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Wax is a prevalent lubrication material extensively employed in various engineering applications. Understanding the degradation characteristics of the waxy lubrication layer under diverse stress variables and levels is crucial for ensuring system security and reliability. Due to the unclear mechanism governing the degradation of the waxy lubrication layer under different stress variables, existing degradation models are unsuitable for modeling waxy lubrication layer degradation data. To address this challenge, we propose a functional data‐driven method leveraging dense observations of waxy degradation. Through extensive simulations and a case study, we demonstrate the superior performance and effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

In mixed elastohydrodynamic lubrication (EHL), the load distribution between the gear meshing surfaces is shared by the oil film and the asperities of the gear's rough surface. Based on the load‐sharing concept, this paper proposes a time‐varying meshing stiffness (TVMS) model for gears with mixed EHL. The initial step involves the utilization of the Greenwood‐Williamson model to calculate the contact stiffness of surface asperities, while the lubricating film is assessed using a curve‐fitting formula to investigate the influence of gear surface morphology on TVMS. Subsequently, the incorporation of gear fillet foundation deformation and friction enables accurate TVMS determination. The proposed method is employed to examine the meshing stiffness of the gear pair under both dry lubrication and EHL conditions. Comparative analysis reveals favorable agreement between the proposed model and experimental results obtained under dry lubrication, thereby highlighting the superior performance of the proposed approach. Moreover, the time‐varying friction coefficient under EHL is computed, and the impacts of gear surface morphology parameters, temperature, speed, and load on lubrication conditions and TVMS are investigated. The findings presented in this paper contribute significantly to advancements in gear design and performance. [ABSTRACT FROM AUTHOR]

The oil film lubrication performance of a large hydrostatic turntable operating at the model of constant surface cutting speed is studied. Firstly, the rotary speed equation which is bound by the constant surface cutting speed is established. According to the fluid lubrication theory, the gap flow equation, the oil film temperature rise equation and the double‐rectangular‐cavity oil pad bearing capacity equation are derived. Further, a prediction model of oil film lubrication performance in the operating mode is established. The change rules of temperature, pressure and other performance indexes of the film with time are obtained by numerical simulation. And, the above laws are verified by design experiments. It is found that the cutting speed, feed rate leaves a significant impact on the law of variations of oil film performance with time. According to the conclusions, it will be beneficial to improve the bearing capacity of the hydrostatic turntable and further improve the machining accuracy by using cutting parameters reasonably to control the speed within a certain range. [ABSTRACT FROM AUTHOR]

In order to predict the spiral bevel gear churning power loss, based on the Computational Fluid Dynamics (CFD) method, the computational model for the splash lubrication of the spiral bevel gear pair is established and validated by experiments. The churning power loss of spiral bevel gears is obtained and the corresponding flow field distribution in the gearbox with a pair of spiral bevel gears is analysed under a standard operating condition. For the churning power loss of spiral bevel gears, the loss of teeth surface is mainly caused by pressure while the loss of gear side is mainly generated by the viscous force. The effects of the gear rotational speed, oil level, oil temperature and oil shroud on the churning loss are also investigated and analysed. Ultimately, an optimisation method is proposed for the original spiral bevel geared transmission. [ABSTRACT FROM AUTHOR]

The locally oriented roughness is a common feature of surface finished by a machining process, such as the surface of the cylinder liner, and may significantly influence lubrication characteristic. A homogenised transient Reynolds equation for the locally oriented roughness is derived. The Jacobsson–Floberg–Olsson (JFO) boundary conditions was implicitly incorporated into the transient Reynolds equation to ensure the mass flow conservation. On this foundation, a model for the transient lubrication in the cylinder liner‐piston ring considering the effects of the surface roughness and cavitation is established. Then, the results of model developed here are compared with those from the stochastic model by Patir and Cheng. and the effect of the direction of roughness on the lubrication properties is analysed. The homogenised transient Reynolds equation and the lubrication model developed here have great potential for understanding and optimising the transient lubrication considering the surface local roughness orientation, cavitation and starved lubrication. [ABSTRACT FROM AUTHOR]

Nanofluids have the tendency to improve thermal characteristics in a broader context, such as in medical processes, industrial cooling applications, the transportation industry, hybrid engines, gas temperature reduction, microelectromechanical systems, refrigerators, nuclear reactors, vehicle temperature control, pharmaceutical processes, thermal management of vehicles, microelectronics, and chillers, etc. Therefore, present study investigates the effects of a two-dimensional magnetohydrodynamics (MHD) peristalsis of the Carreau– Yasuda nanofluid through conservation principles of energy, concentration, mass, and momentum, which is motivated by recent advances in biological engineering. The entire system is coupled through viscous dissipation, Joule heating, a heat sink/source, Brownian diffusion, a radially magnetic field, thermophoresis motion, and slip conditions in a curved geometry. Lubrication theory is employed in order to simplify governing equations. Resulting systems are nonlinear coupled differential equations whose exact solutions are difficult to obtain, therefore, numerical solutions are obtained through NDSolve in Mathematica. The key features of peristaltic movement and rates of heat transfer are disseminated in detail via graphical representations for variation of various physical parameters. According to the findings, for greater values of the Hartman number, temperature increases, and the velocity decreases. The validity of these results has been verified using the existing published articles of Hayat et al. (2018). [ABSTRACT FROM AUTHOR]

