Friction最新文献

Among the mechanical stimuli that arise in the tactile interaction between finger and surface during the tactile exploration, stimulating the mechanoreceptors, Friction-Induced Vibrations (FIV) play a fundamental role for discriminating the surface textures. Although it is well known that vibrational tactile stimuli strongly depend on the characteristics of the explored textures, the correlation between the different FIV features (such as amplitude and spectral distribution) with the texture perception and discrimination is still an open field of research. A vibrotactile rendering device has been here used to replicate the FIV measured when exploring isotropic textures. A sensory campaign has been conducted on 10 participants to investigate their ability to discriminate real and rendered isotropic textures, while the reproduced FIV have been manipulated and altered to mislead tactile perception. By swapping the FIV amplitudes measured from real textures, it has been observed that the participants discriminated the samples consistently with the vibration amplitude. The campaign has allowed to correlate the FIV amplitude and their frequency distribution with the perceptual results of the discrimination campaigns on real and mimicked textures.

Self-lubricating fabric composites significantly enhance the tribological performance of joint bearings by minimizing friction and wear on both inner and outer rings, thereby substantially extending their operational lifespan. These characteristics make them excellent candidates for bearing liner materials. However, conventional PTFE/Nomex phenolic-based fabric composites exhibit limitations in high-temperature environments, necessitating the development of more thermally stable alternatives. To address this challenge, this study introduced a novel PBO/PTFE polyimide (PI)-based self-lubricating fabric composite and proposed a PBO/PTFE-PI@M50 tribo-pair system suitable for high-temperature working conditions, utilizing M50 bearing steel as the counterpart material. Compared to Nomex fiber-reinforced self-lubricating fabric composites, PBO/PTFE-40PI (fabric composites with resin mass fraction of 40%) demonstrated significantly superior high-strength and high-temperature tribological performance. Notably, even at 300℃, it maintained an elastic modulus of approximately 15 GPa and a tensile strength of around 335 MPa, while achieving a low friction coefficient of 0.023 and an impressively low wear rate of 0.83×10^-6mm³/(N·m). The superior properties of PBO/PTFE-PI@M50 tribo-pair system stemmed from the composite's exceptional heat resistance and mechanical stability at high temperatures. Under the combined effects of the 'thermal-mechanical-chemical' interactions, the fiber-reinforced composite material formed a dense, uniform, and strongly stable transfer film on the surface of the M50 steel ring. Detailed analysis revealed that the film's stability primarily arose from the viscoelastic transition of PI and PTFE under high temperature, coupled with their strong tribo-chemical reactions with the steel ring. Given its outstanding performance, the PBO/PTFE-PI@M50 tribo-pair system holds considerable promise for advanced engineering applications.

The poor wear performance and susceptibility to pitting corrosion of titanium alloys in practical applications have attracted increasing attention. Layered double hydroxides (LDH) coatings, with two-dimensional structure, have shown great potential in protecting metals from corrosion and wear. However, the dense oxide layer on titanium alloys has hindered the development of LDH on these materials. In this study, a ZnAl LDH coating was fabricated on the surface of TC4 alloy via an in situ growth method. Molybdic acid anions were subsequently incorporated into the LDH interlayer through an ion exchange process. Inspired by biomimetic principles, a UV-grafted PDMS-infused slippery surface was prepared based on the nanoporous structure of ZnAl LDH, resulting in a protective surface with excellent hydrophobicity, corrosion resistance, and wear resistance. The anti-corrosion performance of the surface was evaluated using Tafel polarization and electrochemical impedance spectroscopy (EIS). The results demonstrated excellent corrosion protection for the TC4 substrate, as indicated by a low corrosion current density of 2.34 × 10^-7 A/cm². Compared with the bare TC4 alloy, the modified surface exhibited improved improved wear performance, owing to the infused silicone oil and ZnAl LDH nanosheets. This work not only provides valuable insights into the controllable in situ fabrication of LDH coatings but also offers a new strategy for the broader application of TC4 alloys and further research in the field of metal protection.

Gearbox efficiency is essential for the range of new energy vehicles. Most of energy in gearbox is consumed on the load-independent factor, e.g., churning loss, which however, has not been deeply addressed. In this study, load-independent losses are inhibited by oleophobic treatment to the surfaces of a transmission component. A polytetrafluoroethylene (PTFE) coating is prepared by electroless chemical plating. The contact angle (CA) and surface morphology of the coated surfaces are tested to elucidate the loss inhibition mechanism on the oleophobic interface. A visualized test rig for measuring the churning oil flow is built with the function of temperature control at a range of -30℃-80℃. Moving Particle Semi-implicit (MPS) method is used to further investigate the mechanism of oleophobic surface regulation. The oil velocity and pressure distributions, the slip characteristics and flow field around the coated surface are investigated. An analytical flow model is established to demonstrate the flow structure and to quantify the relationship with oil properties and surface characteristics. The results showed that the CA increased from 7.8° to 31.2° when the surface is coated by PTFE. The average reduction of the churning torque test values ranged from 20% to 36% across a wide temperature range of -30℃ to 80℃, with a maximum of 50.7% at 40℃. Simulated slip lengths ranged from 2.9 μm to 16.0 μm at different rotational velocities. The coating reduced the oil velocity and pressure, as well as the viscous shear and differential pressure resistance on the surface of the rotating component. This study thus provides scientific support for the efficiency improvement of gearboxes used in complex engineering.

