Abstract
Fatigue crack propagation (FCP) has been studied using CT specimens cut from laser welded butt joints of the coupling of two different steels, cold rolled low carbon steel (SP) and high tensile strength steel (HT). When the FCP direction was parallel to the weld, the FCP rates of the welded specimens characterized in terms of the effective stress intensity factor range were nearly the same as that of the base steel (SP) and thus the weld bead had the same intrinsic FCP resistance as the base steel. When the FCP direction was normal to the weld, FCP rates decreased temporarily within the weld zone. This decrease of FCP rate still existed after allowing for crack closure and was also seen in FCP behaviour of the specimens subjected to stress-relief annealing and in crack closure-free FCP behaviour at a high stress ratio. Fractographic examination revealed that typical fracture mechanism was the mixed mode of intergranular and transgranular fracture in SP plate, while transgranular fracture mode in the weld zone and HT plate.
