A general equation for fitting contact area and friction vs load measurements

The variation of contact area with load between adhesive elastic spheres de pends upon the effective range of attractive surface forces. Relatively sim ple forms to describe limiting cases exist, but the general intermediate ca se requires a more complex analysis. Maugis, using a Dugdale model [D. Maug is, J. Colloid Interf. Sci 150, 243 (1992)], provides an analytic solution, but the resulting equations are cumbersome if one wishes to compare with e xperimental data such as atomic force microscope measurements. In this pape r we present a simpler general equation that approximates Maugis' solution extremely closely. The general equation is amenable to conventional curve f itting software routines and provides a rapid method of determining the val ue of the "transition parameter" which describes the range of surface force s. (C) 1999 Academic Press.