Friction phenomena are strongly affected by interfacial mechanical and tribochemical effects, which involve major factors such as loads, sliding rates, sliding times, humidity, temperatures, and oxide films. For practical applications at different vacuum levels, friction mechanisms (adhesive wear, abrasive wear, fatigue wear, corrosive wear, and micromotor wear) are highly important for the development of advanced materials with desirable tribological properties to promote vacuum tribology. In this review, in combination with the current understanding of friction‒wear interactions, the tribological phenomena caused by changes in the surfaces of friction pairs that are highly dependent on complex conditions in different vacuum environments are analyzed and summarized. Subsequently, protection strategies for different structural materials are summarized. Finally, this work provides an outlook for designing advanced and sustainable protective materials under different vacuum conditions.

Recent studies have indicated that tribochemical reaction layers form on metal-on-metal-bearing surfaces, which may play a significant role in the performance and longevity of artificial joints. The purpose of this study was to determine the role of friction in the formation of tribofilms, and an in situ atomic force microscopy single-asperity sliding setup was used to perform in situ microscopic friction experiments to control the contact area and load. Time-of-flight secondary ion mass spectrometry and Raman spectroscopy were also employed to investigate changes in the composition and structure of the proteins at different sliding cycles. The results revealed that the proteins first unfolded under shear and then underwent chain breakage, dehydrogenation, and desulfurization over time as friction progressed. Finally, the carbonaceous fragments did not show graphitization trends under only shear stress.

High-temperature solid lubricant coatings with decent lubrication performance are essential in critical processes of metal forming and aerospace. However, their preparation is formidably challenging due to the harsh working conditions. Here, we successfully developed a solid lubricant coating via a facile and eco-friendly approach by casting a homogeneous mixture of molybdenum disulfide (MoS₂) and hexagonal boron nitride (h-BN) as lubricants, silicate as the binder, and water as the solvent onto a titanium alloy substrate. This solid lubricant coating exhibited excellent and stable tribological properties with a very low coefficient of friction (COF) of 0.080 at 1,000 °C, yet in an open-air atmosphere. This superior lubrication behavior is attributed to the synergistic effect between the base lubricants h-BN and MoS₂, contributing to the formation of a coating for both lubrication and lubricant protection against oxidation at 1,000 °C in an open-air environment. This work largely extends the operation temperature range of the crucial lubricant MoS₂ in an open-air atmosphere and further sheds valuable light on the design of high-temperature solid lubricants via the synergistic effect between base lubricants.

Reducing the coefficient of friction is a critical method for improving the service life and enhancing the efficiency of artificial implants. Maintaining a robust low-friction effect is essential for optimal artificial implant performance. This work utilizes the mechanism of the interaction between the interfacial charge and microviscosity to design a composite coating for titanium alloys modified with halloysite nanotubes/poly(vinylphosphonic acid) (PVPA). Compared with that of the pure PVPA coating, the coefficient of friction of the composite coating-polytetrafluoroethylene (PTFE) system stabilized at a low-friction state of approximately 0.008, with a 13.40% improvement in the load-bearing capacity. This low-friction state is maintained over a wide range of speeds and for extended periods. Furthermore, the study reveals that the electrical property differences between the inner and outer walls of halloysite nanotubes induce specific aggregation of anions and cations. These ions increase the microviscosity around the tube wall by forming hydrogen bonds with water molecules and attracting water molecules to form hydronium cations, contributing to the low-friction mechanism. The halloysite nanotube/PVPA composite coatings also enhance the toughness of the coating in the body fluid environment by stabilizing the crosslinked core region against perturbations from multivalent cations. The results provide a new approach for achieving low-friction composite polymer coatings with improved frictional properties in biotribology.

Based on the ordinary state-based peridynamics (OSB PD) theory, a 2.5-dimensional (2.5D) PD model for rail crack propagation in railway turnouts was proposed. First, a two-dimensional (2D) model for rail crack propagation in railway turnouts was constructed, with two types of 2.5D additional constraints for crack opening and cross section proposed on the basis of the 2D model. The 2.5D PD model for rail crack propagation in railway turnouts could thus be established. A fatigue crack propagation experiment was subsequently carried out on the U71Mn turnout rail material. The bond fatigue failure condition of the turnout rail material was established on the basis of the experimental results. Finally, the accuracy of the structural deformation and bond fatigue failure conditions was verified. The simulation results for rail crack propagation were compared with field observations and then analyzed in detail. These results show that the proposed 2.5D PD model can be used to accurately simulate the characteristics and rules for rail crack propagation in railway turnouts.

Carbon dots (CDs) are widely recognized for their superior adsorption and film-forming capabilities on metallic surfaces, making them effective as liquid lubricant additives and corrosion inhibitors. However, their applications in solid lubricating and organic anti-corrosion coatings have been less reported. In this study, nitrogen-doped CDs (N-CDs) with a polymer-carbon core hybrid structure are synthesized via a facile aldol condensation of acetaldehyde and urea. The incorporation of these N-CDs as additives into waterborne epoxy (WEP) coatings enhances interfacial compatibility, resulting in remarkable improvements in lubricating performance and corrosion resistance. Compared to the pure WEP coating, the N-CDs based nano-composite coating (WEP(PDMS)@N-CDs) demonstrates a dramatic reduction in the coefficient of friction from 0.760 to 0.049, representing a 93.6% decrease. Additionally, the WEP(PDMS)@N-CDs coating exhibits exceptional corrosion resistance, as evidenced by a stable low-frequency impedance modulus of │z│_{0.01 Hz}=3.5×10⁷ Ω cm². These improvements are primarily attributed to the abundant polymer branched chains on the N-CDs surface, which effectively increase the cross-linking density of the WEP polymer. The resulting WEP(PDMS)@N-CDs coating not only facilitates dynamic repair during friction but also enhances the barrier effect of the coating, leading to significantly improved anti-wear and corrosion resistance.