Crack growth initiation in elastic-plastic materials

The problem of initiation of crack growth in an elastic-plastic material under idealized conditions of plane stress or plane strain was studied. The stress analysis of the cracked plate was performed by using an elastic-plastic finite element computer program based on the J sub(2) flow theory of plasticity and a singular crack tip element. A method for determining the critical quantities at the moment of crack growth was presented. The strain energy density failure criterion was used according to which the crack starts to grow when material elements ahead of the crack absorb a critical amount of stored strain energy density which remains after subtracting the amount of irreversible energy dissipated by permanent deformation. The critical stress and the plastic zone at crack initiation were determined.