Friction最新文献

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.

As a common transport device, pipelines are permanently subjected to pressures generated by external loads and to the erosive effects of the substances transported inside. The addition of structures to the inner surface of the pipe has been demonstrated to enhance its strength and erosion resistance to a certain extent. In this paper, a novel bionic model is innovatively proposed using a leaf blade as a bionic prototype. It involves the leaf vein structure on the surface of the leaf blade and the growth arrangement law of the leaf blade (phyllotaxis-arrangement). A series of rigorous gas-solid erosion tests and compression tests were carried out on a 90° elbow pipe. The effects of the arrangement location (entrance, elbow), arrangement mode (uniform, interlaced, phyllotaxis), phyllotactic coefficient and vein fractal angle (30°, 45°, 60°) on the erosion resistance and compression capacity of the bionic model and pipe were also analysed. The test results demonstrate that, in comparison with standard bends, the dual bionic bends exhibit a maximum increase in erosion resistance of 41.1% and a maximum increase in compression resistance of 88.6%. The optimum erosion and compression resistance of the bionic model was obtained when the leaf vein fractal angle was 60°. In order to investigate the synergistic lifting principle of different bionic models, numerical simulation techniques were used to analyse the flow-solid coupling state inside the pipe, the resistance lifting inside the pipe, and the stress of the pipe when it is subjected to external loads. This study provides new ideas in the field of bionic erosion resistance and shows great potential for practical applications.

Reducing corrosion and wear has been a challenge to metal components in the marine environment for a long time. However, the problem of high cost and low efficiency hinder the discovery of new anti-tribocorrosion multi-principal element alloy (MPEA). This study reported a significant reduction in both wear and corrosion of single-phase CoCrNi MPEA through in-situ Laser-directed energy deposition (L-DED), that had only half tribocorrosion rate than pre-alloyed samples. Further, structure evolution mechanism of in-situ samples was revealed under different scales and interaction mechanism of tribocorrosion was clarified in detail. The results show that in-situ samples had finer cells and higher microhardness due to solid solution strengthening and nano-precipitation strengthening. The higher Cr₂O₃/Cr(OH)₃ ratio, higher R_ct, and a lower I_pass, indicated a denser and more protective passive film of in-situ samples. Further, in-situ sample demonstrated superior tribocorrosion resistance which was mainly due to lower corrosion-intensified wear loss (W_C) value. Moreover, load intensified the material loss of interactions between wear (W) and corrosion (S). This work will provide breakthrough in the wear-corrosion trade-off of MPEA design and promote the application of anti-tribocorrosion MPEAs in marine equipment.

As key supporting components in large-scale equipment, the lubrication performance of hydrodynamic thrust bearings directly determines the operational efficiency, stability and service life of the entire mechanical system. With the rapid development of modern industry, the demand for complex working conditions poses severe challenges to the lubrication systems of hydrodynamic thrust bearings, making the accurate evaluation and prediction of their friction and lubrication behaviors a critical technical issue in the field of mechanical engineering. This paper systematically summarizes the research progress of lubrication theories for hydrodynamic thrust bearings, covering the evolutionary process from early hydrodynamic (HD) lubrication theory to thermoelastic hydrodynamic (TEHD) lubrication theory that integrates thermal and elastic effects, and highlights the breakthroughs of computational fluid dynamics (CFD) technology in simulating complex flow fields. Concurrently, recent advances in thrust bearing performance testing technologies are summarized, which include fundamental tribological tests and bearing model test rigs, with detailed discussion on the progress in monitoring key parameters such as oil film pressure, thickness, and temperature. Performance enhancement strategies are systematically elaborated from two primary perspectives: the improvement of thrust bearing liner materials and the optimization of surface textures. Finally, by comprehensively analyzing existing research, future research directions are outlined, emphasizing the development of high-fidelity multi-physics coupling models, the integration of multi-sensor-integrated distributed dynamic measurement with algorithmic innovation, and the synergistic design and optimization of materials and surface textures. This paper aims to provide a systematic reference for the design, performance improvement, and cutting-edge research of hydrodynamic thrust bearings under complex working conditions.

Enhancing the durability of heavy-duty engines requires a deeper understanding of the wear failure mechanisms in critical big-end bearings. The complex interdependencies among tribology, dynamics, and wear behaviors pose challenges for accurate modeling, and the underlying failure mechanisms remain inadequately understood under demanding operating conditions. This study proposes a novel tribo-dynamic-wear coupling model for big-end bearings that integrates mixed lubrication, multi-body dynamics, and the transient evolution of wear morphology. A full-scale engine experiment is performed to validate the model’s accuracy, and a detailed surface failure analysis offers insights into the wear mechanisms under real-world conditions. The findings reveal a clear wear asymmetry between the upper and lower bearing surfaces, with the upper surface experiencing more severe wear. Additionally, an axial wear gradient is observed, with the test wear depth in the central region being approximately 9.10 μm greater than that at the edges. These distinct wear patterns are successfully predicted by the proposed model. The primary cause of exacerbated wear is identified as a significant reduction in hydrodynamic lubrication, driven by the combined effects of high load and low speed. This results in the highest transient solid contact force ratio (94.72%) among the three representative conditions (1,000, 1,400, and 1,800 r/min at 100% load). Another contributing factor is the concurrent occurrence of multiple wear mechanisms, including abrasive, oxidative, adhesive, and mild fatigue wear.