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Cashew Nut Shell Liquid (CNSL) has been explored in several applications within the sustainability principles and circular economy of agro-industrial product waste. To understand the anticorrosive and lubricant properties of CNSL solutions, a multi-faceted approach, incorporating electrochemical analyses, immersion test, tribological measurements, and tribochemical characterization was carried out for mild steel AISI 1012, stainless steel AISI 420 and Aluminium Alloy 6061. Electrochemical analyses reveal a positive impact of CNSL, inducing a shift in corrosion potential to more positive values and a decrease in corrosion current, indicating effective corrosion inhibition for stainless steel and aluminium alloy. In mild steel, CNSL exhibits a mixed-type inhibition with efficiency increasing in correlation with oil concentration. The lubricating properties of CNSL are evident according to the coefficients of friction (COF) obtained and the elastohydrodynamic lubrication regime observed during tribological tests. Tribochemical tests demonstrate a reduction in wear and an improvement in tribocorrosion behavior under sliding conditions. CNSL emerges as a promising tribocorrosion mitigator, demonstrating multifaceted benefits. The concentration-dependent effects highlight the need for optimization in specific applications, particularly for passive materials. CNSL not only inhibits corrosion through film formation but also provides effective lubrication, reducing friction, wear, and chemical-mechanical degradation. This research contributes valuable insights to corrosion science. It proposes practical applications for CNSL in diverse industrial contexts, showcasing its potential as an environmentally friendly and sustainable solution for tribocorrosion challenges. • The influence of Cashew Nut Shell Liquid (CNSL) on the tribocorrosion behavior across three metallic alloys (mild steel, stainless steel, and aluminium) is explored. • Electrochemical analyses, immersion test, tribological measurements, and tribochemical characterization was carried out for AISI 1012, AISI 420 and AA6061. • CNSL exhibited a positive impact on corrosion inhibition for stainless steel and aluminium alloy, inducing a shift in corrosion potential to more positive values and a decrease in corrosion current. • CNSL demonstrated lubricating properties according to the coefficients of friction (COF) obtained and the elastohydrodynamic lubrication regime observed during tribological tests. • CNSL emerges as a promising tribocorrosion mitigator, demonstrating multifaceted benefits. [ABSTRACT FROM AUTHOR]

The effect of surface roughness, contact pressure and lubrication on the onset of galling of aluminum 6082-T6 is studied with a pin-on-plate tribometer. The design of experiments involves pins with mean arithmetic roughness Ra equaled to 0.2, 0.35 and 0.6 μm, normal loads ranging from 5 to 600 N, and 4 different lubrications: without lubricant, with MoS2 dry lubricant, with pure mineral oil and with a highly chlorinated paraffin oil. Tests are performed at room temperature and are repeated three times. Experimental results show the great sensitivity of the onset of galling to the roughness and the beneficial effect of dry and liquid lubricants. The occurrence of galling is study by optical micrographs, by the analyses of the coefficient of friction, and by the use of finite element simulations. It comes that the variation of the coefficient of friction is not self-sufficient to detect the onset of galling. The finite element computations involves Wilson's lubrication model and Xue's damage model. Galling is assumed when finite elements near the contact area reach the critical damage Dc. This numerical approach leads to a good prediction of the onset of galling for the tests performed under constant normal load. For tests performed with increasing normal loads and various lubricants, the numerical prediction overestimate the sliding length before galling occurs. • Galling of the aluminium alloy 6082 is predicted by means of finite element computations. • Pin-on-plate tests are performed to study the effect of roughness, contact pressure and lubricant on galling. • Wilson's lubrication model is used to compute the friction stresses, and a damage criteria to detect the onset of galling. • Good agreements are obtained between the numerical predictions of galling and experiments. [ABSTRACT FROM AUTHOR]

This study presents a novel and non-destructive method for quantitatively analysing grease lubricated bearing wear by using X-ray microcomputed tomography (μCT). The efficacy of μCT to measure rolling contact wear via wear debris analysis was demonstrated, as was quantifying grease contamination and wear debris identification. Test rig experiments of grease lubricated spherical roller bearings, were performed to simulate rolling contact wear. Six grease samples were collected from two bearings at three different intervals to investigate wear progression. Results showed μCT measured wear volume increased exponentially with increasing bearing operation times. Grease cleanliness (particle counts per ml) worsened nonlinearly due to the exponential growth of wear debris over longer bearing operational times. Comparing the conventional ISO281 bearing assembly and operating condition assessment, a particle-count based method via μCT analysis provided a less subjective and dynamic assessment for quantifying grease contamination. Grease contamination was found to increase with longer operational timeframes due to the combination of wear debris growth and decreased lubrication film thickness. Finally, laminar, chunk and spherical wear particles, associated with rolling contact wear, were identified by the morphometric parameters measured by μCT. This study highlights the potential of μCT as a wear monitoring and grease quality assessment technique for railway bearing applications. • Microcomputed tomography is pioneered to measure wear in test rig bearings. • The proposed method is nondestructive and requires no sample manipulation. • The efficacy in wear measurement is proven through debris analysis in grease. • Quantitative analysis of 3D wear debris images provides wear mechanism assessment. • Grease contamination worsens with wear debris growth exponentially and lubricant film thinning. [ABSTRACT FROM AUTHOR]

The paper proposes a novel numerical framework for modelling of the pitting damage mechanism, based on the application of the three-layered residual control staggered phase-field algorithm. Proposed numerical framework can be applied to all contacting mechanical elements subjected to rolling contact fatigue, but in this paper, it is applied on gears. More precisely, gear teeth flanks subjected to the rolling-contact fatigue conditions are investigated, which consequently results in governing pitting mechanisms. Loading of the teeth flanks is imposed via moving load, with assumption of the full-film lubrication and pressure distribution according to the elastohydrodynamic lubrication theory, as well as Hertzian theory. The Coulomb's law is used to compute the friction force distribution. The numerical framework is embedded into finite element software ABAQUS via user subroutines. The validity of the proposed numerical scheme is tested by comparison to the examples from the literature. The main mechanisms of the pitting formation have been verified, i.e., surface- and subsurface-initiated pitting formation. Furthermore, an influence of the microstructure has been considered in the modelling of pitting phenomena. It has been demonstrated that the proposed numerical framework provides satisfactory results, and it is able to capture governing pitting mechanisms. • A new procedure for modelling of rolling contact fatigue problems based on phase field method is proposed. • New methodology is verified on problems of pitting formation on gear tooth flanks. • Loading is imposed via moving load, with a pressure distribution according to the elastohydrodynamic lubrication theory. • The material utilized is the nodular cast iron EN-GJS-400-18-LT exhibiting nonlinear elastoplastic behaviour. [ABSTRACT FROM AUTHOR]

