BEHAVIOR AND CRITERION OF QUASI-BRITTLE FRACTURE OF METALS

In this investigation complex stress state is related to the stress state in uniaxial tension by use of the concept of effective stress from the elastoplastic theory. Considering that in metals the crack growth is usually accompanied by locally plastic deformation in front of the crack tip, and the extension of a crack will always pass through the plastic zone into the elastic region along a minimum path. Therefore, the cracking direction will be decided by the minimum path between the crack tip and elastic-plastic boundary near the crack tip. On the basis of above discussion the effective stress criterion for mixed mode crack propagation is derived.