Surface topography governs the real contact behavior during wear. Peak-valley topography and load-bearing material distribution further control the evolution of surface damage. This study proposes a topography-driven wear modeling approach based on measured rough surfaces. Under the half-space assumption, the boundary element method (BEM) is employed to compute the contact pressure, displacement, and interfacial gap fields over the discretized rough interface. The incremental geometric update procedure driven by the resolved contact state is then applied to simulate progressive surface wear. Sliding wear experiments with different initial roughness levels are conducted to investigate wear mechanisms. The three-layer method based on the Abbott-Firestone curve (AFC-3L) is employed to analyze layer-resolved topography evolution. The results show that the model predictions capture the experimental trends of wear response and layer-resolved topography evolution. The wear process proceeds sequentially through asperity truncation, core-layer reconstruction, and valley-layer involvement, with wear depth strongly dependent on the initial surface roughness.

Boundary lubrication plays a crucial role in determining the service performance and operational lifespan of mechanical components. However, continuum mechanics models and experimental studies are unable to elucidate the dynamic evolution of intermolecular interactions at the interface under boundary lubrication from a microscopic perspective, including phenomena such as asperity contact and lubricant film rupture. In this study, a molecular dynamics simulation approach was employed to construct a boundary lubrication friction model incorporating lubricant molecules, aiming to investigate the influence of applied load and asperity height on the dynamic evolution of atomic interactions at the interface from the perspective of energy variation, under conditions both with and without asperity contact. The results indicate that van der Waals interactions dominate the frictional response, and severe asperity contact leads to a sharp increase in van der Waals energy, which in turn results in a decrease in normal force, thereby increasing the friction coefficient. When the upper and lower surfaces remain separated by the lubricant, an increase in van der Waals energy leads to higher friction force, consequently elevating the friction coefficient. In the absence of contact, the friction coefficient decreases with increasing load; however, once asperity contact occurs, higher loads accelerate lubricant film failure and intensify direct interfacial contact, leading to more pronounced stick-slip oscillations and increased wear. This study provides atomic-scale insights for the design and performance optimization of boundary lubrication interfaces.

An ultrasonic effective reflection coefficient method is proposed for measuring the lubrication film thickness at the elliptical contact region. The effect of the acoustic main lobe with a larger radius is analyzed, where the superposition of the discretized reflection coefficient at both the contact region and non-contact region is considered. The coupling influences of the lubrication film shape at the non-contact region, the contact pressure distribution at the contact region and the incident acoustic pressure field on the reflection coefficient are eliminated. The proposed measurement method is validated via both simulations and experiments. The results show at small elliptical contact regions, the central film thickness in the range of 0.5 μm-5 μm can be identified accurately with the maximum measurement error of 15.9%.

Quaternary high-entropy metal carbonitrides were designed by using a first-principles high-throughput method. A total of 126 high-entropy carbonitrides (HECNs) composed of transition metals (Ti, Zr, Hf, V, Nb, Ta, Mo, W, Cr) were systematically constructed through virtual crystal approximation. The stability and mechanical performance of these compounds were evaluated through a comprehensive screening protocol based on their phase stability, mechanical stability and elastic properties. Furthermore, the pressure-dependent behaviors of the HECNs were investigated using density functional theory (DFT). Five optimal HECNs were identified, exhibiting outstanding Vickers hardness, high fracture toughness, superior Young’s moduli, and elevated melting points, which are attributed to their strong ionic-covalent bonding characteristics.

The stability and mechanical and thermodynamic properties of medium-entropy diboride (HfNbTaTi)B2 and its constituent binary diborides were investigated using the density functional theory and quasi-harmonic approximation. The effects of high temperature and high pressure were discussed. The results indicate that the diborides can maintain mechanical stability even at 100 GPa or 1,500 K. The elastic constants, moduli, Vickers’ hardness, fracture toughness, mechanical anisotropy, Debye temperature and minimum thermal conductivity of the diborides increased with rising pressure. At elevated temperatures, the mechanical performance of the diborides was reduced, whereas their thermal expansion coefficient and heat capacity increased. The brittleness of the diborides decreased at elevated temperatures or pressures. The diborides exhibited strong covalent and ionic bond characteristics. (HfNbTaTi)B2 had high-temperature mechanical and thermodynamic properties comparable to conventional binary diborides, demonstrating promise as a candidate material for high-temperature applications.

