Application of the local approach to fracture in the brittle-to-ductile transition region of mismatched welds

This paper predicts the cleavage resistance of steel welds in the ductile-to-brittle transition region by the Local Approach. Attention is payed to the strength mismatch effect an the ductile tearing and subsequent cleavage fracture, Welded joints of pipeline steels. X65 and X80 steels according to API 5L, are made with the same electrode under the same heat input condition. ne resultant weld metals are matched for the X80 steel welds and overmatched for the X65 steel welds in terms of the yield strength. The fracture behavior is investigated with 3-point bend specimens and tension plate specimens with a notch in the weld metal close to the fusion line. The strength mismatch and specimen geometry exert a large influence on the cleavage toughness and prior ductile tearing; CTOD toughness and crack growth resistance for the X65 tension welds increased significantly. This is due to a loss of constraint induced by the strength overmatch and tension geometry. The fracture driving force is evaluated by the Weibull stress as a function of the crack growth. The computational cell model is applied for the analysis of crack growth, where the independence of the cell parameters on the strength mismatch and crack specimen geometry is verified Using the Weibull stress fracture criterion coupled with the crack. analysis. 3-point bend toughness results can be transferred to the fracture strength evaluation of tension loaded welds with strength mismatch in the ductile-to-brittle transition region.