The contact behaviour of surfaces of small nominal area

In treating the problem of surface contact it is usually assumed that the asperity radius remains constant during the deformation process. Such an assumption may be valid for the contact of surfaces of large nominal area subjected to moderate normal loads; however, with surfaces of small area where the population of asperities is small the amount of asperity deformation is expected to be relatively large and the displaced material may play an effective role in determining the contact behaviour. In this paper the asperity radius is assumed to increase with deformation and analyses are presented for determining the variation of normal approach with load for rough flat surfaces. The results of such analyses suggest that the deformation process produces increasingly suffer surfaces and are shown to have better agreement with experiment than those results obtained from analyses based on a constant asperity radius.