Abstract: The influences of stress concentration, grain refinement and residual stress on the high cycle fatigue of SMA490BW steel butt joints were systematically analyzed by the comparative fatigue test, and the dominant factor was obtained. The fatigue fracture morphology observation was conducted through a scanning electron microscope to determine failure modes of the welded joints with and without ultrasonic impact treatment (UIT). The results showed that both UIT and mechanical polishing treatment could improve the specimen’s fatigue life to certain extents. And eliminating the weld reinforcement will lead to a remarkable promotion of welded joint’s fatigue life (nearly 100 times larger) compared with the original welded joints. It can be concluded that the contribution ratios of stress concentration, grain refinement and residual compressive stress on the life extension of the welded joint are about 58%,29% and 13%, respectively. The fatigue failure of welded joints mostly comes from the surface of weld toe, and the fatigue crack initiation position shift to the internal defect after UIT.
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2018, Vol. 32 
