Deformation Relief of the Surface as a Characteristic of Fatigue Damage of Clad Aluminum Alloys. Part 1. Deformation Relief Evolution Under Cyclic Loading

The formation and evolution of a deformation relief on the surface of a clad aluminum alloy are examined under cyclic loading. The deformation relief originates on the surface of a clad layer in the form of local plastic strain regions with higher roughness, which characterizes the fatigue damage of the material. Saturation (relative surface area covered with the deformation relief) is a two-dimensional property of the deformation relief, while plastic surface strain is its threedimensional characteristic. The deformation relief can be registered with a contactless interference profilometer. Deformation relief saturation vs number of load cycles relations were plotted. Those relations are established to be similar above a certain level of maximum cycle stresses.The plastic surface strain grows linearly with saturation; the relation possesses two linear sections irrespective of active cycle stresses. The deformation relief examination as an aggregate of fractal clusters demonstrated that the power relation between the total perimeter and area of those clusters was revealed. The two sections of that relation were chosen, and with a certain area of clusters, the exponent is shown to drop from 1.53 to 1.00. Its decrease is indicative of the fractality loss by the deformation relief clusters. The change in the clad layer damage mechanism is established to occur at the deformation relief saturation within 0.22–0.25. At such a saturation level, initial fatigue cracks originate, while fractal relief evolution and plastic surface strain behavior of a clad layer are changed.