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Showing papers in "Journal of Tribology-transactions of The Asme in 2021"


Journal ArticleDOI
TL;DR: This work critically review the literature on textured orthopedic biomaterial surfaces in the context of prosthetic hip implants and discusses the different functions of texture features by highlighting experimental and simulated results documented by research groups active in this area.
Abstract: More than 300,000 total hip replacement surgeries are performed in the United States each year to treat degenerative joint diseases that cause pain and disability. The statistical survivorship of these implants declines significantly after 15-25 years of use because wear debris causes inflammation, osteolysis, and mechanical instability of the implant. This limited longevity has unacceptable consequences, such as revision surgery to replace a worn implant, or surgery postponement, which leaves the patient in pain. Innovations such as highly cross-linked polyethylene and new materials and coatings for the femoral head have reduced wear significantly, but longevity remains an imminent problem. Another method to reduce wear is to add a patterned microtexture composed of micro-sized texture features to the smooth bearing surfaces. We critically review the literature on textured orthopedic biomaterial surfaces in the context of prosthetic hip implants. We discuss the different functions of texture features by highlighting experimental and simulated results documented by research groups active in this area. We also discuss and compare different manufacturing techniques to create texture features on orthopedic biomaterial surfaces and emphasize the key difficulties that must be overcome to produce textured prosthetic hip implants.

35 citations


Journal ArticleDOI
TL;DR: A comprehensive review of the latest developments of FSP in hybrid surface composites manufacturing can be found in this article, where the effects of single-pass, multipass, and change in pass direction on microstructure and resultant properties are summarized.
Abstract: The metal matrix composites combine the metallic properties of a tough and ductile matrix with properties of reinforcement particles, simultaneously develop the functional properties by proper selection of reinforcements for projected applications. However, hard ceramics reinforcements decrease toughness and ductility of soft matrix and restrict their wide applications. The surface metal matrix composites (SMMCs) preserve the matrix properties with added advanced surface properties by reinforcing particles only in the surface layer. The hybrid surface metal matrix composites (HSMMCs) with more than one reinforcement gained attention in material processing due to their noble tribological behavior and surface properties, which cannot be attained in mono composites. Conventional liquid-phase processing techniques to fabricate hybrid surface composites result in the formation of undesirable brittle compounds, detrimental to desirable properties of composites. Friction stir processing (FSP), a solid-state processing technique, has been used by many investigators using different reinforcements to fabricate mono as well as hybrid surface composites. Friction stir processed (FSPed) hybrid surface composites have not been extensively reviewed. The current review provides a comprehensive understanding of the latest developments of FSP in hybrid surface composites manufacturing. This paper review different reinforcement strategies in the fabrication of FSPed hybrid surface composites and also the effects of single-pass, multipass, and change in pass direction on microstructure and resultant properties. Finally, future directions and challenges to FSPed hybrid surface composites are summarized. This review article containing important information on hybrid surface composites fabrication by FSP will be useful to academicians and investigators in the field.

33 citations


Journal ArticleDOI
Peter Renner1, Swarn Jha1, Yan Chen1, Ajinkya Raut1, Siddhi Mehta1, Hong Liang1 
TL;DR: In this paper, the authors studied the mechanisms of the most common failure modes, corrosion and wear, of alloys fabricated through additive manufacturing based on published literature and found that the processing conditions have profound influence on microstructure and thus corrosion and wearable resistance.
Abstract: Products made from additive manufacturing processes have attracted great attention in engineering, health care, and society at large. However, there is little knowledge about the failure of additively manufactured alloys, in particular, corrosion and wear seen in most engineering applications. The haphazard and inefficient usage of such alloys raised concerns about safety, compatibility, reliability, cost, and consumer satisfaction. To address those concerns, we studied the mechanisms of the most common failure modes, corrosion and wear, of alloys fabricated through additive manufacturing based on published literature. It was found that the processing conditions have profound influence on microstructure and thus corrosion and wear resistance of alloys. Because of the layered structure, the initiation and growth of both corrosion and wear exhibited anisotropic behavior. The insights from this review could be used as a reference of the state-of-the art and to help in the development of future additively manufactured alloys with improved corrosion and wear properties.

