bluuebunny/crossref_metadata_2025 huggingface dataset:
Change in Film Thickness Profile of Perfluoropolyethers During Dewetting
Authors: Ohno S. , Kato T. , Kawaguchi M.
Published: March 2009

The physical spacing between a magnetic head and a disk surface has been decreasing in order to achieve the higher recording density for hard disk drives (HDD), and a new head/disk system, such as the contact type, has been proposed in recent years. However, a molecularly-thin PFPE film dewets due to intermolecular forces particularly when the polar interaction is predominant which results in the formation of microdroplets. It was reported that the microdroplets on the disk surface attacked the magnetic head, caused a fluctuation in the physical spacing and made the flying head unstable. Therefore, the precise investigation of the dewetting at head disk interfaces (HDI) is fundamentally needed. The substrates evaluated in this study were 2.5inch glass disks used for HDD. These glass disks are comprised of a magnetic layer and diamond-like carbon (DLC) overcoat, of which the DLC thickness is about 3nm, and have a textured pattern on the surface. PFPE Zdol diluted with HFE-7100DL was coated on the disk surface by a dip-coating method. The change in the film thickness profile was investigated using an ellipsometer for the film under an unstable or metastable condition. It was found from the observation of the unstable film that the development of microdroplets indicates the movement of PFPE molecules through the under layer. For the metastable condition, the surface texture triggered the dewetting and affected the formation of microdroplets. In the “thicknesses spectrum”, a sharp peak was seen at about 7.8nm immediately after the dip-coating, but before the occurrence of dewetting. The peak at 7.8nm easily disappeared and another peak at about 1.6nm appeared instead. This means that the 7.8nm thickness film was unstable and moved to a more stable state. It is noted that the microdroplets were formed by this instability, and the 1.6 nm thickness corresponded to that of the dewetted area.
A Quantitative Solution for the Full Shear-Thinning EHL Point Contact Problem Including Traction
Authors: Liu Yuchuan , Wang Q. Jane , Bair Scott , Vergne Philippe
Published: March 2009

We present a realistic elastohydrodynamic lubrication (EHL) simulation in point contact using a Carreau-like model for the shear-thinning response and the Doolittle-Tait free-volume viscosity model for the piezoviscous response. The liquid is a high viscosity polyalphaolefin which possesses a relatively low threshold for shear-thinning. As a result, the measured EHL film thickness is about one-half of the Newtonian prediction. We derived and numerically solved the two-dimensional generalized Reynolds equation for the modified Carreau model based on Greenwood [1]. Departing from many previous solutions, the viscosity models used for the pressure and shear dependence were obtained entirely from viscometer measurements. Truly remarkable agreement is found in the comparisons of simulation and experiment for traction coefficient and for film thickness in both pure rolling and sliding cases. This agreement validates the use of a generalized Newtonian model in EHL.
Pneumatic Servo Bearing Actuator for Ultraprecise Positioning: Basic Performances of Prototype Model
Authors: Hirayama T. , Sasaki K. , Mizuno R. , Kitagawa T. , Kadotani M. , Matsuoka T. , Yabe H.
Published: March 2009

Advances in various areas of precision mechanics, such as semi-conductor manufacturing equipment, MEMS/NEMS, biomechanics, nano-imprint and nano-technology, have required ultraprecise positioning techniques with nanometer scale accuracy to be developed. To meet such specific needs, many different kinds of actuator capable of ultraprecise motions have recently been produced. However, each actuator has some inherent problems; for example, actuators containing piezoelectric elements have been reported to cause hysteresis errors, thermal drifts, deterioration, and destruction. Based on this background, highly reliable and accurate actuators are strongly required.
Fretting Fatigue Wear Behavior of Cu-Al Coating on Titanium Alloy Substrate
Authors: Lee H. , Mall S.
Published: March 2009

