查看更多>>摘要：Friction and wear are unavoidable in mechanical movement.The use of lubricants with nano-additives can effectively reduce friction and wear,which is of great significance to saving energy and protecting the environment.At present,great progress has been made in the scientific research and industrial application of nano-additives for lubricants.This paper mainly introduces the types of nano-additives for lubricants(such as carbon nanomaterials,nano-metals,nano-oxides,sulfides,complexes,polymers,etc.),the tribological properties of lubricants with different components of nano-additives,and the lubrication mechanisms of the nano-additives(including tribofilm formation,rolling ball bearing effect,repairing effect,polishing effect,and synergistic effect).It also deals with the dispersion of nano-additives in lubricants and the influences of their particle size and microstructure on the tribological properties of lubricants.This review outlines the performance requirements of nano-additives in different lubrication states,discusses the use of nano-additives in challenging working conditions,and identifies various industrial oil nano-additives with reference to the appropriate options in diverse working environments.Furthermore,the existing problems of nano-additives and their application prospects are summarized.This review,hopefully,would help to shed light on the design and synthesis of novel high-performance nano-additives and promote their application in engineering.
Samuel S.GAMANIELPaloma S.DUE?AS ROBLESHans TROMPEls H.A.de HOOG...
1392-1407页
查看更多>>摘要：Consumption of plant-based food products having high composition of polyphenols leads to the sensation of astringency.For sliding oral surfaces,friction is an essential property during the oral perception of roughness and dryness which are attributes associated with astringency.Different factors including the chemical composition of interacting layers,structure and operation of interfaces have an effect on the astringency development process.The manner of interactions occurring at oral interfaces suggest there is a system dependence of astringency and highlights the importance of adopting a tribosystems approach.Available measurement techniques have shown an existing relationship between salivary protein-polyphenol interaction and an astringent mouthfeel.Nevertheless,the tribo-chemistry involved in this multifaceted sensation remains largely unexplored in a comprehensive manner.In this review the underlying tribo-chemical processes useful in understanding the mechanism of astringency are highlighted and discussed considering current techniques employed to investigate astringency perception.Loss of lubrication on oral surfaces owing to the tribo-chemical interactions involving saliva and astringent plant proteins requires subsequent deformations of oral tissues which are significant enough to induce strains at mechanoreceptor locations,leading to the sensation of astringency.It is proposed that micro-scale contact modelling on the interaction of food particles/aggregates,boundary layers and oral surfaces shows potential in addressing the knowledge gap between tribo-chemical measurement techniques and panel tests,making it possible to attain a predictor for astringency.
查看更多>>摘要：Elbow wear is a major threat to the multiphase pipeline transportation industry,which has a negative impact on the stable operation of the transportation system.In order to find the wear reduction methods of elbows in the fluidization pipeline transportation system for 2000-meter-deep coal resources,the swirler was installed upstream of the elbows,and wear simulations and tests of three kinds of elbows were carried out.The results showed that the maximum wear rate(MWR)of elbows increased and then decreased along the elbow angle.Due to the different directions of gravity,the heavy wear position(HWP)of the horizontal-vertical(H-V)elbow was in front of the vertical-horizontal(V-H)elbow.Because the downstream portion of the horizontal-horizontal(H-H)elbow was still a horizontal pipe,the HWP of the H-H elbow almost covered the whole elbow.The swirler placed upstream of the elbows could make the particles at the elbow move to the intrados of the elbows,resulting in less collision between the particles and the extrados of the elbows,thus reducing the wear of the elbows.The wear reduction effects of swirlers on three different elbows were favorably connected with the guide vane angle(GVA)and negatively correlated with the guide vane length(GVL),decreased first and then increased as the guide vane height(GVH)increased,and were little affected by the guide vane number(GVN)and the guide vane thickness(GVT).The mathematical models between the MWR of the elbows and guide vane parameters were established.By bench tests,the wear reduction effect of three kinds of elbows under the optimal guide vane parameters was 58.4%,76.9%,and 78.6%,respectively.The errors between the bench test results and the simulation results were around 10%.
查看更多>>摘要：Extensive efforts have been made to pursue a low-friction state with promising applications in many fields,such as mechanical and biomedical engineering.Among which,the load capacity of the low-friction state has been considered to be crucial for industrial applications.Here,we report a low friction under ultrahigh contact pressure by building a novel self-assembled fluorinated azobenzene layer on an atomically smooth highly-oriented pyrolytic graphite(HOPG)surface.Sliding friction coefficients could be as low as 0.0005 or even lower under a contact pressure of up to 4 GPa.It demonstrates that the low friction under ultrahigh contact pressure is attributed to molecular fluorination.The fluorination leads to effective and robust lubrication between the tip and the self-assembled layer and enhances tighter rigidity which can reduce the stress concentration in the substrate,which was verified by density functional theory(DFT)and molecular dynamics(MD)simulation.This work provides a new approach to avoid the failure of ultralow friction coefficient under relatively high contact pressure,which has promising potential application value in the future.