18 citations


Journal ArticleDOI
TL;DR: In this paper, a three-dimensional (3D) unsteady numerical modeling of a centrifugal slurry pump with Eulerian-Lagrangian approach coupled with the erosion model has been performed to predict the erosive wear of the pump components namely, casing and impeller.
Abstract: Centrifugal slurry pump designed for handling solid–liquid flow experiences performance reduction and shorter service life due to uneven localized erosive wear of the wetted parts. In this work, three-dimensional (3D) unsteady numerical modeling of a centrifugal slurry pump with Eulerian–Lagrangian approach coupled to the erosion model has been performed to predict the erosive wear of the pump components namely, casing and impeller. The erosion model developed to predict the erosion of the pump components of high chromium white cast iron (HCWCI) is employed, and the erosion rate distribution along the complete length and width of the casing and impeller blade surfaces namely, pressure side, suction side, front shroud, and back shroud, is determined. The numerical results showed good agreement with the experimentally measured erosion of the pump casing. It has been found that the erosion of the casing and impeller is non-uniform along the length and width. The zone of higher erosion is at the centerline and the back side of the casing, whereas, for the impeller, it is on the pressure side near the leading edge. The variation in the operating flowrate and particle size greatly influenced the material removal rate and the zone of higher erosion for the casing and impeller blade surfaces.

18 citations


Journal ArticleDOI
TL;DR: In this article, the authors present an overview about particulate wear that occurs in various components of slurry pumps, pipeline systems, and hydraulic turbines due to the mechanical action caused by the flow of solid-liquid mixtures.
Abstract: This paper presents an overview about particulate wear that occurs in various components of slurry pumps, pipeline systems, and hydraulic turbines due to the mechanical action caused by the flow of solid–liquid mixtures. Three most common wear problems, namely, erosion, erosion–corrosion, and abrasion occur in different industries like thermal and hydro power plants, mining, chemical, and marine industries. Therefore, the efficiency of these industries and power plants highly depends on the wear damages. So, it becomes necessary to govern the wear phenomenon. In this paper, the various properties of particles and target are discussed on which the particulate wear depends. Present overview explains the experimental methods of measuring the particulate wear at in situ and ex situ conditions by using the different types of testers, rigs, and pilot plant test loops. Moreover, the empirical and analytical correlations or models for the prediction of particulate wear in pumps, piping circuits, and hydraulic turbines are also discussed in present literature review. By studying the all possible advantages and disadvantages, the gaps in knowledge of wear prediction methods and models are highlighted. At the end, a “think-model” for the prediction as well as reduction of wear in the various components is presented on the basis of different experimental and computational fluid dynamics (CFD) based simulation work. Further investigations can be carried out to develop the more accurate and flexible models that can be used to predict the particulate wear in a wide range of applications.

17 citations


Journal ArticleDOI
TL;DR: In this paper, a new method is proposed to determine the relation between real contact area and normal load by treating the contact of rough surfaces as an accumulation of equivalent circular contacts with varying average contact radius.
Abstract: The accurate calculation of the real contact area between rough surfaces is a key issue in tribology. In this paper, based on the geometrical information of total contact area and the number of contact patches with respect to surface separation, a new method is proposed to determine the relation between real contact area and normal load. The contact of rough surfaces is treated as an accumulation of equivalent circular contacts with varying average contact radius. For a realistic range of separation, the proposed model predicts a linear relation between real contact area and load, and coincides well with direct finite element calculations. Moreover, this model is general and not confined to isotropic Gaussian surfaces.