In this research, an angular contact ball bearing with two‐half inner rings is used as a carrier. Considering the two‐phase flow characteristics of oil and air in the bearing, the flow characteristics of lubricating oil inside the bearing with under‐race lubrication are studied. Based on the volume of fluid (VOF) method and the standard k–ε turbulent flow model, the characteristics of oil and air two‐phase flow inside the ball bearing are analysed. The bearing internal pressure field distribution, streamline distribution, and other flow properties for the different radial working clearances, pocket clearances and guide clearances are determined. The distribution of the lubricating oil in key areas is observed. The oil phase volume fraction of the key lubrication areas, such as the cage pocket surface and the inner and outer ring surfaces is used to evaluate the influence of different structural parameters on the bearing lubrication performance. The lubrication influences of the inner and outer guides of the cage are evaluated, and the internal flow characteristics of the bearing are analysed with different guide clearances. The results show that with the radial working clearance range from 0.100 to 0.145 mm, the pressure in the working contact area of the bearing decreases 26%. The pocket clearance ranges from 0.48 to 0.28 mm, and the pressure in the working contact area of the bearing significant increases from 0.642 to 1.165 MPa. From this perspective, the larger the radial working clearance and pocket clearance are, the more favourable it is for bearing lubrication. For bearings with under‐ring lubrication, when the bearing adopts outer guidance, the distribution of lubricating oil in the key areas of the bearing is worse than that for internal guidance. However, the pressure in the working contact area of the bearing slightly increases from 0.642 to 0.759 MPa with the inner guide clearance increasing from 0.4 to 0.8 mm. [ABSTRACT FROM AUTHOR]

Heat transfer from the solidified shell to the mold, especially in the meniscus region, significantly affects the surface quality of the strand and the stability of the continuous casting process. The mold slag film serves as the sole heat transfer medium between the shell and the mold, and its performance and structure have a substantial impact on the heat transfer efficiency. Thus, since the 1980s, various testing methods are developed to investigate the heat transfer performance of the slag film, including the pouring method, immersion method, parallel plate method, and mold experiment. In this article, the principles, characteristics, and main study results of these methods are reviewed, and the existing issues are highlighted in these methods. Furthermore, specific requirements that shall be satisfied in future research on the heat transfer of slag film are presented. The new approach for testing heat transfer in slag film necessitates ensuring consistency in the heat flux, surface temperature of the shell, interfacial thermal resistance, and thickness and cooling rate of the slag film, aligning with those observed in a mold. This consistency is crucial to ensure the comparable structure and heat transfer characteristic between the experimental and industrial slag films. [ABSTRACT FROM AUTHOR]

Wheel‐rail adhesion is important to the traction and braking of railway vehicles. This paper develops a three‐dimensional numerical model considering surface roughness and temperature to investigate water‐contaminated adhesion characteristics. A simplified elastohydrodynamic lubrication model considering the thermal effect is developed to obtain the normal load carried by liquid film and asperities. Meanwhile, a third body layer (3BL) model, which considers the effects of pressure and temperature on 3BL, is used to calculate the tangential stress and friction coefficient of asperity contact. To verify the numerical model, firstly, the results are compared with the existing experimental results at low and high speeds. In addition, the effects of surface roughness and temperature on adhesion coefficient are investigated. Furthermore, the elastoplastic behaviour of the tangential stress and the adhesion characteristics for large creepages are studied. The obtained adhesion‐creepage curve can represent the decreasing trend after reaching saturation because of temperature. [ABSTRACT FROM AUTHOR]

The variation of friction coefficient (μ) of model wine and model saliva mixtures with entrainment speed (VR) on simulated oral surfaces was evaluated by oral tribology. Combined with techniques of dynamic light scattering (DLS), atomic force microscopy (AFM), rheometer, and quartz crystal microbalance with dissipation monitoring (QCM‐D), the correlation between characteristics of the model wine and model saliva mixtures (particle size and morphology, suspension viscosity, adsorption film thickness, and viscoelasticity) and the oral lubrication loss was established. The results showed that the higher the concentration of tannin in the model wine, the larger the size of the complexes with the model saliva, and the higher the thickness, viscoelasticity, and roughness of the adsorption film formed, which resulted in the increase of friction coefficient in the boundary lubrication regime. Different from previous results, it is found that the maximum value of the friction coefficient (μmax) in the boundary regime has the best positive correlation with the astringency perception intensity of the model wine accordingly. [ABSTRACT FROM AUTHOR]

The elastohydrodynamic lubrication (EHL) model of angular contact ball bearings (ACBB) with local defects under spin condition is established. The local defect surface profile is characterised. On this basis, the modified quasi‐static model of ACBB with local defects is proposed. Then, the comprehensive stiffness model of ACBB with local defect under EHL is built, and the influence of different factors on the mechanical characteristics of ACBB with local defect is investigated. The results show that with the increase of the local defect size, the equivalent contact stiffness of the defect area decreases, and the contact load in non‐defect area increases. Considering EHL, the contact deformation of bearing decreases, the contact load and equivalent comprehensive stiffness increases obviously. The axial contact angle of the defect area largely determines the equivalent comprehensive stiffness of the roller at the defect. [ABSTRACT FROM AUTHOR]

A numerical method is proposed to evaluate the effect of non‐Gaussian roughness on point contact elastohydrodynamic lubrication (EHL). A mixed EHL model of point contact, considering non‐Gaussian roughness, is developed. The oil film pressure in the model was controlled by the Reynolds equation of average flow, and the contact pressure of asperity was obtained by the rough surface micro‐contact model. The influence of non‐Gaussian roughness parameters on contact pressure distribution, film thickness profile and the ratio of asperity pressure to contact load (asperity load ratio) are investigated based on the mixed EHL model. The results show that the asperity pressure increases as root mean square (RMS) roughness increases, skewness and kurtosis. The film thickness also increases with RMS roughness and skewness, but is not sensitive to kurtosis. [ABSTRACT FROM AUTHOR]

