An insight of the structure of stress fields for stationary crack in strength mismatch weld under plane strain mode-I loading – Part II: Compact tension and middle tension specimens

•A stationary crack lying at the centre of a weld in commonly used fracture specimens was analysed.•Global plastic fields were proposed for C(T) and M(T) specimens under plane-strain condition.•Plastic fields of a C(T) specimen having a weld centre crack are similar to that of a SE(PB) specimen.•Effect of weld strength mismatch on the limit load as well as on the crack-tip constraint was studied.•In comparison to slip line field analysis, the modified upper bound theorem is simple and more general.

In-service inspections of many nuclear power plants have revealed that cracks are most likely to occur in a weld or in the regions near the weld. In part-I, the problem of a stationary crack lying at the centre of a weld in a pure bending specimen SE(PB) was analysed. The detailed structure of the global plastic fields for a deep crack, under fully plastic condition, was presented. Aspects related to the state of stress at the base-weld interface were discussed. To enhance our understanding of the weld strength mismatch effects, other commonly used fracture specimens, that is, compact tension C(T) and middle tension M(T) specimens having a weld centre crack were analysed in the present investigation. The influence of weld mismatch on the structure of global stress fields (leading to plastic yielding of the ligament) as well as on the crack tip constraint was studied. It is demonstrated that, when a crack is postulated at the centre of a weld, a family of stress fields proposed in part-I for a SE(PB) specimen is applicable to a C(T) specimen also. The studies performed in this article, along with part-I, have established that in comparison to slip line field analysis, the modified upper bound theorem is simple and more general. It is applicable to macroscopically homogeneous materials and can also account for weld mismatch effects.