The fretting wear behavior of Cu-Al coating was investigated with and without fatigue load under the dry and wet (lubricated) contact conditions. The Cu-Al coating was plasma deposited on titanium alloy, Ti-6Al-4V. Wet contact condition reduced frictional force during cycling as evidenced by the lower tangential force. Wear analysis using the accumulated dissipated energy approach did not show any effect of contact surface condition. In other words, the relationship between the accumulated dissipated energy and wear volume showed a linear relationship, and it was independent of loading and contact surface conditions as well as of the fretting regime.
Elasto-Plastic Contact Behaviors of Nominally Flat Surfaces: Modeling and Parametric Study
Authors: Chen W. Wayne , Liu Yuchuan , Chen Wei , Cao Jiao , Xia Cedric , Talwar Raj , Lederich Rick , Wang Q. Jane
Published: March 2009

Interactions of nominally flat surfaces can be modeled based on the periodic similarity of surface topography and a numerical three-dimensional elasto-plastic contact model with the assistance of the continuous convolution and Fourier transform (CC-FT) algorithm. The rough surfaces were generated by a digital filtration technology with a wide range of topographical parameters. A group of contact simulations were conducted to investigate the effects of surface geometrical characteristics (including RMS roughness, correlation length ratio, skewness and kurtosis), material properties, and load on the elasto-plastic contact performance of materials.
Using Nanotribotesting for the Creation of Modified Exfoliated Graphite-Based Materials
Authors: Nikitin Y. A. , Chernysh I. G. , Zaporozhets V. V.
Published: March 2009

Methodical approach an evaluation of synthesis of alumosilicates on the surface of EG-particles in order to improve the thermooxidazing resistance of the graphite. Using perspective trends in formation of exfoliated graphite (EG)-based lightweight composition materials by synthesis of non-organic combinations on the surface of EG-particles, it was proved the possibility of purposeful change of properties both of EG-powder surface and modified EG-based moulded materials. Using the nanotribospectral test method, we have developed approaches to the study thermo-oxide and product manufacturing processes of the modified EG-based lightweight materials. It has been found that the parameters of the nanotribospectral test method are sensitive to the structural reorganisation processes that proceed in the bulk of the material and may be used for the optimisation product process and high estimation and monitoring of its quality.
Friction and Wear Behaviour of Nanocrystalline Cobalt
Authors: Shafiei M. , Alpas A. T.
Published: March 2009

The friction and wear properties of nanocrystalline cobalt (nc Co) with a grain size of 20±5 nm and a hardness of 503±13 HV were studied using a pin-on-disc tribometer. Tests performed under unlubricated sliding conditions in ambient air showed that large tribolayer area covered the nc Co’s wear track. The oxygen concentration of the tribolayer was higher than that formed on contact surfaces of microcrystalline cobalt (mc Co) with a grain size of 16±3 μm and a hardness of 299±8 HV tested under the same conditions, due to the higher tendency of nc Co for oxidation. Higher rate of oxidational wear in nc Co resulted in higher initial surface damage in this material compared to the mc Co. Once the tribolayer was formed on top of the contact surfaces, a steady-state wear regime prevailed, reducing the coefficient of friction (COF) and the wear rate in this sample.
Tribological Behavior of Self-Lubrication Bearing Materials of Steel-Copper-Polyoxymethylene Containing MoS2-IC Nanoparticles
Authors: Hu K. H. , Wang J. , Schraube S. , Xu Y. F. , Hu X. G. , Stengler R.
Published: March 2009

Intercalation compound of polyoxymethylene into molybdenum disulfide nanoparticles (POM/MoS2-IC) were prepared from trioxane, dioxolane and restacked exfoliated-MoS2. The so prepared nanocomposite was used as the plastic layer of self-lubrication bearing materials of steel-copper-POM. Pure POM was also selected as a comparative sample. Tribological behaviors of the obtained samples were studied on an end-face tribometer. Wear scar surfaces of the two plastic layers were characterized by a field emission scanning electron microscope. The elements of the counterpart steel surface were investigated by X-ray photoelectron spectroscopy. Results showed the wear surface of steel-copper-pure polyoxymethylene consisted of deep furrows, large-area scars and obvious flow marks. However, self-lubrication bearing materials of steel-copper-polyoxymethylene containing MoS2-IC nanoparticles presented excellent friction reduction and wear resistance especially under high loads. POM/MoS2-IC nanoparticles and its tribochemical resultants restrained the plowing effect of the counterpart steel on the plastic layer through forming a transferred film on the counterpart friction surface.
The Effect of Channelling a Polymeric Surface on Its Adhesion and Friction Characteristics
Authors: Pham Duc-Cuong , Singh R. Arvind , Jeong Hoon Eui , Suh Kahp Y. , Yoon Eui-Sung
Published: March 2009

