Tribology Letters最新文献

Machining-induced textures featuring plowing-generated grooves show wavelength variations dependent on cutting precision and feed rates, which may influence tribological performance. In this study, a mixed elastohydrodynamic (EHL) model was developed through the systematic integration of critical tribological parameters, including contact geometry, elastic deformation, lubricant properties, and thermal transport properties. The roughness is simplified using a sinusoidal function. Through extensive numerical analysis, we found that the film thickness and friction coefficient exhibited a strong non-linear relationship with changes in the texture density of the contact surface. Both lubrication and friction deteriorated in a non-monotonic manner. This mechanism was attributed to changes in the inlet micro-topography caused by variations in texture density and the number of sinusoidal asperities actively participating in contact. Additionally, lubrication and friction characteristics under different distribution scales were analyzed with variations in speed, load, and slide-roll ratio (SRR). The simulations showed that the scale effect of surface texture weakened under high-speed and heavy-load conditions, whereas it became more pronounced under low-speed and light-load conditions.

The CoCrFeMnNi high-entropy alloy is a promising erosion- and wear-resistant coating for fracturing pump valves due to its exceptional toughness, hardness, and corrosion resistance. Molecular dynamics simulations of indentation, scratch and impact under high stress reveal that polycrystalline and polycrystalline twin structures exhibit poor erosion resistance due to grain and twin boundary-induced stress concentration. In contrast, the (111) crystal plane in single-crystal structures excels in hardness and wear resistance, benefiting from its triangular atomic arrangement and superior load buffering capacity. However, under severe conditions, the (111) plane generates more surface wear atoms and internal defects, posing risks to pump valve substrates. These findings provide a theoretical basis for optimizing coating selection in engineering applications.

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This study investigates the sliding wear and electrochemical corrosion behaviors of single-crystal copper with (100), (110), and (111) orientations under different loading and frequency conditions. A multifunctional friction and wear tester, an electrochemical workstation, and a scanning electron microscope were employed to observe worn and corroded morphology and to explore the wear and corrosion mechanisms. The experimental results indicate that crystal orientation significantly influences the wear and corrosion resistance of single-crystal copper. The Cu (111) surface, characterized by its high atomic density, exhibits low adhesion and relatively good wear resistance. In contrast, Cu (110) has a lower hardness, a larger wear volume, more severe surface damage, and inferior wear resistance. The wear morphology of Cu (100) is less pronounced, while Cu (111) experiences enhanced wear at higher frequencies. Electrochemical tests revealed that the E_corr followed the order (110) > (100) > (111), with a negative shift of 18.97 mV in the polarization curve. The I_corr increased by approximately 0.93 times.

The strain-hardening effect exerts significant influence on microscale surface contact behavior. This study identifies two critical limitations in existing rough surface contact analyses: insufficient consideration of material strain-hardening effects and discontinuities in asperity contact pressure distributions. By integrating microscale strain-hardening theory with finite element methodology, this paper establishes quantitative relationships between key parameters, including strain-hardening coefficients, material yield strength, and asperity plastic deformation limits. An analytical elastoplastic contact model incorporating strain-hardening effects is developed for individual asperities, complemented by a statistical summation approach for multiscale rough surface characterization. Model validation demonstrates (1) the contact pressure curve for the proposed single micro-asperity model is smooth and continuous. Under varying strain-hardening parameters, the maximum error between the model’s average pressure calculation and the finite element simulation results is 7.03%; (2) the experimental results of rough surface contact align closely with the predicted average contact pressure from the proposed model, with a maximum error of 9.73%, confirming the accuracy of the model; (3) ignoring strain hardening in the analysis, based on the measured surface morphology and operating conditions of the workpiece, leads to an underestimation of the contact pressure by 47.63%. This error increases further with the rise in strain-hardening effects. This paper presents a novel rough surface contact model that incorporates microscale strain-hardening effects, offering a more accurate method for analyzing practical contact problems.

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Alan Roberts in 1966 was the first person to observe experimentally that elastic spheres made from optically smooth rubber could stick together, but he was not honoured for his unique contribution. The same might be said of Isaac Newton who wrote in his 1704 book Opticks that ‘Two polish’d marbles… by immediate contact stick together’. Newton’s postulate was clearly proved wrong in 1882 by Hertz who produced stress theory and observations to demonstrate there was no adhesion between polished glass or metal spheres. However, Kendall in 1970 produced evidence that iron hydroxide nanoparticles stuck strongly together and suggested that application of the energy criterion could explain this by rejecting the stress criterion of fracture. Ken Johnson had already solved the stress problem of sphere contact 12 years earlier in 1958 but suggested that adhesion was impossible because of the infinite tensile stress at the sphere contact edges. This paper describes how the 1970 collaboration between Johnson, Kendall and Roberts provided the correct solution published in 1971, proving Newton was right 266 years after his adhering spheres prediction.

