Friction最新文献

This study evaluated the friction, wear, and airborne brake wear particle (BWP) emissions of aluminum-based metal matrix composite brake discs fabricated from recycled aluminum alloy reinforced with silicon carbide particles (Al-SiCp MMC). The study further conducted a comparative analysis of the friction, wear, and BWP emissions of Al-SiCp MMCs against those of a commercial gray cast iron (GCI) brake disc, which served as a reference. The results show that the steady state coefficient of friction for all Al-SiCp MMC brake discs remained consistently between 0.4 and 0.45, within the typical range of brake materials. A clear transfer layer was observed on Al-SiCp MMC disc surfaces after testing, resulting in apparently milder wear due to material transfer and reduced BWP emissions. Al-SiCp MMC brake discs resulted in higher wear rates on the mating pins compared to GCI discs, with wear rates increasing as the fraction of secondary aluminum in the matrix increased. Within the measurement range of this study, both GCI and Al-SiCp MMC brake discs had mono-modal number-weighted particle size distributions in the steady state, with the mode size around 0.5 µm. Future research should employ advanced particle samplers capable of detecting nanosized particles and explore more severe testing conditions, including higher contact pressures, speeds, and temperatures.

Friction, as a nonlinear and complex phenomenon, significantly affects the performance of mechanical systems requiring high-precision motion control and force feedback. Accurate modeling of frictional behavior is essential for effective control and compensation. The LuGre friction model is widely used due to its computational efficiency; however, it retains only the first-order displacement term, resulting in limited accuracy and noticeable drift, which restricts its use in precision applications. To address these issues, this study proposes an improved friction model based on the LuGre framework. Discrete bristles are introduced to incorporate the influence of surface topography at the contact interface. Additionally, an iterative numerical scheme is employed to enhance computational accuracy. Simulation results demonstrate that the model captures key frictional phenomena, including stick-slip transitions, hysteresis, and friction lag. It also shows clear advantages over the LuGre model in representing non-local memory and non-drift characteristics. Experimental validation was conducted using a constant-velocity reciprocating test and a micro-amplitude sinusoidal excitation test, enabling stepwise parameter identification for slipping and sticking phases. A dual-frequency sinusoidal excitation test was further designed to evaluate model performance under complex dynamic loading. The simulated friction forces agree well with experimental measurements, verifying the model’s effectiveness and robustness. The proposed model enhances both accuracy and physical realism in friction modeling and can be applied in high-precision systems to solve the friction force output under the given input conditions.

Friction hysteresis, a common event in ultrathin two-dimensional materials, is significantly influenced by their deformation. This study explores the friction hysteresis of suspended graphene with varying thicknesses using atomic force microscopy (AFM) conducted under controlled humidity conditions. Compared with that in the supported case, the friction in the suspended graphene cases demonstrates significant hysteresis. The degree of friction hysteresis on suspended graphene increased with decreasing thickness and increasing relative humidity and cut-off load. Both deformation hysteresis and adhesion hysteresis contribute to the friction hysteresis of suspended graphene, with deformation hysteresis playing a dominant role. The finite element simulation revealed that the sliding process enhanced deformation and increased the contact area for the major friction hysteresis. The deformation hysteresis of suspended graphene expands the contact area and increases energy dissipation during unloading, resulting in significant friction hysteresis. These findings advance our understanding of friction hysteresis on graphene in terms of deformation hysteresis.

The rapid evolution of advanced equipment that utilizes gears, including aviation engines, helicopters, and wind turbines, imposes escalating demands for enhanced reliability, prolonged lifespan, increased power density, and sustained durability of gears. Gear contact fatigue issues, associated with materials, geometries, and operating conditions, are crucial to modern gear design. To date, enormous theoretical and experimental studies have been conducted to understand gear contact fatigue mechanisms. To compile and categorize key investigations within a broad and active research field, this work reviews recent studies of gear contact fatigue. Emphasizing theories, tests, and anti-fatigue design approaches, this work aims to provide a comprehensive overview of recent developments in this significant area of research.

