Influence of System Compliance on Contact Stresses in Fretting
01 Jan 2020-pp 489-499
TL;DR: In this paper, a two-dimensional finite element analysis has been carried out for a representative fretting test setup which consists of a flat specimen in contact with a cylindrical pad and subjected to normal load and tangential displacement.
Abstract: System compliance is one of the critical parameters which need to be accounted for precise measurement of loads and displacements from a fretting test rig, irrespective of whether it is fretting fatigue or fretting wear. The system compliance in a fretting setup consists of compliance due to driving element, driven element, and other intermediate subassemblies which are part of the load train. The issue becomes more pertinent in fretting applications which involve loads (of the order of a few Newtons) together with displacement amplitudes (of a few microns), where the stiffness of the system can affect the contact variables significantly. In general, the experimental setup is calibrated at the beginning and requisite corrections are made to account for the system rigidity, but there could be a gradual stiffness degradation over the time which could influence the accuracy of the results. In the present study, two-dimensional finite element analysis has been carried out for a representative fretting test setup which consists of a flat specimen in contact with a cylindrical pad and subjected to normal load and tangential displacement. The loading elements have been represented through the elastic springs whose stiffness can be varied in both tangential and normal direction, to understand the implications of system compliance on both normal and shear tractions. The results of the finite element model are validated with the analytical solutions proposed by Mindlin (J Appl Mech 16:259–268, 1949 [1]).
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TL;DR: In this article, the authors compared the deduced dependence of the experimental observables on the load with the experimental evidence and concluded that the most realistic model is one in which increasing the load increases both the number and size of the contact areas.
Abstract: The interpretation of certain phenomena occuring at nominally flat surfaces in stationary or sliding contact is dependent on the assumed distribution of the real area of contact between the surfaces. Since there is little direct evidence on which to base an estimate of this distribution, the approach used is to set up a simple model and compare the deduced theory (e.g., the deduced dependence of the experimental observables on the load) with the experimental evidence. The main conclusions are as follows. (a) The electrical contact resistance depends on the model used to represent the surfaces; the most realistic model is one in which increasing the load increases both the number and size of the contact areas. (b) In general, mechanical wear should also depend on the model. However, in wear experiments showing the simplest behavior, the wear rate is proportional to the load, and these results can be explained by assuming removal of lumps at contact areas formed by plastic deformation; moreover, this particular deduction is independent of the assumed model. This suggests that a basic assumption of previous theories, that increasing the load increases the number of contacts without affecting their average size, is redundant.
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31 May 1994TL;DR: In this article, it is argued that the fracture problem can be distilled into three separate parts: the contact problem itself in full or partial slip, the initiation of a crack from a surface suffering severe distress, and the propagation of a fracture under combined contact and bulk loading.
Abstract: Several aspects of the mechanics of cracks originating at sites of fretting are considered. It is argued that the problem may be distilled into three separate parts: the contact problem itself in full or partial slip, the initiation of a crack from a surface suffering severe distress, and the propagation of a crack under combined contact and bulk loading. The first of these may be solved by either a classical or numerical means, whilst the last merely requires the careful use of fracture mechanics. However, it is the second element which remains elusive to quantify, and the influence of the intrinsic length scales in the problem, including contact length, surface roughness and amplitude of relative tangential displacement on initiation conditions, is discussed and explored.
589 citations
TL;DR: In this article, a finite element-based method is presented for simulating both the fretting wear and the evolution of fretting variables with number of wear cycles in a cylinder-on-flat fretting configuration for application to aeroengine transmission components.
407 citations