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This study presents the development of an adaptive and interactive algorithm for the evaluation and statistical analysis of the static, dynamic, and integral coefficients of friction (CoF) from high-resolution friction signals. The algorithm is grounded in extensive data collected from a variety of reciprocating friction test configurations, with two representative cases analyzed in detail. Its performance was validated against previously developed semi-automatic evaluation methods. The validation confirmed the algorithm’s robustness and adaptability to different test configurations and varying parameters throughout the testing process. Overall, the algorithm demonstrates high reliability and efficiency, establishing a foundation for a systematic and unified approach to CoF evaluation and addressing a significant gap in tribological data analysis.

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Cattaneo and Mindlin showed that if a Hertzian contact is loaded first by a normal force and then by a monotonically increasing tangential force, the resulting shear tractions can be expressed as a simple superpositon, provided we assume that the frictional tractions in the slip zone are everywhere aligned with the applied force—a result which is strictly true only in the special case where Poisson’s ratio is zero. Ciavarella later showed that with this assumption, a similar superposition applies to any uncoupled three-dimensional contact problem for the half space. Here we relax this assumption and develop a general solution for the case where the tangential force is relatively small, so that the slip annulus is thin compared with other dimensions of the contact area. The local conditions are then characterized by the mode II and III stress-intensity factors in the corresponding adhesive problem. We show that the slip direction depends only on a dimensionless coordinate, so that all points in the slip zone pass through scaled versions of the same expressions as the applied shear force increases. The results show a surprisingly large deviation in slip direction, particularly for incompressible materials.

Hydrogels are ideal substitute materials for articular cartilage. The fretting wear behavior of polyvinyl alcohol (PVA) hydrogel and three types of PVA-based composite hydrogels under dry friction condition is investigated experimentally. Polyvinyl pyrrolidone (PVP), graphene oxide (GO), and multi-walled carbon nanotubes (MWCNTs) are mixed into PVA hydrogels as additives to prepare three composite hydrogels. A sphere-on-flat contact model is established between the PVA-based hydrogel coating and a stainless steel ball. The reciprocating fretting wear equipment is used to conduct fretting tests. Surface wear morphology and wear depth are characterized using three-dimensional (3D) ultra-depth of field microscopy and 3D white-light interference profilometer. The impacts of displacement amplitude, normal force, exposure time, and the number of freeze–thaw cycles on fretting wear behavior of four PVA-based hydrogels are investigated. The results show that the PVA/MWCNTs composite hydrogel exhibits the highest friction coefficient and relatively good wear resistance.

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Pursuing durable superlow friction tribological systems is essential for addressing global energy challenges and achieving carbon neutrality by 2050. Inspired by the exceptional frictional performance of human knee joints, concentrated polymer brushes (CPBs) have emerged as a promising solution for artificial tribological applications. However, a major challenge remains in the reduced durability of CPBs compared to traditional hard materials, particularly in maintaining superlow friction over extended use. This study focuses on understanding the mechanisms behind the vanishing superlow friction and wear of CPBs lubricated with ionic liquids (ILs). To investigate these phenomena, we developed a real-time and spatially resolved “in-operando Raman tribometer” for real-time monitoring of molecular dynamics at friction interfaces. Time and spatially resolved Raman measurements revealed critical insights into the polymer chain behavior, IL film drainage, and internal stress changes that influence friction and wear mechanisms. Our results suggest that the “probe vertical lift” phenomenon and distribution of the solid–liquid interface structure play key roles in the transition from superlow to high friction and accelerated wear. These findings provide a foundation for developing durable, energy-efficient tribological systems in various industrial applications.

Experimental studies on wear often employ incomplete contact configurations which cause variations in uncontrolled variables as wear progresses, ultimately leading to coupled results. This study observes fundamental wear mechanisms under dry gross sliding conditions. Reciprocating wear experiments are conducted at constant normal load using annular samples having flat-on-flat common edge contact configuration that are made of Al 6082 T6. This configuration ensures constant nominal contact area and pressure, nominally uniform contact pressure distribution, an edge-free contact region along the sliding direction and uniform air exposure of the contact area. A comprehensive investigation of fundamental wear behaviour is conducted through measurements of wear mass, tangential and vertical displacement, hysteresis loop area, coefficient of friction and tangential contact stiffness. In contrast to some previous studies on annular contacts, the results show increasing wear mass with normal load. The findings also indicate that a reliable displacement measurement technique, here digital image correlation, is essential for accurate tracking of relative surface displacements. This enables correction for machine compliance and hence accurate tangential contact stiffness measurements, and accurate observation of dilatant motion. In contrast, the test machine’s nominal measurements are shown to be sufficient for work input calculations. The evolution of both the vertical displacement and the hysteresis loop area implies the presence of two distinct processes during the initial transient stage: surface roughening and debris bed formation. Competition between these processes is shown to govern transient wear.

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