Stress/strain behaviour at stable crack tips and effect of strength mismatch on crack growth resistance : Study on evaluation of stable crack growth resistance of mismatched welded joints (1st report)

Abstract Stable crack resistance (R) curves are frequently used to evaluate the integrity of structures containing defects in various loading regimes. The R curves are treated as being inherent characteristics of the materials themselves, though they are known to be affected in practice by a variety of factors. This paper describes an investigation of effect of strength mismatch on stable crack growth resistance. To compare the R curves of bimaterial specimens with those of homogeneous ones, compact tests were conducted. The results of the experiments were used to perform three-dimensional FEM analyses with regard to stable crack growth. In the overmatched specimens (high-strength region including a notch surrounded by a low-strength region), the dCTOD/da value is greater than that of the homogeneous specimens. In the undermatched specimens (opposite of the previous case), the dCTOD/da value is smaller than that of the homogeneous specimens. The strength mismatch affects the CTOD(J)-R curves. The equivale...