Research and /or Engineering Questions/Objective: Brake system is one of the key sub-systems of a high-speed train. It is crucial to the safe operation, steady deceleration and precise parking of trains. The train braking is achieved via the friction between the brake disc and the friction block to consume the kinetic energy of the train. However, the disc–block friction also causes some disturbing problems. For example, stick–slip vibration and large-scale material spalling phenomenon of the train friction block become extremely prominent when braking at relatively low velocities. Stick–slip has strong nonlinearity and it is simultaneously influenced by several factors which share complicated coupling relationship. Therefore, it is urgent to investigate the effect and mechanism of key factors on stick–slip oscillation of the brake system and seek effective methods to improve the braking performance. Methodology: The coefficient of friction is the key factor that reflects the interface friction characteristics and influences the system dynamic response. In this work, the tribological experiments were first conducted to identify the Stribeck model parameters of the disc–block friction interface with different friction block shapes (Pentagon and hexagon). Then, a train brake system dynamics model comprehensively considering the connecting structures of the essential brake units, disc–block nonlinear friction, and wheel–disc relative torsion was established. Further, the identified Stribeck parameters by experiments were integrated into the proposed brake system dynamics model and the corresponding numerical simulation was performed to realize the dynamic response analysis of the braking system considering the friction block shape. Results: The experimental results show that the shape of the friction block has a significantly influence on the friction characteristics within the disc–block interface. The decay factor, static and kinetic coefficients of friction of the Stribeck model parameters for the hexagonal block are different from that of the pentagonal block. The numerical simulation results depict that the brake system adopting the pentagonal friction block undergoes more violent stick–slip oscillation than that using the hexagonal friction block. Moreover, its torsional vibration and wheel–disc interactions are more complex. These results indicate the hexagonal friction block can effectively regulate the friction characteristics of the disc–block interface, then reducing the stick–slip vibration of the block. Limitations of this study: The parameters of friction model are obtained by rig test adopting a scaled friction block and disc. There are many friction blocks of the brake pad with different friction radius. It is better to further identify the parameters of Stribeck model using a full-size brake system, which could help the results more accurate. What does the paper offer that is new in the field in comparison to other works of the author? The dynamic relationship between the friction characteristics of the disc–block interface and the dynamic response of the brake system is established, and the cross-sale analysis from the interface tribological behaviors to the system dynamic behaviors was realized in combination with the tribological experiments and numerical simulation. Conclusion: The identification of the Stribeck model parameters, the establishment of the train brake system dynamics model, and the proposed cross-scale analysis method from the interface tribology to the system dynamics can provide references for the evaluation of the brake system dynamic performance and the suppression methods of the unstable vibration.
Dr. Zhiwei Wang, Assistant Professor, Southwest Jiaotong University; Mr. Quan Wang, No, Southwest Jiaotong University; Prof. Dr. Jiliang Mo, Professor, Southwest Jiaotong University