Abstract
An experimental confirmation of the relaxation behaviour of welding residual stresses under fatigue loading was made using more than 30 plate specimens. Type 316 stainless steel plates in 4mm thickness (0.2% proof stress=255MPa, UTS=568MPa) were butt welded by electron beam welding. The longitudinal welded joint specimens were machined out, and a center hole of 8mm diameter was drilled at the center of the specimen in order to localize the fatigue crack initiation point. The specimen was subjected to one cycle static loading or to fatigue cycling with reversed axial loading in the crack initiation life range between 104 and 107 cycles. A specimen was removed from the testing machine after the repetition of load cycling of a given number in order to measure the change of residual stress distribution. In addition comparative fatigue tests of both base plates specimens and longitudinal butt welded joint specimens were conducted using specimens with a center hole.
The peak value of longitudinal welding residual stress decreases remarkably by the first cycle of fatigue loading, showing 48% reduction by 200MPa maximum load and 23% reduction by 130MPa loading. The welding residual stress then decreases gradually with the followed repetition of fatigue loading. The fatigue strength of longitudinal welded joint specimen is considerably lower than that of base plate specimen especially in higher cycle regime.
