Friction最新文献

Hydrostatic oil grooves in the friction pair are responsible for guiding, storing, and distributing lubricating oil, widely applied to ultra-high-power hydraulic motors of tunnel boring machines, aerospace variable pumps, and hydrostatic precision guideways/spindles of high-end industrial mother machines, etc. The traditional design methods for oil groove patterns highly rely on the designer's experience and size optimization of preset shapes, making it difficult to achieve optimal lubrication. For that, this study proposes the intelligent self-evolving design method of oil grooves, in which the AI-assisted generalized pattern search algorithm (GPS+AI) is designed to make an oil groove pattern self-evolve towards maximizing load-bearing capacity according to the friction pair’s contact force feedback from a lubrication model. The designed oil groove pattern is machined onto the piston of a hydraulic motor and is experimentally evaluated for its lubrication load-bearing capacity through the home-made quasi-actual roller-piston pair testing rig. Comparing two traditional oil grooves, the new oil groove can reduce the friction torque (contact force) by a maximum of 88%, which is very significant for improving efficiency and lifespan of ultra-high power hydraulic motors (power > 10⁶ W), especially under the dual-carbon target. 

This paper presents a NURBS-based isogeometric analysis framework for modeling both hard and soft elastohydrodynamic lubrication (EHL) contacts under the fully flooded condition. Unlike conventional approaches, the framework incorporates nonlinear solid deformation within a unified weak formulation and employs a mortar method to flexibly couple the fluid and solid domains with independent discretizations. Benchmark tests show excellent agreement with reference ANSYS FSI simulations while reducing the computational time by about 99% for both hard and soft EHL line contacts. The framework is further applied to a soft EHL point contact between a hyperelastic hemisphere and a rigid plane, confirming that nonlinear solid deformation strongly affects the film thickness and frictional response. Finally, the influence of surface roughness is investigated, revealing that transversely oriented topographies yield superior lubrication performance, as indicated by a higher transition load and a lower friction coefficient.

This study proposes a numerical methodology based on the application of first, second, and third-order derivatives to analyze the evolution of the coefficient of friction (CoF) obtained from ball-on-disc (BoD) wear tests. The approach aims to provide an objective and quantitative identification of mechanisms, wear stages, and transition points, overcoming the subjectivity commonly associated with conventional friction curve interpretation. Before derivative computation, the CoF signal was smoothed to reduce experimental noise while preserving the morphological features of the friction curve. The methodology was applied to a newly developed multicomponent Al80Mg10Si5Cu5 HPDC alloy tested under dry sliding at room temperature (RT). The derivative-based analysis enabled the identification of successive wear stages, from the initial settling and running-in to transient and quasi-stationary regimes, and the determination of characteristic transition points, correlated with wear mechanisms through surface and microstructural analyses. The results demonstrate that the proposed methodology enables an objective determination of the duration and sequence of wear stages, reveals that the transition to stable sliding does not coincide with the maximum CoF value, and improves the identification of highly dynamic early wear regimes that are often underestimated by visual analysis. Due to its low computational cost and reliance on signals commonly available in tribological systems, the proposed derivative-based methodology shows strong potential for real-time friction and wear monitoring, predictive maintenance, and the automation of tribological control systems, although further validation under industrial operating conditions is required.

Due to the outstanding tribological and wear properties at cryogenic temperatures, Diamond-Like Carbon (DLC) materials are widely used in fields such as deep space exploration and superconducting magnets. Wherein, the temperature dependent frictional behavior of DLC is expected to follow the conventional thermally activated process. In this article, the frictional properties of DLC are scrutinized in the temperature range of 300 to 100 K by reciprocally scanning a DLC coated atomic force microscopy (AFM) tip against a DLC substrate in ultra-high vacuum (UHV) conditions. The results reveal a remarkable monotonical temperature dependence of frictional behavior, which remains robust under varying normal loads and sliding velocities. Specially, the overall friction force raises as temperature decreases, with a distinct friction peak at T_max = 215 ± 10 K. While a logarithmic dependence of friction on velocity is observed at temperatures far from T_max, friction becomes nearly velocity-independent in the vicinity of T_max. This non-monotonically temperature dependence of friction beyond conventional thermally activated framework is well interpreted involving the formation/rupture of interfacial bonds. This work provides new insights into the interfacial bonding mechanisms affecting the tribological properties of DLC materials at cryogenic temperatures.