In recent years, a new approach towards enhancing tribological properties at small-scale by the fabrication of nano/micro-scale polymeric patterns using soft lithography has gained popularity. These patterned surfaces provide promising solutions to the tribological issues in small-scale devices such as micro/nano-electromechanical systems (MEMS/NEMS). In the present study, we investigate the nano-scale tribological properties of a novel topography, namely submicrometer-scale channels fabricated on thin polymeric films using a soft lithographic technique. Results show that these surfaces have superior nano-tribological properties, as they reduce adhesion and friction forces to a significant extent when compared to silicon wafer and non-patterned polymeric thin film.
Temperature Dependent Nanotribological Behavior of Ultrathin Thermoplastic Polymeric Resist Films Studied by Use of AFM
Authors: Koszewski Adam , Reuther Freimut , Rymuza Zygmunt
Published: March 2009

Nanoimprint Lithography (NIL) is emerging novel high resolution fabrication technique. In principle it is a hot embossing of a polymer resist used as a mask in further process steps. Currently, a much effort is ongoing on optimizing the properties of the polymer resists by chemical modifications. To assess the influence of them on the polymer properties it was required to develop a methodology for testing these materials in terms of their use in the NIL process. It turned out that the temperature dependent tribological properties of them are especially useful. In this study an atomic force microscope (AFM) with a modified silicon spherical-tip cantilever was used to test the temperature dependent nanotribological properties of mr-I 7000E amorphous thermoplastic polymer resist devoted to NIL. The methodology, the equipment used in these studies as well as the results of the estimation of lateral forces versus temperature will be presented and discussed.
Numerical Study on Load Carrying Mechanism of Two Parallel Lubricated Rough Surfaces With Relative Motion
Authors: Yao Hua-Ping , Huang Ping
Published: March 2009

In the present paper, the load carrying mechanism of two parallel lubricated rough surfaces with relative motion is numerically analyzed from the microscopic view. It is found that each asperity of the surface forms mini-type convergent and divergent wedge sliders. The convergent wedge can create positive hydrodynamic pressure and forms a hydrodynamic lubrication film so that pressure is produced to bear an outside load. The Reynolds equation is used to analyze the influence of the roughness on the performances such as the pressure distribution, the load carrying capacity, the shearing force, the friction force and etc. The varying rules of the load carrying capacity and friction coefficient with the peak height of roughness are discussed in detail, and the influence of the minimum film thickness on lubrication state is also analyzed. The results indicate that under a given lubrication film thickness the load carrying capacity can achieve the maximum value and then decrease slowly with the peak height increasing, while the friction coefficient can achieve the minimum value. Furthermore, under the given condition of the peak height and 1 μm⩽h0⩽100 μm of the minimum film thickness the load carrying capacity drops down gradually, while the friction coefficient increases gradually with increase of the minimum film thickness.
Development of a New Tribological Multi-Function Simulator
Authors: Hua Zikai , Zhang Jianhua , Xue Ke
Published: March 2009

In this study, a new developed tribological multi-function simulator system, SHU-MFS is firstly introduced. By changing of the holder, a hip joint simulator and a POD tester can be generated in the new system. The simulator is designed not only for wear tests of the total hip prostheses, but also applicable in common tribological study. As to the module of hip joint simulator, this design can be described as having the basic motion components in human hip joints. A frequency control system is developed to offer a wide range of rotation frequency so as to provide proper experiments towards different groups. In the POD part, eight precision-made pins are generated and an advanced computer system is built up to measure the friction coefficient of the test samples.
Rough Contacts Modeled by Nonlinear Coatings
Authors: Kudish I. I.
Published: March 2009

