Braking Process in Automobiles: Investigation of the Thermoelastic Instability Phenomenon

During the braking action, the kinetic energy produced at the wheel is transformed into heat energy, which doesn’t dissipate fast enough into the air stream from the brake to the brake disk; as a result, the thermal conductivity plays a critical role in handling such heat generated. Thermal judder, which is a result of non-uniform contact cycles between the pad and the disk brake rotor, which is primarily an effect of the localized Thermo-Elastic Instabilities (TEI) at the disk brake rotor surface. Localized TEI act at the friction ring surface generating intermittent hot bands around the rubbing path which may in turn leads to the development of so-called hot spots. In this chapter a case study regarding a transient analysis of the thermoelastic contact problem for disk brakes with frictional heat generation, performed using the finite element analysis (FEA) method is described in details. The computational results are presented for the distribution of the temperature on the friction surface between the contacting bodies (the disk and the pad). Also, the influence of the material properties on the thermoelastic behavior, represented by the maximum temperature on the contact surface is compared among different types of brake disk materials found in the literature, such as grey cast iron (grey iron grade 250, high-carbon grade iron, titanium alloyed grey iron, and compact graphite iron (CGI)), Aluminum metal matrix composites (Al-MMC’s), namely Al2O3 Al-MMC and SiC Al-MMC (Ceramic brakes). This comparison was performed in order to improve the conceptual design of the disk brakes. The results obtained from the suggested model are compared with actual measurements obtained from experiments performed by Cueva et al.(2003). The FEA results were in excellent agreement with the actual measurements reported by Cueva et al. for all of the suggested brake disk materials. A comparison between two different brake disk rotor designs was performed as well in order to study the effect of the perforated brake disks on the maximum temperature, the temperature distribution, and the heat flux produced under the same braking conditions.