Stress/Strain Behavior at Stable Crack Tip and Effect of Strength Mis-Match on Crack Growth Resistance. Study on Evaluation of Stable Crack Growth Resistance of Mis-matched Weld Joints (Report 1).

Stable crack resistance (R) curves were frequently used for assessing the integrity of structures containing defects in loading regimes. In that case, R curves are treated as characteristics of materials, but it is known that R curves are actually affected by various factors.The effect of strength mis-match on stable crack growth resistance is discussed in this paper. In order to compare the R curve of bimaterial materials with that of homogeneous ones, compact type tests are carried out. 3-dimensional FEM analyses taking into account the stable crack growth are also executed using the result of performed experiments. In the case of over-matched specimens (high strength region including a notch are surrounded with low strength region), dCTOD/da apparently increases comparing with homogeneity. In the case of under-matched specimens (opposite of the previous case), dCTOD/da apparently decreases comparing with homogeneity. Strength mis-match affects on CTOD(J)-R curves. On the other hand, the equivalent plastic strain at stable crack tip obtained from 3D analyses may be generally independent of the strength mis-match during ductile fracture process.