14 citations


Journal ArticleDOI
TL;DR: In this article, the current-carrying tribological properties including friction, wear, and electrical stability of the Cu/graphene composites with brass pairs were investigated by varying normal applied load and sliding speed under multiple applied voltages.
Abstract: Excellent current-carrying tribological properties including the low-friction, high anti-wear, high current-carrying efficiency, and stability are important for the current-carrying application in transmitting electrical signals and power. Here, the Cu/graphene composites with graphene uniformly distributed in Cu matrix were successfully prepared by combining the electroless plating process and powder metallurgy process. The current-carrying tribological properties including friction, wear, and electrical stability of the Cu/graphene composites with brass pairs were investigated by varying normal applied load and sliding speed under multiple applied voltages. The friction reduction and anti-wear properties of Cu/graphene composites were enhanced by the introduction of graphene. The friction coefficient of the Cu/graphene composites keeps stable under current-carrying and non-current-carrying conditions due to the benefit of the graphene enhancement to Cu. The graphene on wear surface reduces friction force and wear. The current-carrying efficiency and stability increased with the increase of applied load but decreased with increasing sliding speed. The contact stability increased with applied load, while high sliding speed caused the drastic vibration of sliding contact. The studies can provide a beneficial guideline for the current-carrying applications of Cu/graphene composites to reduce the friction and wear.

13 citations



Journal ArticleDOI
TL;DR: In this paper, the authors investigate the transition between churning and windage phenomena for a spur gear rotating in an oil bath at numerous oil immersion levels and propose a criterion to indicate which power loss model to use.
Abstract: Oil sump lubrication is commonly used in gearboxes. When considering consistent speeds, oil immersion is usually set to low level in order to reduce associated power losses. This configuration is already used in some parts of helicopter mechanical transmissions, and it is under consideration as a lubrication solution for future electric powertrain where gearbox input speeds may be very high. The gear drag power losses are generally evaluated from either a churning power loss model for classic oil sump lubrication or a windage power loss model for oil jet lubrication. One may thus wonder how to estimate drag losses when considering a gear that only a small part is immersed. In this study, the authors investigate the transition between churning and windage phenomena for a spur gear. A series of torque measurements on a single spur gear rotating in an oil bath at numerous oil immersion levels have been carried out. Based on these results, a criterion to indicate which power loss model to use is proposed.

13 citations



Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate a novel morphing surface and its realization using additive manufacturing (AM), using a diaphragm structure, which is achieved even if a hard resin material is used.
Abstract: As the need for higher efficiency of engineering components increases, so does the demand for functional surfaces. While various tribosurfaces (e.g., texturing and coatings) have been developed, many researches are aimed at static functionality. On the other hand, due to a wide range of environmental adaptability and active control, active-morphing surfaces can be highly efficient and robust. In this paper, we demonstrate a novel morphing surface and its realization using additive manufacturing (AM). By using a diaphragm structure, morphing performance is achieved even if a hard resin material is used. When air pressure is applied to the backside of the diaphragm, it changes to a convex shape and vice versa. The concept requires a complex structure for arranging airflow and a solid morphing system. The AM is one great technique to create such complex structures. As a result of actual manufacturing, the created morphing structure realizes a large morphing of 600 μm or more. In addition, the shape changes reversibly depending on the air pressure. The surface also exhibits very interesting tribological characteristics. The surface shows a friction coefficient of about 0.3 with a concavity, and then increases to 0.5–1.7 with a convexity. A real-contact area measurement reveals that the novel property occurs due to change in the real-contact area depending on surface morphology. In conclusion, the present paper provides a new concept of a novel morphing tribosurface, which selectively performs as a low-friction or break-like surface, created using AM.