The distribution of lubricant flow field inside the two‐stage transmission reducer is very complicated during splash lubrication, which is difficult to be visually simulated and analysed using traditional finite element methods (FEM). There are many problems in model processing, algorithm selection, mesh division, and computational workload. Through sufficient investigation and experimental validation based on literature, the moving particle semi‐implicit (MPS) method is proposed to study the splash lubrication characteristics of a rail vehicle reducer. Through this method, the visual simulation calculation of multiple working conditions of reducer with complex structure is realised, and the unreasonable structure of the gearbox body is optimised. The model of oil supply demand in the Hertz contact zone of gear transmission is established, and the time‐domain variation law of oil particles number in the contact zone and oil supply state are analysed. It is found that the optimised reducer model can meet the demand of oil supply under the four typical working conditions of the rail vehicle. The higher the initial oil volume is, the more sufficient the oil supply is. Compared with the working temperature conditions of 20 and 80 °C, the lubrication effect is better at 40 and 60 °C. By analysing the power loss proportion of each gear, it is found that the sum of power loss of gear 1 and gear 2 is dominant under different working conditions, reaching 76%–99.5% of the total churning power losses. [ABSTRACT FROM AUTHOR]

In this paper, a tribo‐dynamic model of a helical gear is established. For the lubrication sub‐model, a finite line thermal elastohydrodynamic lubrication model of helical gear is adopted. The lateral vibration, axial vibration of gear and torsional vibration of the gear shaft are considered in the dynamic sub‐model. Results show that the tribological parameters of helical gear under the tribo‐dynamic model deviate significantly from that of the quasi‐static model, especially in the engaging‐in region of tooth pair. The friction excitation mainly affects the vibration along the off‐line‐of‐action direction of the gears. The influence of operating conditions on the tribological and dynamic properties of a helical gear pair is significant, especially in the case related to the characteristic frequency of gears. [ABSTRACT FROM AUTHOR]

Electrophoretic deposition was used to deposit carbon nanotube/polyether ether ketone (CNTs/PEEK) composite coatings onto porous titanium‐tantalum (Ti‐30Ta) substrates at different PEEK concentrations (4.5, 6.0, and 7.5 mg/mL). Coatings were analyzed for thickness, porosity, surface roughness, microhardness and bonding strength, with higher PEEK concentrations producing thicker and more uniform coatings. However, optimal coating thickness showed highest bonding strength; lower and higher thickness led to decreased bonding strength. The tribological properties of the CNTs/PEEK coated Ti‐30Ta samples of different thicknesses (50, 70, and 100 μm) were evaluated using ball‐on‐flat linear reciprocating sliding tests under dry and wet conditions using simulated body fluid (SBF) as a lubricant. The CNTs/PEEK coatings provided excellent tribological protection under dry friction, with thicker coatings having lower friction and negligible wear. However, under wet sliding, the coating's wear rate increased significantly due to softening of the rubbing surface caused by SBF lubrication that increase transfer film onto the counter body surface. Coating with optimal thickness of 74 μm demonstrated the lowest friction and wear under SBF lubrication due to its highest hardness and bonding strength. This study highlights the importance of controlling coating thickness in determining the performance of the CNTs/PEEK coatings for orthopedic implants. [ABSTRACT FROM AUTHOR]

A series of polyimide (PI)/V2CTx MXene composites was synthesized via polyamide acids (PAA) and two‐dimensional (2D) V2CTx MXene obtained by etching precursor V2AlC. PI/V2CTx MXene composites with different mass ratios were obtained by blending and heating with PAA. The results showed that V2CTx MXene has excellent dispersion in PI. In particular, V2CTx MXene exhibited excellent friction reduction and anti‐wear properties as a solid lubricant additive, and the wear rate (WR) was reduced by 43.2% by incorporating only 0.8 wt% of V2CTx MXene in the pristine PI and 71.9% by incorporating 1.2 wt%. Scanning electron microscopy (SEM) and x‐ray photoelectron spectroscopy (XPS) analyses showed that the continuous transfer film consisting of a high proportion of tribo‐chemical products formed on the contact surface is significant to improve the lubrication performances of the PI composites. This work broadens the application of MXene in the field of tribology and contributes to energy conservation and sustainable development of human society. Highlights: The tribological properties could be tuned by changing the ratio of PI to V2CTx MXene.The WR of PI composites was reduced by 71.9% with incorporating 1.2 wt% of V2CTx MXene.The formation of transfer films on the contact surface is significant for improving anti‐wear of PI. [ABSTRACT FROM AUTHOR]

In this article, the dynamic characteristics of Co‐curing Damping Sandwich Composites with Different Lay‐up Angles (CDSCDLA) are studied by means of modal analysis and numerical simulation to optimize the structure of co‐curing composites. The vibration equilibrium equation of CDSCDLA is derived according to first order shear deformation theory and Hamilton equation. The dynamic model of the structure is established by finite element simulation to verify the accuracy of the theoretical calculation. The influence of different lay‐up angle and the damping film thickness on the free vibration of CDSCDLA is explored under the condition of constant skin thickness. The theoretical derivation and finite element simulation results reveals that the overall dynamic characteristic of damping sandwich composite with a lay‐up angle of 45° is optimal when the damping film thickness is constant. In particular, when the thickness of the damping film is 0.1 mm, the first‐order mode damping and mode frequency of composite plate with a lay‐up angle of 45° reach the maximum value of 0.1495 and 747.9 Hz, respectively. The first order damping loss factor of the CDSCDLA with different layup angles is maximum when the damping film thickness is 0.3 mm. However, blindly increasing the damping layer thickness can not always improve the damping performance of the composite structure, but will greatly reduce the stiffness of the composite. The work provides a reference for dynamic performance optimization and structural design of sandwich plate with high strength and large damping loss factor. Highlights: Free vibration of sandwich composites with lay‐up angles is investigated.The dynamic analytical model of the structure is established.The validity of the derived theory is verified by numerical simulation. [ABSTRACT FROM AUTHOR]

The rheological and tribological properties of environmentally compatible lubricants of different bases (native oil, synthetic ester, polyalkylene glycol‐containing oil) compared to a conventional, mineral oil‐based lubricant are investigated in order to develop toxicologically harmless and technically suitable lubricants for electromechanical drives. The aging of the oil is also considered. The results of this study reveal that the properties of polyalkylene glycol‐containing and synthetic ester‐based lubricants have the potential to act as substitutes for lubricants containing mineral oil. By examining and improving the properties of sustainable lubricants, gear oils that are partially or totally non‐mineral oil based will be highly attractive in the future. [ABSTRACT FROM AUTHOR]

