Abstract
The axial fatigue tests with constant load and 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 2〜3×10^6 cycles, 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. Next, the axial fatigue tests with repeated two-step loading and stress rations of -1.0 were conducted in order to investigate the effects of the LP treatment on the fatigue strength and the fatigue crack behaviors. In the case of LP treated materials, it is found that the high stress has effect on the fatigue life but the low stress has little effect on the fatigue life.