Journal ArticleDOI
TL;DR: In this article, a data surrogate model construction method is proposed for the friction coefficient of a wet clutch under different engagement conditions, and the decoupling between different influencing factors of friction coefficient is realized.
Abstract: In this study, an experiment is conducted for assessing the friction characteristics of a wet clutch on actual working conditions, to determine how various factors influence the friction coefficient in the actual working process of a wet clutch. Based on the experimental data of a wet clutch under different engagement conditions, a data surrogate model construction method is proposed for the friction coefficient. According to this model, the decoupling between different influencing factors of friction coefficient is realized, and their influence on friction coefficient is obtained. To reveal the change mechanism of the friction coefficient, a theoretical analysis model of the friction coefficient is established by using the elastic contact theory and the elastic fluid dynamic pressure lubrication theory. In addition, based on the constructed friction coefficient data surrogate model, the sensitivity of different influencing factors on the friction coefficient and the coupling relationship between the different influencing factors are studied.



Journal ArticleDOI
TL;DR: In this paper, an extensive survey of the thermal modeling methods and effects in journal bearings is presented, including various bearing types, and recent progress in thermal bearing design and thermal instability problems observed in fluid and gas film hydrodynamic bearings.
Abstract: Traditional analysis of journal bearings assumed a constant viscosity which simplified the solutions for static and dynamic characteristics and responses. Today's high-performance machinery requires more accurate models wherein temperature and viscosity distributions in the film must be calculated. Thermal effects in journal bearings have a strong influence on both static and dynamic properties, and consequently play a critical role in determining rotor-bearing system performance. This paper presents an extensive survey of the thermal modeling methods and effects in journal bearings. The subjects include various bearing types, and recent progress in thermal bearing design and thermal instability problems observed in fluid and gas film hydrodynamic bearings. The extent of the survey ranges from conventional Reynolds equation models to more advanced computational fluid dynamics models.

Journal ArticleDOI
TL;DR: In this article, the authors present a computational fluid dynamics (CFD)-based approach for tilting pad journal bearing (TPJB) modeling including thermo-elasto hydrodynamic (TEHD) effects with multi-mode pad flexibility.
Abstract: The core contributions of Part I (1) present a computational fluid dynamics (CFD)-based approach for tilting pad journal bearing (TPJB) modeling including thermo-elasto hydrodynamic (TEHD) effects with multi-mode pad flexibility, (2) validate the model by comparison with experimental work, and (3) investigate the limitations of the conventional approach by contrasting it with the new approach. The modeling technique is advanced from the author’s previous work by including pad flexibility. The results demonstrate that the conventional approach of disregarding the three-dimensional flow physics between pads (BP) can generate significantly different pressure, temperature, heat flux, dynamic viscosity, and film thickness distributions, relative to the high-fidelity CFD model. The uncertainty of the assumed mixing coefficient (MC) may be a serious weakness when using a conventional, TPJB Reynolds model, leading to prediction errors in static and dynamic performance. The advanced mixing prediction method for “BP” thermal flow developed in Part I will be implemented with machine learning techniques in Part II to provide a means to enhance the accuracy of conventional Reynolds based TPJB models.

Journal ArticleDOI
TL;DR: In this paper, the influence of various postprocessing methods such as heat treatment and electric discharge alloying (EDA) on ambient and elevated temperature wear behavior of selective laser melted AlSi10Mg alloy was investigated.
Abstract: Selective laser melting (SLM) is an emerging additive manufacturing (AM) technology for fabrication of complex lightweight components along with improved mechanical properties. However, the properties are highly influenced by the continual heating and cooling during deposition, variation in local temperature, size, and shape of melt pool, and solidification growth rate. Therefore, postprocessing is very often required to control various properties of additive manufactured components. The present work investigates the influence of various postprocessing methods such as heat treatment and electric discharge alloying (EDA) on ambient and elevated temperature wear behavior of selective laser melted AlSi10Mg alloy and compared with its tribological behavior with cast AlSi10Mg. The dry wear tests were conducted using a pin on disk (POD) tribometer with EN-31 as counter body. The EDA treated SLM AlSi10Mg showed the least wear-rate and coefficient of friction (COF) at both ambient and elevated temperatures (1.05 × 10−4 mm3/Nm and 0.434 and 3.12 × 10−5 mm3/Nm and 0.531, respectively) due to its higher hardness (189.8 HV) as compared with other samples. The wear-rate and COF of cast specimen are found to be highest among all specimens at both ambient and elevated temperatures (1.34 × 10−4 mm3/Nm and 0.528 and 4.49 × 10−5 mm3/Nm and 0.724, respectively). Lower wear-rate and higher COF are observed at elevated temperature due to the excessive formation of wear-resistant oxides (Al2O3, SiO2, and MgO) and glaze layers for all samples compared with ambient temperature wear behaviors of its counterparts. Abrasive wear, adhesive wear, oxidation wear, and surface delamination are the prominent wear mechanisms observed for ambient and elevated temperatures for all the specimens.