Porous materials are widely used in friction pairs. The transient squeezing flow of the lubricant significantly affects the lubrication quality. The study found that the lubricant penetrates into the porous matrix in the contact area and exudes upward to the entrance of the contact area. The maximum stress occurs at the subsurface of the contact zone, and the maximum pressure occurs at the contact centre. In the early loading stage, the lubricant exudates, resulting in a higher liquid‐phase load. With the prolongation of the time, the average stress decreases and then increases gradually, whilst the average pressure has the opposite change. In the late loading stage, the load is completely borne by the solid phase. Increasing the load will increases the seepage velocity of the lubricant, which enhance the pumping effect of the friction interface. The findings can help for better understanding of the self‐lubrication mechanism of the porous materials. [ABSTRACT FROM AUTHOR]

The synergistic effects of carbon fiber (CF) and polytetrafluoroethylene (PTFE) on the friction and wear behavior of polyarylene ether nitrile (PEN) under dry lubrication condition were studied. According to the scanning electron microscopy (SEM) on the composites' surface after wear, the wear mechanism of the composites under dry sliding condition was analyzed. The research results show that the addition of solid lubricants PTFE and carbon fibers to PEN helps to enhance the properties of friction and wear. The specific wear rate is decreased to 5.7 × 10−7 mm3/N m at a PTFE composition of 5 wt%, which is optimized by 33.4% more than PEN/CF composites. In addition, wear mechanisms are mainly abrasive wear, accompanied by adhesive wear and plowing of the friction ring. [ABSTRACT FROM AUTHOR]

In this paper, a simulation model of reciprocating rod seal systems when there is axial texture on the rod surface due to wear is studied. The model includes macroscopic solid mechanics analysis, microscopic contact mechanics analysis and fluid mechanics analysis, and on this basis, the change of surface pressure when the sealing ring fall into a texture is calculated by the micro‐deformation mechanics analysis of the seal surface. Then, the stiffness matrix method is used to find the film thickness when the three pressures in the sealing area are in equilibrium, completing the fluid–solid coupling calculation. Combined with the above simulation process, the performance parameters of the sealing system such as leakage and friction can be obtained. Results show that axial texture will degrade sealing performance, which increases leakage and friction. The simulation results can quantitative characterise the influence of rod wear on sealing performance and provide some theoretical basis for the study of seal failure mechanism and prediction of seal life. [ABSTRACT FROM AUTHOR]

In the actual working condition, due to the manufacturing errors, improper installation, load, thermal deformation or other factors can cause the journal surface to produce the form and position errors. The mathematical models are developed that takes into account the form and position errors, the lubrication performance of four‐recess capillary restrictor hybrid journal bearings with different journal tilt angles and cylindricities is studied, and the effect of eccentricity on the oil film lubrication performance is analysed. The results show that the dimensionless oil film pressure and loading capacity increase as the journal tilt angle and eccentricity increase considering journal tilt, and the friction coefficient tends to increase and then decrease. Compared with journal alignment, the oil film thickness distorts, the oil film pressure peak shifts to the edge of bearing, and the horizontal tilt has a greater impact on bearing when the journal is tilted. The oil film pressure distribution has no significant change considering cylindricity errors, while the oil film pressure value increases, the loading capacity increases and the coefficient of friction decreases as the cylindricity and eccentricity increase. The research shows that the presence of a certain cylindricity error contributes to the lubrication performance of four‐recess capillary restrictor hybrid journal bearings. [ABSTRACT FROM AUTHOR]

Structural optimization design is a promising way to further promote the lubrication performance of the artificial hip joint (AHJ). In this work, a non‐spherical shape optimization design strategy for the femoral head is firstly proposed. The generatrix, the line rotated about an axis that generates the bearing surface of the femoral head, is characterized based on a third‐order Bezier curve. The performance of the AHJ under steady‐state condition is analyzed by solving the governing equations of the elastohydrodynamic lubrication problem, and the minimum lubricating film thickness of the AHJ is maximized by adjusting the positions of four control points of the Bezier curve based on the simulated annealing method. The results show that, when compared with the standard spherical femoral head, the optimized non‐spherical femoral head can significantly improve the minimum thickness and reduce the maximum pressure of the lubricating film of the AHJ. Through the analysis of the optimization process, the results further reveal that the shape of the femoral head has a direct impact on the thickness distribution of the lubricating film. This research will provide guidance and theoretical support for novel design of AHJs. [ABSTRACT FROM AUTHOR]

This article aims to investigate the percolation and supply behavior of lubricant on the porous self-lubricating material. The numerical model is established to describe the infiltration-exudation response in the deformed porous material. It is found that the lubricant stored in the pores is forced to flow when the loaded porous matrix deforms. The flow drives the seepage stratification in the porous body and forms an interlayer flow zone. The fluid pressure gradient in the normal direction is the internal factor of the seepage stratification. The interlayer flow zone first appears in the middle of the vertical direction of the porous matrix. With the increase of loading time, the interlayer flow zone gradually moves from the middle to the bottom of the porous matrix, which means that the quantity of the lubricant stored in the porous surface decreases. In the whole process of the seepage response, the lubricant flows out from the inlet and continuously supplies lubricant to the contact area. Delaying the downward movement of the interlayer flow zone can ensure the continuous exudation of the lubricant, which is beneficial to maintain excellent lubrication characteristics. [ABSTRACT FROM AUTHOR]

This contribution presents an elastohydrodynamic lubrication (EHL) model for pneumatic spool valves. For an accurate estimation of the transient friction of this tribological sealing system, the surface topography of the cylindrical sealing counterfaces of the valve housings are measured and analyzed with an optical surface measurement instrument. Based on the surface topography data, tribological properties and flow factors of the system are derived. It has been found that the consideration of the surface topography has a significant influence on the simulation results of the EHL model, lowering the calculated friction force by up to 20 %. [ABSTRACT FROM AUTHOR]

