Experiments and analysis of the thermoelastic behavior of a brush on a slipring

Experimental data are analyzed for carbon block sliding on the surface of a metal disk. Conduction measurements suggest that the constriction resistance is much lower than expected for a contact area that is controlled by the hardness of the carbon. Analysis of heat transfer over a range of sliding speeds supports the idea of a thermoelastic phenomenon which leads to concentration of load on the peak of a single thermal asperity. The contact area predicted by this analysis is considerably larger than that predicted by plastic yielding of the asperities in accord with classical contact theory. The single-asperity model leads to an upper bound of predicted temperature, and this is found to be moderate over a large range of sliding speeds at loads comparable to those used on brushes