The Johnson-Kendall-Roberts (JKR) theory remains the most cited model of adhesive contact. It was demonstrated that the JKR theory can be substantially extended, allowing adhesive JKR-type contact problems to be solved through an explicit transformation of the corresponding non-adhesive Hertz-type load-displacement curve. This framework enables application of the extended JKR theory to non-classical scenarios where analytical non-adhesive solutions are unavailable, and therefore numerical methods can be employed. However, the transformation formulae involve the first and second derivatives of the load-displacement curve, posing challenges when applied to discrete numerical data. This study presents a straightforward and effective numerical approach that converts a numerically obtained data series of load – displacement – contact radius for a non-adhesive contact problem into the corresponding JKR-type adhesive solution. While any appropriate numerical method can be used to generate these data, the finite element method is employed here. The proposed approach is validated by comparing numerical results with established analytical solutions for adhesive contact problems involving an elastic half-space and a thin elastic layer bonded to a rigid substrate, as well as with experimental data. These comparisons demonstrate excellent agreement between the numerical and analytical solutions. It is argued that the proposed method offers significant potential for solving many important practical problems, e.g., adhesive contact analysis for coated or multi-layered media.

Atomic surface of silicon (Si) wafers without particulate contamination achieved by chemical mechanical polishing (CMP) is highly desired for advanced chip manufacturing. Traditional CMP processes usually employ abrasive-containing slurries, resulting in significant particulate residues and high-cost post-treatments. To settle this challenge, a novel abrasive-free CMP slurry only including designated chain-length alkylamine was developed based on the observed dependence between the Si surface roughness and alkylamine chain length. After polishing by the long-chain hexylamine slurry, an atomic surface without particulate contamination is achieved with surface roughness as low as 0.13 nm, which is 85% lower than that obtained using short-chain methylamine slurry, while maintaining a material removal rate of 57.7 nm/min. Then, we established an atomic mechanistic framework that integrates interfacial chemistry with mechanical action to understand how alkylamine chain length modulates mechanochemistry in abrasive-free Si CMP. Density functional theory calculations show that long-chain alkylamines adsorb more readily but have a milder weakening effect on Si–Si bonds, whereas short-chain counterparts, despite weaker adsorption, more effectively weaken these bonds. Nanowear tests and X-ray photoelectron spectroscopy corroborate that the dynamic equilibrium between the adsorption strength and bond weakening promotes the formation of a mechanically vulnerable reaction layer composed by O_x–Si–N_y compounds amenable to abrasive-free removal for atomic smoothness. Our findings shift the mechanistic paradigm from conventional abrasive-involved interfacial interactions to abrasive-free, chemically driven, adsorption-controlled removal processes. These insights offer valuable theoretical guidelines for both academic research and industrial practice in ultra-precision manufacturing and advanced semiconductor processing.

The tribological mechanisms governing microstructure evolution in incremental sheet forming (ISF) were investigated through comparative analysis of three friction modes: sliding friction (ISF-SF), rolling friction (ISF-RF), and frictionless free-deformation (ISF-FD). Systematic characterization of interfacial interactions, grain refinement mechanisms, and texture evolution demonstrated that friction-induced shear deformation served as the dominant factor in determining forming performance. Crucially, ISF-RF preserved {110} texture integrity via nondirectional shear deformation, where effective lubrication suppressed interfacial plowing, adhesion, and oxidation, thereby achieving superior surface finish and minimal twist angle in formed parts. Conversely, ISF-SF drove directional shear deformation that actively reoriented grains toward {001} texture. Reduced lubrication efficacy intensified texture strength while amplifying interfacial plowing, adhesion, oxidation, and crack propagation, ultimately increasing part twist angle. The study elucidated the mechanism by which friction governs forming performance through shear deformation: moderate deformation coupled with grain refinement enhanced formability, whereas excessive deformation led to detrimental effects, including stress concentration, interface defects, and oxidation-accelerated failure. These findings establish a microstructure-property-process relationship, advancing ISF technology towards texture-regulated friction mode selection and adaptive lubrication strategies that balance grain refinement and defect suppression. This theoretical foundation enables next-generation ISF systems with enhanced forming limits and tailorable material properties.

