRACK TOP ENERGY DISSIPATION AND ELASTIC-PLASTIC FRACTURE TOUGHNESS PARAMETER WITH DUCTILE CRACK EXTENSION.

A newly developed technique for large plastic strain measurement, that is, the recrystallization-etch technique, was applied to compact tension and three-point bend specimens with a crack length/specimen width of 0. 6 that were tested to draw resistance curves for stable crack extension. The plastic energy dissipation or work done within an intense strain region at the crack top accompanying ductile crack extension was measured experimentally. The size and loading condition effects on this crack top energy dissipation rate were examined in comparison with other candidate parameters for crack extension criteria. The size of the intense strain region could be regarded as equal to the process zone size where the fracture is taking place. Formation and extension characteristics of this zone were discussed from a view point of elastic-plastic fracture toughness parameters.