It was clarified that strength mis-match induces a significant effect on stable crack growth resistance in the previous paper. Extensive experimental and numerical works should be done for establishing a method for assessing a defect in heterogeneous material such as weld joints.
This paper describes the effects of strength mis-match and plastic restraint on equivalent plastic strain at the stable crack tip. The CTOD-R curves are experimentally obtained using homogeneous and bimaterial compact specimens produced by diffusion bonding. In the under-matched bimaterial specimens, the ratios of the width of low strength region including a notch to the thickness (H/t) are 1/4 and 1/2. The shallow (a/W=0.15) and deep (a/W=0.5) notched specimens are tested to study the effect of plastic restraint on ductile crack behavior. A 3-dimensional analysis is carried out to get the strain near the crack tip using the results of performed experiments.
The equivalent platic strain is expected to be a characteristic value independent of the existence of strength mis-match in the ductile fracture process. In the range of stress triaxiality obtained in the present works, the equivalent plastic strain does not change during the stable crack growth irrespectively of the difference in stress triaxiality. The load-load displacement curve obtained from the stable crack growth simulation using the equivalent plastic strain agrees well with the data obtained from the compact test.