Rolling contact fatigue of M50 steel is investigated with consideration to the elasto-plastic behavior of materials. The multiaxial stress model is used for evaluating the influence of both the normal stress difference and shear stress on the fatigue evolution. The effect of material distortion induced by the normal stress difference is specifically analyzed during the initiation and propagation processes of spalling. Changes in the multiaxial stress on different surfaces, as well as their effect on the fatigue evolution are discussed. The results show that in addition to the shear stress, the normal stress difference has significant effect on fatigue evolution as well. Especially on certain rough surfaces, the stress concentration in near-surface layers generates obvious difference among the normal stresses in the orthogonal direction. The corresponding material distortion energy due to the increasing elastic strain accelerates the crack initiation in near-surface layers, which consequently reduces the rolling contact fatigue lifetime.

Quinary high-entropy carbonitrides (HECNs) were designed using high-throughput first-principles calculations. A total of 126 equimolar quinary HECNs generated from transition metals (TMs) (Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W) were modeled using virtual crystal approximation (VCA) and special quasi-random structure (SQS) approaches. The phase and mechanical stability, mechanical performance, and elasticity-derived thermophysical indicators of these ceramics were systematically evaluated. Furthermore, the pressure-dependent mechanical stability and mechanical and thermophysical properties of the prioritized candidates were investigated using density functional theory (DFT) calculations. Five quinary HECNs were identified as theoretically promising candidates within the present high-throughput screening framework. For these candidates, the predicted Vickers hardness (HV), fracture toughness (KIC), Young’s modulus (E), bulk modulus (B), Poisson’s ratio (v), Pugh’s ratio (B/G), anisotropy indices, Debye temperature, and minimum thermal conductivity all increased with rising pressure. The ductility of HECNs increased with valence electron concentration (VEC). A VEC window of 9.3-9.7 was identified as the range in which phase-stable and mechanically stable HECNs most frequently satisfied the combined screening thresholds of HV > 20 GPa, KIC > 4.5 MPa·m1/2, E > 500 GPa, and B > 330 GPa.

ABSTRACT Polymer nanocomposites are widely used in high‐end bearings and gear components; their friction and wear mechanisms are significant for improving the service performance and lifespan of high‐end equipment. However, traditional experiments are expensive and time‐consuming and often fail to comprehensively reveal the friction and wear mechanisms of materials, posing challenges in predicting the wear scar morphology. To overcome this issue, this study employs a multiscale approach combining molecular dynamics (MD) simulations, finite element (FE) friction simulations, experiments, and machine learning (ML) to predict the friction and wear mechanisms of graphene (Gr)/polytetrafluoroethylene (PTFE) nanocomposites. Under velocities of 0.064 and 0.08 m/s and loads of 2–10 N, the optimal Gr mass fraction is 1.0 wt.%. Then this study extracts the microstructural information of the nanocomposites from the multiscale friction model (MD and FE) and couples it with experimental parameters to construct an ML prediction model based on an artificial neural network algorithm. By leveraging the trained nonlinear input–output relationships, the model successfully predicts the friction coefficient, wear amount, and wear scar morphology. The predicted wear amount deviates from experimental values by only 2.8%, and the wear scar depth profile shows 96.8% overlap. Furthermore, its reliability was experimentally verified. The results demonstrate that the coefficient of friction (COF) initially increases with load, then decreases, while wear amount rises monotonically; these trends are validated by experimental errors of 2.35%–13.36% across different loads. This validated multiscale prediction framework provides actionable insights for the wear‐resistant design and lifespan prediction of Gr/PTFE components in engineering applications.

