Molecular Dynamics Study Of The Role Of Nanoparticles In Fluid Lubrication

As a kind of economic and environmental friendly nano material,nanoparticles have the characteristics of small volume and large specific surface,and are often used as lubricating additives in the field of tribology.However,at present,the experimental testing technology can only reveal the micro phenomenon produced by nanoparticles at the atomic and molecular scales,and the mechanism of friction and lubrication of nanoparticles is still unclear.In this work,nanoparticles was taken as the research object,and molecular dynamics simulation was used to reveal the mechanism of nanoparticles in friction and lubrication at the nanoscale,which can provides a certain theoretical basis for the mechanism of friction reduction and anti-wear in lubrication.Based on the Couette flow model,the molecular dynamics model of friction lubrication is established,and the flow characteristics and lubrication mechanism of nanofluids in the friction process are investigated.The results show that,a layer of atomic adsorption layer with regular arrangement and protective effect was formed on the friction surface.The "quasi solid" was produced during the friction lubrication process,and the nanoparticle improved the accelerated liquid flow and improved the carrying capacity of the fluid.The rolling effect of the nanoparticles obviously reduced the friction of the friction surface,while the wear debris and some nanoparticles were filled into the pits on the friction surface and improved the surface finish.In order to explore the effect of the nanoparticles on the friction surface,the evolution of friction surface morphology was analyzed,and found that,the friction surface was severely rubbed by the nanoparticles under high load condition.The morphology of the friction surface changed most obviously at the speed of 30 m/s,and the roughness of the friction surface is more effectively decreased by increasing the nanoparticle size.The ultrasonic cavitation phenomenon in nanofluids is simulated and the movement characteristics of nanoparticles under the ultrasonic cavitation are illustrated.The results show that,three impacts were produced on the friction surface due to the collapse of cavitation bubbles,and the maximum impact force is higher in nanofluids than the impact force produced in the basic flow system.The impact force on the friction surface produced by nanoparticle is larger than that produced by cavitation bubble,indicating that nanoparticles enhanced the effect of ultrasonic cavitation.