Tribology Letters最新文献

A novel oil-soluble ionic liquid (ILs), benzotriazole-functionalized quaternary phosphonium salt (BTAP₈₈₈DOSS), has been synthesized. This proposed oil formulation incorporates the BTAP₈₈₈DOSS additive into poly-α-olefin (PAO10) oil. The tribological, corrosion, and thermal properties were investigated. The wear patterns and tribofilm formation mechanisms for the formulated lubricant are discussed using advanced technologies (SEM, XPS, and TOF–SIMS). Moreover, the molecular models of cations and anions were generated and optimized using density functional theory (DFT). Notably, the oil prepared with 0.5 wt% BTAP₈₈₈DOSS additive exhibited superior lubrication performance, minimizing the friction coefficient by 34–36% and disc wear volume by 80–85% compared with the baseline lubricant. This reinforcement is attributed to the additive’s ability to form a lubricating layer with low shear forces, as demonstrated by the simulation results. Ultimately, our results will support the advancement of eco-friendly ILs as multifunctional oil additives to reduce power losses caused by friction in various mechanical systems.

Contact between elastic rough surfaces is one of the fundamental problems in tribology. We study with a Boundary Element Method the influence of anisotropy of roughness on the real contact area and on load-separation for both a classical gaussian height distribution and a weibull one, in the common case of power law PSD. We find that anisotropy affects contact area and load-separation similarly for gaussian or non-gaussian surfaces, and therefore the effect can be captured by a single parameter which we extract from Persson’s theory. We further use the results to extend BAM theory of long-range adhesion to gaussian and non-gaussian (weibull) surfaces both isotropic or anisotropic. For the real contact area, results for weibull surfaces are known in the literature.

Sensory evaluation techniques have been used to investigate rich tactile sensations experienced by humans. Sensory evaluations typically incorporate quantitative measurement methods that rely on the subjective judgment of participants to assess tactile sensations. Although the relation between friction coefficient, skin surface and fingertip, contact surface, and the effect on tactile perception for various materials and textures is a critical topic of research, such underlying mechanisms are yet to be understood comprehensively. In this study, the frictional properties and tactile sensations of the human index finger on textured glass surfaces were investigated during swipe motions. Friction tests were conducted using a six-axis force sensor to measure the coefficient of friction (CoF) across textured and flat glass surfaces. Surface texturing reduced the CoF by decreasing the real contact area. Furthermore, the sliding direction of the finger influenced the CoF. Using the semantic differential method, sensory evaluations revealed higher tactile scores for the textured glass surfaces regarding smoothness, lightness, and silkiness than those for flat surfaces. The findings demonstrated a strong correlation between frictional behaviour and tactile sensations, providing insights for designing textured glass in touch-based applications.

During the turning operation with cemented carbide tools, plastic deformation of the workpiece, along with intense friction between the tool and the chip, inevitably induces tool wear. The rational implementation of surface texture technology on the tool surface can enhance the machining quality of the workpiece surface and significantly extend the tool’s service life. In this study, laser processing technology was employed to fabricate single textures and multi-scale composite textures featuring circular, elliptical, and V-shaped patterns on the surface of YT-15 cemented carbide. Friction and wear experiments were conducted to investigate the effects of various shapes, arrangements, and combinations on the friction properties of textured surfaces under dry friction and oil lubrication conditions. The results indicate that compared to the non-textured surface, the textured surface exhibits a lower and more stable friction coefficient. Additionally, surface texturing mitigates wear by trapping materials such as wear debris. The circular texture with a staggered arrangement among single textures demonstrates the most effective friction-reducing performance. Furthermore, multi-scale composite textures, through the reasonable combination of different texture shapes, enhance the synergistic effect, leading to improved friction reduction and lubrication performance.

The pressing need to develop reliable and cost-effective Environmentally Acceptable Lubricants (EALs) is a challenge to the entire lubrication field in academia and industry. In this work, we propose blending low-viscosity polyalpholefins (PAOs) and synthetic esters as base fluids, as a strategy to formulate cost-effective EALs. Pentaerythritol polyol ester (PEPE) and 2-ethylhexyl palmitate (2-EHP) are the synthetic esters chosen. Tributyl(ethyl)phosphonium diethyl phosphate (PEP) ionic liquid, dialkyl dithiophosphate (DDP), and alkoxylated long chain ether phosphate (AEP) have been chosen as lubricant additives. Two reference lubricant additives were also tested for comparison, i.e., hexadecanoic acid (palmitic acid, C16) as friction modifier, and primary zinc dialkyl dithiophosphate (ZDDP) as anti-wear additive. Stainless steel AISI 316L disks were tested against alumina balls using a ball-on-disk tribometer to evaluate the performance of the formulated lubricants. All additives improved the performance of plain PAO, while in the case of esters competition with the additives was observed due to their high polarity. The blends performed better than the lubricants with a single base fluid. ToF–SIMS studies showed richer sulfur and phosphorus-based tribofilms for those samples lubricated with blends than with single base fluids. The blends also helped improving the solubility of the ionic additives with respect to plain PAO. Overall, the results confirmed the better performance of blends as a strategy for formulating cost-effective EALs and for improving the solubility of ionic liquids in non-polar base fluids.