Surface roughness is significant to friction and wear. However, the influence remains elusive, especially at the nanoscale. This study aimed to explore the effect of the nanoscale surface roughness on sliding friction and wear. For bearing steel tribo-pairs, the surface roughness can affect the lubrication state transition. The lower the surface roughness is, the easier it is to enter mixed lubrication and full film lubrication. Moreover, reducing the surface roughness can decrease friction and wear in mixed lubrication. At 94 mm/s sliding speed, as the surface roughness S q decreases from 769.7 nm to 21.1 nm, the average friction coefficient first remains unchanged and then decreases by 20%, while the wear rate decreases by 85%. However, further reducing the surface roughness may result in friction failure, raising friction and wear. At 10 mm sliding radius, about 20∼40 nm S q can lead to the minimal friction and wear. For the mechanism, as the surface roughness decreases, the asperity contact diminishes. Therefore, friction and wear decrease. However, when the surface roughness passes the critical point, asperities cannot fully accommodate the interfacial wear debris. Consequently, friction failure occurs. The findings may provide an enhanced understanding of the role of surface roughness in tribology. [Display omitted] • The surface roughness can affect the lubrication state transition. • Reducing the surface roughness can decrease friction and wear in mixed lubrication. • Too low surface roughness may result in friction failure, raising friction and wear. [ABSTRACT FROM AUTHOR]

Undeniably, advances in water-based nano-additives play a considerable role in energy conservation and pollution reduction accompanied by the resurgence of water-based lubricants. Graphitic carbon nitride quantum dots (g-CNQDs) have attracted remarkable attention in water-based lubricant additives owing to their strong designability, favorable mechanical property, and unique self-lubricating effect. Therefore, a series of different-sized g-CNQDs with good water dispersibility were expediently synthesized via a hydrothermal strategy and directly used as water-based lubricant additives. Tribological tests indicated that the tribological behaviors of the g-CNQDs-based additives displayed an obvious phenomenon of performance-dependent physical dimensions. With the introduction of g-CNQDs-based additives (1.0 wt%) into the water-based lubrication system, which friction-reduction, anti-wear, and load-supporting performances can be maximally increased by 45.5%, 94.0%, and 233.3%, respectively. Meanwhile, the long-term operating performance of the lubrication system can be promoted under high-load conditions. The formed tribo-film caused by tribo-chemical reaction integrated with the nano-lubrication effect of g-CNQDs collectively contributed to their good tribological performances. • Various g-CNQDs-based additives of water lubrication were synthesized. • g-CNQDs as additives have excellent anti-friction and anti-wear functions. • g-CNQDs-based additives displayed great performance-dependent physical dimensions. • g-CNQDs showed outstanding film-forming and nano-lubrication effects. [ABSTRACT FROM AUTHOR]

Lubrication is often employed in fretting contacts to reduce wear and stresses associated with high friction. Owing to the very small displacements associated with fretting, penetration of lubricating oils into the contact may not be effective. The efficacy of the penetration of the lubricant into the contact is very difficult to observe experimentally, and accordingly, this paper presents a numerical simulation of a lubricated fretting contact using a Coupled–Eulerian–Lagrangian (CEL) finite element method. Meso-scale CEL finite element models are developed to simulate the cylinder-on-flat arrangement used experimentally at the University of Nottingham in which the roughness of contact surfaces is characterized as fractal geometry by the Weierstrass-Mandelbrot (W-M) function. The fluid–solid and solid–solid contact in the lubricated fretting contact are simulated, and from these, wear and friction coefficients are determined. The effects of contact geometry on lubricated fretting contacts and lubricant on fretting wear are modelled and compared with experimental observations. Results indicate that oil lubrication reduces fretting wear and friction effectively in the less-conforming contacts but has little effect in the more-conforming contacts. • A novel approach of modeling lubricated contacts using a CEL finite element method. • The efficacy of the penetration of lubricant into the fretting contacts is simulated. • The wear and friction coefficients in a lubricated fretting contact are determined. • The effects of contact geometry on lubricated fretting contacts are simulated. [ABSTRACT FROM AUTHOR]

Adhesive wear in mixed elastohydrodynamic lubrication (EHL) has been one of the most prominent problems for heavy-loaded helical gears. However, this issue was rarely investigated in previous researches. In this work, an adhesive wear model for helical gears is established in line-contact mixed EHL. The contact parameters of the pinion and gear are derived according to the equivalent tapered roller contact model, and the load is attained in consideration of the varying contact line ratio. Then the asperity contact pressure is calculated according to Hertz's elastic contact theory and load sharing. Moreover, the sliding distances of the points on tooth surface of driving pinion and driven gear are achieved by a single point observation method, and Archard theory in dry contact is extended to the mixed lubrication to estimate the wear rate in mixed EHL by using fractional film defect. The modified Archard's wear model is then employed in formulating and accounting for the gear tooth wear. Effects of surface roughness, geometrical parameters and working parameters on wear depth of the driving pinion are furtherly investigated. The results show that the wear depth in mixed EHL is lower than that under dry contact, which indicates that tooth wear can be reduced with the reasonable lubricants. As the surface roughness becomes large, the asperity contact pressure, the tooth surface temperature and wear depth are increased. Additionally, the wear depths decrease with the increase in module, helix angle, pressure angle, tooth width or rotation speed but increase with input torque. • An adhesive wear prediction method is developed for helical gears in mixed EHL. • Effects of tooth surface roughness on the wear of helical gear are investigated. • Efficient lubrication can greatly reduce the wear depth of tooth surface. • Geometrical and working parameters optimization is beneficial for wear resistance. [ABSTRACT FROM AUTHOR]