The transient micro-adhesive behavior at asperity contact is investigated by using the thermo-elasto-plastic finite element method. The plastic flow accompanied by locally high stresses and temperature rise are analyzed during the sliding contact of surface asperities. The effect of frictional work and plastic deformation work are evaluated. The results show that obviously plastic deformation is generated on the asperities due to the locally high stresses. The subsequently plastic dissipation and frictional heat lead to transient temperature rise, which in turn influents the plastic deformation at the asperity contact due to the thermal softening effect. At the given operational conditions, the temperature rise due to the plastic deformation work account for approximately 17%.

Friction energy consumption represents the predominant form of energy loss in rolling bearings, and the friction torque is a crucial indicator of rolling bearing quality. To comprehensively characterize the friction performance of grease-lubricated bearings, a kinetic energy deceleration method was proposed to evaluate friction torque of rolling bearings. A series of experiments were performed on deep groove ball bearings (DGBB) lubricated with various greases using a dedicated test platform. Friction torque behavior was measured of DGBB with greases differing in base oil, thickener, and thickener content by employing the kinetic energy deceleration method. The results indicated that mineral oil-based grease exerted a greater influence on friction torque than synthetic oil-based grease under the same viscosity grade. Additionally, for lithium grease-lubricated bearings, the friction torque consistently exceeded the expected value in the low-speed region. As speed increases, the measured values gradually converge with the theoretical ones with a critical speed identified beyond which the two coincide. The friction torque in grease-lubricated bearings rises slightly with increased load, while the difference in torque across various loads narrows as angular speed rises.

The effect of frictional heat accumulation on the surface damage initiation at cyclic sliding contacts of M50 steel is investigated. The surface damage is detected by a sudden increase in the frictional coefficient during the ball-on-disk sliding contact test. The periodically thermal response of the rotating disk during tests is correspondingly calculated by using a numerical method based on Fourier transform. The results show that while the final failure mode is consistent under fixed pressure and velocity, the time to failure is controlled by the heat accumulation rate, which is highly sensitive to cyclic frequency. A smaller rotational radius increases contact frequency and reduces heat dissipation within a single cycle, accelerating temperature rise and surface damage initiation. The parametric analysis revealed the distinct effects of contact pressure, sliding velocity, and friction coefficient on frictional heat flux and heat dissipation. The study concludes that controlling heat accumulation behavior is critical for predicting and mitigating surface damage at cyclic sliding contact.

Under the reality that the working conditions of main shaft bearings are increasingly harsh with the continuous increase in aero-engine rotational speed, to meet the actual demand of researching the working surface micro-topography characteristics of aero-engine main shaft bearings, this paper proposes a novel numerical simulation method, which improves the problem that the controllable parameters of the existing method are limited. Firstly, based on the two-dimensional (2D) digital filter method and Kernel Ridge Regression (KRR), combined with correlation analysis, the prediction model from the target three-dimensional (3D) characterization parameter set to the interpolation nodes is constructed, then the areal material ratio curve (AMRC) is reconstructed by particle swarm optimization (PSO) assisted curve interpolation, and finally the spatial position distribution of the surface height is set by reordering, so as to realize the surface numerical simulation with the target 3D characterization parameter set and spatial position distribution. On this basis, the impact of 3D characterization parameters of the working surface on the lubrication performance of aerospace ball bearings are analyzed by mixed thermal elastohydrodynamic lubrication (TEHL) calculation, and the practical value of this method is verified, which shows that this method can provide the research with an effective simulation tool on how the surface micro-topography characteristics impact the lubrication performance of aero-engine main shaft bearings, and has important engineering practical value.

A dynamic model is established for angular contact ball bearings with double half inner rings incorporating misalignment and skewness conditions. Cage dynamics, including collisions, motion, and stability, are analyzed. Results show that increasing misalignment or skewness angles suddenly increases the normal force between the cage and the outer ring and intensifies the impact between pockets and balls. Higher axial load on the inner ring reduces the cage whirl ratio. However, significant differences in the density of the normal force between the left and right sides of the cage-outer ring occur, potentially causing the cage to experience eccentric wear. Silicon nitride balls reduce the impact between pockets and balls under misalignment and skewness conditions and decrease the normal force between the outer ring and one side of the cage.

