查看更多>>摘要：With the development of green tribology in the shipping industry,the application of water lubrication gradually replaces oil lubrication in stern bearings and thrust bearings.In terms of large-scale and high-speed ships,water-lubricated bearings with high performance are more strictly required.However,due to the lubricating medium,water-lubricated bearings have many problems such as friction,wear,vibration,noise,etc.This review focuses on the performance of marine water-lubricated bearings and their failure prevention mechanism.Furthermore,the research of marine water-lubricated bearings is reviewed by discussing its lubrication principle,test technology,friction and wear mechanism,and friction noise generation mechanism.The performance enhancement methods have been overviewed from structure optimization and material modification.Finally,the potential problems and the perspective of water-lubricated bearings are given in detail.
查看更多>>摘要：MXene possesses great potential in enriching the functionalities of hydrogels due to its unique metallic conductivity,high aspect ratio,near-infrared light(NIR light)responsiveness,and wide tunability,however,the poor compatibility of MXene with hydrogels limits further applications.In this work,we report a uniformly dispersed MXene-functionalized poly-N-isopropylacrylamide(PNIPAM)/poly-2-acrylamido-2-methyl-1-propanesulfonic acid(PAMPS)double network hydrogel(M-DN hydrogel)that can achieve switchable friction regulation by using the NIR light.The dispersity of MXene in hydrogels was significantly improved by incorporating the chitosan(CS)polymer.This M-DN hydrogel showed much low coefficient of friction(COF)at 25 ℃ due to the presence of hydration layer on hydrogel surface.After illuminating with the NIR light,M-DN hydrogel with good photothermal effect rapidly raised the temperature to above the lower critical solution temperature(LCST),which led to an obvious increase of surface COF owing to the destruction of the hydration layer.In addition,M-DN friction control hydrogel showed good recyclability and controllability by tuning"on-off"of the NIR light.This work highlights the construction of functional MXene hydrogels for intelligent lubrication,which provides insight for interface sensing,controlled transmission,and flexible robotic arms.
查看更多>>摘要：To date,MoS2 can only be achieved at microscale.Edge pinning effect caused by structure defects is the most obvious barrier to expand the size of structural superlubricity to macroscale.Herein,we plan to pin edge planes of MoS2 with nanospheres,and then the incommensurate structure can be formed between adjacent rolling nanoparticles to reduce friction.The sputtered MoS2 film was prepared by the physical vapor deposition(PVD)in advance.Then enough Cu2O nanospheres(~40 nm)were generated in situ at the edge plane of MoS2 layers by liquid phase synthesis.An incommensurate structure(mismatch angle(θ)= 8°)caused by MoS2 layers was formed before friction.The friction coefficient of the films(5 N,1,000 r/min)was~6.0×10-3 at the most.During friction,MoS2 layers pinned on numerous of Cu2O nanoparticles reduced its edge pinning effect and decreased friction.Moreover,much more incommensurate was formed,developing macro-superlubricity.
查看更多>>摘要：Superlubricity provides a novel approach to addressing friction and wear issues in mechanical systems.However,little is known regarding improving the atomic force microscope(AFM)friction coefficient measurement resolution.Accordingly,this study established the theoretical formula for the AFM friction coefficient measurement and deduced the measurement resolution.Then,the formula was applied to the AFM probe with a rectangular cross-section cantilever.The measurement resolution is associated with the dimensional properties of the AFM probe,the mechanical properties of the cantilever material,the properties of the position-sensitive detector(PSD),and probably the anti-vibration performance of the AFM.It is feasible to make the cantilever as short as possible and the tip as high as possible to improve the measurement resolution.An AFM probe for measuring an ultra-low friction coefficient was designed and fabricated.The cantilever's length,width,and thickness are 50,35,and 0.6 μm,respectively.The tip height is 23 μm.The measurement resolution can reach 7.1×10-6 under the maximum normal force.Moreover,the AFM probe was applied to measure the superlubricity between graphene layers.The friction coefficient is 0.00139 under 853.08 nN.This work provides a promising method for measuring a～10-5 friction coefficient of superlubricity.
查看更多>>摘要：A comprehensive modeling strategy for studying the thermomechanical tribological behaviors is proposed in this work.The wear degradation considering the influence of temperature(T)is predicted by Archard wear model with the help of the UMESHMOTION subroutine and arbitrary Lagrangian-Eulerian(ALE)remeshing technique.Adopting the proposed method,the thermomechanical tribological behaviors of railway vehicle disc brake system composed of forged steel brake disc and Cu-based powder metallurgy(PM)friction block are studied systematically.The effectiveness of the proposed methodology is validated by experimental test on a self-designed scaled brake test bench from the perspectives of interface temperature,wear degradation,friction noise and vibration,and contact status evolution.This work can provide an effective way for the investigation of thermomechanical tribological behaviors in the engineering field.
