As two bodies come into contact, attractive forces occur wherever a gap exists between the two surfaces. The forces are significant at distances of atomic order but become negligible at much larger separations. Their effect is insignificant in most situations for which engineers wish to understand the state of the contact since the adhesive forces are usually much smaller than the net load applied and/or surface roughness results in non-contacting areas being far enough apart that the attractive force is negligible. There are, however, certain cases in which adhesion forces do contribute to the contact mechanics and must be accounted for in any valid analysis. Materials with low elastic modulus, such as rubber, may deform sufficiently around surface asperities such that the surface separation is small and adhesion is apparent.
A model for arbitrary geometry (with surface roughness) that includes adhesive forces is reported here. It is based upon the multi-level method of contact analysis developed by Venner and Lubrecht . Adhesion has been implemented using the Lennard-Jones potential as applied to two parallel surfaces, adding the requirement of specific negative pressures for the separated surface nodes . The model is then compared to theoretical and numerical analysis of smooth spherical contacts and to rough contacts of different scales and material properties.