Frictional vibration is a common but not entirely understood tribological phenomenon in water-lubricated rubber stern bearings. This paper proposes a transparent glass cylinder and rubber block model which reveals the frictional contact area under a high-speed camera. The local displacements of different grid points on the contact area can be measured by machine vision. A conjoint analysis method for friction coefficient, vibration, noise, and image information is used to determine the mechanisms of frictional vibration. The frequency of noise accompanying the vibrations can be exploited to divide frictional vibration phenomena in the bearing into "squeal" and "chatter" categories, each with different vibration modes. The frictional force and image information can be compared to determine the causes of frictional vibrations in different frequency bands. And a physical model which reflects frictional vibration effects on the stern tube bearing is created by images captured by high speed camera. The results presented here may provide a theoretical foundation for the manufacturing and optimization of water-lubricated rubber stern bearings. • A transparent glass cylinder was used to observe the contact area under high-speed camera. • A conjoint analysis method is used to determine the mechanisms of frictional vibration. • Frictional vibration phenomena was divided into "squeal" and "chatter" categories. • A physical model is created by images captured by high speed camera. [ABSTRACT FROM AUTHOR]

Floating ring bearing has the advantages of simple structure and high operating speed and is widely used in turbocharger and aero-engine. However, many harsh working conditions cause the floating ring bearing to produce starved lubrication and failures. Here, we investigated the starved lubrication characteristics of floating ring bearing via theoretical modeling and numerical simulation. We first established a theoretical model of starved-boundary lubrication based on the Reynolds equation for floating ring bearing. And meanwhile, an oil-film ratio coefficient is introduced into the theoretical model to reflect the degree of starved lubrication. We then analyzed the influence of inlet-boundary conditions (flow rate, oil-film thickness) on the starved-lubrication performance of floating ring bearings. The results showed that the flow rate obviously affects the bearing area of inside and outside oil film, and the oil-film ratio coefficient inside the bearing. When the oil supply is lower than 10 mL/min, the floating ring bearing is in a serious starved-lubrication state, and the oil-film area of bearing is reduced by 30%. The favorable oil supply flow rate can obviously improve the lubrication conditions, and also can predict the starved state of inner oil-film. Our study provides a theoretical basis for the fault detection of floating ring bearing. • Studied the mechanism of oil-starved lubrication on floating ring bearing. • Established model of oil-starved lubrication to calculate lubrication characteristics for floating ring bearing. • Calculated lubrication characteristics under different lubrication conditions. • Analyzed the influence of oil supply on bearing lubrication characteristics. [ABSTRACT FROM AUTHOR]

A 3D time-domain modelling approach is developed with the explicit finite element method to simulate transient meshing contact of gear pairs and the resulting wear. Taking a helical gear pair used in a locomotive as an example, the dynamic contact states of gear teeth are predicted for different speeds in consideration of actual geometries (including those of damaged teeth), time dependent torques, and structural and continuum vibrations of the gear system. The friction between mating teeth is taken into account by a non-Newtonian EHL friction model. A tiny time step of 4.5 × 10−8 s determined by conditional stability of the explicit time integration ensures the capture of transient effects. Based on detailed contact solutions during meshing, the dynamic wear on teeth is further calculated using an Archard wear model to predict tooth profile evolvement. Taking initial involute profiles and a speed of 120 km/h, the model is first validated for dynamic contact solutions. More results show that structural vibrations and worn profiles influence the dynamic meshing contact significantly, tooth wear increases as lubrication fails, and tooth pitting's influence is localized. This approach provides key load boundaries for detailed studies on mating gears, and may be employed for studies on tooth damages and as a reference for lumped parameter dynamic models of gear pairs. • A 3D time-domain approach developed for transient meshing contact of worn gears. • Normal and tangent contact solutions obtained in dynamics for teeth at any instant. • Tooth wear is calculated from transient contact solutions during gear meshing. • Influence of vibrations, worn profiles, pitting and lubrication failures identified. [ABSTRACT FROM AUTHOR]

Stern shaft deformation caused by ship maneuvering will lead to stern bearing lubrication failure and wear. Based on the displacement superposition method, the deflection equation of the stern shaft under the action of the interface force and the propeller load was established. The fluid-solid coupling model of the stern bearing was established by using the averaged Reynolds equation, the Greenwood-Tripp model, and the influence coefficient method. The model was experimentally validated. The influence of the shaft bending deformation caused by the propeller load change on the lubrication characteristics is discussed. The results show that the shaft bending deformation leads to the changes in lubrication characteristics along the axial and circumferential directions. Compared with the vertical load alone, the existence of horizontal propeller load will significantly reduce the minimum nominal oil film thickness and friction coefficient. Under hydrodynamic lubrication, the direction of horizontal load has little effect on friction coefficient. • The displacement superposition method is used to calculate the bending deformation of the propeller shaft. • A fluid-solid coupling model of marine stern bearing is established. • The friction coefficient of the oil-lubricated bearing were tested to verify the model. • The lubrication performance of stern bearing during the ship severe turning maneuver is discussed. [ABSTRACT FROM AUTHOR]

