Experimental Verification of Thermoelastic Instabilities in Sliding Contact

Abstract

In the design of sliding seals, uniform loading is often assumed in order to calculate leakage, pressure, and surface temperature. Previous theoretical and experimental evidence has shown that for some material properties and operating conditions, nonuniform contact between the sliding surfaces can result. This nonuniform contact is exhibited as a concentrated region of higher pressure and temperature which moves under the influence of thermal expansion and wear. This paper describes the results of experiments which have been performed to verify the existence of the concentrated loading in a seal configuration. Nonuniform surface contact can be caused by a thermoelastic phenomenon which is a balance between the thermal expansion of the sliding materials and the wear resulting from their interaction. If the effects of thermal expansion are greater than the wear, the load will concentrate to a small region of the nominal contact area. The occurrence of this unstable operation can be written in terms of the critical sliding speed necessary to produce it. Sliding experiments were performed using several different material combinations and the critical speeds were measured. The results of the experiments have been compared with the small perturbation stability analysis published previously. Although the magnitude of the critical speed could not be accurately calculated using the analysis, the results indicated that the relative performance of different material combinations could be predicted.