Abstract
Finite element computation had been undertaken to evaluate the J-integral of bi-material interfacial crack of three points bending specimens (TPB) loaded normally. The numerical results indicated that the path-independence of total J-integral and the expression of J = J_I + J_<II> are still valid even the interface is involved, whereas J_<II> and J_I respectively increased and decreased as the crack tip is approached. The fracture toughness for crack growth along the interface can be characterized by J-integral, which could be obtained directly from TPB testing because the J values from the path integrals are agreed well with those from the P 〜 δ curves described in ASTM E813-87. The mechanical property mismatch causes an opposite kind of deformation (sharpening-blunting) at the two sides of the crack tip and a high stress triaxiality on the softer metal side even for the symmetrical loading. That is, a crack may grow along the interface or deviate into the softer metal, but never turn into the harder one. A new parameter is proposed to represent the mixed ratio of loading mode, which is sensitive only to the mismatch in mechanical properties but not to the loading level and the distance from the crack tip.
