Tribology Letters最新文献

The tribo-dynamic behaviors of third-body colloidal particles (CPs) at the soft–hard contact interface significantly impact the substrate surface performance. To explore the differences of the stick-slide and roll-slide tribo-dynamic behaviors of CPs, the tribological behaviors of fixed and free CPs on hydrophilic silicon substrates were investigated using the colloid probe and nano-manipulation technology in atomic force microscopy, respectively. In contrast to the velocity-enhanced static friction commonly observed in fixed CPs, the static friction of free CPs exhibits a logarithmic decrease with increasing velocity. This phenomenon can be attributed to the transition from a “sliding-dominated” to a “rolling-dominated” driving state of the CPs as velocity increases. The findings enhance the understanding of tribo-dynamic behaviors of CPs at the nanoscale and provide a foundation for the deliberate design and optimization of CP-based applications in chemical mechanical polishing (CMP) and post-CMP cleaning technologies.

In this paper, MoS₂–ZrN composite coatings with a Chromium interlayer were fabricated using magnetron sputtering technique. The structure and properties of the MoS₂–ZrN composite coatings with different ZrN contents were systematically investigated. It was observed that both hardness and elastic modulus improved with increasing ZrN content, reaching peak values of 6.60 GPa and 109.95 GPa, respectively, at 30% ZrN. Tribological performance was assessed using steel balls with varying surface roughness, where the lowest coefficient of friction of 0.09 was recorded when the coating was paired with a smoother counterface. Abrasive wear was identified as the dominant wear mechanism. Additionally, a contact mechanics model was developed to describe the interaction between a rough spherical indenter and the coating surface. This model enabled analysis of how surface roughness and coating mechanical properties jointly affect macroscopic contact parameters, such as real and nominal pressure distributions and contact radius. A good qualitative agreement was found between the experimental results and theoretical predictions, confirming the model's validity.

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This study examined the impact of sliding speed on the wear process of brass by integrating thermodynamic principles with molecular dynamics simulation. The simulation findings indicate that as the sliding speed increases, the strain rate of the workpiece rises while the tensile stress decreases and the compressive stress increases. Consequently, the tangential force remains constant regardless of sliding speed, whereas the normal force increases with higher speeds. Additionally, the temperature of the workpiece rises with increasing sliding speed, leading to a more significant thermal softening effect. Due to the interplay between strain rate hardening and thermal softening, the wear of the workpiece initially decreases and then increases as the sliding speed continues to rise. The specific wear rate, specific wear amount, and degradation coefficient all decrease with increasing sliding speed, suggesting that cutting becomes more challenging at higher speeds. Therefore, careful consideration is necessary when selecting the cutting speed to achieve efficient machining. This study serves as a valuable reference for the machining of metal materials.

Three different reinforcing fillers were selected for winter tire tread rubber. After improving the testing method using the LAT100 testing machine, tests were conducted on the effect of rubber surface roughness on ice grip and wet grip performance, as well as research on the effect of load and speed on the rubber-ice friction coefficient at different temperatures. The results showed that with the increase of the macroscopic roughness of the rubber surface, the frictional force between the rubber and the ice surface decreased, the frictional force between the rubber and the wet road surface increased; With the increase of load and speed, the friction coefficient of rubber on the ice surface decreases, and the change is more obvious on the – 15 ℃ ice surface compared to the – 5 ℃ ice surface, and the friction coefficient on the – 15 ℃ dry ice surface is greater than that on the – 5 ℃ wet ice surface; In order to better predict the results of the real vehicle test, in the LAT ice friction test, the load was selected from 75 to 100N, the speed was selected from 0.6 km/h, and the run-in conditions specifically for winter tread rubber were determined. This provided theoretical support for improving the accuracy of indoor predictions of real vehicle ice grip test results and enriched the research on the rubber-ice friction mechanism.

Using a custom-built microtribometer, the stick–slip behavior of a single elastic string in Hertz contact with a cylindrical glass lens was observed in situ, collecting dynamic contact area and friction force data during the adhesion phase. The results indicate that stick–slip occurs periodically due to repeated contact and elastic deformation. The friction pair was modeled for both translational and rotational movement, quantifying energy changes during the adhesion phase. It was inferred that slip occurs due to instability when the contact area reaches its maximum, which is possibly determined by a combination of factors including surface roughness, rubber deformation, and cylindrical rotation. These findings provide new insight into the macroscopic frictional properties of fiber-structured surfaces.