Journal ArticleDOI
TL;DR: In this article, a finite element (FE) model was developed to study the third body effects on the fretting wear of Hertzian contacts in the partial slip regime, and the relation between the number of cycles and the hardening process was evaluated.
Abstract: In this investigation, a finite element (FE) model was developed to study the third body effects on the fretting wear of Hertzian contacts in the partial slip regime. An FE three-dimensional Hertzian point contact model operating in the presence of spherical third bodies was developed. Both first bodies and third bodies were modeled as elastic–plastic materials. The effect of the third body particles on contact stresses and stick-slip behavior was investigated. The influence of the number of third body particles and material properties including modulus of elasticity, hardening modulus, and yield strength were analyzed. Fretting loops in the presence and absence of wear particles were compared, and the relation between the number of cycles and the hardening process was evaluated. The results indicated that by increasing the number of particles in contact, more load was carried by the wear particles which affect the wear-rate of the material. In addition, due to the high plastic deformation of the debris, the wear particles deformed and took a platelet shape. Local stick-slip behavior over the third body particles was also observed. The results of having wear debris with different material properties than the first bodies indicated that harder wear particles have a higher contact pressure and lower slip at the location of particles which affects the wear-rate.


Journal ArticleDOI
TL;DR: In this paper, a graphene-based additive was applied as a lubricant additive in paraffin grease for steel tribo-pair, and the results showed that a loose fiber network of soap in the presence of the additive allowed their facile release for efficient lubrication.
Abstract: Pristine, reduced, and alkylated graphene oxides are applied as lubricating additives in paraffin grease. It has revealed that their crystalline structure governs the tribological properties of grease for steel tribo-pair. The microstructural analyses of grease samples showed that a loose fiber network of soap in the presence of graphene-based additive allows their facile release for efficient lubrication. The surface analyses based on the microscopic and elemental mapping show the development of a graphene-derived protective film on the worn scars, which protected the tribo-surfaces and subsided the wear. The reduced graphene oxide (rGO) with the interlamellar distance of 0.35 nm in the (002) plane provided minimum resistance to shear and exhibited maximum reduction in coefficient of friction (COF) for the paraffin grease. The presence of oxygen functionalities in the basal of pristine and alkylated graphene oxide (GO) compromised the interlamellar shearing under tribo-stress; consequently, higher COF than that of rGO.