A number of experimental studies [1–3] revealed that the normal displacement in a contact of rough surfaces due to asperities presence is a nonlinear function of local pressure and it can be approximated by a power function of pressure. Originally, a linear mathematical model accounting for surface roughness of elastic solids in contact was introduced by I. Shtaerman [4]. He assumed that the effect of asperities present in a contact of elastic solids can be essentially replaced by the presence of a thin coating simulated by an additional normal displacement of solids’ surfaces proportional to a local pressure. Later, a similar but nonlinear problem formulation that accounted for the above mentioned experimental fact was proposed by L. Galin. In a series of papers this problem was studied by numerical and asymptotic methods [5–9]. The present paper has a dual purpose: to analyze the problem analytically and to provide some asymptotic and numerical solutions. The results presented below provide an overview of the results obtained on the topic and published by the author earlier in the journals hardly accessible to the international tribological community (such as Russian and mathematical journals) and, therefore, mostly unknown by tribologists. A number of recent publications on contacts of rough elastic solids supports the view that these results are still of value to the specialists involved in nanotribology. The existence and uniqueness of a solution of a contact problem for elastic bodies with rough (coated) surfaces is established based on the variational inequalities approach. Four different equivalent formulations of the problem including three variational ones were considered. A comparative analysis of solutions of the contact problem for different values of initial parameters (such as the indenter shape, parameters characterizing roughness, elastic parameters of the substrate material) is done with the help of calculus of variations and the Zaremba-Giraud principle of maximum for harmonic functions [10,11]. The results include the relations between the pressure and displacement distributions for rough and smooth solids as well as the relationships for solutions of the problems for rough solids with fixed and free contact boundaries. For plane and axially symmetric cases some asymptotic and numerical solutions are presented.
Test Methods to Visualize the Break-Down Behaviour of Sliding Bearing Materials
Authors: Gruen Florian , Godor Istvan , Eichlseder Wilfried , Gaertner Walter
Published: March 2009

In the context of this work, testing methods of model scale size have been developed, which are based on the ring-on-disc system. These methods enable the visualization of the events in the sliding materials during operation and subsequent breakdown with high time resolution. Therefore, it is possible to visualize and analyze the events taking place at the time of failure. The new test method was benchmarked using the materials AlSn20Cu, CuPb22Sn2 and SnSb7.5Cu3.5. The resulting data enabled the generation of models that characterize the events of the different tribo-materials. Therefore, the proposed method supports the trial-and-error approach of material optimization.
Experimental and Theoretical Studies of the Fractal Scaling Parameter and the Lateral Scale Dependence of the Asperity Interference
Authors: Wang Shao , Leong Yi Hui
Published: March 2009

The fractal scaling parameter was released in a recent study from its artificially assigned constant value to become a measurable parameter for simulated surface profiles. In the present study, this concept was extended to develop schemes for determining the fractal scaling parameter from experimental power spectral density data. The difference in the trends of peaks has been observed between experimental power spectral density data and those of the Weierstrass-Mandelbrot function. A modified W-M function was proposed based on a peak splitting behavior of the power spectrum. To verify a relationship between the interference and lateral length scale for asperities, which is commonly assumed in fractal modeling, a numerical scheme was developed to truncate measured surface profiles for finding asperity interferences for microcontacts of various sizes. This relationship was confirmed by the favorable results from a comparison of the power values obtained from truncation of a surface profile to those obtained by using the fast Fourier transform. A numerical scheme was developed to generate random power spectral density curves and fractal surface profiles for given values of the fractal scaling parameter.
Nanoscale Studies of the Role of ZDDPs in the Wear Protection in the Automobile Engine
Authors: Norton P. R. , Pereira Gavin , Li Yue-Rong , Lachenwitzer Andreas , Kasrai Masoud , Simpson Todd , Shakhvorostov Dmitry , Muser Martin H. , Botton Gianluigi , Alpas Ahmet , Capehart T. W. , Perry Thomas A.
Published: March 2009

