DEFORMATION RELIEF AND DESTRUCTION OF SURFACE AS AN ALUMINUM ALLOY CLAD LAYER FATIGUE DAMAGE INDICATOR

Abstract

The article presents the results of the study of changes in the state of the structural alloy D16AT surface with the operating time at various stress levels. The state of the surface of the material was monitored by an interference nanoprofiler. The main feature of the D16AT alloy is that to protect against corrosion, the material is coated on both sides with a thin layer of clad, the thickness of which is about 5 % of the sheet total thickness. During loading, the deformation of the cladding layer and the base material due to the existing difference in the yield strength values differs significantly. Such a composition of inextricably bound materials will contribute to the intensification of plastic deformation of the surface layer. During cyclic loading, areas of plastically deformed material are formed and developed on the surface of a clad aluminum alloy with a special representation of the surface relief caused by dislocation mechanisms (steps and slip bands, extrusion, intrusion etc.). Quantitative indicators of deformation relief (DR) are the area and perimeter of plastic-deformed areas, their fractal characteristics and plastic deformation of the surface. These parameters can act as indicators of the alloy fatigue damage, but it is hard to identify the boundary state that is the fatigue crack initiation. Such a diagnostic parameter is the destruction of the clad layer to determine in order are used basic indicators of DR. Destruction (increase in the volume of the clad layer) is physically objective that is associated with an increase in surface area during the formation and extended of DR. Destruction can be considered as the main factor in the fatal destruction of clad aluminum alloys. It is shown that when saturated with a deformation relief, approximately 25 ... 30 % of the total surface area of the destruction of the clad layer increases abruptly due to the change in the nature of the plastic deformation of the surface that is an increase in the growth of its plane at high saturation values. This saturation value can be used as a diagnostic indicator of the initial fatigue cracks initiation.

Keywords

• деструкция
• плакирующий слой
• деформационный рельеф
• фрактальная размерность