New post-yield fracture toughness parameters for engineering materials

Micromechanics approach is employed to investigate the constraint effect on postyield fracture toughness. Relationships between the conventional post-yield fracture toughness values, J_ICand δ_Cand crack tip constraint characterized by the crack tip stress triaxiality are derived on the basis of an improved micromechanics criterion for ductile fracture. Then, new crack tip parameters J_mcand δ_mc(and associated new criteria for ductile fracture) are proposed, in which the effects of crack tip deformation and constraint are taken into account. Experiments show that both Jmc and 6mc are material constant independent of stress state or specimen geometry. They can serve as new post-yield fracture toughness parameters to differentiate the fracture toughness of engineering materials, which provide new approaches for fracture assessments of engineering structures.