Characterizations of material constraint effect for creep crack in center weldment under biaxial loading

Material mismatch effect on the cracking behavior is an important topic for those welding structures. Characterization of the material constraint effect based on rigorously asymptotic solution is studied in this paper. Based on decomposition of the second order term, the constraint effect characterization parameter is decomposed as material constraint parameter and geometry constraint parameter. In general, the total constraint level for crack tip under undermatch condition is higher than overmatch condition. The specimen with positive biaxiality could lead to a higher constraint level compared with that of negative biaxiality. Geometry constraint effect and material constraint effect could not be separated independently from rigorously asymptotic solution for those cases with positive biaxiality. For a crack tip field under non-positive biaxiality, the material constraint effect can be characterized independently although it is approximate. For these conditions, the proposed material constraint effect and geometry constraint effected characterized are approximately independent on material mismatch factor, crack depth ratio and stress biaxiality. An empirical formula has been presented to characterize the geometry constraint effect and material constraint effect for the crack tip in the weldment under biaxial loading, which has been verified with fine accuracy.