Real Area of Contact between a Rough Surface and a Softer Optically Flat Surface

The mean number of contact spots per unit area and their mean radius were measured and hence the real area of contact deduced for a rough-to-flat interface under normal loading. The contact pressure was varied from zero to half the micro-hardness of the softer material. The resulting experimental evidence did not endorse the predictions from the recent theory of Tzukizoe and Hisakado, which incorrectly assumes that the real contact area is given by the applied pressure P divided by the micro-hardness M of the softer material. It was found that this area equalled K(P/M) ⁿ , where the coefficient K and index n depend upon the applied pressure range. A maximum number of contact points was encountered at a dimensionless loading (P/M) approximately equal to 7·5 × 10^-3.