Thermal Effects and Pressure Distributions in Brakes

Abstract

Heat generated at the sliding interface between the friction material and the mating surface of a friction brake is not uniformly distributed over the sliding surfaces but depends upon the local interface pressure. Many thermal problems associated with brake friction pairs, including performance variation (fade, speed sensitivity) and rotor damage (heat spotting and thermal cracking) can be analysed in terms of localized frictional heat generation as discussed here. This paper describes how the thermal effects of interface pressure distribution may be divided into bulk temperature effects, such as brake drum expansion and brake disc coning, and its macroscopic thermal effects, such as heat spotting, and suggests how the two are related through the process of thermoelastic instability. The results of analyses, using finite element methods, indicate that uniform friction interface pressure is very important in minimizing brake thermal problems. However, more basic research in the area of interface contact and pressure distribution, and frictional heat generation and dissipation, still remains to be done in order to understand fully the role played by each part of the friction pair in thermally related braking problems.