Material failure caused by load impacts frequently results in significant economic losses and negative effects. The application expansion of shear thickening fluid (STF) under special impact conditions is expected to lead to the design of a prospective impact-resistant structure because of its shear thickening effect, with an instantaneous response and reversible viscosity change. Herein, core–shell nanospheres (PS@ZIF-8) were synthesized using polystyrene (PS) nanoparticles as the base template. PS@ZIF-8 was used as the unique dispersed phase and was introduced uniformly into hydroxyl-functionalized ionic liquids (ILs) via simple ball mill dispersion to obtain novel STF systems. The performance of novel STF systems, such as the critical shear viscosity and peak viscosity, could be enhanced with increasing PS@ZIF-8 content. Importantly, the STF systems retained a significant shear thickening effect even after several shear scanning cycles because of the interaction between the dispersed phase (PS@ZIF-8) and the dispersion medium (ILs). The structural stability of PS@ZIF-8 in ionic liquids was also investigated, and the STF suspensions exhibited excellent stability in quantitative comparison experiments after centrifugal disruption at 8,000 r/min and standing for 60 days. In addition, a loading impact experimental method was developed to better investigate the anti-impact-wear performance of STF systems filled with limited space. The results of the tests revealed that the novel STF systems had outstanding flexibility in terms of energy absorption capacity and impact wear resistance. This study provides a strategy to prevent material failure under load impact and highlights the potential of these novel STF systems for designing efficient and stable impact-resistant structures.

Ultra-low wear technology provides an effective solution to prolong the service life of mechanical equipment. However, there are still significant challenges in achieving ultra-low wear at the steel/steel interface over long periods. In this work, a PAO10-SPAN65 composite semisolid lubricant (PAO10/SP65) was designed with sorbitan tristearate (SPAN65) and base oil poly α-olefin 10 (PAO10). The wear rate of the steel lubricated with PAO10/SP65 (1.31×10⁻⁸ mm³·N⁻¹·m⁻¹) was 96% lower than that of PAO10 (3.52×10⁻⁷ mm³·N⁻¹·m⁻¹). In addition, after 10 h of friction testing at a contact pressure of 0.82 GPa, the wear of the steel surface is still close to zero, with a wear rate of 4.13×10⁻⁹ mm³·N⁻¹·m⁻¹. This study provides a new design idea for realizing ultra-low wear of engineering steel.

This article provides a thorough review of the advancements in acoustic emission (AE) technology used for monitoring journal bearings. First, the AE sources generated from journal bearings under different lubrication regimes are classified and discussed. Next, a comparative analysis of parametric analysis, waveform, and artificial intelligence recognition methods for bearing AE signal analysis is conducted, highlighting their respective principles, pros and cons, and applications. Additionally, an overview of physical models representing AE waves on relatively sliding surfaces is provided from the wave generation mechanism perspective, and each model’s applicable conditions are compared. Finally, an in-depth discussion is presented, and future research directions are highlighted.

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 the 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 modelling, 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.

Skidding in angular contact ball bearings can significantly increase friction, wear and temperature, affecting bearing performance and service life. Despite its important impact, few studies have systematically investigated lubrication behavior under skidding conditions, where conventional lubricants often fail to provide stable low-friction operation. To address this issue, this study first calculated the critical skidding parameters of angular contact ball bearings using a quasi-static model. Then, experimental parameters of bearings with skidding and non-skidding were selected to study their tribological behaviors under lubrication with three different lubricants (base oil, commercial lubricant, and diketone lubricant). The study found that when the bearing had skidding behavior, the lowest friction coefficient and temperature rise (0.0008, 2.8℃) can be achieved only under lubrication with PAO=14(20%) (diketone lubricant). In addition, the bearings lubricated with diketone show excellent anti-wear performance and extremely short running-in period. The mechanism of the excellent tribological performance of diketone-based lubricants came from the synergistic effect of diketone molecular adsorption layer and chelation, which can reduce friction and temperature rise. These findings highlight the potential of diketone lubricants to improve bearing performance and durability under extreme operating conditions.

Nanocomposites have attracted significant attention as lubricant additives due to their advantages in reducing friction, enhancing wear resistance, and improving thermal and oxidative stability. In recent years, increasing research has explored how different types of nanomaterials (such as carbon-based materials, metallic nanoparticles, and ceramic phases) can use synergistic effects to achieve performance surpassing that of their single components. This review focuses on relevant studies published between 2020 and 2025, providing an updated overview of the advantages, synthesis methods, structures, dispersion stability, lubrication mechanisms, and tribological behavior of nanocomposites. Various structural types are discussed, including core-shell, layered, and in-situ hybrid systems, along with their fabrication routes such as sol-gel processing, hydrothermal synthesis, and surface modification strategies. The lubrication mechanism of nanocomposites is analyzed based on the material structure and the testing conditions. Particular attention is paid to the synergistic effects among multiple components within the nanocomposites and how these synergies enhance tribological performance. Furthermore, the challenges faced by nanocomposites and potential future developments are discussed. This review aims to clarify the current status of nanocomposites as lubricant additives and facilitate their future application in advanced lubrication systems.