Variation Of Real Contact Area Between Surfaces With Contact Pressure And Material Hardness

The real area of contact between solids under high contact pressure is examined, and values obtained experimentally are compared with theoretical predictions. The theory considers the compression of an array of uniform prismatic wedges, and predicts a rise in the strength of the asperities when adjacent plastic deformation fields interact. It is assumed that the material on which the wedge-shaped asperities are supported is in a state of hydrostatic stress; this is replicated in the experiment by constraining the bulk material of the specimens. One specimen was single point machined to produce a uniform array of wedges and the other specimen abraded to produce a more random surface texture. Good agreement was found between the compression of the machined surface and the theory. The behaviour of the abraded surface was found to be in good agreement with predictions based on an equivalent uniform array; however, the rigorous theory gave too much strength to the smaller asperities, as their substrate material was found to deform both elastically and plastically. It is demonstrated that material hardness is an important variable; knowledge of initial hardness is not adequate since final contact area depends on final hardness.