Friction最新文献

While amorphous carbon-based films are recognized for their efficacy in mitigating fretting wear, owing to the fact that tribopairs demonstrate divergent tribological responses under different fretting states, it remains essential to explore their friction-mitigation mechanisms across distinct fretting regimes and elucidate the evolutionary patterns of these regimes. This effort is critical to gaining a thorough and systematic insights into the fretting characteristics of amorphous carbon-based films. The running conditions fretting map was constructed via friction force-displacement curves, and the evolutionary relationship between the two fretting regimes was explored. Additionally, the wear mechanisms and friction-mitigation mechanisms under these two regimes were systematically investigated via advanced characterization techniques, including FIB-TEM, SEM, Raman spectroscopy, and XPS. Results show that increasing normal load shifts fretting regime toward partial slip regime, leading to a decreased friction coefficient and increased wear volume, dissipated energy, and tangential stiffness. Increasing displacement amplitude drives the fretting regime to evolve toward the slip regime, resulting in increased friction coefficient, wear volume, and dissipated energy, along with decreased tangential stiffness. Notably, an amorphous-nanocrystalline composite structure, in which iron oxides are encapsulated by graphitized carbon film, forms on the surface of counterpart balls in the slip regime. This structure exerts a pivotal effect on mitigating the friction coefficient and fretting wear. Furthermore, this work advances the fundamental understanding of the mechanisms governing the tangential fretting wear of DLC films, and offers valuable design guidance and a robust theoretical basis for alleviating fretting damage.

Classical hydrodynamic lubrication simulation solves Reynolds equation to unveil the lubrication pressure and film thickness distributions, yet it overlooks the latent high-level representations buried beneath the lubrication data. While deep learning has illustrated that the mining of high-level representations helps to generate desired outputs from input prompts, the lubrication research, however, has not fully exploited generative deep learning in lubrication prediction and generation. Here, we propose to adopt a deconvolutional neural network to learn the latent representations in hydrodynamic lubrication data and directly generate 2D lubrication scenario from the given working condition without solving any governing equation. Compared to classical method, our approach can output the distribution of lubrication pressure and film thickness in less than 0.1 s on a personal computer and be extended to more complicated scenarios including cavitation.

Although coating protection mechanisms are well understood for individual corrosion or wear conditions, tribocorrosion presents a unique challenge where synergistic interactions between mechanical friction and electrochemical corrosion accelerate coating degradation. Here, polyaniline microcapsules containing linseed oil, 2-mercaptobenzothiazole, and rhodamine B were in-situ loaded onto MXene nanosheets, and subsequently incorporated as multifunctional fillers into an epoxy coating. The tribocorrosion behaviors and the relevant mechanism of as-prepared coatings were evaluated via experiment characterization and molecular dynamics simulation. During the tribocorrosion process, the epoxy coating with pH/mechanical dual-responsive characteristics demonstrated the highest and most stable open-circuit potential (-0.44 V, ∆_OCP < 0.09 V). Its coefficient of friction was the lowest (0.16), and the wear rate (1.8 × 10^-6 mm³/N·m) was reduced by two orders of magnitude compared to pure epoxy coating (3.68 × 10^-4 mm³/N·m). The Raman characterization of worn surface at different durations revealed that the signals of MXene and linseed oil at the friction interface gradually increased as the process progresses. The lubricating film composed of MXene and linseed oil progressively evolved from an initially fragmented and discontinuous state into a compact and well-organized composite network as the tribocorrosion duration increased. Furthermore, the intelligent tribocorrosion system possessed a 105% self-healing efficiency with significant fluorescence quenching, ultimately realizing a remarkably low tribocorrosion synergy coefficient of only 1.18. The combination of experimental analysis and molecular dynamics simulations revealed that the excellent tribocorrosion resistance originated from an active-passive protection mechanism constructed by the microcapsules@MXene network. The formation of a linseed oil/MXene-based lubricating film reduced interfacial friction, while the strong interfacial bonding improved resistance to mechanical deformation. This work designed an intelligent anti-tribocorrosion coating, expanding the strategy for protecting equipment surfaces in harsh environments.

