Two-Parameter Fracture Mechanics Theory and Applications

A family of self-similar fields provides the two parameters required to characterize the full range of high- and low-triaxiality crack tip states. The two parameters, J and Q, have distinct roles J sets the size scale of the process zone over which large stresses and strains develop, while Q scales the near-tip stress distribution relative to a high triaxiality reference stress state. An immediate consequence of the theory is this it is the toughness values over a range of crack tip constraint that fully characterize the materials fracture resistance. It is shown that Q provides a common scale for interpreting cleavage fracture and ductile tearing data thus allowing both failure modes to be incorporated in a single toughness locus. The evolution of Q, as plasticity progresses from small scale yielding to fully yielded conditions, has been quantified for several crack geometries and for a wide range of material strain hardening properties. An indicator of the robustness of the J-Q fields is introduced Q as a field parameter and as a pointwise measure of stress level is discussed....Constraint, Stress triaxiality, Elastic-plastic fracture, Fracture toughness, Crack initiation, Cleavage, Ductile testing J- integral and finite element method.