Numerical Analysis on Nanoparticles-laden Gas Film Thrust Bearing

Nanoparticles can be taken as additives and added into various fluids to improve their lubricating performances. At present, researches in this area are mainly concentrated on the improvement effects of nanoparticles on the lubricating performances of liquid such as oil and water. Nanoparticles will also affect gas lubrication, but few related studies have been reported. Nanoparticles-laden gas film (NLGF) is formed when adding nanoparticles into gas bearing. Then, the lubricating performances of gas bearing including pressure distribution and load-carrying capacity will change. The variations of pressure distribution and load-carrying capacity in nanoparticles-laden gas film thrust bearing are investigated by numerical method. Taking account of the compressibility of gas and the interactions between gas and nanoparticles, a computational fluid dynamics model based on Navier-Stokes equations is applied to simulate the NLGF flow. The effects of inlet nanoparticles volume fraction and orifice radius on film pressure distribution and load-carrying capacity of the NLGF are calculated. The numerical calculation results show that both of the film land pressure and the maximum film pressure both increase when the nanoparticles are added into gas bearing, and the film pressures increase with the rising of the inlet nanoparticles volume fraction. The nanoparticles have an enhancement effect on load-carrying capacity of the studied bearing, and the enhancement effect becomes greater as the film thickness decrease. Therefore, nanoparticles can effectively improve the lubricating performance of gas bearing. The proposed research provides a theoretical basis for the design of new-type nanoparticles-laden gas film bearings.

Friction contact mechanisms of layered surface

In this paper,we firstly review the carbon layered surface prepared with electron cyclotron resonance (ECR) plasma sputtering. Secondly,the friction behavior of carbon layered surface under pin-on-disk testing is described. Furthermore,the contact stress evolution processes of layered surface with and without transfer layer during wear are given for understanding the contact mechanisms. Finally,a three-dimension (3D) local yield map of layered surface is introduced,which is useful to predict the possible contact mechanisms.

Abrasive Wear Mechanisms of Sand Particles Intruding into ATM Roller-scraper Tribosystem

The roller-scraper tribosystem of automatic teller machine（ATM） plays an important role in reliable cash requests.However,the abrasive wear of the polymer tribosystem becomes a prominent problem when operating in sandy environment.The wear behavior of the tribosystem in a simulated sandy environment has been experimentally studied previously.However the abrasive wear mechanism of roller-scraper tribosystems is still unknown to new design.The wear rates of polymer rollers were examined comprehensively and several jumping variations were found in the full data extent.Three wear stages were classified by the magnitude of wear rates,and different dominant wear mechanisms corresponding with different particle diameter were found by examining the worn surfaces.Accordingly a presumption was proposed that wear mechanisms in different stages were correlated with sand particles of different diameter.In a verification experiment,three typical wear mechanisms including cutting,ploughing,and wedging were found corresponding with different wear stages by scanning electron microscope（SEM） examination.A theoretical analysis was carried out with a simplified sphere particle intrusion model and the transfer conditions for different wear mechanisms were studied referring to the slip-field theory.As a main result,three typical wear models versus friction coefficient of particle/roller,and particle radius were mapped with variant hardness of the polymer roller and ratio of contact shear stress to bulk shear stress.The result illuminated the abrasive wear mechanism during particle intrusion.Particularly,the critical transition conditions gave the basis for improving the wear performance of roller-scraper tribosystems in a sandy environment.

Effect of Heat Source Sliding Contact on the CoPtCr-based Magnetic Recording Disk

Effect of heat source sliding contact on the CoPtCr-based magnetic recording disk was investigated.A tribo-test of the disk with low load heat source and the scan of disk with magnetic head were sequentially carried out.Then disk samples in the contact area were observed by atomic force microscopy(AFM)and magnetic force microscopy(MFM).A finite element model using thermomechanical coupling was developed to calculate the mechanical and thermal response of the disk under heat source sliding contact based on the experimental results.It was found that data loss load under sliding contact with a heat source was far less than that without a heat source,and mechanical scratches and demagnetization did not occur in the data loss area under the experimental conditions.The finite element analysis(FEA)results indicate that the thin surface DLC coating has more significant effect on the mechanical response than the thermal response of the magnetic layer.

Intrusion Simulation of a C60 Ball into Sliding Contact Space with Graphene Layered Surfaces

The intrusion process of a C60 molecular ball into a sliding contact space with garaphene layered surfaces was simulated using the Molecular Dynamic approach.The contact space was made up by two silicon substrates with graphene layered on the surface of the upper substrate forming an included angle which was defined as initial entry angle changing from 20°to 90°.Then a linear velocity of 30/ps was applied to the lower substrate along horizontal direction.The simulation was carried out using Tesoff potential of C and Si atoms at room temperature 300K.The simulation results showed that when the intrusion angle exceeded a critical angle of 80°,the C60 ball could not intrude the contact space,and the number of the sticking atoms sharply increased.Also,the dependence of maximum pull-off force acting on the upper substrate on the initial entry angle during the C60 intrusion process was calculated in which the critical force for C60 intrusion is found.All the results showed that the upper silicon substrate was well protected by the mono graphene layer.

Critical Maximum Contact Pressure for Yielding in Hard Coating under Sliding Contact

In order to design the best combination of the coating and the substrate for preventing the yield,the semi-analytical method(SAM)was used to analyze the von Mises stress distributions in the contact system,and calculate the critical maximum contact pressure for yielding at the interface and surface in hard coating under both normal and tangential loads on three-dimensional elastic half space.From the results,it can be concluded that,to obtain a higher maximum critical contact pressure for the yield at the interface,increasing the substrate hardness and the ratio value of the coating thickness to the Hertzian contact radius(t/a0)is more effective when t/a0 is larger than 0.5 while increasing the substrate hardness or making the friction coefficient smaller is better when t/a0 is very small;to prevent yielding at the surface,choosing a relatively lower friction system or increasing the yield strength ratio of the coating to the substrate(Yf/Yb)will be effective.

Co Filled Porous Anodic Alumina Film Fabricated on ECR-Al Film with Silicon Substrate

Magnetic Co nanodots embedded in the porous anodic alumina films(AAFs)on silicon substrate can be used as the magnetic recording material with high area recording density.For this purpose,pure aluminum films were deposited on Si substrate with the Electron Cyclotron Resonance(ECR)plasma sputtering technique,and AAFs with vertical nano holes were synthesized with the two-step anodization process in oxalic acid.Finally magnetic material Co was deposited into the nano holes with electrochemical method.The results showed that polycrystalline ECR-Al films are homogenous and fit for the synthesis of AAFs with uniform distributed nano holes when ion sheath formed in front of the substrate surface.The diameters of AAF nano holes were in the range from 30 to 70 nm,and the hole pitches were approximately 100 nm,the AAF on silicon substrate was about 100 nm thick after two-step anodization.Magnetic Co nanodots filled into the nano holes of AAF exhibited both fcc and hcp structures.