Supramolecular gel holds great potential in engineering applications as lubricant. However, pure organic network of the gel limits their rheological and lubrication performance. Here, we report a nanoporous materials-functionalized supramolecular composite gel lubricant by incorporating polymer brush-grafted metal-organic frameworks (MOFs) nanoparticles (NPs) as nano additive. The composite gel was produced by encapsulating poly(lauryl methacrylate) (PLMA) polymer brushes functionalized UiO-67 (UiO-67@PLMA) NPs in 500 SN base oil of a 3D network formed by 12-hydroxystearic acid (12-HSA) through hydrogen bonding and van der Waals (vdW) interactions. The addition of UiO-67@PLMA NPs largely improved the thermal and rheological properties of the 12-HAS/500 SN gel, and the storage modulus and loss modulus increasing significantly. Tribological tests showed that incorporating 0.40 wt.% UiO-67@PLMA NPs into the composite gel reduced the coefficient of friction and wear volume by 45.68% and 86.85%, respectively. Furthermore, the UiO-67@PLMA gel demonstrated remarkable tribological performance under challenging conditions, such as 400 N, 65 Hz, and 160 °C. The outstanding lubrication performance of the supramolecular composite gel arises from shear-triggered release of base oil and nanoadditves, acting as nano ball-bearings and promoting protective film formation.

A timely trend in gear transmission involves the replacement of steel with polymers. Nevertheless, the absence of fundamental durability data for polymer gears impedes their reliable application during power transmission. The expensive and time-consuming gear fatigue experiments make it impossible to rely merely on experimental data. In this study, a strategy for contact fatigue life prediction of polymer gears via an experimental-simulated hybrid data-driven model is presented. The hybrid data are established with a certain mixture ratio of experimental and simulation data and are augmented by the conditional tabular generative adversarial network (CTAB-GAN) algorithm. This specific algorithm was combined with the extreme gradient boosting (XGBoost) algorithm to predict the contact fatigue life of gears made from different polymer materials, with the prediction accuracy controlled within a 3-fold scatter band. Moreover, an empirical predictive formula for contact fatigue life was developed. The hybrid data-driven model, which merges experimental and simulated data, allows for efficient estimation of fatigue life and material selection strategies, generating insight into the anti-fatigue design of polymer gears.

Understanding the tire‒road friction system is fundamental for evaluating the skid resistance of asphalt pavements. Literature analysis reveals that the trajectory of tire–road friction research aligns with the evolution of scientific research paradigms: experimental science, theoretical science, computational science, and data science. Research in this field can be categorized into three scales: the rubber‒pavement scale, the tire‒road scale, and the vehicle scale. Experimental observations have yielded numerous patterns and empirical models, which serve as the foundation of this research field. Although numerical measurement devices have been used for decades, the reproducibility and comparability of the results require further improvement. Tire‒road friction theory and simulations have been well developed across these three scales, but these scales remain largely independent and unconnected. With the advancement of sensing technology, texture features have been widely exploited and used as inputs for various machine learning models to estimate pavement skid resistance. However, these models are limited in their ability to integrate friction mechanisms, resulting in relatively low interpretability. In summary, the synergistic development of the four research paradigms can promote and advance the understanding and application of tire‒road friction mechanisms. This review concludes with a discussion of current challenges and future trends, drawing implications for further research in this field.