In this work, the idea of water lubrication enhanced by a small quantity of oil was tested for the first time in a rubber journal bearing. A small quantity of silicone oil was supplied to an eight-groove rubber bearing through a small nozzle, aiming to improve the lubrication of the bearings under short-time severe working conditions. Results demonstrated that the addition of small-quantity silicon oil can significantly reduce friction, with the coefficient of friction (COF) at certain speeds being lower than that achieved with either pure water or pure oil. If the oil was given under frequent and small-quantity supply, smaller time interval of oil supply has little impact on friction reduction. Moreover, a simple method based on the Stribeck curve was proposed to roughly predict the COF reduction of water-lubricated journal bearings with small-quantity oil supply at low speeds. Additionally, computational fluid dynamics (CFD) simulations provided insights into the migration/diffusion of injected oil within the bearing, revealing a correlation between oil side leakage and COF.

Normal and tangential forces coexist between rough surfaces in engineering components under most operating conditions. Accurate measurement of contact forces (both normal and tangential forces) on rough surfaces is critical for the safety and stability of engineering equipment, as interfaces are typically discontinuous regions within mechanical systems. However, existing contact mechanics and electrical contact models mostly neglect tangential force effects, hindering their application to shearing behavior research and precluding the development of a contact force measurement methodology applicable to simultaneous normal and tangential force quantification. Inspired by the yield criterion for material damage, a contact mechanics model was developed that simultaneously accounts for the effects of normal and tangential forces. Then, a new principle of contact forces measurement is developed by correlating the contact resistance with the real contact area, which enables the simultaneous measurement of normal and tangential forces between rough surfaces based on the single contact resistance under steady-state contact conditions. By proposing a “static friction surface”, the static and dynamic friction stage is effectively differentiated, and the reasons for the sudden drop in friction force and the sudden increase in contact resistance during the static and dynamic transition stages are given. This work proposes a novel explanation for the friction mechanism in terms of mechanical deformation and electrical resistance changes.

Reliability is critical in high-power density engines, where components operate under extreme conditions to achieve optimal performance. These demanding conditions give rise to complex multiphysics and multiscale interfacial phenomena, contributing to early wear stages, poor performance and catastrophic engine failure due to severe mixed lubrication, cavitation damage, fatigue, and overheating effects. Therefore, enhancing the durability of such engines is paramount. This study investigates cavitation erosion in high-power density engines, with a particular focus on the connecting rod journal bearing. A novel multiscale cavitation erosion model is presented, integrated with a mixed-elastohydrodynamic lubrication simulation framework. Realistic boundary conditions for bearing load, oil supply hole position, and pressure are obtained from a multibody dynamic simulation analysis of the entire system. The proposed multiscale cavitation erosion model predicts the cavitation damage energy at each computational mesh node within the macroscopic bearing domain. This energy serves as a threshold to erode the corresponding microscale area surrounding the macroscale node region. The equivalent microscale area is then coupled with the bearing surface topography, and material removal is simulated using a novel cavitation erosion algorithm. The proposed model is applied to evaluate the evolution of cavitation damage in the connecting rod bearing of a motorsport engine. The analysis considers various influencing factors, including engine speed, bearing clearance, lubricant formulation, and oil temperature. The findings reveal key insights into the cavitation erosion mechanisms, highlighting the significant influence of lubricant formulation and engine speed on erosion severity in the studied bearing.