The optimization of lubricated sealing systems with respect to the stick‐slip effect requires a friction model that describes the complex friction behavior in the lubricated contact area. This paper presents an efficient dynamic friction model based on the Stribeck curve, which allows to investigate the influencing parameters through finite element (FE) simulations. The simulation of a tribometer test using this friction model proofs that the model correlates well with the tribometer test results. It is shown that the system stiffness has a significant influence on the stick‐slip tendency of the system. [ABSTRACT FROM AUTHOR]

Based on the lubrication angle field and the locus of lubricating weak point, the lubricating characteristic of the toroidal surface enveloping cylindrical worm drive is globally investigated. The nonlinear equation system to determine the lubricating weak point is established by utilising the lubrication angle. Generally speaking, the weak locus always exists roughly in the middle of the tooth surface of cylindrical wormgear and a zone with worse lubricating behaviour is around the locus. By increasing the number of worm thread, the locus of lubricating weak point can be completely removed from the wormgear tooth surface, and the locus approximately is in the shape of the inverse capital letter L. On this occasion, the entire wormgear tooth surface is half surrounded by the locus, and the overall lubrication performance of the worm drive is improved. The current research is an application of elastohydrodynamic lubrication (EHL) on worm drive. [ABSTRACT FROM AUTHOR]

Recently emerged on‐skin electronics with applications in human–machine interfaces and on‐body healthy monitoring call for the development of high‐performance skin‐like electrodes and semiconducting polymers. The development of waterproof and breathable membranes that can provide a high level of protection for human skins and a comfortable contact between electronics and skin are the pressing demands for on‐skin electronics. However, major challenges remain, such as the limited mechanical durability and permeability of gas and liquid, hindering long‐term stability and reusability. Herein, a fibrous electrolyte containing polymer matrix and ionic liquid, which is highly robust, breathable, waterproof, and conformal with human skin is reported. Serving as fibrous substrate and electrolyte of organic electrochemical transistors (OECTs), a high transconductance of ≈0.8 mS, stability over pulsing and time (≈1000 cycles and 30 days) are achieved. The softness of fibrous OECTs enables a comfortable contact after attaching to human skin, which can reduce the interfacial impedance to achieve a high‐quality local amplification of the electrocardiography signals (signal‐to‐noise ratio of 21.7 dB) even in skin squeezed state or after one week. These results indicated that our fibrous OECTs have huge potential for versatile on‐skin electronics such as non‐invasive medical monitoring, soft sensors, and textile electronics. [ABSTRACT FROM AUTHOR]

To improve the tribological characteristics of the face seal, the squamous groove micro textures with different area proportion and the circular dimple micro texture were designed and manufactured. The disc‐disc friction and wear experiments and numerical simulation were carried out in oil lubrication. The pressure distribution, friction coefficient, fluid temperature and wear morphology are investigated. The study show that the friction coefficients of the micro textured and untextured samples decline with the increase of load, but first increase and then decrease with the rise of rotational speed. Micro textured samples could decline the friction coefficient effectively, and the asymmetric structure in the lubricant inflow and outflow region of the squamous groove micro texture makes it have better tribological performance. In addition, the micro texture can increase heat dissipation area, reduce heat production and collect wear debris, which could modify the lubricant temperature and wear morphology effectively. [ABSTRACT FROM AUTHOR]

The oil storage effect of textures is beneficial for lubrication performance under starved lubrication. When the larger of the two surfaces in friction pairs is textured, the moving textures should be considered because the boundary conditions are transiently changed at each moment. This is especially for the cross‐hatched textures, which are manufactured on the cylinder liner while not on the piston ring. However, it means that the calculation cost will be very expensive for engineering friction pairs because the required calculation scale is very large and the required time step is very small. So the dynamic characteristics of moving textures on engineering surfaces are normally neglected in the existing researches. In this study, a starved lubrication model of the piston ring‐cylinder liner (PRCL) system is established considering the oil storage effect, local hydrodynamic effect and dynamic characteristics of the moving cross‐hatched textures. To speed up the calculation, an efficient parallel algorithm is developed. The results show that there is a significant difference in minimum oil film thickness (MOFT), wear load and oil film boundaries between stationary textures and moving textures, so the moving textures should not be simplified. This is helpful to find a better design of textures for engineering friction pairs. [ABSTRACT FROM AUTHOR]

In practice, due to bearing load there is a generation of pressure in the lubricant film, which leads elastic deformation on the bounding surfaces and causes variation in the film thickness. As film thickness plays an important role in performance of the slider‐bearing designs; an attempt has been made to study numerical simulation of elastic deformation effect in one‐dimensional inclined slider‐bearing with ferrofluid (FF) lubricant. The modified Reynolds equation is derived using ferrohydrodynamic theory by Shliomis with transverse uniformly strong magnetic field, and continuity equation. Using this equation dimensionless load‐carrying capacity (W¯$\bar{W}$) is studied for different parameters. The results show the better performance of W¯$\bar{W}$ for lower convergence ratio and higher effective viscosity. However, elastic deformation has no effect on W¯$\bar{W}$. Some comparisons are also made with the previous literature. [ABSTRACT FROM AUTHOR]

Reciprocating spur gear rack is prone to lubrication failure near the reversing dead center position. Ree‐Eyring lubrication fluid, multigrid method and multigrid integral method were used to calculate the pressure profile, film thickness and oil temperature rise. Compared with linear motion, the process of reciprocating commutative movement is more complicated and the lubrication state are more unstable. The effects of different reversing duration time and commutation meshing state on lubricant film were analysed. The results show that, the oil thickness during the gear reversing process is significantly reduced. While shortening the reversing time can improve the lubricating film thickness, it causes the instantaneous oil temperature to rise. Therefore, the gear tooth damage caused by high temperature can be avoided by prolonging the reversing duration time properly. The longer the reversing duration time, the minimum value of central film thickness and central pressure is closer to the meshing outlet area. No matter what the reversing time change, the minimum lubrication film thickness is in the reversing dead center position. So the reversing dead center is still the dangerous point for the lubrication failure of the spur gear rack mechanism. When the reversing dead center is in the leading tooth of double‐tooth meshing, the gear has the largest film thickness and the largest contact area. In addition, the synthetic radius of curvature and entrainment velocity become larger so the lubrication conditions have been improved. The results provide the theoretical basis and guidance for the reasonable design of the spur gear rack and the improvement of its lubricating performance. [ABSTRACT FROM AUTHOR]

