Current Issue : April - June Volume : 2018 Issue Number : 2 Articles : 6 Articles
This study investigates the effect of laser surface texturing on the friction behavior of\ngrey cast iron reciprocating under boundary, mixed lubrication conditions and cyclic loading.\nFour geometrical parameters of micro-textures (feature depth, feature diameter, area fraction,\nand sliding direction) were studied using a design of experiments (DoE) approach. The results\nshowed that depending on the geometry, micro-textures can have either a positive or a negative effect\non the friction behavior. The DoE analysis revealed that the coefficient of friction is mainly affected\nby the interaction of the feature depth and its diameter. It was found that this can be related to the\naspect ratio of the dimples, and the best results were obtained for an aspect ratio of 0.1 and 0.17....
Nanoemulsions have been widely used as additives for drilling fluids in recent years. With the development of nanotechnology,\nmultifunctional nanomaterials have been added to nanoemulsions. The improvement of wettability of the surfaces, alteration\nof oil-wet on shale rock surfaces, and environmentally friendly conditions are considered as the future development directions\nof nanoemulsions. In this work, a novel nanoemulsion was prepared by using hydrocarbon-based polyoxyethylene ether, oil\n(hydrocarbon), distilled water, and formation crude oil as the main raw materials. The shale rocks before and after immersion\nwith as-prepared nanoemulsion were characterized by contact angle measurement, atomic force microscope (AFM), and Fourier\ntransform infrared spectroscopy (FTIR). It is clearly observed that the nanoemulsion greatly improved the wettability of the\nsandstone and rock surface by forming a layer of active agent film on the surface of the rock. The as-prepared nanoemulsion had\ngood ability to curb the anticollapse and lubricate and protect the oil and gas layer....
Tetraalkylammonium salts have larger ions than metal ions, which can greatly change the interlayer space and energy, and\nthen potentially tune the properties of graphite. In this work, various graphite intercalation compounds (GICs) have been\nsynthesized by intercalating tetraoctylammonium bromide (TOAB) ions into graphite through electrochemical interactions under\ndifferent reduction potentials. Different degrees of expansion between graphite layers as well as their corresponding structures\nand topographies have been characterized by different analytical techniques. The nanoscale friction and wear properties of these\nGICs have been investigated by AFM-based nanofrictional and scratch tests. The results show that electrochemical intercalation\nusing tetraalkylammonium salts with different interaction potentials can tune the friction and wear properties of graphite. Under\nrelatively large applied loads of AFM tips, friction increase and wear can be easier to occur with the increase of the intercalation\npotential. It is inferred that the increases of both the interlayer space of graphite and the number of ions on the surface give rise to\npuckered effect and formation of rougher surfaces. This work gives us deep insight into the friction and wear properties of GICs as\ncomposite lubrication materials, which would be of great help for material design and preparation....
With rotating machineries working at high speeds, oil flow in bearings becomes superlaminar.Under superlaminar conditions, flow\nexhibits between laminar and fully developed turbulence. In this study, superlaminar oil flow in an oil-lubricated tilting-pad journal\nbearing is analyzed through computational fluid dynamics (CFD). A three-dimensional bearing model is established. CFD results\nfromthe laminarmodel and 14 turbulence models are compared with experimental findings.Thelaminar simulation results of padside\npressure are inconsistent with the experimental data.Thus, the turbulence effects on superlaminar flow should be considered.\nThe simulated temperature and pressure distributions from the classical fully developed turbulence models cannot correctly fit the\nexperimental data. As such, turbulence models should be corrected for superlaminar flow. However, several corrections, such as\ntransition correction, are unsuitable. Among all the flow models, the SST model with low-Re correction exhibits the best pressure\ndistribution and turbulence viscosity ratio. Velocity profile analysis confirms that a buffer layer plays an important role in the\nsuperlaminar boundary layer. Classical fully developed turbulence models cannot accurately predict the buffer layer, but this\nproblem can be resolved by initiating an appropriate low-Re correction. Therefore, the SST model with low-Re correction yields\nsuitable results for superlaminar flows in bearings....
The real-time change of tire-road friction coefficient is one of the important factors that influence vehicle safety performance.\nBesides, the vehicle wheels� locking up has become an important issue. In order to solve these problems, this paper comes up with\na novel slip control of electric vehicle (EV) based on tire-road friction coefficient estimation. First and foremost, a novel method\nis proposed to estimate the tire-road friction coefficient, and then the reference slip ratio is determined based on the estimation\nresults. Finally, with the reference slip ratio, a slip control based on model predictive control (MPC) is designed to prevent the\nvehicle wheels from locking up. In this regard, the proposed controller guarantees the optimal braking torque on each wheel by\nindividually controlling the slip ratio of each tire within the stable zone. Theoretical analyses and simulation show that the proposed\ncontroller is effective for better braking performance....
The mechanical and tribological properties of polyvinyl alcohol hydrogel as an artificial cartilage were studied under water and\nbovine serum albumin-lubricated sliding conditions. The frictional properties of the polyvinyl alcohol hydrogel were investigated\nvia reciprocating frictional tests. The effect of surface mechanical deformation on the tribological properties of the\npolyvinyl alcohol hydrogel as an artificial cartilage was studied by concurrently recording the z-axis displacement and friction\ncoefficient time. Three different factors were chosen including load, speed, and lubrication. The results showed that the albumin\nsolution could reverse the trend in the coefficient of friction in tests at different loading levels. There was no improvement in the\nfriction condition in albumin at low speeds. However, when the speed was increased to 2 Hz, the coefficient of friction was\nsignificantly reduced. Wear testing was also conducted, and wear tracks were found on the sample surface. The results also\nshowed that even though the surface deformation could recover as the water phase of the porous structure recovered, the\ncoefficient of friction continued to increase simultaneously. This relationship between mechanical and frictional tests indicated\nthat biphasic lubrication effects may not be the only dominant factor underlying the excellent friction properties of polyvinyl\nalcohol hydrogel....
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