The Effect of Ultrasonic Impact Treatment on the Fatigue Resistance of Friction Stir Welded Panels

In this work, the results of an experimental study for assessing the effects of Ultrasonic Impact Treatment on the fatigue resistance of Friction Stir Welded aluminum alloy panels are presented. Although the significant compressive residual stress introduced on the material by ultrasonic impact treatment (UIT) was expected to cause retardation in the crack growth rate, this was only noted at low initial ΔΚ values. At high ΔΚ values, the effect of UIT practically diminishes. The phenomenon was attributed to the relaxation/redistribution of the residual stresses with fatigue damage. This provides an alarming situation where damage tolerance design relies on models where only the initial residual stress profile is taken into account without knowledge of the potential re-distribution of the residual stresses caused by the fatigue damage accumulation. The findings of this work also indicate that any FCG tests performed can only be considered as case-specific and conclusions can only be drawn for the case studied.