Tribology Letters最新文献

Friction-induced stick–slip vibrations (FISSV) commonly occur in mechanical systems, posing risks to equipment like high-speed train brakes, causing instability, and threatening safety. To address this, we propose using textured surfaces of friction pairs to suppress FISSV. Through simulations on a friction testing machine, we explored the impact of surface texturing on FISSV. The results indicate that surface texturing significantly influences interfacial wear debris flow and contact characteristics, thereby regulating FISSV behavior. Textured surfaces better collect and store debris, reducing its involvement in friction and forming larger contact platform of metal substrate. This increases interface contact stiffness, preventing FISSV. A combination of macro-grooves and microtextures was particularly effective. Thus, appropriate surface texturing design can enhance system stability and reliability by effectively suppressing FISSV.

Macrotextured silicone breast implants are associated with several complications, ranging from seromas and hematomas to the formation of a rare type of lymphoma, known as breast implant-associated anaplastic large cell lymphoma (BIA-ALCL). The presence of silicone wear debris has been detected within the peri-implant region and fibrotic capsule and histological analyses reveal inflammatory cells surrounding debris particles. However, it is unclear how these debris particles are generated and released from macrotextured implant surfaces, and whether wear debris generation is related to implant stiffness. In this study, we created an accelerated implant aging model to investigate the formation of silicone wear debris produced from self-mated (“shell-shell”) tribological interactions. We created implant-like silicone elastomers from polydimethylsiloxane (PDMS) using Sylgard 184 base:curing agent (10:1, 12:1, and 16:1) and quantified their mechanical properties (E* = 1141 ± 472, 336 ± 20, and 167 ± 53 kPa, respectively). We created macrotextured PDMS samples using the lost-salt technique and compared their self-mated friction coefficient (< µ > = 4.8 ± 3.2, 4.9 ± 1.8, and 6.0 ± 2.3, respectively) and frictional shear stress (τ = 3.1 ± 1.3, 3.2 ± 1.7, and 2.4 ± 1.4 MPa, respectively) to those of the recalled Allergan Biocell macrotextured implant shell (E* = 299 ± 8 kPa, < µ > = 2.2, and τ = 0.8 ± 0.1). Friction coefficient and frictional shear stress were largely insensitive to variations in elastic modulus for macrotextured PDMS samples and recalled implant shells. The stiffest 10:1 PDMS macrotextured sample and the recalled implant shell both generated similar area fractions of silicone wear debris. However, the recalled implant shell released far more particles (> 10×), mainly within the range of 5 to 20 µm² in area. Bone marrow-derived macrophages (BMDMs) were treated with several concentrations of tribologically generated silicone wear debris. We observed widespread phagocytosis of wear debris particles and increasing secretion of inflammatory cytokines with increasing concentration of wear debris particles. Our investigation highlights the importance of avoiding macrotextured surfaces and mitigating wear debris generation from silicone implants to reduce chronic inflammation.

Investigating the relationship between the frictional performance and dynamic behavior of fullerenes under extreme conditions is crucial for the better development of fullerene-based lubricating materials. In this study, molecular dynamics simulations were used to investigate the boundary lubrication behavior of fullerenes confined between two carburized iron surfaces. Our findings demonstrate that the interlayer friction coefficient decreases exponentially with increasing applied load, increases with higher shear rates, and decreases with rising temperatures. The exponential decrease allows fullerenes to achieve ultra-low friction under high pressure, primarily due to their strong resistance to compressive deformation and the “ball-bearing effect”. Furthermore, as the applied pressure increases, the confinement becomes more pronounced, further accelerating the transition from sliding to rolling friction, thereby enhancing lubrication performance. This study deepens the understanding of the boundary lubrication mechanisms of fullerenes at carburized iron interfaces, offering valuable guidance for their application in advanced lubrication systems under extreme working conditions.

Graphical Abstract

Frictional vibration often occurs in sliding process, or called stick–slip phenomenon, which is easier to exist in the range of Stribeck curve where friction and velocity have negative gradient characteristics. The kinetic friction force can be approximately linearly increased with velocity in the sliding stage of solid lubrication. Solid lubrication avoids the negative gradient friction range under dry friction and has a good inhibiting effect on stick–slip phenomenon. In this study, by applying ultrasonic vibration to metal/metal sliding friction pairs, the friction reduction and stick–slip inhibition effects of ultrasonic vibration on sliding friction pairs moving at low velocities (0.05–1.0 mm/s) under solid lubrication was studied. In solid lubrication, the reduction of ultrasonic vibration on static friction force reached 60%, and the maximum reduction in kinetic friction force was 83%, which decreases with the increase of sliding velocity. A pre-displacement model of ultrasonic vibration friction reduction is proposed which is in good agreement with the experimental data. Under the condition of solid lubrication, when the driving velocity is 0.05 and 0.1 mm/s, the slider has a low displacement fluctuation, and the application of ultrasonic vibration has little change in the displacement fluctuation. When the velocity continues to increase, the displacement fluctuation increases rapidly, and ultrasonic vibration can effectively inhibit the displacement fluctuation with the rapid increase of velocity. The velocity range of high-precision motion under solid lubrication after applying ultrasonic vibration is increased.

