Guest editorial: Recent progress in tribology in China – Part 1

Tribological challenges – notably high friction and severe wear – significantly contribute to energy dissipation and material failure across all scales from earthquakes down to micro/nano-device (Chen and Qian, 2020; Xiao et al., 2019; Luo et al., 2022). On a global scale, it is estimated that approximately 23% of energy consumption is attributed to mechanical losses arising from friction and wear (Berman et al., 2015). Tribology research in China commenced later than elsewhere, but has undergone extremely rapid development in the past 20 years. China has now surged to the top globally in terms of research scale and publication count within the field (Zhou, 2025).

This special issue seeks to compile cutting-edge research across diverse topics within the scope of “Recent progress in (nano)tribology in China”. This issue compiles tribology research on innovations, trends, challenges and solutions relevant to transportation, energy, components and materials engineering. The contributed research topics are organized into two distinct sections. The section I has four groups, involving bearing lubrication, gear drive, tribology of wheel rail and tribology of rail brake. The contribution of each contribution is described briefly here.

• Effect of surface sector or Fibonacci-like micro grooved top foil on the performance of gas foil conical bearing (Hu et al., 2025).

This study investigates the effects of top foil groove micro-structure on the load capacity and dynamic stability of gas foil conical bearings. Compared to sector groove, the Fibonacci-like shape is particularly advantageous, offering a substantial increase in axial load capacity with minimal extra torque and providing the most favorable stability enhancement. The result presents an effective way to boost performance of gas foil conical bearings and can even be applied to upgrade existing bearings in service:

• Study on the dynamic characteristics of double row self-aligning roller bearings with surface faults (Yang et al., 2025).

This study develops nonlinear dynamic equations for double-row self-aligning roller bearings with surface faults and simulates their effects across varying positions, sizes and speeds using MATLAB. Experimental results verify the model’s correctness and show that impact load increases with both rotational speed and fault size, and the duration of the impact load lengthens as the fault size grows larger. This validated nonlinear dynamic model provides a theoretical foundation for diagnosing bearing faults and predicting fatigue life in double-row self-aligning roller bearings:

• Investigation on the nonlinear behaviors of floating ring bearings based on nonlinear stiffness and damping coefficient models (Zhao et al., 2025).

This paper introduces a new method using models of these nonlinear coefficients instead of traditional analytical solutions. This approach significantly improves computational speed and accuracy in capturing nonlinear behavior of floating ring bearings, especially in turbochargers. The study also finds that the FRB clearance ratio and load strongly influence these nonlinear coefficients.

• Study on oil film spreading characteristics on the jet lubricating tooth surface of aviation herringbone gear (Chu et al., 2025).

This study examines the effect of injection parameters and gear operating conditions on oil film deposition during spray lubrication of aviation herringbone gears. Key findings show oil film thickness decreases with distance from the injection point, increases with higher injection velocity or lower gear speed and is minimally affected by injection distance beyond dynamic spreading behavior. The obtained results can provide the optimized lubrication parameters for precise aerospace gear design:

• Research on the wear model of ADC12-POM gear pair based on Archard theory (Xiong et al., 2025).

This work establishes an Archard-based numerical framework for mapping wear distribution on ADC12/POM gear tooth profiles. Different from wear spanning the entire meshing tooth profile in simulations, experimental validation revealed that wear occurs predominantly on the POM gears. To resolve this discrepancy, a curvature-incorporated tooth surface reconstruction model was developed and experimentally validated using a custom test rig and 3D wear measurements under controlled conditions:

• Study on the sealing mechanism of ribbed oil-slinging ring composite seal at the axle-end of high-speed train gearboxes (Lin et al., 2025).

This work presents a rib-enhanced oil-slinging ring seal featuring inclined edges for enhanced axle-end sealing in train gearboxes. Simulations show that the ribbed oil-slinging ring composite seal can reduce oil leakage versus traditional seals, shifts turbulence dissipation intensity and enhances jet strength through optimized geometry and vortex control. Strategic rib configurations further refine sealing by managing vortices and pressure zones, advancing high-speed train sealing technology.

• Study on influence of friction conditions on the friction and wear performance of high-speed rail brake materials under high humidity environment (Ding, 2025).

This study reports that contact pressure and sliding speed significantly impact high-speed train brake material performance under high humidity and high initial disc temperature conditions. Higher contact pressure stabilizes the friction coefficient but shifts wear from primarily abrasive and adhesive wear to a combination including fatigue wear. Increasing sliding speed reduces friction and worsens adhesive wear alongside abrasion and fatigue. The results provide crucial theoretical and technical guidance for safe and efficient high-speed train braking in humid environments:

• Calculation and experimental study in the braking temperature of aluminum-based and cast steel brake discs (Zhao et al., 2025).

