Friction最新文献

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.

This work explores the bi-stable behaviour of a frictional system susceptible to mode-coupling instability. The focus is placed on the variations of the energy flows at the contact, due to external perturbations, and the role of contact nonlinearities on the system dynamic response. A lumped parameter numerical model, incorporating contact nonlinearities, is developed, allowing transitions between sliding, sticking, and detachment contact conditions. While prestressed Complex Eigenvalue Analysis (CEA) allows to identify instabilities in the linearized frictional system, transient simulations were conducted to investigate the nonlinear system dynamics and the possibility to switch between two stable states (mode-coupling or stable sliding) by an external perturbation. The investigation of the bi-stable state has been carried out by performing an energy balance of the system, accounting for the exchanged mechanical energies at the contact, to highlight the key role of contact nonlinearities in driving the power flows at the origin of the different stable states and respective limit cycle. The findings underscore the critical role of contact nonlinearities in shaping the power flows at the contact interface, determining the transition between stable sliding and mode-coupling, providing further insights on the “fugitive” feature of mode-coupling instabilities.

In this work, a friction-induced vibration model for water-lubricated bearings (WLBs) is developed. The model incorporates interfacial mechanical effects, including the stiffness and damping coefficients of the water film, contact stiffness of asperities, elastic deformation of the bush, etc. To evaluate the friction-induced vibration state, i.e., stability of WLBs, the complex eigenvalue analysis is employed. A frictional noise experiment for a WLB is performed to validate the effectiveness of the developed model. Based on this model, the stability diagram of friction-induced vibrations in WLBs under various parameters is obtained, and the effects of key parameters, such as radial clearance, angular groove amplitude, and boundary coefficient of friction, on the stability are investigated. Numerical results indicate that increasing the boundary coefficient of friction, surface roughness, radial clearance, and angular groove amplitude elevates the risk of unstable friction-induced vibration. Furthermore, numerical studies reveal the existence of a critical rotational speed at which friction-induced vibration transitions from being unstable to stable. As the rotational speed approaches the critical value, the risk of unstable friction-induced vibration rapidly decreases. Within the hydrodynamic lubrication regime, the maximum vibration attenuation index tends to remain constant, regardless of any further increases in the rotational speed.

To address the persistent environmental concerns of petroleum-based lubricants, we report on a new class of high-performance, sustainable greases. These were formulated by combining select vegetable oils, including the structurally unique Orychophragmus violaceus (OV) seed oil, with an oleic acid-functionalized organo-modified montmorillonite nanoclay thickener. The sustainable samples consistently outperformed an industrial-grade lithium soap grease in tribological experiments. Remarkably, under harsh conditions of high load (up to 500 N) and temperature (150 °C), both 5 and 10 wt.% nanoclay-thickened OV-based greases exhibited superlubricity, with the coefficient of friction of approximately 0.008. Surface analysis using Raman spectroscopy after the tribological experiments revealed that this exceptional performance was not a result of typical carbon-based tribofilm formation but from a novel lubrication mechanism: the in-situ formation of an adhesive, low-shear solid tribofilm composed of the nanoclay itself. The formulated greases also exhibited excellent low-temperature fluidity and structural stability, with complete recovery after freeze-thaw cycles to -20 °C. These results highlight a new design methodology for creating reliable and biodegradable lubricants suitable for extreme industrial applications.

Lubrication failure of moving parts at extremely cryogenic temperatures poses a major challenge for advancements in space exploration, superconductivity, and other technologies. This study systematically investigates the tribological behavior of hydrogenated amorphous carbon (a-C:H) films in vacuum from -200 to 25 ℃. Notably, as temperature decreases, the friction coefficient and the wear life of the a-C:H films exhibit an abnormal increase. At -200 ℃, wear life exhibits a remarkable enhancement of at least two orders of magnitude. Introducing in situ mass spectrometry and cryogenic micro/nano indentation, the dynamic monitoring of interface damage, hydrogen passivation, and hardness evolution was conducted during the friction process. The work indicated that cryogenic temperatures significantly reduce damage of a-C:H films, leading to changes in the synergistic lubrication involving hydrogen passivation, graphitization, and transfer films, resulting in high friction and low wear. It is fundamentally attributed to cryogenic temperatures altering the interfacial activity, which is the key factor in activating the synergistic lubrication of the above mechanisms.

Crucially，with a suitable interfacial activity at -75 ℃, a-C:H films can achieve an ultralow friction coefficient of ~0.015 and a wear rate of ~ 10⁻⁸ mm³/N·m. The work provides critical insights and establishes a foundation for deploying a-C:H films for cryogenic applications.

Wear debris particles play a crucial role in frictional interfaces. Conventional understanding holds that the debris accumulation causes severe wear. Interestingly, the debris from metal friction pairs includes anti-wear metal oxides generated by tribochemical reactions, which can form a protective oxidation film to resist wear. However, minimizing the abrasive damage caused by accumulated debris and using the anti-wear property of the metal oxides can be mutually exclusive. Here, a rational design of a coupling surface that manipulates nanoscale wear debris to resist further wear is reported. It consists of surface textures used to capture and temporarily store excess nanoscale wear debris, a deposited self-cleaning coating that subsequently helps transfer part of the captured debris into the sliding-contact interface, where it converts into a protective oxidation film. The coexistence of the two elements with contrasting properties in manipulating nanoscale wear debris considerably reduces wear under conditions of water lubrication, oil lubrication, and macroscale superlubricity. Our strategy achieves the manipulation and utilization of wear debris for anti-wear purposes. This work holds the potential to promote further investigation into the role of nanoscale wear debris and its utilization approaches.

This study uses rollers with curved profiles to explore the phase stability of austenitic matrix AISI 304 exposed to the rolling contact wear under the variable slip ratios in the range from -0.23 up to 8.81%. The wear track is formed under the cyclic surface delamination and the asymmetric extrusion of matrix towards the track side. The size of wear track and the fraction of extruded materials grow along with the slip ratio. Severe plastic deformation makes the parental matrix susceptible to phase transition when the ferromagnetic martensite replaces the paramagnetic austenite. The extent of this transition and the preferential alignment of neighbouring phases were found to be more complex under the higher slip ratios. The matrix is preferentially strained along the wear track width when the slip ratio is close to zero, whereas the presence of friction components at the higher slip ratios preferentially strains the matrix closer to the rolling direction. The sandwich-like microstructure is formed when the extremely refined layer containing a mixture of strain-induced martensite and austenite on the free surface is replaced by the thermally softened one due to friction heating, containing mostly strain-induced martensite, followed by the plastically strained region with prevailing austenite fraction. The heat release due to plastic deformation of austenite, phase transformation, and friction contribute to elevated temperatures, especially at the higher slip ratios. The enhanced thermal softening at the higher slip ratios reduces the compressive residual stresses, but the dislocation density in austenite as well as martensite is increasing. The study also demonstrates that this phase transformation can be reliably monitored by magnetic Barkhausen noise, which increases with the slip ratio due to the growing preferential straining of both phases into the direction of rolling. The high sensitivity of this non-destructive magnetic method is based on the medium-increasing fraction of the strain-induced martensite and its distinct preferential straining along the rolling direction at higher strain rates. The influence of residual stress state on magnetic emission is only minor.