The 8Cr4Mo4V steel is the key material used in aero-engine main shaft bearings. However, the mechanism its surface roughness controls tribological properties under coupled multi-physics service conditions remains unclear, which restricts the long-life design of aerospace bearings. In this study, 8Cr4Mo4V steel specimens with controlled surface roughness (Ra = 0.02, 0.04, and 0.06 μm) were prepared, and ball-on-disk tribological tests were conducted under variable loads, sliding speeds and ambient temperatures to clarify the roughness-dependent friction and wear behavior. The results show that the effect of surface roughness on the tribological properties depends strongly on working condition: it was the most prominent under low load (8 N) and low speed (0.1 m/s), where the coefficient of friction (COF) increased by 22.95

Aeroengine bearings operate in boundary, mixed, and elastohydrodynamic lubrication regimes, with very thin film, where lubrication performance is significantly affected by surface topography. To replace measurement methods for studying 3D surface topography, this paper addresses the issue that existing surface simulation methods are difficult to fully characterize all the detailed features of the surface, based on the inverse process of the basic principle of white light interferometry (WLI), proposes a complete 3D surface reconstruction method, which considers the macro-geometric shapes. Firstly, this method uses 2D digital filter combined with the Johnson transform system and iterative approximation method to compute a Roughness Height Lattice (RHL). Then, the macro-geometric shapes are superimposed by direct geometric mapping. Finally, the surface is fitted by cubic B-spline interpolation. Through this process, the complete surface reconstruction of key components of ball bearings, considering the macro-geometric shapes, have been achieved. Additionally, simulation analysis of the influences of the micro-rough surface scale, the macro-geometric scale, and 3D characterization parameters (CPs) on the reconstruction are conducted. This provides an effective tool for 3D lubrication research of aeroengine ball bearings, which has significant practical value.

Dynamic characteristics of ball bearings with different cage pocket shapes are investigated with consideration to the concurrent rotation of the inner and outer rings. Contact models of balls with cylindrical, elongated cylindrical, and rectangular pockets are established. The ball excursion, cage trajectory, contact force, and cage speed are analyzed. The results show that the elongated cylindrical pocket leads to a more stable trajectory of the cage since balls always impact the leading side of the pocket. However, for the cylindrical and rectangular cage pockets, both the leading and trailing sides of the pockets are randomly impacted by balls, which may cause chaotic motions of the cage.

An ultrasonic residual amplitude coefficient model is proposed for optimally estimating the lubricant film thickness at coated interfaces with unidentified coating thickness. The residual amplitude coefficient is defined as a function of the lubricant film thickness rather than the coating thickness, which eliminates the influence of the coating-induced phase shift. The minimum root mean square of the residual amplitude coefficient is utilized to determine the lubricant film thickness. Both the simulation and test results show that at different coated interfaces, the proposed model is capable of determining the lubricant film thickness in a wide range from 1 mu m to 95 mu m. The relative errors are less than 11.3 %.

The new contact model for arc end surfaces of rollers and flanges is established in a dynamic model for cylindrical roller bearings. The dynamic behaviors between roller arc end surfaces and flanges, i.e., contact pressures, sliding velocities, and PV values (peak contact pressure P × sliding velocity V), are investigated and compared to those between roller corners and flanges. Based on the indicators of contact heights and axial clearances, the selection ranges of layback angles, flange axial clearances, and end radius of rollers are proposed, thereby ensuring the bearing operates normally. The results indicate that arc end surfaces are beneficial in reducing contact pressures, sliding velocities, and PV values acting on flanges, especially under high-speed conditions. With less layback angles of flanges and end radii of rollers, contact positions on rollers are more concentrated and the sliding velocity decreases obviously. However, flange heights need to be increased to prevent contact heights between rollers and flanges within the limited zones. Furthermore, since the end radius of rollers leads to a decrease in the axial clearance of flanges, the actual clearance of flanges under axial direction needs to be widened.