Journal ArticleDOI
TL;DR: In this paper, a real-time dynamic modeling of cryogenic ball bearings, where the rotating inner race accelerates to the operating speed, is based on integration of classical differential equations of motion of bearing elements, when experimentally measured ball/race traction behavior is used to compute the imposed acceleration on the rolling elements.
Abstract: Real-time dynamic modeling of cryogenic ball bearings, where the rotating inner race accelerates to the operating speed, is based on integration of classical differential equations of motion of bearing elements, when experimentally measured ball/race traction behavior is used to compute the imposed acceleration on the rolling elements. The dynamic performance simulation provides a realistic coupling between traction behavior in the ball-to-race contacts and dynamics of bearing element motion as the bearing goes through the transient speed variation. However, due to vastly different mechanical and thermal time scales, heat generation in the bearing is time-averaged over a relatively large thermal time-step to model temperature fields as a step change, while the bearing motion is simulated in real-time. The emphasis is on dynamic modeling with thermal coupling in a static sense. Under stable conditions, the step change in temperature field converges to operating value as the bearing approaches a dynamic steady-state condition, which demonstrates acceptable significance of the dynamic simulation with coupled thermal interactions. Both all steel and hybrid ball bearings for liquid oxygen (LOX) turbo pump applications are modeled. Bearing performance simulations are closely modeled over experimental time cycles in both transient and steady-state domains. Steady-state solutions are shown to be independent of initial conditions to demonstrate acceptable convergence of time domain integrations. Model predictions of heat transferred to circulating LOX is within the range of variation in experimental data. Parametric evaluation of bearing performance as a function of operating conditions demonstrate that while the ball/race contact stress is higher in a hybrid bearing, contact heat generation is significantly lower in comparison with that in the all steel bearings.


Journal ArticleDOI
TL;DR: In this paper, the surface analysis and wear behavior of spindles of a cotton picker in field work was studied and it was shown that the worn surface was smoother and wear trend of surface topographies tend to consistent along with the rotation direction of the spindle and found a significant reduction in roughness and coating thickness.
Abstract: Spindles in cotton picking machinery are the key component, wear of the spindles significantly reduces harvest efficiency of the cotton picking process. To improve its wear resistance, the substrate surfaces of spindles are usually electroplated with chromium coating. But the failure process and wear mechanism of the spindle have not been studied so far. In this paper, based on the surface analyses and wear behavior of spindles of a cotton picker in field work, the test results showed that the worn surface was smoother and wear trend of surface topographies tend to consistent along with the rotation direction of the spindle and found a significant reduction in roughness and coating thickness. The coating of the spindle surface has not been damaged in the picking process, the wear mechanism was mainly abrasive wear. After the worn out of surface coating, abrasive wear is always present accompanied by oxidation wear. Multi-oxides were deposited on the substrate surface; the oxide particle was sheared by cotton fiber in the subsequent picking, leading to an increase in surface roughness and aggravating substrate wear. These in filed wear mechanisms and processes of spindles could be of help for the design and surface modification with longer working life.

Journal ArticleDOI
TL;DR: In this article, a thrust foil bearing with taper-flat configuration and pocket grooves on the bearing top foil as a secondary pressure boosting mechanism is presented, which can reduce power loss by 10% with increased average film thickness.
Abstract: The integration of foil bearing technology into high-speed oil-free machines has been slow in progress, in part, due to the low load-carrying capacity of the foil thrust bearing. It is crucial this issue is addressed through innovative solutions without overcomplicating the bearing design because simplicity is one of the attractive features of the foil bearing. This work presents novel thrust foil bearing with taper-flat configuration and pocket grooves on the bearing top foil as a secondary pressure boosting mechanism. Parametric study of the pocket dimensions on a rigid bearing reveals that the bearing static performance is the most sensitive to the pocket angular span. Further two-dimensional fluid–structure interaction analyses on foil thrust bearing predict a reduction of power loss by 10% with increased average film thickness. Minimum film thickness also increases when the bearing is lightly loaded but it is reduced 20% at the taper-flat transition area under high loading condition. This issue can be overcome by using stiffer bump foil; however, this is not implemented in this work due to other design constraints. Test results at 90,000 rpm and 140,000 rpm show, by adding the pocket groove pattern on the top foil, the power loss is reduced by 16% compared to the traditional taper-flat configuration.

