A critical assessment of elasto-plastic fracture mechanics

The authors presents a critical review of the methods most commonly used to evaluate elasto-plastic fracture toughness, namely the J integral, equivalent energy and crack opening displacement. Their theoretical justification as crack-tip field parameters and fracture criteria is discussed, together with their equivalence and relationship with the linear elastic fracture toughness, Ksub(IC). Methods of experimental determination and application to structural performance have also been assessed. It is concluded that the concept of a single-valued fracture criterion for ductile fracture that is both a material characteristic and geometry-independent has yet to be validated. Theoretical justification for the proposed relationships with Ksub(IC) is restricted to conditions of small-scale yielding and their use under conditions of more extensive plasticity prior to fracture is based on limited experimental data. The present lack of standard test procedures and the occurrence of stable crack growth on limited experimental data. The present lack of standard test procedures and the occcurence of stable crack growth produces uncertainties in using the criteria to assess structural performance. Existing methods based on crack initiation can be very conservative as ultimate failure criteria whilst the inclusion of stable crack growth is presently not adequately quantified. (Auth.)