查看更多>>摘要：In this paper,a PZT(lead zirconate titanate)-based absorber and energy harvester(PAEH)is used for passive control of friction-induced stick-slip vibration in a friction system.Its stability condition coupled with PAEH is analytically derived,whose efficiency is then demonstrated by numerical simulation.The results show that the structural parameters of the PAEH can significantly affect the system stability,which increases with the mass ratio between the PAEH and the primary system,but first increases and then decreases with the natural frequency ratio between the PAEH and the primary system.The impacts of the electric parameters of the PAEH on the system stability are found to be insignificant.In addition,the PAEH can effectively suppress the stick-slip limit cycle magnitude in a wide working parameter range;however,it does not function well for friction systems in all the working conditions.The stick-slip vibration amplitude can be increased in the case of a large loading(normal)force.Finally,an experiment on a tribo-dynamometer validates the findings of the theoretical study,in which the vibration reduction and energy harvesting performance of the PAEH is fully demonstrated.
查看更多>>摘要：The remarkable mechanical adaptability of arapaima(Arapaima gigas)scales has made them an important subject of study.However,no research has been conducted into their tribological properties,which are crucial for the protectability and flexibility of arapaimas.In this study,by combining morphological characterizations,friction experiments,and theoretical analyses,the relationship between the surface morphology and tribological properties of arapaima scales is determined.These results indicate that arapaima scales exhibit varying surface morphologies in different regions.More specifically,the exposed regions of scales feature grooves and a circulus,whereas the covered regions exhibit bumps.The specific surface morphology of arapaima scales produces varying tribological properties across different regions and sliding directions.The unique tribological properties of arapaima scales influence the forces received from predator attacks and neighboring scales,directly influencing the arapaima's protective capabilities.This study provides new insights into the mechanisms of natural flexible dermal armors,and it has potential applications in personal protective systems.
查看更多>>摘要：Surface moisture or humidity impacting the lubrication property is a ubiquitous phenomenon in tribological systems,which is demonstrated by a combination of molecular dynamics(MD)simulation and experiment for the organic friction modifier(OFM)-containing lubricant.The stearic acid and poly-α-olefin 4cSt(PAO4)were chosen as the OFM and base oil molecules,respectively.The physical adsorption indicates that on the moist surface water molecules are preferentially adsorbed on friction surface,and even make OFM adsorption film thoroughly leave surface and mix with base oil.In shear process,the adsorption of water film and desorption OFM film are further enhanced,particularly under higher shear rate.The simulated friction coefficient(that is proportional to shear rate)increases firstly and then decreases with thickening water film,in good agreement with experiments,while the slip length shows a contrary change.The wear increases with humidity due to tribochemistry revealing the continuous formation and removal of Si-O-Si network.The tribological discrepancy of OFM-containing lubricant in dry and humid conditions is attributed to the slip plane's transformation from the interface between OFM adsorption film and lubricant bulk to the interface between adsorbed water films.This work provides a new thought to understand the boundary lubrication and failure of lubricant in humid environments,likely water is not always harmful in oil lubrication systems.
查看更多>>摘要：Nanomaterials as lubricating oil additives have attracted significant attention because of their designable composition and structure,suitable mechanical property,and tunable surface functionalities.However,the poor compatibility between nanomaterials and base oil limits their further applications.In this work,we demonstrated oil-soluble poly(lauryl methacrylate)(PLMA)brushes-grafted metal-organic frameworks nanoparticles(nanoMOFs)as lubricating oil additives that can achieve efficient friction reduction and anti-wear performance.Macroinitiators were synthesized by free-radical polymerization,which was coordinatively grafted onto the surface of the UiO-67 nanoparticles.Then,PLMA brushes were grown on the macroinitiator-modified UiO-67 by surface-initiated atom transfer radical polymerization,which greatly improved the lipophilic property of the UiO-67 nanoparticles and significantly enhanced the colloidal stability and long-term dispersity in both non-polar solvent and base oil.By adding UiO-67@PLMA nanoparticles into the 500 SN base oil,coefficient of friction and wear volume reductions of 45.3%and 75.5%were achieved due to their excellent mechanical properties and oil dispersibility.Moreover,the load-carrying capacity of 500 SN was greatly increased from 100 to 500 N by the UiO-67@PLMA additives,and their excellent tribological performance was demonstrated even at a high friction frequency of 65 Hz and high temperature of 120℃.Our work highlights oil-soluble polymer brushes-functionalized nanoMOFs for highly efficient lubricating additives.
查看更多>>摘要：The main cable bent around the saddle of the suspension bridge is subjected to the wind,the vehicle,the bridge's own weight and the corrosive media.The coupling of the three loads and the environments causes the friction,the corrosion,and the fatigue(tribo-corrosion-fatigue)among the wires inside the main cable.In this paper,a wire bending tribo-corrosion-fatigue test rig was designed and developed.The effect of fatigue load on the bending friction behaviors between the cable wires in ultrapure water and 3.5%NaCl solution was explored.The tribological properties and electrochemical corrosion behaviors under different fatigue loading ranges were investigated.The tribo-corrosion-fatigue interaction between the cable wires was quantitatively characterized,and the mechanism of the interaction was analyzed.The results demonstrate that the increasing fatigue load exacerbates the coupling damage of the cable wires attributed to the enhanced interaction.The findings carry theoretical importance when assessing the main cable's deterioration and the load-bearing safety of a suspension bridge.
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