In this study, an interfacial slip model including the limiting shear stress is proposed and applied to the thermal elastohydrodynamic lubrication (EHL) analysis of a helical gear pair. The main difference between the proposed model and the classical EHL model is that, the term of entrainment velocity in Reynolds equation is modified. The influences of interfacial slip, thermal effect, initial limiting shear stress and operating conditions on the tribological properties are evaluated. Due to the interfacial slip, the pressure distribution moves towards the inlet region, and the fluctuation distributions of entrainment velocity and film thickness are similar to the trigonometric function. The influence of thermal effect on interfacial slip cannot be ignored, especially in the case of high speed and heavy load. As the input torque and input rotational speed increase, the interfacial slip gradually extends to the whole meshing process. [ABSTRACT FROM AUTHOR]

Slippery liquid‐infused porous surface (SLIPS) has received widespread attention in the antifouling field, while its controllability of surface lubricity and durability of lubricant are relatively insufficient. In this study, inspired by the hagfish's defensive behavior of secreting mucus to escape from predators, a smart SLIPS marine antifouling coating is prepared, which possesses responsively switching lubrication modes and self‐healing property. The responsive supramolecular interaction between azobenzene (Azo) and α‐cyclodextrin (α‐CD) is introduced to regulate the lubricity of SLIPS. cis‐Azo is converted to trans and combined with α‐CD by supramolecular interaction under visible light or heating, driving the shrinkage of polymer chains to squeeze the stored lubricant to the surface. The responsive self‐replenishment of lubricant can adjust the surface lubricity to switch antifouling modes between "enhancive" and "normal" smartly, which adapts to different occasions. Moreover, disulfide and hydrogen bonds are introduced to enhance self‐healing performance (91.73%). In summary, it has efficient self‐cleaning, anti‐protein, antibacterial, anti‐algae properties, and 180‐day real marine field antifouling performance during boom season (the longest antifouling period in real marine field test of reported SLIPS materials), which demonstrates the promising application in neritic sea equipment and other antifouling fields. [ABSTRACT FROM AUTHOR]

Objective: Drawing parallels from rheotribology can be used to develop a robust instrumental protocol for non‐subjective characterization, product development and design of topical dosage forms with desired sensory attributes. However, instrumental characterization of cosmetic products can be influenced by the measurement protocol, thixotropy, flow anomalies like shear banding or wall slip and nature of the film formed on the skin surface. In this study, we evaluated the influence of above parameters on the instrumental sensory evaluation of 12 topical formulations of different galenic forms. Methods: Oscillatory strain sweep measurements (SAOS and LAOS) were performed to investigate the influence of frequency and wall slip on the material parameters. The textural attributes at different consumer touchpoints were evaluated by accounting time‐dependent simulation of viscoelastic flow. Further, the influence of film thickness and sample drying on the tactile properties of the topical formulations were studied on a non‐biological skin model using a sliding probe tribometer. Results: The study shows that the flow properties of the semi‐solid formulations depend on the timescale of the problem. A few formulations exhibited wall slip to varying degrees in the linear viscoelastic regime where the behaviour was found not to be characteristic of a particular topical dosage form. The material functions obtained from the Lissajous plots suggest that the non‐linear flow behaviour of different galenic forms is least influenced by the boundary conditions imposed by the measurement geometry. The results were statistically analysed using principal component analysis where the attributes used for discriminating skin creams during pick up and rub out are found to be closely associated with non‐linear rheology. The friction coefficient exhibited speed dependence where it formed different parametric group with rheological data depending on the lubrication regime. Conclusion: The study highlights that correlations are possible amongst rheological, tribological and instrumental textural analysis data, which can act an impetus for the development of models to predict attributes that drive perception at different consumer touchpoints. However, the choice of instrumental settings, anomalies associated with rheological measurements and friction dependence on a number of parameters can influence the model prediction. [ABSTRACT FROM AUTHOR]

In this work, effects of sealing temperature, time, pressure, as well as sealant thickness and viscosity on squeeze out flow (SOF) in heat sealing were examined. A new image analysis approach is presented to quantify SOF in heat sealing. It was found that increasing temperature or pressure could improve SOF but only in thick 130 μm sealants and reducing the sealant thickness to 50 μm suppressed SOF. Reducing viscosity in 50 μm sealant films was also found to improve SOF only at high‐sealing pressure and long sealing times. Three approaches were used to model SOF: analytical one‐dimensional model, numerical one‐dimensional model using finite difference method (FDM), (iii) Numerical two‐dimensional model using finite element analysis. Heat transfer was modeled, and it was shown that heat transfer induces a delay in SOF. When the FDM and the heat transfer models were combined, a good agreement between experimental and model prediction could be obtained. In addition, modeling results showed that SOF occurred in shear rates within the transition region between the Newtonian and Power‐law regions. This indicates the importance of considering the Carreau‐Yasuda fluid behavior in modeling of SOF. [ABSTRACT FROM AUTHOR]

