Normal stiffness and damping at lightly loaded rough planar contacts

Two features of contact between rough surfaces are localized interactions between asperities and the presence of air in the gap. This gives rise to a contact compliance, a static and local property and, when contacts vibrate, mechanical damping due to squeeze films of air. We examine the stiffness characteristics of clean surfaces in primarily elastic contact and both new worn surfaces in elasto-plastic contact. The squeeze-film damping can be related to the average gap between the surfaces. Experimental results are compared with analytical models. Qualitative and quantitative insight into both the stiffness and the gap can be obtained from the Greenwood-Williamson (1996) [1] paper that we are honoring at this symposium.