The fretting behaviour of AISI 52100 steel and low alloy steel under grease lubricated conditions is investigated. The friction behaviour is characterized by a high friction regime for the smallest displacement amplitudes below and next to the partial-slip transition whereas a low friction regime is stabilized above a threshold sliding amplitude when a lubricating tribofilm is generated in the interface. In order to quantify the influence of different contact parameters like surface roughness, contact size and contact geometry, a new fast simplified fretting methodology is introduced. This method allows scanning the entire fretting regime through a single experiment. An experimental comparison of smooth and rough surfaces shows that the effect of surface roughness influences the stability and the performance of the lubricating tribofilm. Experimental results obtained through changing the contact size of the cylinder-on-flat configuration permit identifying two contact size regimes. For small interfaces, the effective fretting sliding amplitude triggering the tribofilm activation is proportional to the contact size, whereas for large contacts this amplitude appears to be constant. The comparison with a punch-on-flat interface suggests that the lubrication activation is better captured by considering the peak pressure width rather than the nominal contact size. • Experimental study of surface roughness, contact size and geometry effects in a grease-lubricated fretting contact. • Introducing simplified variable displacement method to assess grease effects. • Lubrication activation is better described considering peak pressure width rather than nominal contact size. [ABSTRACT FROM AUTHOR]

Total Hip Replacement (THR) is generally a highly successful treatment for late stage hip joint diseases and wear, however, wear continues to be one of the major causes of metal-on-metal THR's failure. Hip replacements typically experience a two-stage wear; a higher initial wear rate in the beginning followed by a lower steady-state one with the surface profile changed. This alludes to the potential use of a cup with a non-spherical interior cavity with an initial geometry similar to a worn surface which may benefit from lower wear rate. In this paper wear is numerically simulated with a cup having a non-spherical geometry inspired by the initial stage of wear. A wear model was recently developed by the authors for the THR, which considered the lubricated contact in both elastohydrodynamic lubrication (EHL) and mixed lubrication regime, rather than a dry contact used in most of other studies of wear modelling in the academic literature. In this study the wear model has been updated by introducing the ‘ λ ratio’ (the ratio of film thickness to surface roughness) and addressing the non-Newtonian shear-thinning properties of the synovial fluid. This wear model was able to describe the non-linear wear evolution process due to the change of worn profiles. Firstly the wear of a spherical hip joint was simulated until a steady-state wear rate is achieved. Then a non-spherical joint was proposed in which the cup bearing geometry was generated by the previously predicted worn profile from the spherical joint. At last the wear of this “pre-worn” hip bearing was simulated and compared to the spherical one. Approximately 40% reduction in the steady-state wear rate and 50% in the total accumulated wear has been observed in the non-spherical hip joint. This study presented a full numerical analysis of the relationship between lubrication, wear reduction and the geometry change, and quantitatively suggested the optimal geometry to reduce running-in wear. [ABSTRACT FROM AUTHOR]

A three-dimensional numerical model of wheel/rail in rolling contact is established to study the adhesion characteristics under interfacial contamination considering surface roughness at high speed. The thermal partial elastohydrodynamic lubrication (EHL) theory in elliptical contact is used in the model. The numerical model is successfully solved by applying the iterative algorithm between the pressure field and temperature field. Multilevel method is used to solve modified Reynolds equation. Sweeping column method is used to solve energy and heat conduction equations. The effects of train speed, surface roughness amplitudes, roughness orientation and axle load on the adhesion coefficient under interfacial contamination are numerically investigated. A typical creepage-traction curve under oil contamination is obtained at high speed by the present model. In addition, the effects of temperature and the elastic-plastic deformation behaviour of asperities on the adhesion coefficient are discussed in the paper. Furthermore, the effect of different interfacial contaminations on wheel/rail adhesion using the present model on the adhesion coefficient is investigated. In order to validate the present model, the numerical results are compared with the experimental results that were obtained by JD-2 high-speed wheel/rail rolling contact machine under water/oil contaminations. [ABSTRACT FROM AUTHOR]

Friction modifiers (FMs) are widely used in wheel-rail applications. This paper presents a method to analyze the starved elastohydrodynamic lubrication (EHL) of the wheel-rail surface coated with FMs. Combined with rough surface simulation techniques, starved EHL analysis and film thickness analysis, the pressure distribution and adhesion coefficient under different film thickness states are obtained. The effect of film thickness of the FM supply layers and surface roughness on the adhesion coefficient is studied. The adhesion coefficient increases with the decrease in the effective FM film thickness and increase in the surface roughness. Based on the subsurface stress model, the subsurface stress distribution is studied. Then the influence of FMs on the fatigue of wheel and rail is analyzed on the basis of the shakedown map. Finally, the fatigue index of rail is explored in starved EHL state. • A friction modifier (FM) starved EHL numerical model considering the effective film thickness was established. • Roughness and the effective film thickness could remarkably affect the lubrication state of contact zone. • The adhesion coefficient gradually increases as decreasing the effective film thickness. • With the increasing roughness, the lubrication of wheel/rail surface gradually fails. • The fatigue index will be increased as increasing the roughness and decreasing the effective film thickness. [ABSTRACT FROM AUTHOR]

The textured surface is one of the hotspots in the field of tribology research on reducing friction and wear. By calculating and optimizing the micro-texture structure, researchers designed and prepared textures with excellent tribological properties on the mechanical part surfaces. In this work, the tribological performance of 42CrMo matrix composite textured surfaces (CTSs) with different textured densities under grease lubrication was studied. The CTS was composed of 42CrMo alloys and SnAgCu-MXenes-Ti 3 C 2 (SACM). The results showed that when the textured density ρ of CTS was 36%, the friction coefficient (0.090) and wear rate (5.4 × 10−9 mm3N−1m−1) of counterpart ball could be respectively reduced by 75.7% and 38.6% compared with those of counterpart ball against the untextured sample. CTS could enhance the stability of friction system. Mxenes-Ti 3 C 2 wrapped by SnAgCu could form the lubricating layer containing sub-micron rollers on the worn surface, effectively reducing the friction and wear of samples under grease conditions. [Display omitted] • The composite textured surfaces (CTSs) were designed and prepared. • MXenes wrapped by SnAgCu could form sub-micrometer rollers in wear scar. • CTS exerted tribological enhancement function under starvation. • CTS could produce excellent synergistic effect with grease. [ABSTRACT FROM AUTHOR]