In mixed lubrication, material wear is inevitably caused due to solid contact. Simultaneously, the surface morphology after wear will affects the lubrication performance. To understand this coupling process, virtual surface reconstruction technology and mixed lubrication sliding wear model were applied to predict the evolution of wear characteristics and lubrication characteristics during wear in this study. The effects of the roughness root mean square (RMS), roughness direction and wavelength ratio on the contact area ratio, the contact load ratio, accumulated wear, film thickness and the friction coefficient were analysed. The results indicated that the contact area ratio and the contact load ratio and the friction coefficient decreased and average film thickness increased with the increase in the number of the wear cycles. In addition, a surface with low‐roughness RMS, longitudinal roughness texture and high‐wavelength ratio is suitable for improving lubrication performance and reducing wear. [ABSTRACT FROM AUTHOR]

The lubricities of glycerol solutions with different viscosities were investigated at various frictional pairs, speeds, and loads to explore the lubrication regulations of diverse foods in mouths of different people. The friction pairs were characterized in terms of mechanical properties, surface morphology, and hydrophobicity. The results showed that the partial or complete Stribeck curves occurred with different speeds and viscosities. Various friction pairs had great influences on the boundary lubrication zone, but little influences on the elastohydrodynamic lubrication (EHL) zone. Increasing loads caused the friction coefficient decreasing in boundary lubrication zone; however, the friction coefficient changed a little in the mixed lubrication and EHL zones. [ABSTRACT FROM AUTHOR]

This paper derived generalized ferrofluid based lubrication equation (based on the Shliomis model) from the basic theory for variable as well as uniform (transverse) strong magnetic fields. The variable magnetic field (VMF) is used because of retaining contributions from all magnetic terms of the Shliomis model. Moreover, it has an added advantage of generating maximum field at the required active contact zone in the bearing design system. Using above equation for variable and strong magnetic field, the case of porous journal bearing (PJB) is studied by considering equation of continuity in the film as well as porous region. The validity of the Darcy's law is assumed in the porous region. The modified Reynolds‐Darcy equation for PJB is derived by considering the effects of squeeze velocity, anisotropic permeability and slip velocity. The results show that dimensionless load‐carrying capacity increases with the increase of eccentricity ratio and the effect of magnetic field, and performed best for the decreasing values of the dimensionless permeability parameter in the x‐direction for a thin layer of the porous region. Moreover, the results are also compared with the behavior of different types of journal bearing designs discussed by different authors. [ABSTRACT FROM AUTHOR]

Recent efforts in stimuli‐responsive soft materials have enabled wirelessly controlled actuation with increasing degrees of freedom, yielding miniature robots capable of various locomotion in open environments such as on a plane or inside fluids. However, grand challenges remain in harnessing photomechanical deformation to induce locomotion and control of friction during the movement, especially for robotic actuations within constrained spaces. Here, the authors report a centimeter‐long polymer strip made of a liquid crystal network that is capable of versatile light‐fueled motions along a human hair. The soft polymer robot can translocate directionally upon temporally modulated excitation and climb vertically through friction control with light. A self‐oscillating strip is demonstrated to continuously translocate along the hair upon a constant light stimulus, and its gaiting is associated to the smoothness of the hair surface. The results offer new insights to small‐scale photo‐actuator, mechanical control, and automation in soft micro robotics. [ABSTRACT FROM AUTHOR]

Calculating the flow of a film of lubricant between rough surfaces by solving the Reynolds equation requires a very fine mesh to capture the details of the topography and is thus very time consuming. In the present paper, a multiscale method is proposed. The domain is divided into an appropriate number of subdomains on which deterministic simulations are performed. The results of this microscale solution are coupled at the macroscale by employing a macromesh on which a mass flow balance is implemented. This method has already been successfully applied to liquid lubrication and is extended to gas lubrication. A significant reduction in computation time is obtained compared to a fully deterministic solution. The calculation of the load is also accurate. [ABSTRACT FROM AUTHOR]

Free surface lubrication of rotating cylinders by Newtonian liquid jets was investigated at different impingement positions, jet‐ and circumferential velocities. The interaction between impinging round laminar jet and rotating surface was characterised by high‐speed imaging. Compared to flat surface impingement, the liquid deposition mechanism is more complex and often accompanied by phenomena such as splashing, jet deflection and formation of radial surface stripes. Liquid splashing initially develops in direct deposition regime due to hydraulic jump‐induced droplet shedding, transitioning to lamella instability splash at higher Reynolds numbers. The critical Reynolds number for splash onset is of same order of magnitude as for flat surface impingement and fairly constant at low relative jet impingement angles, but increases exponentially when angle approaches 90°. Liquid film width and thickness were both determined proportional to the square root of the jet/surface velocity ratio, with respective power law models in good agreement with measured values. [ABSTRACT FROM AUTHOR]

This study proposes a tribo‐dynamic model for point contacts under lubrication, focusing on the excitations caused by surface movement, defect and load impact. Surface movement and load impact can cause changes in contact force, resulting in acceleration and dynamic displacement, which may affect the flow of the lubricant. The traditional lubrication model is usually steady or transient, and load balance is used to correct the normal height, ignoring a series of influences such as the mass, stiffness and damping. It requires repeated corrections to obtain a balanced position, which is very time‐consuming. By combining tribology and dynamics, dynamic excitation is introduced in the contact process in this study. After determining the initial value, the normal height can be directly obtained from the dynamic equation. Besides, a comparison between the tribo‐dynamic model and the steady‐state model is presented. It is found that the film thickness and pressure distribution calculated by the two models are almost the same at medium and low speeds, while the calculation results of the two models are different at high speed or under load impact, which emphasises the importance of considering the dynamic behaviour in the study of contacts. [ABSTRACT FROM AUTHOR]

At present, the main frictional components of artificial hip joint (AHJ) are mainly the combinations of hard materials (metal, ceramic) and soft materials (polymer), such as, metal‐on‐metal (MoM), ceramic‐on‐ceramic (CoC), metal‐on‐polymer (MoP), and ceramic‐on‐polymer (CoP). As a new type of AHJ, the polymer‐on‐polymer (PoP) combination has gradually begun to be explored and studied. In this paper, PoP AHJ of CF/PEEK composite are studied, and elastohydrodynamic lubrication analysis based on the solution of the Reynolds equation is performed, and the results are compared with the MoM and MoP AHJs. The comparison shows that under the same steady‐state condition, the PoP AHJ has better lubrication performance. The influence of the key structural parameters of the CF/PEEK PoP AHJ is also analyzed in this paper, and the results show that the femoral head size and radial clearance have great influence on the thickness and pressure distribution of the lubricating film. The research results in this paper further confirm the application potential of the PoP AHJ, and are helpful to its practical application and structural design. [ABSTRACT FROM AUTHOR]

