Thermal and Thermomechanical Effects in Rolling/Sliding Contacts.

The program involved analysis and experimentation relating to thermal effects in two important systems: elastohydrodynamically (EHD) lubricated bearings or gears, and high-current-density electrical brushes. A thermodynamic heat balance has been applied to an EHD contact utilizing experimental values for surface pressure and temperature distributions. The results showed that the magnitude of compressive and shear heating in the lubricant were higher than that due to convection to the fluid. Experimental measurements of axial film thickness profiles for rolling/sliding disks were made using an X-ray shadow technique. The objective was to determine if the profile under load will vary due to nonuniform heating and thermal expansion at the disk contact leading to scuffing failure. No significant changes in profile were measured, but a limited range of experimental conditions were studied. A high-current-density electrical slip ring apparatus was constructed and used to study the effect of material properties on the contact between the stationary brush and the copper slip ring. The results showed that above a particular threshold speed, the brushes exhibited a sparking phenomenon which consisted of periodic motion of a cluster of small sparks at the brush/slip ring interface.