Friction最新文献

Hydrogel is an ideal material for replacing natural articular cartilage. However, their inadequate mechanical properties, such as severe dynamic damage, restricted its application in the field of joint replacement. Herein, based on Schiff base bond (dialdehyde starch (DS) with acrylamide (AM)) and metal coordination bond (Fe³⁺ with DS), we designed a self-healing bio-lubricant hydrogel coating (DS/AM/Fe³⁺). Moreover, the nano-composite metal-organic framework (ZIF-8) was applied to the DS/AM/Fe³⁺ hydrogels to improve its mechanical properties. The 1000ppmZIF-8/DS/AM/Fe³⁺ hydrogel coatings show excellent tribological properties and corrosion resistance, with wear rate reduced by 32.94%, friction coefficient reduced to 0.104, corrosion inhibition efficiency up to 79.63%, and active antibacterial and biological activity. The designed hydrogel provides potential applications for artificial joint replacement.

Superelastic NiTi alloys produced through laser powder bed fusion (LPBF) hold great promise in advancing wear-resistant transmission devices for aerospace and related applications. However, limited research on their wear behavior and strategies for enhancing wear resistance raises concerns about their future application prospects. In this study, a straightforward yet highly effective pre-strain treatment method is introduced, resulting in a nearly twofold improvement in the wear resistance of LPBF-fabricated NiTi alloys. This method prunes microstructure characteristics, influences the martensitic transformation process that improves cyclic compression superelasticity and transforms the distribution characteristics of adhesion stress acting on the indenter during wear processes, thereby effectively enhancing wear resistance. Additionally, the present study proposes an analytical model that establishes a link between superelastic metal cyclic compression characteristics and wear behaviors, providing insight into the wear characteristics, especially for adhesive wear patterns of superelastic metals including LPBF-fabricated NiTi alloys through analysis of cyclic compression curve. This research contributes to the fundamental understanding of wear resistance mechanisms in superelastic engineering materials and opens avenues for further optimization in related applications.

Rubber is widely used as a crucial sealing material in aerospace, petrochemical, and automotive industries to prevent contaminants from entering enclosures and lubricants from leaking. However, severe wear and friction occur during sliding motion, which are major causes of seal failure and significantly impact the safety and service life of equipment. To enhance the wear resistance of rubber surfaces, diamond-like carbon (DLC) coatings have been extensively studied due to their low friction coefficient, high hardness, excellent wear resistance, and chemical inertness. The hardness, elasticity, and adhesion of the coating can be effectively controlled by adjusting deposition parameters. This allows the film to accommodate the deformation of the soft rubber substrate, preventing delamination while avoiding thermal degradation or damage to the rubber. Additionally, the chemical composition of carbon-based films, primarily consisting of carbon and hydrogen, exhibits good compatibility with rubber, ensuring strong interfacial adhesion.

In this paper, research progress on the tribological properties of carbon-based films for rubber surface modification over the past two decades is reviewed. In contrast to previous reviews that primarily focused on general applications and fundamental properties of DLC coatings, this work delves into the distinctive advantages of DLC coatings on rubber surfaces under various deposition conditions. It explores the underlying mechanisms for friction reduction and wear resistance enhancement, while also identifying critical research gaps and proposing future directions for the field.

Planetary gear journal bearings (PGJBs) are critical components of wind turbine gearboxes that significantly influence the reliability and cost-effectiveness of wind energy systems. Under harsh, low-speed, high-load, and high-torque conditions, PGJBs remain insufficiently optimized, necessitating precise performance simulations and enhancements. In this study, a comprehensive thermo-elastohydrodynamic mixed-lubrication model was developed by integrating the thermal effects, cavitation, asperity contact, and deformation. The model was validated through comparative analyses with existing approaches, revealing critical lubrication characteristics. Excessively thin oil films at the bearing edges induced severe asperity contact, posing substantial wear-induced failure risks. To address this, a running-in model coupled with wear and mixed lubrication analysis was established to investigate the edge modification of PGJBs. The results indicated that the optimized profile derived from the running-in model increases minimum oil film thickness by 3.97  under rated conditions while reducing the contact pressure from 8.98  to approximately 0.001 , with even more pronounced improvements under overload scenarios. The proposed modification geometry enhances the operational performance and reliability of the PGJB, thereby advancing the development of clean energy technologies.

Rapid dissipation of shear stress and frictional energy in the matrix of polymer-based self-lubricating composites can improve their friction-reduction and anti-wear performance. In this work, regenerated lignocellulose (RLC) with a flexible architecture was used to assist ball-milling to exfoliate bulk molybdenum disulfide (MoS₂) and introduce it into an epoxy (EP) resin matrix to improve the mechanical and tribological properties of the final products. The abundant functional groups (hydroxyl and aldehyde groups) in RLC undergo an additional reaction with the active hydrogen atoms or epoxy groups in the EP resin, improving the curing performance of the EP matrix and enhancing the flexibility and interfacial strength of the carbon fiber/epoxy (CF/EP) composites. Owing to the simultaneous introduction of rigid MoS₂ nanosheets and flexible plant-fiber constructs in the EP matrix, external stresses can be transferred from the polymer matrix to the reinforcement fibers more efficiently. The tensile strength and toughness of the final products increased by 42.71% and 53.38%, respectively, and the friction coefficient and wear rate decreased by 37.50% and 30.77%, respectively, over those of the CFs/EP@RLC composites. This approach of using RLC to assist in exfoliating MoS₂ nanosheets and building a “flexible & rigid” transition framework in an EP matrix provides a valuable reference for improving the interfacial strength and friction properties of polymer-based self-lubricating composites.

