Ultrasonic combined enhancement on hole entrance chamfers

Crack initiation at the edges and chamfer surfaces of holes is often caused by non-uniform residual stresses and surface irregularities after machining. In order to improve the fatigue performance of the hole entrance chamfer, a novel ultrasonic impact treatment (UIT) approach and its combination with the taper surface burnishing (TSB) technique were employed. Taking 7050-T7451 aluminum alloy and the example, the effects of UIT, TSB, and combined methods on the surface morphology, roughness, residual stress, and fatigue performance of hole chamfers were evaluated. The results show that the combination of UIT and TSB processes provided the best chamfer surface integrity, leading to a significant reduction in the fatigue crack propagation rate and in turn a remarkable increase in fatigue life.