Determination of wear rate in spur gears requires treatment of the mixed elastohydrodynamic lubrication problem along the gear's line of action (LoA). For this purpose, a procedure is developed to predict the film thickness, traction coefficient and the wear rate with provision for the interactions between the surface asperities of the gear's teeth at each point on LoA. The results reveal that the surface finish has a more pronounced influence on the wear rate compared to the traction coefficient. The wear results are also compared to those obtained by an engineering approach that utilizes an estimate of the contact flash temperature with reasonable accuracy. Also investigated is the effect of starvation on the wear rate for applications where the inlet is not fully flooded. The results show that wear rate can be enormously large depending on the degree of starvation. [ABSTRACT FROM AUTHOR]

Nitrile butadiene rubber (NBR) is a water-lubricated bearing material that demonstrates excellent vibrational absorption and impact resistance; however, rapid wear under abnormal conditions is still a serious problem. Graphene (Gra) and carbon nanotubes (CNTs) are two types of carbon nanomaterials with different dimensions and excellent mechanical and friction properties. In this work, Gra and CNTs were used to fill the NBR, and a multifunctional friction and wear testing machine was used to study their impacts on the friction between NBR and ZCuSn10Zn2 under water lubrication conditions. The results indicate that both Gra and CNTs can effectively reduce the adhesion and the friction coefficient of NBR during the friction process. The two-dimensional lamellar structure of Gra is more likely to precipitate from the NBR matrix to generate a surface lubrication film, which can effectively reduce the friction coefficient. Both Gra and CNTs can prevent crack initiation and propagation in NBR during the wear process, thereby effectively reducing the wear of NBR. Compared with the two-dimensional structure of Gra, the one-dimensional linear structure of carbon nanotubes can "trap" the NBR molecular chains more effectively during the friction process, thus reducing the initiation and propagation of wear cracks and further improving the wear performance of NBR. • Effect of different dimensions of carbon nanomaterials on friction behavior of NBR. • Effect mechanism of two-dimensional graphene and one-dimensional carbon nanotubes on friction behavior of NBR. • NBR wear mechanism enhanced by two-dimensional graphene and one-dimensional carbon nanotubes. [ABSTRACT FROM AUTHOR]

Due to the operation in mixed and boundary friction, minimization of friction losses in automobile powertrains offers high potential for lowering of greenhouse gas emissions and saving fossil fuels. In cooperation between Surface Engineering Institute (IOT) and Gear Research Center (FZG), surface modifications in terms of stochastic and deterministic structures, diamond-like carbon (DLC) and nitride hard physical vapor deposition (PVD) coatings were tested in lubricated rolling-sliding contacts in twin-disk and gear efficiency test-rig. It was found that deterministic structured surfaces provide for reduction of friction losses by up to 7% under extreme boundary friction conditions at high Hertzian stresses and small relative lubricant film thicknesses. Application-oriented tests using DLC coated gear wheels in gear efficiency test-rig exhibited a reduction of friction losses between 10% and 21% compared to uncoated gear wheels. The DLC coating ZrC g developed at IOT provided for friction reduction of 15% for small circumferential speeds in boundary friction. Friction losses were reduced by up to 39% at higher circumferential speeds in spite of fully separated surfaces in the fluid friction regime. Due to their thermophysical properties, it is assumed that DLC coatings have an impact on viscosity and shear resistance of the lubricant. [ABSTRACT FROM AUTHOR]

Friction, wear and plastic deformation of copper (Cu) and α/β brass were studied under lubrication conditions. Hardness and microstructure of surface layers were evaluated. The friction properties were presented by Stribeck curves. The friction coefficient and wear of brass were significantly larger in comparison to Cu. The critical load of transition from the elasto-hydrodynamic lubrication (EHL) to boundary lubrication (BL) was two times lower for brass. Superplastic deformation of α-phase grains in brass is appeared under friction in BL, whereas plastic deformation localized at thin surface layers is observed for Cu. Intragranular sliding in α-phase is accompanied with the formation of shear bands and many pores coalesced to cracks. Thickness of the wear particles of brass is close to the width of shear bands. The deformation hardness of brass is significantly higher in comparison to Cu rubbed in the BL region. [ABSTRACT FROM AUTHOR]

Abstract: A preliminary two dimensional numerical model of wheel/rail in rolling contact is established to study the adhesion characteristics of wheel/rail with considering surface roughness under oil and water mixed contamination. A partial elastohydrodynamic lubrication (EHL) theory in line contact is applied in the model. The present numerical model is used to investigate the effects of contact pressures of wheel/rail, the volume fraction of oil and their locations in the contact zone, train speed on the adhesion coefficient under oil and water mixed contamination condition. In addition, the effects of oil contamination, water contamination and water/oil mixed contamination on the adhesion coefficient are compared. The numerical results show that the adhesion coefficient is greatly influenced by the train speed, the volume fraction of oil and their locations in the contact zone. Furthermore, in order to verify the accuracy of the numerical model, the numerical results are compared with the experimental results that were obtained by JD-1 wheel/rail simulation facility. [Copyright &y& Elsevier]

Abstract: The continuum damage mechanics (CDM) approach in conjunction with the load sharing concept is applied to predict steady state lubricated line-contact wear. Empirical formula for the maximum contact pressure in dry rough contact is employed together with the lubricant film thickness equation to estimate the portions of the load carried by the asperities and the lubricant. Effect of contact temperature on wear is also included using a simplified thermo-elastohydrodynamic analysis in conjunction with fractional film defect concept. While most wear models require experimental calibration, current study attempts to predict wear purely based on numerical simulation. The proposed methodology is quite fast and easy to implement for practical engineering applications. Comparison of numerical calculations with available experimental wear data show very good agreement. [Copyright &y& Elsevier]

Abstract: This paper proposes an experimental methodology for the analysis of the lubrication regime and wear that occur between vanes and pressure ring in variable displacement vane pumps. The knowledge of the lubrication regime is essential for the improvement of the performance of high pressure vane pumps by reducing wear, increasing the volumetric efficiency and decreasing maintenance costs. Tests using pressure rings of different materials were carried out in order to identify the best material in terms of wear and friction. The proposed methodology is based on Archard's law and takes advantage of wear experimental measurements, an empirical model for the estimation of contact pressure forces and hardness standard tests. The results of the analysis state that low wear and reduced friction can be obtained if elasto-hydrodynamic lubrication between vanes and pressure ring is established. Results have been also verified by an analytical elasto-hydrodynamic model. [Copyright &y& Elsevier]