This study compares temperature characteristics between aluminum-based and cast steel brake discs paired with copper-based brake pads during rail vehicle braking. Under the given conditions, cast steel brake disc consistently reached higher maximum temperatures than aluminum-based disc, with the temperature gap widening as speed/pressure increased. Cast steel brake disc also exhibited a “three-peak” surface temperature distribution versus “single-peak” profile of aluminum-based disc. The quantified temperature differences and thermal behavior patterns provide critical data for promoting implementation of aluminum-based disc in rail braking systems:

• Research on thermal effect of braking interface of urban rail train under continuous braking condition through thermo-mechanical model (Gao et al., 2025).

This study investigates heat accumulation effects on temperature/stress distributions in a Q345B steel brake disc and copper-based PM pad system during continuous braking. Based on a tailored thermo-mechanical model, band-shaped high-temperature zone formation and stress evolution were analyzed. By revealing mechanisms behind band-shaped high-temperature zones and stress concentration shifts, this work enables fatigue prediction in continuous braking and provides theoretical foundations for establishing operational speed standards.

• Research on wheel wear evolution of inside axlebox metro vehicles (Qi et al., 2025b).

This study establishes dynamic and wheel wear models for metro vehicles with outside versus inside axlebox configurations to analyze their curve negotiation performance and wheel wear evolution. Inside axlebox vehicles demonstrate enhanced safety and curve-passing performance while reducing wheel tread/flange wear. Optimal wear minimization occurs when wheel profiles align with vehicle parameters. The work pioneers a wheel wear evolution analysis framework for inside axlebox vehicles, quantifying the impact of critical design parameters on wear reduction:

• Wheel wear of mountain metro vehicles with complex line conditions (Qi et al., 2025a).

Mountain metro vehicles experience accelerated wheel wear due to frequent traction/braking on complex slopes and curves, necessitating specialized analysis of their unique wear characteristics. Dynamic and wear modeling reveals ramp tracks increase maximum wheel wear depth by 13.2% versus flat tracks, while implementing variable-stiffness rotary arm nodes reduces wear depth by 10.79% compared to constant-stiffness designs. The study pioneers a wear suppression solution through optimized rotary arm stiffness, effectively mitigating wheel profile degradation under extreme mountain rail conditions:

• Mechanism of novel phenomenon of rail corrugation on small radius curves with rail joint in mountainous city metros (Cui et al., 2025).

This study systematically investigates a novel rail corrugation phenomenon on mountain metro curves using field-survey-based finite element modeling. Short-wavelength corrugation stems primarily from wheel-rail friction self-excited vibration, while long-wavelength corrugation originates mainly from feedback vibration induced by rail joint irregularities. The work advances fundamental understanding of vibration-induced corrugation mechanisms in extreme mountain metro environments by decoupling these dual-wavelength formation processes:

• Analysis of the wear performance of thin flange wheel for high speed trains (Wang et al., 2025).

This study investigates the wear evolution of thin-flange wheel profiles to analyze wheel-rail contact mechanics and sensitivity to rail deviations using a validated vehicle dynamics model. Thin-flange profiles reduce overall wheel wear but exhibit increased wear with larger flanges. The work clarifies thin-flange wheel wear evolution post-reprofiling, providing essential data for optimizing maintenance strategies and wheel lifespan extension in high-speed operations:

• Application of a non-Hertzian model to wheel/rail frictional contact and wheel surface damage analysis of heavy-haul locomotives subject to braking loads (Chen et al., 2025).

This study develops an advanced heavy-haul train-track dynamics model incorporating non-Hertzian contact algorithms to analyze wheel-rail frictional behavior and surface damage. Increasing braking effort expands slip regions and elevates shear stress, while low-adhesion conditions induce near-full-slip contact patches with reduced shear stress and fatigue indices. Wheel fatigue life correlates directly with surface damage severity, where fatigue indices rise with braking load but decrease under low adhesion due to dominant wear mechanisms, highlighting the need for enhanced damage prediction models validated by field data:

• Research on the wheel wear prediction of heavy-haul freight wagon based on the roller rig test and line test (Zhang and Qi, 2025).

This study enables condition-based maintenance for freight wagons by developing an Archard-theory wheel wear model integrating vehicle dynamics, interpolation iteration, and intelligent simulation. Roller-rig-calibrated predictions show ≤7% deviation in nominal rolling circle wear depth during line validation, establishing reliability for Chinese heavy-haul operations.

The section I of this special issue on “Recent progress in (nano)tribology in China” provides comprehensive studies on various topics such as bearing lubrication, gear drive, tribology of wheel rail and rail brake that play significant roles in the long service life and high operational reliability of core mechanical parts and traffic transportation. Collectively, these studies advance fundamental understanding of tribological mechanisms critical for extending component durability in China’s high-speed rail and precision manufacturing sectors.