COMPARISON OF THERMOELECTRIC MEASUREMENTS WITH MODELS OF SLIDING ASPERITY CONTACT FLASH TEMPERATURES

摘要

The temperature of sliding components is of essential importance for understanding friction, wear, and generation of chemical reaction films that may form in oil-lubricated systems. In boundary regime sliding, most of the load is carried by the surface asperities in which (real area of contact) « (apparent area of contact) which produces large asperity or "flash" heating. At asperities, heat can be either deformational or frictional. The temperature of microscopic asperities in area of sliding is difficult to measure because it is brief, localized, and inaccessible. The flash heating may affect the substrate microstructure, enhance surface reaction rates, produce thermomechanical wear, or promote EP additive activation. The heating can occur in the following regimes. 1) Bulk heating of the entire system. Bulk heating is easy to calculate and can be determined from heat flow calculations assuming frictional heating is dissipated into the counterfaces with partition factor a. 2) Band heating in which the nominal Hertzian contact area exhibits predictable pulsed heating/cooling cycles. Band or spot heating over a defined contact area has been analyzed by many workers and is summarized well by Kennedy. In band heating, the heat density and pulsed temperature rise is a strong function of Hertzian contact size, sliding speed, and coefficient of friction. 3) "Flash" temperature heating of individual random asperities due to asperity interactions only. The treatment of asperity interactions is more difficult but is addressed by Archard . In flash heating, the temperature pulses may be strongly affected by sliding speed, and less affected by Hertzian contact size because it is only the asperities themselves that are rubbing/shearing against each other and experiencing transitory (us) flash heating. Fig. 1. is a depiction of the three regimes.