Abstract
The numerical results of stable crack growth simulation (3D FE analysis) using equivalent plastic strain showed good agreement with the experimental results irrespective of the heterogeneous specimen presented in the previous papers. From the results, it can be seen that the equivalent plastic strain is a characteristic value that is independent of the existence of strength mis-match in ductile fracture process. However, in order to obtain the equivalent plastic strain, it is needed to perform 3D FE calculation. On the other hand, the local displacement obtained from the experimental measurement is beneficial regardless of numerical simulation.
The local displacement is influenced by the measurement distance from the initial crack tip. The value of local displacement measured at the shifted location of crack tip does not change with an increase in stable crack growth. A similar relation between equivalent plastic strain and stable crack growth was also observed in the previous publication of authors. The local displacement measured at the mid-thickness is independent of the existence of strength mis-match. While, in practice, the local displacement is measured on the surface, discussion is about the effect of the strength mis-match on the ratio of local displacement at the surface to its value at the mid-thickness.
The strain estimated by the local displacement can be used as a substitute for the equivalent plastic strain. Moreover, it is expected to express the stable crack growth resistance of mis-matched joint in terms of the local displacement measured at the surface of specimen.
