Javier BLANCO-RODRíGUEZJacobo PORTEIROJosé A.LóPEZ-CAMPOSMartí CORTADA-GARCíA...
1785-1800页
查看更多>>摘要：Durability and reliability have been studied for decades through intensive trial-error experimentation.However,there are numerous fields of application where the costs associated with this approach are not acceptable.In lubricated machines with severe dynamic loads,such as high-power-density engines,simulation tools offer clear advantages over intensive testing.Prototypes and multiple scenarios can be cost-effectively simulated to assess different lubricants and engine configurations.The work presented here details the study of wear based on a validated elastohydrodynamic(EHD)simulation model of the connecting rod journal bearing.This model accounts for elastic deformation through a connecting rod finite element model(FEM).In addition,multiple lubricant rheological and tribological dependences,determined by specific experimental tests,are applied in the model through their interaction with the simulation software.Correspondingly,a novel wear algorithm is proposed to predict wear depth over time evolution along a proposed wear cycle based on the typical working ranges of high-performance engines.A final assessment is presented to compare 4 different ultralow-viscosity lubricants in their protective performance under severe conditions.The results show the evolution of the wear load and wear depth over the wear cycle.This evaluation is key to describing a lubricant selection procedure for high-power-density engines.
查看更多>>摘要：Polymers are widely used in bearing applications.In the case of water-lubricated stern tube bearings,thermoplastic polyurethane(TPU)-based composites are used due to their excellent wear resistance,corrosion resistance,and tunable mechanical properties.Their tribological performance,however,depends on operating conditions.In this work,TPU was blended with carbon fiber,graphene platelet,and ultra-high molecular weight polyethylene(UHMWPE).Friction tests of TPU based-composites against copper countersurface were carried out in water to mimic the actual operating conditions of the bearing.Most of the resulting contacts were in the boundary lubrication regime,in which friction was attributed to both contact mechanics of asperities as well as water lubrication.Our results show that the viscoelasticity of TPU has a considerable impact on its tribological performance.Water lubrication at 50 ℃promotes the softening of polymer surface material during sliding,resulting in higher fluctuation in the coefficient of friction and wear loss.This is attributed to the reduced thermomechanical properties.In addition,Schallamach waviness is observed on worn surface.The tribological properties of TPU are significantly improved by the inclusion of carbon fiber,graphene platelet,and UHMWPE.The formation of graphene transfer-layers and UHMWPE transfer film reduces friction and wear loss,while the inclusion of carbon fiber enhances wear resistance due to improved mechanical properties and load bearing capacity.
查看更多>>摘要：To expand the use of metal-organic frameworks(MOFs)based self-lubricating composite,flexible MOFs MIL-88D has been studied as a nanocontainer for loading lubricant.In this work,the mechanism of oleamine adsorption and desorption by MIL-88D was investigated through molecular simulations and experiments.Molecular simulations showed that the oleamines can be physically adsorbed into open MIL-88Ds with the Fe and O atoms of MIL-88D interacting with oleamine NH2-group.Higher temperature can cause Ole@MIL-88D to release more oleamines,while higher pressure on Ole@MIL-88D caused less oleamines released.Moreover the Ole@MIL-88D was incorporated into epoxy resin(EP)for friction tests.The optimum mass ratio of MIL-88D to EP is 15 wt%,and the EP/Ole@MIL-88D prefers light load and high frequency friction.This work suggests that flexible MOFs can be used as a nanocontainer for loading lubricant,and can be used as a new self-lubricating composite.
查看更多>>摘要：Sliding-mode triboelectric nanogenerator(S-TENG)is based on the coupling of triboelectrification and electrostatic induction,converting electrical energy from sliding motion.Introducing micro-textures into the sliding surface,and adjusting the angle between the texture and sliding direction(direction angle)may achieve performance anisotropy,which provides novel ideas for optimizing the tribology and electrification performance of S-TENG.To guide the performance optimization based on the anisotropy,in this paper,groove micro-textures were fabricated on the surface of S-TENG,and anisotropic tribology and electrification performance were obtained through changing the direction angle.Based on the surface analysis and after-cleaning tests,the mechanism of the anisotropy was explained.It is shown that the anisotropy of friction coefficient can be attributed to the changes of texture edge induced resistance and groove captured wear debris,while the voltage anisotropy is due to the variations of debris accumulated on the sliding interface and the resulting charge neutralization.Among the selected 0°-90° direction angles,S-TENG at angle of 90° exhibits relatively small stable friction coefficient and high open-circuit voltage,and thus it is recommended for the performance optimization.The open-circuit voltage is not directly associated with the friction coefficient,but closely related to the wear debris accumulated on the sliding interface.This study presents a simple and convenient method to optimize the performance of S-TENG,and help understand the correlation between its tribology and electrical performance.