Journal ArticleDOI
TL;DR: In this article, the authors investigate the impact of varying surface inclination angles with respect to the build direction on the resultant surface textures and find that the resulting surface topographies are strongly correlated with the surface inclination angle.
Abstract: Additive manufacturing offers the advantage of infinite freedom to design and fabricate complex parts at reduced lead-time. However, the surface quality of additively manufactured parts remains well behind the conventionally processed counterparts. This paper aims to systematically investigate the impact of varying surface inclination angles with respect to the build direction on the resultant surface textures. A bespoke metal truncheon artifact with inclination angles varying from 0 deg to 180 deg was built by selective laser melting. Focus variation microscopy was used to measure the topography of inclined surfaces with a tilt angle of up to 132 deg. The measurement data were then analyzed to characterize the staircase effect and the particles adherent to the artifact surface. Areal surface texture parameters, including height parameters, spatial parameters, functional parameters, and feature parameters, were explored to quantify the general surface topography, the staircase effect, and the particle features. The areal surface texture characterization and particle analysis reveal the resulted surface topographies are strongly correlated with the surface inclination angles.


Journal ArticleDOI
TL;DR: In this paper, the performance of a fluid-film thrust bearing using micro-texture on pads has been investigated, and it has been found that the minimum film thickness has increased up to 48%, and the friction coefficient reduced up to 24%.
Abstract: This paper presents the performance behaviors (coefficient of friction, minimum film thickness, and pressure distributions) of a fluid film thrust bearing using a newly conceived micro-texture on pads. In the numerical investigation, the Reynolds equation has been discretized using the finite element formulation followed by the solution of algebraic equations employing the Fischer-Burmeister-Newton-Schur (FBNS) algorithm, which satisfies the mass-conservation phenomenon arising due to the commencement of cavitation in the lubricating film. The effects of parameters (micro-texture/pocket depth, circumferential/radial length of micro-texture and pocket, etc.) of new texture on the performance behaviors of the thrust bearing have been explored and presented herein for the range of input data. It has been found that the minimum film thickness has increased up to 48%, and the friction coefficient reduced up to 24% in comparison to conventional plain pad case.

Journal ArticleDOI
TL;DR: In this article, four kinds of aviation liquid lubricants (i.e., 4010#, 4050#, 4106#, and 4109# oils) were homogeneously coated on the graphene/MoS2 composite coating through a spin-coating method to form the solid-liquid lubricating combinations.
Abstract: Four kinds of aviation liquid lubricants (i.e., 4010#, 4050#, 4106#, and 4109# oils) were homogeneously coated on the graphene/MoS2 composite coating through a spin-coating method to form the solid–liquid lubricating combinations. The tribological properties of the obtained solid–liquid combinations and pure graphene/MoS2 coating were investigated experimentally. Effects of the liquid lubricant type on the friction and wear behaviors of the solid–liquid combinations and pure graphene/MoS2 coating were studied at different applied loads and rotational speeds. Within the ranges of the applied load varying from 10 to 50 N and rotational speed varying from 750 to 1500 rpm, the presence of the above-mentioned liquid lubricants significantly reduces the friction coefficient of the pure graphene/MoS2 coating, and the reduction rate is as high as 24%. Additionally, the coating-4109# combination has the best synergistic effect under the above operation condition.

Journal ArticleDOI
TL;DR: The semi-system approach has proven to be highly useful for improving the stability and robustness of mixed lubrication simulations as mentioned in this paper, but care should be taken when making quantitative predictions.
Abstract: The ability to simulate mixed lubrication problems has greatly improved, especially in concentrated lubricated contacts A mixed lubrication simulation method was developed by utilizing the semi-system approach which has been proven to be highly useful for improving stability and robustness of mixed lubrication simulations Then different variants of the model were developed by varying the discretization schemes used to treat the Couette flow terms in the Reynolds equation, varying the evaluation of density derivatives and varying the contribution of terms in the coefficient matrix The resulting pressure distribution, film thickness distribution, lambda ratio, contact ratio, and the computation time were compared and found to be strongly influenced by the choice of solution scheme This indicates that the output from mixed lubrication solvers can be readily used for qualitative and parametric studies, but care should be taken when making quantitative predictions