The combination of texturing pretreatments and lubricant films was researched to improve the dry friction and wear performance of aluminium alloys. Three linear microtextures with different spacings were fabricated on the aluminum alloy substrates by ultrasonic surface rolling processing (USRP). The surface characteristics of different microtextures, such as micromorphologies, hardnesses, and wettability, were tested. PTFE/PPS lubricant films were prepared onto the textured surfaces by electrohydrodynamic atomization (EHDA), and micromorphologies of the films were observed. The friction and wear performance of aluminum alloy substrate and the films with texturing pretreatments were tested by ball-on disk reciprocating sliding dry friction experiments, and the countball material was 316L steel. The test data indicated that all films effectively reduced the friction coefficient of the substrate surface, and among them, the film sample URTC100 with a combination of 100 μm spacing texture and PTFE/PPS film exhibited the best effect of anti-wear while dry reciprocating sliding. Compared to the unpretreated film sample, URTC100 increased the wear life by 10% and reduced the wear track width and adhesion width by 35% and 25%, respectively. • Ultrasonic surface rolling processing was used to prepare surface textures. • Electrohydraulic atomization was used to fabricate PTFE/PPS lubricant films. • The above two methods were synergistic on dry tribological property improvement. [ABSTRACT FROM AUTHOR]

Double helical gears are widely applied in the aviation, marine and energy equipment, and generally required to be modified as the crowned since the machining error and assembling error of the gear drive are inevitable. The crowned gears usually operate in point contact mixed elastohydrodynamic lubrication (EHL), and adhesive wear has been one of the most prominent problems, but few previous researches were focused on this problem. In this work, a wear life prediction model of crowned double helical gears in point contact mixed EHL is proposed. The tooth profiles of the crowned gears are obtained according to the generating principle, and the load is attained in consideration of multi-tooth pairs contact. The contact pressure is derived from Hertzian elastic contact theory and load sharing concept, and the sliding distance is determined by a generalized model. Then, the wear rate in point contact mixed EHL is evaluated by extending the Archard theory to lubricated case, and the extended Archard's wear model is used to formulate the gear tooth wear. Moreover, the wear life prediction model which takes account of rotation speed and input torque is established, and the influences of surface roughness and crowned amount on the wear life of the crowned gears are further studied. Results show that surface roughness has a great influence on the wear life at different rotational speeds, while input torque has a great influence on the wear life at different crowned amount. It indicates that the wear life of the crowned double helical gears can be improved by reasonable matching lubrication, modification and working parameters. • A wear life model is developed for crowned double helical gears in point contact mixed EHL. • Surface roughness has a great influence on the wear life at different rotational speeds. • Input torque has a great influence on the wear life at different crowned amount. • Lubrication, modification and working parameters optimization is beneficial for wear life. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a method of utilizing oil-based nanolubricants containing abrasive nanoparticles for in-situ nanopolishing (ISN) of surfaces of rolling elements. Nanopolishing reduces the composite surface roughness of bearing elements and results in an increased film thickness ratio. Using a four-ball tester, the test and material conditions such as normal load, rotational speed, and initial surface roughness of balls were selected so that the initial film thickness ratio λ varied in the 1–3 range, i.e. within the partial (mixed) elastohydrodynamic (EHL) regime. The lubricant was either engine oil or engine oil-based nanolubricants containing diamond nanoparticles. The rolling ring track on the top ball was examined by a non-contact profilometer. The root mean square (RMS) roughness of the wear track using the nanolubricant was decreased. In-situ nanopolishing by the nanolubricant resulted in a significant increase in the film thickness ratio and a lower frictional torque. [Copyright &y& Elsevier]

Abstract: The tribological properties of rhenium-doped inorganic fullerene-like MoS2 nanoparticles were studied in poly alpha olefin oil, and compared to inorganic fullerene-like (IF) MS2 (M=Mo,W) nanoparticles and 2H-MoS2 platelets. For this purpose a rotational disc tribometer was used. Different regimes in the Stribeck curve, i.e., boundary, mixed and elasto-hydrodynamic lubrication conditions were studied. A precipitous reduction in friction and wear of oil suspensions with nanoparticles were observed for the entire IF samples. However, Re-doped IF exhibited the best results, presumably due to their reduced tribocharging and agglomeration. The various tribological mechanisms of solid state additives are discussed. [Copyright &y& Elsevier]

The friction and wear behavior were studied for three materials typically found in industrial bearing applications: a Sn-based Babbitt, polytetrafluoroethylene (PTFE) and a polyether ether ketone (PEEK) composite. Test conditions were unidirectional sliding with a ball-on-disc geometry where the counter surface material was a 440C stainless steel ball (6.35 mm dia.). The tests were also in the presence of a lubricant, ISO46 oil, with the sample and contact submerged throughout the test. The relative effects of load and sliding velocities on the wear rates were assessed by means of regression analysis. Connections between wear and the materials mechanical properties, which were measured by instrumented indentation, were also made. The ranking of wear performance of the materials correlated best to the ratio of H/(E*)0.447, where H is the test material's hardness and E* is the reduced modulus for the contact. The power applied to the reduced modulus is that used in previous studies to estimate the oil film thickness for an isoviscous, elastic lubrication regime. • Friction and wear rates of bearing materials are measured in oil-lubricated sliding against a stainless steel ball. • The mechanical properties were assessed by instrumented indentation at different loads and loading rates. • Good correlation between the wear rates and the ratio between the materials' hardness H and reduced moduli E*0.447. • The H/E*0.447 ratio is proposed as a new means to rank the wear resistance of materials in boundary lubricated contacts. [ABSTRACT FROM AUTHOR]