Low friction on snow has been attributed to the formation of a frictional meltwater layer for many years, yet experimental evidence for this mechanism has remained inconsistent. In a large-scale snow tribometer lab, we measured the snow surface temperature behind a sliding cross-country ski and a flat sliding sample with an infrared camera to study the meltwater film at realistic skiing conditions.

At speeds ranging from 5 to 25 m/s and an initial snow temperature of −3.5 °C, surface temperatures increased locally to as high as −0.09 °C. At 15 and 25 m/s, the temperature decay following a ski passage deviated notably from the expected exponential cooling behavior. Instead, the post-passage temperature profile exhibited two distinct phases: an initial slow decline, attributed to latent heat release during the freezing of meltwater, followed by a phase of exponential cooling. This two-phase behavior provides clear evidence for the presence of frictionally generated meltwater. Although the presence of meltwater was most clearly observed after repeated passes over the same track and only at the higher speed, its presence at lower speed or during initial runs cannot be ruled out. The infrared system monitored only the exposed snow surface and may have missed transient meltwater that refroze beneath the ski.

In seawater hydraulic pumps, the cross-contamination between oil and seawater is frequently observed, significantly influencing both the operational efficiency and the service life of the pumps. In this research, the tribological behavior of brass/steel pairs in hydraulic oil with artificial seawater (3.5 wt.% NaCl) intrusion was examined. The results revealed that the NaCl solution concentration in the emulsions has an essential influence on the lubrication state and wear mechanism of brass/steel pairs. As the viscosity of the emulsion increases, the lubrication state at the wear interface improves, which reduces the contact stress at the friction interface and reduces abrasive damage. Moreover, with the increase of NaCl solution concentration, the primary wear mechanism underwent two transitions: initially shifting from abrasive wear to a combination of adhesive and corrosion wear, ultimately evolving into corrosion wear. These findings are crucial for understanding the tribological behavior of brass/steel pairs in seawater-in-oil emulsions. This study provides a valuable experimental basis for improving the performance of the marine equipment.

The superficial zone of articular cartilage plays a vital role in maintaining low friction and wear within joints due to its excellent lubricating properties. While the tribological properties of cartilage with an intact superficial zone have been widely studied, it remains unclear how different degrees of superficial zone damage affect cartilage lubrication, friction, and wear. In this study, we conducted friction and wear experiments to assess changes in cartilage performance before and after damage, examining surface roughness and microstructure to understand lubrication and wear mechanisms. We also used finite element method (FEM) simulations to study the evolution of wear behavior in damaged cartilage. The research shows that as damage to the superficial zone of cartilage worsens, its lubricating performance continuously decreases, leading to more intense wear. The cartilage friction coefficient exhibited varying degrees of dependence on pressure and speed at different periods, suggesting that superficial zone damage might cause a shift in the lubrication state of the cartilage. Furthermore, based on the observed cartilage wear parameters and morphological features, we further confirmed that fatigue wear is the primary wear mode, and proposed a numerical model for predicting cartilage wear volume based on the degree of damage. This emphasizes the importance of protecting and restoring the superficial zone in cartilage repair and regeneration strategies.

Rolling contact fatigue (RCF) failures in critical components like precision gears and high-performance bearings, have become increasingly prominent under demanding conditions. Conventional lubricant additives struggle to simultaneously reduce friction, resist wear, and repair dynamic micropitting. To address this challenge, a composite material of ionic liquid-functionalized magnesium silicate hydroxide ([DDP][TOA]/MSH) was synthesized using hydrothermal synthesis and non-covalent modification. This composite exhibited remarkable dispersion stability and copper corrosion inhibition, as well as superior tribological properties including friction reduction, wear mitigation, and micropitting repair during rolling-sliding contact. Tribological evaluations revealed that 1.0 wt% [DDP][TOA]/MSH reduced friction coefficient by 17.2% and wear volume by 52.5%, demonstrating unprecedented load-bearing capacity and frequency adaptability. Notably, in rolling-sliding contact fatigue conditions, commercial gear oil exacerbated micro-pitting damage continuously, whereas the composite material could repair it, with a repair efficiency of 72.0%. Surface characterization reveals a three-stage mechanism for the dynamic repair of worn metal surfaces: (1) micro-asperities are removed through mechanical grinding, (2) micro-cracks are filled via tribochemical deposition of FeS/phosphate phases, and (3) a hybrid a-SiC/a-SiO_x repair layer is formed with improved mechanical strength, effectively preventing fatigue wear propagation. This work demonstrates the synergistic effect of ionic liquids and layered silicate additives on micropitting repair under rolling contact fatigue, expanding the application of MSH in the field of commercial lubricant additives.

Lubricants are essential in machining as they significantly affect workpiece surface quality. However, due to the diversity of lubricant types and the complexity of infiltration physics, there remains an urgent need to improve infiltration performance based on the underlying physical processes. This paper systematically reviews the infiltration mechanisms of lubricants under different machining conditions. First, the influence of lubricant morphological characteristics and physicochemical properties on infiltration behavior is analyzed at the microscale, clarifying the mechanisms governing different states, including liquid, gas, and multiphase flow. Second, the interaction between tool geometric boundary conditions and lubricant infiltration behavior is examined, providing an evaluation of infiltration performance at the workpiece surface. Finally, the microscopic mechanisms of lubricant behavior under the influence of typical energy fields are discussed, and the regulation effect of these fields on lubricant infiltration is revealed. This review offers a theoretical reference for advancing the understanding of lubricant infiltration mechanisms and improving infiltration performance in machining.