ABSTRACT
Some particularly interesting work has been performed in applying contact mechanics to the surface forces apparatus (SFA), which can be viewed as a single asperity contact of larger scale than the AFM, and with important capabilities including the direct measurement of the contact area [34, 35]. The SFA typically consists of thin mica layers on a compliant (glue) backing. The consequences of this geometry have been studied by Johnson and Sridhar [36]. They find that the JKR model works well for a sufficiently thick layer, as well as for a sufficiently thin layer, but layers of an intermediate thickness violate the conditions of the JKR theory. In between these limits the contact behavior is modeled by the numerical results. Violations of the JKR model were found to be due to the small size of the contact radius compared to the layer thickness.