The transient non-Newtonian thermal micro-elastohydrodynamic lubrication point contact model and the adhesive wear model in mixed lubrication point contact are applied to a heavy-loaded modified herringbone gear drive respectively in steady running phase and start-stop phase. The fundamental parameters of both elastohydrodynamic point contact and wear model are derived from the meshing characteristic and kinematics analysis of herringbone gears. The effects of pinion torque, rotational speed and surface roughness on the maximum pressure and temperature rise and the minimum film thickness are discussed in gear steady running condition for full film lubrication contact. Meantime, the asperity load ratio, contact flash temperature and tooth wear depth are investigated in gear start-stop phase for mixed lubrication point contact. The results show that the lubrication performance of herringbone gear is deteriorated by substantially increased pressure and temperature rise resulting from a larger tooth surface roughness and rotational speed. The tooth wear depth of herringbone gear in start-stop phase is likely greatly reduced with a larger start-stop acceleration. Moreover, the lubrication and wear performances for the complete running cycle of herringbone gear drive from start-up to stop indicate that large tooth surface roughness rather than high load are more prone to herringbone gear thermo-mechanical and wear failures. • A Non-Newtonian thermal transient point contact EHL model is applied to modified herringbone gears. • A mixed EHL point contact wear model is developed for herringbone gears. • Gear thermo-mechanical failure can occur at pitch point due to large tooth roughness. • Tooth wear in start-stop phase can be greatly reduced with large start-stop acceleration. [ABSTRACT FROM AUTHOR]

Two dimensional (2d) lubricant materials further explore their application in oil and gas field with the research direction of reducing friction and wear. In this study, we added multilayer graphene into water-based sand cleaning liquid to reduce friction and wear of the CT80 coiled tubing. The results showed that the addition of multilayer graphene significantly improved the anti-friction and wear resistance. Adding 0.5% multilayer graphene effectively reduced COF and wear by 75%. Additionally, the higher multilayer graphene concentration, the greater CT80 material withstood the load of severe wear. Multilayer graphene can be adsorbed on the wear debris or form a lubrication film on both worn surfaces, which facilitated the transportation of the debris. Moreover, the wear analysis indicated the main wear form of the CT80 material was abrasive wear and fatigue wear. • Multilayer graphene reduces friction and wear of CT80 coiled tubing in water-based sand cleaning liquid. • The higher multilayer graphene concentration, the greater CT80 material withstand the load. • Abrasive and fatigue wear are the main form of the CT80 material. • Multilayer graphene can be adsorbed on the debris and contact surfaces to form lubrication films. [ABSTRACT FROM AUTHOR]

Tribo-machineries employ machine elements, such as discs and gears, which are frequently subjected to Hertzian loads that cause their mechanical failure. Case hardening is a popular method that ensures better productivity and performance of such elements compared to its untreated variants. This paper presents a wear and fatigue model for case hardened steels under Hertzian loads in line contact. Steel discs with different case hardening depths were tested using a three-disc testing machine, and the samples were analyzed using optical microscopy, SEM and a portable X-ray diffractometer. The influence of type of contact, case hardening depths, normal force (contact stress) and slip conditions on the damage process are investigated in detail. It was found that the hardening layer should be adapted to the load, since a too large hardening depth means a shorter service life due to higher residual stresses gradients. The transferability of results to increase the service life of real-life components is an essential component of this work. • Wear & fatigue model for case hardened steels under Hertzian loads in line contact. • Steel with different case depths tested using a three-disc machine. • Influence of contact, normal force and slip conditions on the damage investigated. • It was found that the hardening layer should be adapted to the load. • The transferability of results to real-life components is highlighted. [ABSTRACT FROM AUTHOR]

This paper describes the evolution of friction-induced microstructures underneath the wear surfaces of nickel single crystals, and their role in influencing the steady state coefficient of friction. Using a custom built tribometer, friction measurements were made on {001} and {011} crystal faces along several crystallographic directions in unidirectional linear mode with a Si 3 N 4 ball. Cross-sections of wear scars were prepared by focused ion beam (FIB) microscopy, and electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to analyze the evolution of crystallographic texture and recrystallization. The formation of a thin (10–15 nm) ultra-nanocrystalline layer in the {011}<211> orientation resulted in significant reductions in the coefficient of friction for that configuration, from the initial maximum of 0.64 to a steady state value of 0.32, after approximately 500 cycles of linear, unidirectional sliding. Crystal plasticity theory was used to describe the evolution of dislocation content in the worn material, which in turn provides an estimate of the characteristic grain size as a function of the imposed strain. An analysis of grain boundary sliding in ultra-fine-grained material suggests a mechanism for friction reduction. Model predictions of the contribution of grain boundary sliding (relative to plastic deformation) to friction provide a phenomenological description of the lubrication due to ultra-nanocrystalline surface microstructures. • A novel combination of electron microscopy and tribotesting techniques were utilized. • Friction measurements on single crystal surfaces along specific crystallographic directions was demonstrated. • Subsurface characterization provided insights into the relationships between microstructure and friction. • A model was proposed to help understand the relationships between plasicity, microstructure, and friction. • The model predictions agree well with the available observations and measurements. [ABSTRACT FROM AUTHOR]

Pitch bearings in wind turbines are affected by reciprocating motion due to pitch control. The combination of oscillating operation, high loads, and mixed lubrication often leads to wear. Grease lubricants in wind turbine pitch bearings should be designed to avoid such wear. Due to different available grease lubricants, the anti-wear properties are investigated under downscaled wind turbine pitch bearing conditions. The downscaling is accomplished by load simulation for a pitch bearing and analysis of the pitch movements for a 7.5 MW reference turbine. The operational conditions of the four point contact ball bearing with 5 m outer diameter are scaled to angular contact ball bearings of the size 7208. The investigations are concluded with contact model experiments. Six Industrial grease lubricants for wind turbine pitch bearings are tested that follow very different compositions. The investigations reveal, that none of the tested grease lubricants was able to reduce wear for all tested conditions. After 250 000 cycles certain conditions lead to severe wear. Therefore, the pitch controller should avoid such conditions if possible. Nevertheless, grease lubricants with low base oil viscosities and high bleeding rates are best on average for the tested conditions. Furthermore, the results of the bearing experiments are comparable to the model experiments. • Operating behaviour considered of pitch bearings under individual pitch control. • Method for scaling the operating behaviour to test rig conditions. • Experimental investigations on six commercial greases used in pitch bearings. • None of the greases was able to show satisfactory wear protection for all conditions. • Greases with low base oil viscosities and high bleeding rates showed the least wear. [ABSTRACT FROM AUTHOR]