查看更多>>摘要：By simply switching the electrical circuit installed on steel/steel contact,the tribological behaviors of nanofluids(NFs)can be regulated in real time,thereby achieving the desired performance of friction reduction and wear resistance.Herein,solvent-free carbon spherical nanofluids(C-NFs)were successfully prepared for intelligent lubrication regulation.C-NFs with excellent lubrication performance can immediately reduce the coefficient of friction(COF)despite applying a weak electric potential(1.5 V).Moreover,polyethylene glycol 400(PEG400)containing 5.0 wt%C-NFs remained responsive to electrical stimulation under the intermittent voltage application with an average coefficient of friction(ACOF)reduction of 20.8%over PEG400.Such intelligent lubrication regulation of C-NFs under an external electric field(EEF)mainly depends on the orderly arranged double-electric adsorption film of ion canopy-adsorbed carbon spheres(CSs).The intermittent electrical application can continuously reinforce the adsorption film and its durability for real-time controlling the sliding interfaces.Electrical-stimulation-responsive intelligent lubricants provide a new technical support for realizing intelligent stepless control of devices.
查看更多>>摘要：Two-dimensional(2D)transition metal dichalcogenides(TMDCs)have layered structures with excellent tribological properties.Since the energy difference between hexagonal-molybdenum ditelluride(2H-MoTe2)and distorted octahedral-molybdenum ditelluride(1T′-MoTe2)is very small among the transition metal dichalcogenides(TMDCs),MoTe2 becomes one of the most promising candidates for phase engineering.In our experiment,we found that the friction force and friction coefficient(COF)of 2H-MoTe2 were an order of magnitude smaller than those of 1T′-MoTe2 by the atomic force microscope(AFM)experiments.The friction difference between 1T′-MoTe2 and 2H-MoTe2 was further verified in molecular dynamics(MD)simulations.The density functional theory(DFT)calculations suggest that the friction contrast is related to the difference in sliding energy barrier of the potential energy surface(PES)for a tip sliding across the surface.The PES obtained from the DFT calculation indicates that the maximum energy barrier and the minimum energy path(MEP)energy barrier of 2H-MoTe2 are both smaller than those of 1T′-MoTe2,which means that less energy needs to be dissipated during the sliding process.The difference in energy barrier of the PES could be ascribed to its larger interlayer spacing and weaker Mo-Te interatomic interactions within the layers of 2H-MoTe2 than those of 1T′-MoTe2.The obvious friction difference between 1T′-MoTe2 and 2H-MoTe2 not only provides a new non-destructive means to detect the phase transition by the AFM,but also provides a possibility to tune friction by controlling the phase transition,which has the potential to be applied in extreme environments such as space lubrication.
查看更多>>摘要：Tribological applications of polytetrafluoroethylene(PTFE)are often limited by technological complexity to overcome its poor wear resistance.Here,a PTFE/polyetheretherketone(PEEK)heterolayer(HL)was proposed and evaluated as a new solid lubrication solution.Pin-on-disk tribometry found the lowest friction coefficient(μ)of 0.031 and ultralow wear for the PEEK/HL under typical conditions.The friction coefficient of the HL surpasses those of the state-of-the-art polymeric coatings/composites by at least 200%,and approaches that of highly lubricated interfaces.Mechanistic investigations revealed multi-length physical and chemical heterogeneity of the HL that best facilitates a tribofilm with high subsurface stability and surface instability.The technological simplicity and robustness of the HL's high lubricity make it a promising new type of solid lubrication toward greater reliability and longevity.
查看更多>>摘要：The process design of flat die rolling operations can be a tedious and costly process due to the challenges posed by small process windows.Within this work,an effort is made to closely investigate and understand the process limits caused by excessive slippage of the workpiece.Optical measurements are carried out to capture the characteristics of excessive slippage and the influence of the stroke rate and the tribological system on this process limit.Large differences in slippage were observed,depending on the tribological system.While systems with polymer based lubricants showed excessive slippage at low stroke rates,systems using oil or no lubricant endured higher stroke rates before process limits were reached.The optical measurements revealed three major forms of slippage:successful rolling without slippage,failure due to excessive slippage at process start,and failure due to excessive slippage at around one workpiece rotation.
Guilherme Oliveira NEVESNicolás ARAYADiego Berti SALVAROThiago de Souza LAMIM...
144-163页
查看更多>>摘要：Carbon-based solid lubricants are excellent options to reduce friction and wear,especially with the carbon capability to adopt different allotropes forms.On the macroscale,these materials are sheared on the contact along with debris and contaminants to form tribolayers that govern the tribosystem performance.Using a recently developed advanced Raman analysis on the tribolayers,it was possible to quantify the contact-induced defects in the crystalline structure of a wide range of allotropes of carbon-based solid lubricants,from graphite and carbide-derived carbon particles to multi-layer graphene and carbon nanotubes.In addition,these materials were tested under various dry sliding conditions,with different geometries,topographies,and solid-lubricant application strategies.Regardless of the initial tribosystem conditions and allotrope level of atomic ordering,there is a remarkable trend of increasing the point and line defects density until a specific saturation limit in the same order of magnitude for all the materials tested.
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