A New Approach to the Calculation of Flash Temperatures in Dry, Sliding Contacts

The work done in overcoming frictional resistance between sliding surfaces is transformed into heat at the separate, very small and very highly loaded asperity contacts that make up the real area of contact. The temperatures at these initial asperity contacts (the ‘flash temperatures’) are usually much higher than the bulk temperatures and, although of very short duration, can cause potentially major local changes at the surfaces, such as softening, chemical transformations, and local melting. A new approach to calculating these flash temperatures is presented, which relies on the solution, by finite-element analysis, of the three-dimensional equation for transient heat flow in an hemispherical asperity. A Design of Experiments (DoE) exercise showed that the major influential factors on flash temperature were the thermal conductivity, the product of friction coefficient and hardness, the velocity of sliding, and the radius and degree of wear/flattening of the hemisphere. The DoE analysis also produced predictions for the flash temperature, which agreed extremely well with the FE calculations. Response surfaces of flash temperatures are presented, which facilitate the determination of flash temperatures without resorting to FE analysis.