It was shown in a previous paper that friction in highly loaded non-conforming contacts correlated with the formation of a glassy state of the lubricant, for the only lubricant studied (benzyl benzoate). The aim of the present paper is to extend this conclusion to other types of fluid: a model fluid from the literature (glycerol) and a well-known lubricant (squalane). The characterization of these fluids in the bulk by Brillouin spectroscopy shows a similar evolution of their behavior with pressure and makes it possible to identify their glass transition pressure. Furthermore, comparison of this characterization with friction data for squalane validates the correlation previously established for benzyl benzoate. In a second part, the structural relaxation time of benzyl benzoate is derived from Brillouin spectra to probe the influence of hydrostatic pressure on fluid dynamics. This parameter, superimposed on the previous friction measurements, shows that the dynamics of the molecules is highly reduced at high pressures, which explains the macroscopically solid-like behavior of the lubricant. This result suggests that the relaxation time is an essential parameter for the correct modeling of highly loaded lubricated contacts.

Accurately predicting the interfacial gap and stiffness between rough solids is essential for understanding contact behavior in tribological, sealing, and thermal systems. This work proposes a novel model that accurately captures the evolution of mean interfacial gap and stiffness from initial finite contacts to accumulated statistical response. The obtained load-gap relationship is validated against boundary element simulations of elastic rough contact, showing excellent agreement across a wide range of normal loads. Unlike conventional models, the proposed approach captures finite-size effects at light loads, yielding a sublinear power-law scaling of stiffness with load, and transitions seamlessly to the linear regime at higher loads. The model provides a simple, parameter-free tool for quantitative analysis of rough surface contacts.

The Stribeck curve forms the backbone of our understanding of frictional behavior. It has traditionally been associated with lubricated journal bearings and later on with EHL lubricated rough contacts. Still later, this behavior appeared to manifest itself also in dry rough contacts. While in this latter case, the Stribeck behavior has been simulated theoretically, in the lubricated case, the models have been confined to a few restricted cases. Here, I show that the Stribeck behavior emanates directly from the most basic/generic type of hydrodynamic bearing; namely the Rayleigh-step bearing, without resort to the EHL/mixed-lubrication assumption. This bearing type can be taken in the macro sense, as a self-standing bearing; or in the micro sense, as an elemental roughness feature, which can be aggregated to understand rough lubricated sliding contacts. Furthermore, this simple model of a step bearing allows us to establish the dynamic behavior of the Stribeck curve; in particular, the friction lag phenomenon and the rate-state law. Main results show that the normalized CoF is a universal function of the normalized Sommerfeld number, reduced by the aspect ratio of the bearing, and that the dynamic Stribeck effect cannot be decomposed into time-dependent Stribect effect combined with time-independent (instantaneous) viscous effect.

Accurate in situ wear measurements of polymer-polymer wear combinations using techniques like ball-on-prism tribometers pose a significant challenge. Simultaneous wear of both counterparts complicates obtaining continuous wear data without interrupting experiments to perform slow, intermediate measurements. Building on Harden et al. (Tribol Lett 71(3):1–14, 2023), this work develops an accurate, low-noise measurement approach to enable reliable in situ measurements. The method employs a laser line scanner and a precision linear axis for accurate positioning within the test stand, complemented by an algorithm for debris detection and data smoothing to minimize noise from wear residue. This approach achieves up to a 98% reduction in peak-to-peak noise levels, enabling high-resolution measurements and supporting parallel experiments with various polymer-polymer wear combinations. Unlike existing non-in situ methods, this technique offers efficient and accurate in situ wear measurements, advancing tribological research and polymer material testing.

This study investigates the influence of the gas atmosphere on friction and wear characteristics of transition metal dichalcogenides synthesized via an in-operando method. MoSe₂ and WSe₂ layers are formed through tribochemical reactions between molybdenum or tungsten coatings and nanosized selenium powder. Their tribological behavior is evaluated under nitrogen and ambient air conditions using a ball-on-disc tribometer within a custom-built inert gas chamber. The results indicate that both MoSe₂ and WSe₂ layers exhibit consistently low friction coefficients (below 0.1) across different atmospheric conditions, with slightly lower friction coefficient observed in air compared to nitrogen. However, the durability of the transition metal dichalcogenide layers is significantly extended under nitrogen, particularly for MoSe₂, which demonstrates superior durability compared to WSe₂ in nitrogen. This disparity becomes less pronounced under ambient air conditions. The enhanced wear resistance of MoSe₂ in nitrogen may be attributed to easier in-operando formation, as confirmed by transmission electron microscopy analysis, which reveals a thicker and more well-defined layered tribofilm. These findings suggest that in-operando synthesized MoSe₂ and WSe₂ layers serve as effective solid lubricants, offering promising potential for a broader range of solid lubrication applications.

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