Recent studies suggest that the joints of beetles and other insects comprise micro-structured surfaces in combination with lubricants. Here, we utilize friction force microscopy (FFM) to analyse the tribological properties of the femoro-tibial leg joints by the example of Coelorrhina aurata (metallic green flower beetle) and Otiorhynchus sulcatus (black vine weevil). To preserve the original state of the lubricant as well as the microstructures, the FFM measurements were conducted in silicone oil, which satisfies our requirements of transparency, customizable viscosity, absent health risks and lower density compared to the expected density of the lubricant. Microscopic friction was measured on fresh and air-dried samples to stress the change of the lubricant properties over time. Despite the similarity of the two beetle joints, the FFM measurements reveal different frictional properties of the respective lubricants.

In sediment environments, water-lubricated rubber bearings are inevitably subjected to particle abrasion, especially during frictional vibration. However, the invasion-migration-wear mechanism of hard particles under frictional vibration excitation remains unclear. This study analyzes the contact strain at the friction interface and the dynamic response of the friction system by constructing a visualized friction pair at the interface and employing digital image processing technology. The results reveal that the friction-induced vibration in the water-lubricated rubber bearing-rotor system primarily manifests as chatter and squeal. Chatter represents a more intense stick–slip behavior, during which larger sediment particles are allowed to invade. These invading particles tend to sink deeper into the friction pair during the stick phase and migrate with the water flow during the slip phase, leading to combined wear in the form of scratches and pits. During squeal, the amplitude of stick–slip behavior is relatively small, allowing only small sediment particles to invade, which result in scratches on the bearing surface. When the system does not experience friction vibration, sediment particles are unlikely to enter the friction interface, even in a sediment-rich environment, and therefore, no significant wear occurs.

Graphical abstract

This study investigates a method combining a porous bush and herringbone groove to extend the effective working speed range of conventional fluid film journal bearings for machine tool spindles. A novel bearing, termed the porous herringbone groove journal bearing (PHGJB), is proposed. However, existing literature lacks a model that accurately describes the lubrication behavior of the PHGJB. To address this gap, this paper presents a lubrication model for the PHGJB that incorporates velocity slip, angular misalignment, and turbulence effects. This model employs the boundary-fitted coordinate system and finite control volume methods to address the challenges posed by the herringbone grooves and three-dimensional flow within the porous bush. The performances of the PHGJB, a typical hydrodynamic herringbone groove journal bearing (HGJB), and a hydrostatic porous plain journal bearing (PPJB) are compared. Differences between the calculated results from the one- and three-dimensional flow models for the flow within the porous bush are also analyzed. Results show that the PHGJB significantly improves stiffness at low speeds, while enhancing stability and controlling temperature rise at high speeds compared to the HGJB and PPJB. Consequently, it offers a broader operating speed range. The proposed model offers an effective tool for structural design and performance analysis of PHGJBs.

The Weierstrass-Mandelbrot (W-M) function method is commonly used in surface reconstruction, which integrates parameters such as fractal dimension (D) and fractal roughness (G). The parameter G is typically calculated using the power spectral density (PSD) method. This study identifies deviations in the G calculations. These deviations arise from simplifications made during the derivation process when applying the PSD method. To address this issue, this paper introduces a novel approach based on statistical methods to define the scale interval. This approach involves calculating the G post-alignment of the generated target profile within this interval, followed by surface generation using the W-M function. A comparison between the scale interval method (SI) and the PSD method reveals that the SI method demonstrates better accuracy. A comparative analysis between the generated and actual surfaces substantiates the accuracy of the G calculations using the SI method. This method provides a theoretical foundation for subsequent fractal surface measurements, reconstructions, contact calculations, and dynamic characterizations.

The development of green and environmentally friendly lubricant additives is crucial in the field of friction. A green modifier, Cardanol polyoxyethylene ether xanthate (CPEOCS₂K), was synthesized from natural cashew nut shells derived from Cardanol. Cu nanoparticles were prepared using a simple one-step reduction method, which involved modifying metallic Cu with CPEOCS₂K. The long chains of the modifier on the surface of the nanocore interconnected to form a nano-network, and the resulting Cu nanochains exhibited excellent lubrication performance when applied to a water-ethylene glycol (EG) system as a lubricant additive. This encapsulated nanoparticle structure not only enhances the dispersion stability of the nanoparticles but also generates a chemically reactive film that adsorbs onto the wear surface during friction, thereby improving the lubrication effectiveness of the water-based lubricant. The use of natural organic compounds to synthesize modifiers enhances the environmental friendliness of metal nanoparticles as lubricant additives, and the outstanding lubricating performance demonstrates the potential of green lubrication technology.

Graphical Abstract

Physical vapor deposited (PVD) molybdenum disulfide (MoS₂) solid lubricant coatings are an exemplar material system for machine learning methods due to small changes in process variables often causing large variations in microstructure and mechanical/tribological properties. In this work, a gradient boosted regression tree machine learning method is applied to an existing experimental data set containing process, microstructure, and property information to create deeper insights into the process-structure–property relationships for molybdenum disulfide (MoS₂) solid lubricant coatings. The optimized and cross-validated models show good predictive capabilities for density, reduced modulus, hardness, wear rate, and initial coefficients of friction. The contribution of individual deposition variables (i.e., argon pressure, deposition power, target conditioning) on coating properties is highlighted through feature importance. The process-property relationships established herein show linear and non-linear relationships and highlight the influence of uncontrolled deposition variables (i.e., target conditioning) on the tribological performance.