Rail vehicles are developed towards high speed and high axle load, requiring robust mechanical brake systems for running safety. One of the most important mechanical brake systems is the disc brake, which transforms the kinetic energy of rail vehicles into thermal energy. A high brake disc temperature reduces the coefficient of friction between the brake disc and the brake pad, and causes large thermal stress which induces thermal cracks on the brake disc. To avoid these negative impacts, it is necessary to have a good understanding of how friction heat is generated and dissipated. Simulating the brake disc temperature is an effective method to study these issues. To calculate the temperature of the brake disc, there are several methods to input the heat flux. The most common one is to directly input calculated heat flux which is based on the law of conservation of energy, while other methods are based on calculation of friction heat between the brake disc and pad. The main difference between these methods is how the heat flux is calculated and distributed in the contact interface. Until now, the influence of these different methods on the calculated temperature of the brake disc is not well addressed and needs further investigation. This work studies the influence of different types of heat flux calculation on the average and maximum temperatures of brake discs. The research method used in this work is thermomechanical coupling simulation. The brake disc temperature is calculated according to the following three methods: the first is without both thermal expansion and wear on the brake pad and brake disc, which is the most common method; the second is with thermal expansion but without wear on the brake pad and disc; the last is with both thermal expansion and wear on the brake pad and disc. The calculated temperatures in these three methods are checked against experimental results. The results show that when the brake pad and disc's thermal expansion is considered, the contact area decreases and thus, the maximum temperature increases, e.g., hot spots or hot bands appear on the brake discs. In contrast, with wear considered, the contact area increases, and the maximum temperature is thus reduced. For the average temperature of the brake disc, the three methods give very similar results, but regarding the maximum temperature of the brake disc, the three methods result in big differences in the preliminary simulation results. We are in the process of implementing more realistic material properties to get more realistic simulation results. This study shows that when analysing thermal cracking and hot spots on the brake disc, the heat calculation method should consider both thermal expansion and wear of the brake pad and disc to achieve an as accurate solution as possible.

Mr. Yanjun Zhang, PhD Student, KTH Royal institute of technology; Dr. Zhendong Liu, Researcher, KTH Royal institute of technology; Prof. Dr. Sebastian Stichel, Professor, KTH Royal institute of technology; Prof. Junying Yang, Associate Professor, Dalian Jiaotong University; Prof. Fei Gao, Professor, Dalian Jiaotong University