The improvement of fuel consumption is an important driving force for research and development in the automobile industry in order to minimize greenhouse gas emissions as well as improving fuel economy. Aluminum alloys are a class of alternative materials that are being used to replace cast iron in motor components due to the concomitant weight savings which result in improved fuel efficiency, and cost savings. Our research focuses on these alternative Al-based alloys as well as traditional steel interfaces, and the protective films that form on the surfaces. Currently the zinc dialkyl-dithiophosphates (ZDDPs) have been used as engine oil additives for over 60 years. They are important chemically-active additives, known for their antioxidant and antiwear characteristics. ZDDPs are known to form a protective film (tribofilms) at rubbed surfaces, typically on iron containing metals surfaces commonly used in the automotive industry; however ZDDPs and the products formed are not well suited for the environment as they can readily poison the catalytic converters and their efficacy on Al-Si alloys is not well established.
Rheological Behaviors of Pressure-Driven Radial Flow
Authors: Xie Z. , Zou Q. , Yao D.
Published: March 2009

The characteristics of fluid flows confined within microscale space are of theoretical and practical interest [1]. Such flow includes the thin lubrication films, the liquid flow between biological cells, and the flow of polymer melts in a micro-injection molding machines, etc. A pressure-driven radial flow microrheometry (PDRFM) is used to characterize high-shear microscale fluids. The shear-dependent viscosity of the pressure-driven radial flow is modeled to investigate the possible size effect on the fluid viscosity. In the modeling, the surface shear rate and surface shear stress at the edge of the radial flow are expressed in terms of three measurable parameters, i.e. the flow rate, the loading force, and the fluid film thickness. By decreasing the fluid film thickness to microscale level, this model can be used to study the microscale effect of any homogeneous fluids. The analysis has been verified by using CFD simulations as digital testing platforms. Furthermore, the preliminary experimental results of Newtonian and non-Newtonian flows also proved the rheological modeling.
Analysis of Surface Textured Air Bearing Sliders With Rarefaction Effects
Authors: Murthy Aravind N. , Etsion Izhak , Talke Frank E.
Published: March 2009

A numerical model is developed to study the effect of texture on air bearing sliders at large Knudsen numbers. The effect of texture location, texture size, and density on the pressure generation is studied. First, a textured plane slider parallel to the disk surface is investigated and the texture parameters are determined that result in optimum pressure generation. Then, a plane inclined slider is studied using optimum texture parameters found in the parallel slider case. Thereafter, the effect of texture on the steady state flying characteristics of an actual magnetic recording slider is investigated. Finally, the flying height modulation, pitch and roll motion of a textured slider (pico and femto form factors) are determined numerically by exciting the slider using a step on the disk. Comparison of the results for textured and untextured sliders is made. It is found that textured sliders show better dynamic performance compared to the untextured sliders in terms of stiffness and damping.
Slurry Erosion Behaviors of Pseudoelastic TiNi Alloy
Authors: Xu Renbo , Cui Lishan , Zheng Yanjun , Zhang Siwei
Published: March 2009

The slurry erosion behaviors of pseudoelastic TiNi alloy were studied using the liquid/solid impingement system and compared with SUS 630 and 2Cr12NiMo1W1V alloy. The influences of erosion time and angle on erosion resistance of three materials were surveyed. The experimental results show that TiNi alloy has the highest erosion resistance among the three materials and SUS 630 stainless steel is more resistant than 2Cr12NiMoW1V alloy. The KQL-300 indentation tester was used to simulate the impact of particle on material surface during erosion process. The results show that the deformation mode of indention can be pile-up or sink-in and there is a good correlation between erosion resistance of material and its indentation deformation mode. The sink-in deformation mode indicates the higher resistance to erosion, and the pile-up deformation mode implies the lower erosion resistance.
Reducing the Magnetic Tape/Guide Friction Coefficient by Laser Surface Texturing: Experimental Analysis
Authors: Raeymaekers Bart , Etsion Izhak , Talke Frank E.
Published: March 2009

The friction coefficient is an important parameter in designing magnetic tape transports. We have introduced laser surface texturing to reduce the friction coefficient between guides and magnetic tape. The surface features enhance the formation of an air bearing and hence, reduce the friction coefficient.
A Model for the Magnetic Tape/Guide Interface With Laser Surface Texturing
Authors: Raeymaekers Bart , Etsion Izhak , Talke Frank E.
Published: March 2009

The spacing between a magnetic tape and a guide in a tape path can be increased by creating dimples on the guide surface. The dimples enhance the formation of an air bearing. A model is presented to maximize the average air bearing pressure.
Numerical Simulations of Soft Coating Deformation by Particle Method
Authors: Hikita Y. , Kato T.
Published: March 2009

