Tribological and dynamic behaviors of high-speed train braking systems on long steep slopes

Rapid expansion of global rail transit requires higher operating speeds for high-speed trains, posing considerable challenges to the safety and reliability of braking systems, particularly under demanding conditions such as long, continuous, steep slopes. In such scenarios, stable speed regulation requires prolonged mechanical friction braking to complement electrical braking. This extended braking action causes a rapid temperature increase at the brake disc/pad interface, and this temperature often reaches extreme levels. Such thermal stress leads to significant degradation in braking performance and reduced reliability of brake components, with a greater risk of brake failure. Despite the critical nature of these issues, research on the tribological behavior and dynamic responses of braking systems under prolonged slope conditions remains insufficient.

This review synthesizes experimental studies and numerical simulations to elucidate the mechanisms underlying braking system performance degradation on long steep slopes. Experimental research reveals wear patterns and damage behaviors of friction pairs during prolonged braking, highlighting the roles of heat accumulation and friction reduction at the brake disc/pad interface. Fully coupled thermal-mechanical-wear finite element models have been employed to explore the interrelated effects of temperature, stress, and wear throughout the braking process. Lumped parameter models offer a detailed characterization of contact behaviors in friction pairs and their impact on dynamic system responses, incorporating principles from fractal theory and Hertz contact theory to develop mathematical models for contact stiffness and damping. Additionally, two-degree-of-freedom models have been utilized to analyze braking system stability under realistic operational conditions. Furthermore, dynamic models incorporating wheel/rail adhesion have been developed to examine the coupled torsional interactions between the brake disc/pad subsystem and the wheel/rail subsystem, as well as the impacts of the interactions on system vibration behavior. These models also assess the influence of diverse service conditions, brake disc/pad friction properties, and wheel/rail adhesion characteristics on system stability and vibration dynamics, thereby revealing the interaction mechanisms among various components of the braking system.

Future research should account for complex environmental factors encountered at high altitudes and on steep slopes and elucidate the mechanisms of braking degradation under multi-factor coupling. Particular attention should be given to the effects of low temperatures, snow, and low pressure on the performance of friction pairs. Moreover, the integration of intelligent monitoring and predictive technologies will be crucial for developing efficient real-time monitoring systems capable of dynamically assessing braking performance and identifying potential failure risks at an early stage. These advancements will enhance the safe operation of trains under challenging conditions and provide a robust theoretical and technical foundation for improving the braking performance and safety of high-speed trains while contributing to the sustainable growth of the rail industry.