Key Takeaways & Executive Findings
- •• • Pad A, rich in graphite and low hardness, achieved the lowest friction coefficient and vibration amplitude, demonstrating that lubricating film formation reduces interfacial shear and normal stiffness, critical for suppressing noise in AMC brake systems. • • Pad B, with highest surface hardness, exhibited high and fluctuating friction coefficient, leading to pronounced vibration and noise; its high hardness increased normal contact stiffness, promoting modal coupling and dynamic instability. • • Pad C, with least lubricating phase but low hardness, formed stable third-body layers that buffered loads, yielding moderate friction and lowest normal stiffness, effectively attenuating vibration and noise. • • Numerical simulations confirmed that friction coefficient and normal contact stiffness synergistically regulate system stability; high friction and large stiffness (Pad B) induce modal coupling, while low friction and low stiffness (Pads A and C) enhance stability, guiding material selection for low-noise lightweight brakes.
Abstract
The vibration and noise issues of lightweight friction pairs in suburban train braking systems have become a critical bottleneck restricting their engineering application. This study investigated lightweight friction pairs composed of three representative synthetic brake pads and an aluminum matrix composite brake disc. Utilizing tribological tests, interfacial wear analysis, and dynamic modeling, the study investigated the impact of interfacial wear and contact behaviors on vibration and noise and elucidated the mechanisms by which pad material properties influence these responses. The experimental findings revealed that the pad material properties significantly affect the wear behavior and friction-induced vibration and noise responses of lightweight friction pairs. The pad enriched with lubricating phases (Pad A) readily established stable lubricating films, while the highly plastic pad (Pad C) effectively captured wear debris to build the third-body layers that cushioned loads. Both reduced friction fluctuations and contact stiffness, thereby attenuating vibration and noise. Conversely, the high-hardness pad (Pad B) failed to form continuous lubricating films, leading to intensified friction, higher contact stiffness, and pronounced vibration and noise. Numerical simulations further confirmed that the friction coefficient and normal contact stiffness synergistically regulated system stability, directly affecting the vibration and noise responses. Systems characterized by high friction and large contact stiffness (Pad B) were particularly susceptible to modal coupling, resulting in dynamic instability and elevated vibration and noise levels. Therefore, optimizing the pad material properties and regulating the behavior of wear debris to facilitate the stable formation of lubricating films or third-body layers can effectively suppress friction coefficient fluctuations, reduce normal contact stiffness, and enhance interfacial stability, thereby mitigating vibration and noise. The findings provide a theoretical foundation and engineering guidance for optimizing the design of low-noise lightweight braking systems and selecting appropriate friction materials.
1. Introduction
Suburban railway systems, integral to China's urban agglomeration strategy, face a critical trade-off between increasing operational speeds (up to 160 km/h) and traction energy consumption. Lightweighting braking systems, by substituting conventional ferrous pairs with aluminum matrix composite (AMC) discs and synthetic pads, reduces unsprung mass by over 50%, saving approximately 0.065 kWh/km per kilogram reduction. For a six-car train set, this translates to annual electricity savings of ~50,000 kWh and ~50 t CO2 reduction. However, the adoption of lightweight friction pairs is hindered by severe friction-induced vibration and noise, a bottleneck restricting their engineering application.
Existing commercial solutions have failed to systematically address the coupled effects of pad material properties, interfacial wear, and contact stiffness on dynamic instability. This study establishes a material–interface–system analytical framework, integrating tribological tests, wear morphology analysis, and dynamic modeling, to elucidate how pad composition and hardness govern friction and contact stiffness, thereby controlling vibration and noise. By comparing three representative pads—lubricant-rich (Pad A), high-hardness (Pad B), and highly plastic (Pad C)—the research identifies optimal interfacial behaviors that suppress instability, offering engineering guidance for low-noise lightweight brake design.
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LIAO Caiqi, MO Jiliang, WANG Quan, WANG Zhiwei, ZHANG Qixiang, JIN Wenwei (2026). Mechanistic Investigation of Friction-Induced Vibration and Noise Behaviors of Lightweight Brake Material. SinoTechIntel Verified Research. https://doi.org/10.26599/FRICT.2026.9441216
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
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Frequently Asked Questions
What are the dominant wear mechanisms that differentiate the vibration and noise responses of the three pad materials?
Pad A forms stable lubricating films due to graphite enrichment, reducing friction and contact stiffness. Pad B undergoes intense shear and abrasive plowing, leading to high and fluctuating friction and increased stiffness. Pad C captures wear debris to form third-body layers that cushion loads, yielding moderate friction and lowest stiffness.
How does normal contact stiffness quantitatively influence the onset of modal coupling and dynamic instability in the braking system?
Numerical simulations show that high normal contact stiffness, as with Pad B, promotes modal coupling, leading to dynamic instability and elevated vibration and noise. Lower stiffness, as with Pads A and C, enhances system stability by reducing the likelihood of mode coalescence.
What specific material properties of the brake pads are most critical for achieving low-noise performance in AMC brake systems?
Low hardness and the presence of lubricating phases (graphite) are critical. Pad A, with low hardness and high graphite content, achieved the lowest friction coefficient and vibration amplitude. Pad C, with low hardness but less lubricant, also performed well due to third-body layer formation. High hardness (Pad B) is detrimental.
Can the findings be scaled to full-scale braking systems, and what are the potential trade-offs in terms of wear life and braking performance?
The study provides a mechanistic framework that can guide material selection for full-scale systems. However, trade-offs exist: while low hardness and lubricating phases reduce noise, they may compromise wear resistance and braking torque. Further validation on full-scale dynamometers is required to assess long-term durability and braking effectiveness.
What is the role of wear debris in stabilizing the friction interface, and how can it be engineered to suppress vibration?
Wear debris can form third-body layers that cushion loads and reduce contact stiffness, as seen with Pad C. Engineering pad materials to effectively capture and retain debris, or to promote the formation of stable lubricating films (Pad A), can reduce friction fluctuations and noise. This can be achieved by optimizing material composition and surface texture.
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