Conformability is one of the most important property for sliding bearings at the initial running-in stage. In order to improve this property, most bearings are coated with a soft overlay by several microns in thickness. The conformability relates closely to the plastic deformation and the slight wear of the coating made of resin or soft metal. To evaluate this conforming process, various tests have been conducted, and at the same time numerical simulations needs to be established. We try to develop a numerical simulation by a discrete particle method for analyzing elastic-plastic deformation of a soft coating. This particle method treats relatively larger space scale (discrete particles at 1 micron intervals) compared to the molecular dynamics simulations (MD). And there is no element consisting of nodes unlike finite element method (FEM). Therefore the particle method is convenient for treating failure behaviors (delamination or adhesion). But until now particle methods have never been applied for tribological soft coatings. So we have established a particle method for analyzing elastic-plastic deformation of the coatings in micron order scale and 3D system. Indentation tests were conducted to evaluate elastic-plastic deformations in several simulations and experiments, because indentation tests are popular for soft or hard tribological coatings to evaluate their elastic and plastic properties. In each test, the indenter is loaded and subsequently unloaded. During the loading-unloading process, the load and indentation depth relations were evaluated. In simulations by the discrete particle method, the elasticplastic deformations were reproduced. These results coincide with the prediction that the elastic deformations relate to both loading and unloading processes whereas the plastic deformations relate to only loading process. These tendencies are confirmed by the relations of load and indentation depth. In addition, compared several simulations with several experiments, the deformations of soft coatings made of resin or soft metal were well described by the discrete particle models with two parameters of Young’s modulus and yield stress.
Numerical Analysis on Flying Static Characters for Gas Film Lubrication of Magnetic Heads
Authors: Wu Yan-Hua , Niu Rong-Jun , Huang Ping
Published: March 2009

Based on the iterative finite difference algorithm developed by authors, distributions of gas pressure are calculated. Four flying static characteristics: the gas floating force, the pitch moment, the maximum pressure and minimum pressure under the influence of three important flying parameters: the minimum film height, the pitch angle and the disk velocity are numerically investigated. The results show that with decrease of the minimum film height and the pitch angle, the stiffness of the gas film becomes more rigid. After the disk velocity reaches in an appropriate speed, its role becomes more significant on the gas floating force.
All-Atom Molecular Dynamics Simulation of Submicron Thickness EHL Oil Film
Authors: Washizu Hitoshi , Sanda Shuzo , Hyodo Shi-Aki , Ohmori Toshihide , Nishino Noriaki , Suzuki Atsushi
Published: March 2009

All-atom molecular dynamics simulations of an elastohydrodynamic lubricating oil film have been performed to study the effect of the oil film thickness (large spatial scale; thickness: 430 nm, MD time: 25 ns) and the effect of pressure (long time scale; thickness: 10 nm, MD time: 50 ns, external pressure: 0.1 to 8.0 GPa). Fluid layers of n-hexane are confined between two solid Fe plates by a constant normal force. Traction simulations are performed by applying a relative sliding motion to the Fe plates. In a long spatial scale simulation, the mean traction coefficient was 0.03, which is comparable to the experimental value of 0.02. In a long time scale simulation, a transition of the traction behavior is observed around 0.5 GPa to 1.0 GPa which corresponds to a change from the viscoelastic region to the plastic-elastic region which have been experimentally observed. This phase transition is related to a suppressed fluctuation of the molecular motion.
Dynamic Analysis of Cage Stress in Needle Roller Bearings Under Planetary Motions
Authors: Sakaguchi Tomoya , Nishikawa Makoto , Kazama Sadatsune , Hasegawa Hisataka , Satou Masanori
Published: March 2009