Rolling contact fatigue (RCF) damage is the critical damage form faced by rails, especially under rainy and humidity conditions. In order to deeply explore the mechanisms of RCF damage under such conditions, a novel wet-dry alternation testing method (D/W-A test) was proposed, and rail RCF damage evolution tests were conducted in this study. Detailed comparisons between the novel testing method and three widely used rail RCF methods were analyzed. The results show that under wet-dry alternating conditions, the crack growth rate and wear rate were initially low, with cracks predominantly located in the region near the rail surface. Thus, there was a significant competitive relationship between crack propagation and wear in this period. Then, with the increase in cycling number, RCF damage was gradually dominated by crack propagation, which extended deeper into the material along its deformation orientation. Meanwhile, the severe material spalling led to a rapid increase in wear rate. Through comparative analysis of the accuracy, repeatability, evaluability, rationality, and practicability of the four testing methods, it was found that the novel method proposed in this study had significant advantages in rationality and accuracy compared with traditional RCF testing methods, providing a more effective tool for systematic studies on RCF performance of rail materials.

Lubricants are widely employed in mechanical systems to reduce energy loss and the wear induced by friction. With increasing concern for environmental protection, the development of eco-friendly lubricants has become increasingly significant. Nanocellulose, a natural material derived from cellulose, attracts increasing research attention in the field of lubrication due to its renewable, non-toxic, and biodegradable properties. Focusing on this emerging research topic, this state-of-the-art review first analyzes the theoretical basis of applying nanocellulose as a thickening agent in eco-friendly lubricating formulations. The following presents an overview of research advances in cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), categorized by their applications as additives or thickeners in aqueous, oil, and grease lubricants. This study also highlights the challenges associated with eco-friendly lubricants based on nanocellulose and offers suggestions for future investigations in this field. It is hoped that this review will inform the research direction of eco-friendly lubricants and promote the development of nanocellulose materials for industrial lubrication applications.

Sustainable lubrication of biomedical hydrogels with high stability is important for their application in dry eye disease (DED) treatment but remains a challenge. We report a novel strategy to achieve sustainable superlubricity under ocular conditions on the basis of the degradation of a thermosensitive P-C_nPEG (polyethylene glycol (PEG)) hydrogel. First, by adjusting the composition and chemical structure of the P-C_nPEG complex, its aqueous solution undergoes an adaptive sol‒gel transition at 25.1 °C during heating, resulting in a gel state upon injection onto the ocular surface (35 °C). In addition, the P-C_nPEG hydrogel obtained at 35 °C also shows superior performance, such as shear resistance, high transmittance (> 80%), rapid swelling, self-healing, and Ca²⁺ responsiveness, making it suitable for ocular applications. In the tear environment of DED patients with high reactive oxygen species (ROS) content, the P-C_nPEG hydrogel degrades within 6 days through the breakage of crosslinking sites. The degradation solution of each day presents ultralow coefficients of friction (COFs) under ocular conditions through the hydration effect. Finally, the excellent biocompatibility of the hydrogel demonstrates its potential for ocular applications. This study systematically discusses the mechanism of sustainable degradation-induced superlubricity of P-C_nPEG hydrogels, introducing a novel and promising strategy for DED treatment.

The persistent economic and environmental challenges arising from friction-induced energy losses underscore the critical need for innovative lubrication technologies. Two-dimensional transition metal dichalcogenides (2D TMDs), characterized by their layered architecture and weak interlayer van der Waals (vdW) interactions, have emerged as promising nanolubricants due to their well-documented shear properties and ability to form low-friction tribofilms. However, practical applications of TMDs are hindered by inherent limitations, including insufficient load-bearing capacity and high sensitivity to environmental conditions. Accordingly, extensive research efforts have been directed toward the rational design and structural modification of TMD-based lubricants. This review outlines recent advances in TMD-based tribological systems, beginning with their structural characteristics and synthesis routes, followed by an in-depth discussion of lubrication mechanisms and key performance-influencing factors. This paper explores modulation strategies for TMD-based lubricants, from conventional methods to emerging approaches, along with their applications across diverse environments. Finally, the review identifies prevailing challenges and suggests promising research directions to guide the development of next-generation high-performance TMD-based lubricants.