Impact of initial braking temperature on thermal-induced brake fade during long-downhill operations

Abstract

The advancement of high-speed railways and the widespread application of complex terrains have highlighted the issue of performance degradation in braking friction pairs during long-downhill braking, especially under high-temperature conditions. This study addressed this problem using a self-developed high-speed train braking simulation test rig to investigate the effects of varying initial braking temperatures (IBTs) on the performance degradation of braking friction pairs. A combination of thermal imaging, energy dispersive spectroscopy (EDS), high-temperature hardness testing, and X-ray diffraction (XRD) was employed to assess performance changes under different temperature conditions. By controlling the IBT of the brake disc, a detailed analysis of the coefficient of friction (COF), frictional heat distribution, wear morphology, hardness variation, and residual stress were conducted to uncover the brake fade mechanisms. The findings reveal that as IBT increases, COF decreases with greater fluctuations, resulting in significantly extended braking times and distances. At elevated IBTs, the brake disc and friction block materials experience reduced hardness, increased tangential residual stress, decreased radial residual stress, and accelerated wear, leading to unstable COFs and extended braking distances. This work provides valuable insights into the mechanisms of thermal-induced brake fade during long-downhill braking, offering crucial technical guidance for enhancing the safety and reliability of high-speed train braking systems under extreme conditions.