Thrust bearings are widely used in many rotary industrial applications. In this work, a thrust bearing surface under the mixed lubrication regime is analysed and then optimised with aim for use in an injection moulded polymer bearing. A model which couples the mechanical deformation, boundary lubrication and solid contact is developed to investigate the behaviour of the thrust bearing under the load balance condition. This model provides the predictions of important quantities such as load carrying capacity from fluid and solid contact, minimum film thickness and contact pressure. More important, the large‐scale surface geometry is optimised using a quadratic geometry and this large‐scale surface is superimposed with the small‐scale roughness from measured surface to form an optimised surface. This large‐scale geometry might be controlled in the injection moulding process of polymer thrust bearings, whereas it is more difficult to control the roughness. The fluid load carrying capacity for the optimised surface has more than doubled compared to the fluid load carrying capacity for the measured surface. [ABSTRACT FROM AUTHOR]

Many contributions have focused on the pitting analysis in gear transmissions. However, studies on pitting fatigue in spiral bevel gears are limited due to the complexity of tooth contact and lubrication analysis. This paper is to present a reasonable methodology to simulate the pitting crack nucleation of spiral bevel gears considering the real three‐dimensional (3D) rough surface contact where the intermittent asperity stress concentrations is prominent. The proposed model includes a loaded tooth contact analysis model, a mixed elastohydrodynamic lubrication model proposed previously, 3D stress filed formulation, and multi‐axial fatigue criterions. In order to determine an appropriate multi‐axial fatigue criterion for spiral bevel gear, a characteristic plane approach and a conventional critical plane approach are employed in this study. The predicted micro‐pitting lives are compared to published micro‐pitting investigations to assess the reliability of two fatigue criterions in simulation of the micro‐pitting failure. It is observed that the characteristic plane approach is better to reveal the failure mechanism in spiral bevel gears. [ABSTRACT FROM AUTHOR]

Gear contact fatigue is becoming a primary limitation for the growing demand of power density and service life in gear‐driven equipment. The unchecked surface fatigue crack could further cause premature failure and put a serious risk to the safety and reliability of mechanical systems. In this work, an attempt is made to investigate the effects of rolling‐sliding and mild wear on contact fatigue behavior. A contact model is developed to capture the variation of instantaneous pressure and stress field, which are calculated with the transient mixed elastohydrodynamic lubrication (EHL) approach. Rolling‐sliding contact is simulated with the time‐varying roughness topography, which is updated by Archard wear equation. The stress cycles are extracted, and the relative contact fatigue life is obtained by using the Zaretsky criterion. Results suggest that in rolling‐sliding contact, the contact fatigue life is obviously lower compared with pure rolling. The increases in the number and amplitude of stress microcycles is found to be the main contributors to the reduction of fatigue life. Mild wear tends to smooth the surface, subsequently mitigates the stress concentration, and reduces stress cycles, and then decreases the risk of surface contact fatigue. [ABSTRACT FROM AUTHOR]

Summary: MoS2 thin films for unsynchronized, dry‐running screw machines Unsynchronized, dry‐running screw machines have great potential to provide a resource‐saving alternative to conventional screw machine designs. By saving external synchronization and the absence of a liquid lubricant, there are economic and ecological advantages. The use of materials and energy are reduced and the purity of the process gas is increased, the impact on the environment is minimized. Vacuum coating processes are one of the key technologies for realizing an unsynchronized, dry‐running screw machine. The synthesized thin films can be optimally conditioned thanks to the near‐net‐shape coating and the possibility of changing the structural properties of the coating in a targeted manner. MoS2 thin films as solid lubricant exhibit improved friction properties. As a result there is also a great potential to reduce friction and thus the use of energy. [ABSTRACT FROM AUTHOR]

The study presents a profile design method to improve the wear performance of misaligned water‐lubricated bearing based on the modified Archard model. This method takes into account the variation of the film thickness under the mixed elastohydrodynamic lubrication (mixed‐EHL). A transient hydrodynamic Reynolds equation model with the Patir–Cheng flow factors is used to predict the evolution of the mixed‐EHL performance over time. The Archard model is extended to predict the time‐varying wear based on the fatigue concept. To verify the effectiveness of the proposed profile design method; the simulation results, including the transient contact pressure, wear depth and wear volume, between the considering and not considering the profile design are compared. To gain insight, several illustrative examples are presented to show the amelioration of the profile design. Parametric studies are reported to show the applicability of the profile design and emphasise the profile height selection. Therefore, the profile design is an extraordinary method to reduce the edge wear. [ABSTRACT FROM AUTHOR]

A mixed elastohydrodynamic lubrication (EHL) model for a coated angular contact ball bearing is developed by coupling the influence coefficients with the unified deterministic mixed EHL model. Based on the bearing quasi‐dynamics analysis, the influences of the surface roughness, coating thickness, and boundary friction coefficient on the mixed EHL performance of the coated bearing are discussed. The results reveal that high surface root‐mean‐square roughness can be detrimental to bearing lubrication performance and increase the risk of coating failures. Coating thicknesses on the order of a few microns have a limited effect on the contact load ratio, film thickness ratio, and friction coefficient while having a significant effect on the maximum surface tensile stress and interfacial shear stress, especially for high‐friction low‐speed conditions. A low‐friction self‐lubricating coating can effectively improve the tribological performance and prolong the service life of the bearing, especially in the bad lubrication state with severe asperity contacts. [ABSTRACT FROM AUTHOR]