Effects of laser peening treatment on high cycle fatigue strength and fatigue crack behaviors under axial loading of aluminum alloy

The axial fatigue tests with stress rations of -1.0 and 0.1 were conducted in order to investigate the effects of the laser peening (LP) treatment on the fatigue strength and the fatigue crack behaviors in the rolled aluminum alloy A7050 for aircraft structures. The LP treatment was effective for fatigue strength improvement in the fatigue lives before 2-3 × 10 6cycles, but the treatment reduced the strength after the cycles at the both stress ratio conditions. Fatigue cracks initiated at the surface on the higher stress amplitude levels, but the cracks initiated in the internal positions on the lower stress levels. From the observation results of fatigue crack behaviors, it was clear that the LP treatment could control the crack initiation and the propagation behaviors. The fatigue strength behaviors by the LP treatment were evaluated by the stress intensity factor range including the residual stress induced by the LP treatment. © 2010 The Society of Materials Science, Japan.