An improved mathematical elastic-plastic model for the contact of rough surfaces that is based on an accurate finite element solution of a deformable single asperity and a rigid flat surface is developed to provide dimensionless expressions for the contact area and contact load. This model differs from the existing models, in that it accounts for the level of interference beyond expected failure. The finite element solution is used to define the limits at which failure occurs. A fictitious ultimate-stress asperity is introduced to facilitate the derivation of the contact model. This model considers a realistic picture of elastic- plastic deformation where elastic, plastic and failure behaviors can occur simultaneously for an asperity. Subsequent comparison of the results for estimating contact area and load using the present model and the earlier methods shows identical results for pure elastic contacts with plasticity index values at about 0.5 but substantial difference for the net elastic-plastic contacts having plasticity index values above 0.8. When plasticity index reaches 6 and beyond, the three models predict similar total contact area and load values and that the contact is purely plastic.
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