Effect of quality control parameter variations on the fatigue performance of ultrasonic impact treated welds

Fatigue tests were conducted of steel non-load carrying filet welded attachments subjected to ultrasonic impact treatment (UIT) at various levels simulating proper, under-, and over-treatment. Two loading histories were investigated: one constant amplitude and one with high compressive under-load cycles. Local properties were measured, finite element (FE) analyses were performed to obtain stress concentration factor (SCF) distributions for the measured weld toe geometries, and a fracture mechanics model was validated and used to investigate the effects of the local property variations on the fatigue life. UIT significantly improved the fatigue lives of the welded specimens in all cases. A strong correlation was seen between the measured indent depth and the local residual stresses and microhardness. The fracture mechanics analysis predicts the fatigue performance of the specimens and finds it to be most sensitive to variations in the residual stresses and initial defect depth.