Traditional methods for monitoring lubrication and wear typically rely on indirect indicators such as temperature changes, vibration, or lubricant contamination. However, these approaches have limitations in that they are unable to provide real-time, direct insights into the micro-scale interactions occurring between frictional interfaces. This paper aims to explore the mechanisms and characteristics of acoustic emission (AE) signals generated by lubricants, particularly greases, in hydrodynamic lubrication (HL) regime, thereby enabling early detection of surface wear and degradation in mechanical systems. Based on the fundamental theory of elastic deformation strain energy release from micro-asperities, a model for AE signals of lubricants in HL regime was established. Experimental studies using a rheometer platform were conducted on lubricants to compare their flow properties and related friction signals. The results indicate that both lubricating greases and oils share similar characteristics, where shear rate and lubricant viscosity are significant factors affecting AE signals. These findings provide essential references for monitoring the lubrication state of friction pairs and the health condition of lubricants, especially in detecting early surface wear.

As direct byproducts of frictional interactions between contacting surfaces, oil wear particles exhibit varied physical properties that provide essential insights into the underlying wear mechanisms and degree of wear severity. Current online optical microfluidic monitoring sensors demonstrate inadequate imaging quality, especially in ferrograph sensors, where particles frequently form chains, hindering real-time monitoring. To address this challenge, an integrated optimization approach has been developed, emphasizing two key aspects: the structural redesign of the online optical sensor and the enhancement of wear particles imaging. We develop a high-precision optical monitoring sensor, which facilitates both conventional particle counting and size detection, as well as the extraction of high-definition texture images of particles in real time. Initially, as the scattering accounts for the majority of the total light energy attenuated, we compute the light intensity scattered by particles in oil. The influence of particle size, scattering angle, particle type, and incident light wavelength on scattering intensity is analyzed, establishing the basis for improving the image quality of wear particles. Then, to alleviate the substantial image degradation induced by oil, characterized by diminished contrast, color attenuation, blurring, and indistinct features, we propose a hybrid image enhancement method MRCAHE, which integrates Multi-scale Retinex with Color Restoration (MSRCR) and Contrast-Limited Adaptive Histogram Equalization (CLAHE). The sensor’s performance is ultimately validated on a high-speed, heavy-load gear fault simulation test bench. Experimental results demonstrate that the sensor consistently collects distinct images of wear particles, and the MRCAHE enhancement method significantly improves deblurring, texture extraction, color restoration, and sharpness. This portable oil wear particle monitoring sensor provides a robust technical foundation for condition monitoring, fault diagnosis, and intelligent maintenance of rotating machinery.

Fretting-wear-induced failure of contacting surfaces threatens the safety of assemblies, which means the wear behavior on both contacting surfaces should be fully considered. In this paper, a finite element simulation method was proposed to reveal fretting wear behavior, which simultaneously considered double-side wear of both contacting surfaces. The user subroutine UMESHMOTION based on Archard’s equation was used to describe the fretting wear behavior. The finite element model was tested and validated using results obtained from cylinder-on-flat tangential fretting wear tests conducted under varying fretting amplitudes. The topography and cross-sectional profile characteristics of fretting scar were compared. The dynamic wear behaviors and fretting regime were analyzed from the tangential force–displacement curves and the ratio of shear stress to contact pressure. Besides, the variation of wear volume with fretting cycles was also analyzed. The results obtained from model considering double-side wear shown a better agreement with the experimental results compared to those from model considering single-side wear.

The friction anisotropy arising from the unique deformation mechanism of insect setae holds significant potential for object transport applications. This study presents a biomimetic setal array, which is capable of achieving controllable bidirectional transport of objects under vibration excitation. Experimental results reveal a complex phenomenon: as the vibration frequency increases, the transport velocity of the object initially increases, subsequently decreases and reverses direction, and ultimately undergoes another reversal of transporting direction at a significantly higher velocity. The effect of friction anisotropy on this phenomenon is thoroughly investigated through analysis of the transport process and the friction behavior of insect setae in nature. Additionally, an analytical model is developed, revealing the underlying mechanism of transport and providing a guidance for transport regulation. Following a detailed discussion on the effect of object mass on this novel transport strategy, this biomimetic setal array is demonstrated to enable controllable sorting and intelligent transport of objects.

Graphical Abstract

Persson et al. in (Rubber wear: experiment and theory. arXiv:2411.07332, 2024) and Xu and Persson in (Sliding wear: role of plasticity. arXiv: abs/2412.13129, 2024) have recently proposed an interesting theory of wear which is based on particle formation due to fatigue crack growth at different scales of roughness. The theory perhaps is the first one to take into account of a full characterization of the roughness, and obtains semi-quantitative prediction of wear coefficients for rubber and PMMA, but in the original form, many details of actual roughness features and the material properties do not permit to elucidate general simple trends. We attempt to make general comments to show the main effects of the various macroscopic parameters in the theory, with qualitative comparisons having in mind the case of metals wear for which we found experimental trends, at least for the dependence on friction coefficient. It is found that wear rate in the elastic theory very strongly depends on friction coefficient and on rms roughness, showing even a regime of wearless behaviour below friction coefficient of about 0.2—which may indicate transition to other mechanisms, like adhesive wear. It is shown that an elasto-plastic theory probably mitigates these effects, as a fully plastic one depends only quadratically on friction coefficient, and has no dependence at all on any feature of roughness. However, the present oversimplistic perfectly plastic model truncating the elastic prediction, and the use of a crack propagation theory which is irrespective of large plastic flow can make the theory more hardly quantitative in general. In addition, hardness at asperity scale may increase due to size effect, so the elastic model may be the most appropriate choice in many cases. Along with many other complex effects known in wear (even limiting attention to fatigue wear), it remains, therefore, to be investigated how generally the Persson theory can result in quantitative predictions.