查看更多>>摘要：This manuscript presents an innovative methodology for the assessment of the friction torque of ball slewing bearings.The methodology aims to overcome the limitations of state-of-the-art approaches,especially when the friction torque is conditioned by the preload of the balls.To this end,the authors propose to simulate the preload scatter when solving the load distribution problem,prior to the friction torque calculation.This preload scatter allows to simulate a progressive transition of the balls from a four-point contact state to a two-point contact one.By implementing this capability into an analytical model,the authors achieve a successful correlation with experimental results.Nonetheless,depending on the stiffness of the structures to which the bearing is assembled,it is demonstrated that the rigid ring assumption can lead to inaccurate friction torque results when a tilting moment is applied.The methodology described in this research work is meant to have a practical application.Therefore,the manuscript provides guidelines about how to use and tune the analytical model to get a reliable friction torque prediction tool.
查看更多>>摘要：This study is an optimized extension based on the authors'previous research on the tribo-chemical reaction under constant temperature field of two-stroke internal combustion engines(ICEs).It establishes a coupled analysis model that considers the tribo-chemical reactions,dynamic contact,and interface lubrication of the piston ring-cylinder liner(PRCL)system under transient temperature conditions.In this study,for the first time,the prediction of the tribofilm thickness and its influence on the surface micro-topography(the comprehensive roughness)are coupled in the working temperature field of the PRCL system,forming an effective model framework and providing a model basis and analytical basis for subsequent research.This study findings reveal that by incorporating temperature and tribofilm into the simulation model,the average friction deviation throughout the stroke decreases from 8.92%to 0.93%when compared to experimental results.Moreover,the deviation during the combustion regime reduces from 39.56%to 7.34%.The proposed coupled model provides a valuable tool for the evaluation of lubrication performance of the PRCL system and supports the analysis software forward design in two-stroke ICEs.
Julio A.CAO-ROMERO-GALLEGOSSaeid TAGHIZADEHOscar A.AGUILAR-ROSASR.S.DWYER-JOYCE...
1882-1896页
查看更多>>摘要：This work explores experimentally the effects of DC electrical currents on lubricant film thickness alteration in lubricated sliding steel contacts in the boundary and mixed regime as measured by ultrasound.The experiments were performed in a two-electrode cell-based pin-on-disk tester instrumented with ultrasonic transducers.Unelectrified and electrified tribological tests were conducted on steel flat-on-flat contacts under various speeds and loads using both a mineral base oil and a gear oil.Film thickness,coefficient of friction(CoF),and electrical contact resistance(ECR)were measured during short experiments(30 s)in unelectrified and electrified(1.5 and 3 A)conditions.The results suggest that film thickness,CoF,and all ECR are altered by passing DC currents through the contact.In particular,film thickness increased and decreased,respectively,by applying electricity at the different speeds and loads tested.These alterations were majorly ascribed to oil viscosity decrease by local heat and surface oxidation caused by electrical discharge and break down at the interface.
查看更多>>摘要：Two-dimensional materials are excellent lubricants with inherent advantages.However,superlubricity has been reported for only a few of these materials.Unfortunately,other promising two-dimentional(2D)materials with different physical properties cannot be discovered or applied in production;thus,energy consumption can be greatly reduced.Here,we carry out high-throughput calculations for 1,475 2D materials and screen for low-friction materials.To set a standard,we propose,for the first time,a geometry-independent lubricating figure of merit based on the conditions for stick-slip transition and our theory of Moiré friction.For the efficient calculation of this figure of merit,an innovative approach was developed based on an improved registry index model.Through calculations,340 materials were found to have a figure of merit lower than 10-3.Eventually,a small set of 21 materials with a figure of merit lower than 10-4 were screened out.These materials can provide diverse choices for various applications.In addition,the efficient computational approach demonstrated in this work can be used to study other stacking-dependent properties.
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