The lubrication ability of various polymers and polymer composites fed into a steel/steel contact were assessed on a block-on-ring configuration under dry sliding conditions. The friction performance and lubricating mechanisms of the polymer materials were discussed. It was revealed that transfer of materials into the steel/steel contact and the friction behavior between steel and polymer play a dominant role on determining the friction performance of a steel/steel tribosystem. This work gains a new insight in the lubrication of steel/steel contacts and paves a route for developing polymer-based solid lubricants for such applications. • Novel concept for lubricating steel/steel contact by using polymer-based solid lubricants. • Assessment of the lubricating effect of various polymer materials. • Outstanding lubrication effect of graphite- and PTFE-based materials. • Elucidation of lubricating mechanisms. [ABSTRACT FROM AUTHOR]

Experimental and numerical analyses were conducted to explore the influence of DLC/TiAlN-coated die surfaces in sheet-metal forming under dry and oil-lubricated conditions. In this study, ironing and deep-drawing experiments were performed to determine the potential of the DLC/TiAlN coating in the sheet forming of stainless steels under different tribological conditions. The performance and physical properties of the DLC/TiAlN-coated die surface were obtained through load, surface roughness, and wear measurements as well as hardness and microstructure examination. The experimental results indicated that the DLC/TiAlN coating strongly resists galling under dry friction and thin film lubrication conditions that reduces the friction and forming load. The presence of a thin oil film reduces the sliding-originated surface tensile stresses of the DLC/TiAlN coating, improving the wear resistance of the die surface even at high temperatures and high contact pressures. Thermomechanical numerical analysis supported the experimental results, which confirmed that the lubricant discharged the heat generated in the die–workpiece contact region to reduce the friction and forming load. With the DLC/TiAlN coating, the plain mineral oil with no extreme pressure additives can function as effective as chlorinated paraffin oil for protecting the die surface, thus extending the die service life. Image 1 • Ironing and deep drawing tests performed under different tribological conditions. • DLC/TiAlN coating resists galling under dry friction and thin film lubrication. • DLC/TiAlN utilized more environment-friendly oils than chlorinated paraffin oil. • TiAlN interlayer coating enhanced DLC performance. [ABSTRACT FROM AUTHOR]

Extensive wear appears in the case of dry contacts, or when the lubrication of the contacting surfaces is not appropriate. The aim of this research is to improve the mixed elastohydrodynamic lubrication in hypoid gears by the optimization of manufacture parameters for tooth surface processing. A full numerical analysis of the thermal mixed EHL in hypoid gears is applied. The equation system and the numerical procedure are unified for a full coverage of all the lubrication regions including the full film, mixed, and boundary lubrication. In the hydrodynamically lubricated areas the calculation method employed is based on the simultaneous solution of the Reynolds, elasticity, energy, and Laplace's equations. In the asperity contact areas the Reynolds equation is reduced to an expression equivalent to the mathematical description of dry contact problem. The real geometry and kinematics of the gear pair based on the manufacturing procedure is applied, thus the exact geometrical separation of the mating tooth surfaces is included in the oil film shape, and the real velocities of these surfaces are used in the Reynolds and energy equations. The transient nature of gear tooth mesh is included. The oil viscosity variation with respect to pressure and temperature and the density variation with respect to pressure are included. The non-Newtonian behaviour of the lubricant is considered. Using this model, the pressures, film thickness, temperatures, and power losses in the mixed lubrication regime are predicted. By using the developed method, the influence of the manufacturing parameters on the conditions of mixed elastohydrodynamic lubrication is investigated. On the basis of the obtained results recommendations are formulated to improve the mixed EHL and the efficiency of face-milled hypoid gears. • A full numerical analysis of the mixed EHL in hypoid gears is performed. • The influence of the manufacture parameters on mixed EHL in hypoid gears is investigated. • Recommendations are formulated to improve the EHL characteristics of hypoid gears by optimizing the manufacture procedure. [ABSTRACT FROM AUTHOR]

The shear strength at the interface contributes to the overall friction force experienced by the contacting bodies sliding against each other. In this article, an experimental technique to characterize the shear strength at the interface of metallic bodies in sliding contact has been developed. The boundary layers formed at interface in a lubricating contact have been varied by using two different types of lubricants in combination with both zinc coated and uncoated steel sheets. The empirical relations between the experimental parameters such as contact pressure and sliding velocity and the interfacial shear strength have been expressed by fitting the experimental results. These expressions have been incorporated in the Material Point Method (MPM) based ploughing model. The coefficient of friction and ploughing depth obtained from the numerical simulations have been validated relative to the experimental results with a good agreement for both lubricated and unlubricated substrates, different loads and spherical indenter sizes. Furthermore, the interfacial shear strength has been varied in the MPM-based ploughing model and ploughing experiments to study the contribution of interfacial shear strength to overall friction, deformation and wear. • An experimental characterization technique of interfacial shear strength from the measured friction force and the contact area in line contact loading on coated sheet metals is developed. • The interface is varied using zinc coated and uncoated steel sheets, with different surface roughness and conditions, with or without using one of the two given lubricants. • The interfacial shear strength is measured and plotted for different interfaces over a range of contact pressures and sliding velocities and curve-fitted to mathematical relations. • The shear strength relations are included in the MPM-ploughing model whose results are compared with ploughing experiments on steel sheets for varying interfaces and applied loads. • The effects of varying interfacial shear strength on ploughing friction, substrate deformation and abrasive wear are studied using the MPM-ploughing model and ploughing experiments. [ABSTRACT FROM AUTHOR]