A dynamic analysis tool for calculating cage stress in needle roller bearings under planetary motions was developed to examine the mechanism of rising cage stress. This analysis considers three degrees of freedom of a cage and rollers and two degrees of freedom of a planetary gear in two-dimensional model. Moreover, the elastic deformation of the cage is implemented to determine the cage stress by using a Component-Mode-Synthesis method. In order to validate this dynamic analysis, two needle roller bearings with different structural cage strengths were tested in a planetary gear system. In cases where the weaker cages were damaged, the analyzed stress of the cages nearly reached or exceeded the material fatigue strength. This high stress was observed when a roller passed the load zone collided with the pocket bar due to the centrifugal force of planetary motion. The maximum cage stress increased with the carrier rotation speed and the stress of the damaged weaker cage only exceeded the fatigue strength in the experimental range of carrier speed. These results indicate that the dynamic model is effective and valid for the current application.
Film Height Optimization of Hydrodynamic Slider Bearings
Authors: van Ostayen Ron A. J. , van Beek Anton , Munnig-Schmidt Rob H.
Published: March 2009

The film height distribution which yields the maximum load carrying capacity for the rectangular slider is determined using a PDE-constrained optimization solver. The gradient of the objective function, i.e. the load, with respect to the design variable, i.e. the film height distribution, is calculated using a discrete adjoint approach. It is shown that, in contrast to the linear slider, the load carrying capacity per unit length and at constant width of the optimized slider steadily increases with increasing length over width ratio.
Contact Pressure of Indented Wide Elliptical Contacts: Dry and Lubricated Analysis
Authors: Biboulet N. , Lubrecht A. A. , Houpert L.
Published: March 2009

Indents in roller bearings perturb the pressure and stress distribution and increase the failure risk. A numerical study of the pressure perturbation is proposed. An existing dry contact model is extended to account for the indent shoulder influence and the pressure collapse in deeper indents. Moreover, results on pure-rolling lubricated contacts are presented. Finally, the ellipticity influence is studied both for dry and lubricated contacts.
A Simplified Dynamic Model for the Analysis of the Slider Off-Track Motion Due to Head-Disk Interactions
Authors: Yuan Yanhui , Wang Shao
Published: March 2009

The slider off-track motion is a growing concern for hard disk drives with higher densities. In the present study, a five-degree-of-freedom model was developed for the analysis of the slider off-track motion. The situations of a slider in contact with a single bump and multiple bumps were studied. For a single bump, the excitation to the transverse displacement of the slider is close to an impulse. However, for multiple bumps in a sequence, the excitation gives an effect of a step force function with its plateau value dependent on the circumferential spacing of the bumps, and the rotational speed of the disk. In the case of a bump spacing of 50 μm and a rotational speed of 7200 rpm, the transverse displacement may reach a steady-state of more than 1 μm within 10 ms. The off-track motion of the slider is dominated by the rotational mode of the actuator arm and the sway mode of the suspension, and is very weakly affected by other modes.
Oil Flow and Temperature Predictions for a Big-End Bearing
Authors: Wang Ducai , Jones Graham , Mian Omar , Merritt David , Simon Theo
Published: March 2009

This paper reports on the analysis of a big-end bearing in a 2.0 liter gasoline engine, using a thermo-elastohydrodynamic (TEHL) model. The analysis uses a concise and robust mass conservation algorithm together with a fast TEHL solver. Comparisons are made between the theoretical predictions and the experimental measurements of both total oil flow rate and bearing shell temperatures. Good correlation between theory and experiment was found both parameters.
A Finite Element Approach of the Fully Coupled Elastohydrodynamic Problem
Authors: Habchi W. , Eyheramendy D. , Bair S. , Vergne P. , Morales-Espejel G.
Published: March 2009

Up to now, most of the numerical works dealing with the modelling of the isothermal elastohydrodynamic problem were based on a weak coupling resolution of the Reynolds and elasticity equations (semi-system approach). The latter were solved separately using a Finite Difference discretization. Very few authors attempted to solve the problem in a fully coupled way, thus solving both equations simultaneously (full-system approach). These attempts suffered from a major drawback which is the almost full Jacobian matrix of the non-linear system of equations. This work presents a new approach for solving the fully coupled isothermal elastohydrodynamic problem using a Finite Element discretization of the corresponding equations. The complexity is the same as for classical algorithms, but with an improved convergence rate, a reduced size of the problem and a regular sparse Jacobian matrix. This method is applied to the case of a Generalized Newtonian lubricant using a powerful shear-thinning model. The results are compared with experimental data.
Evaluation of Friction Behavior and Contact Area Dependence at the Micro and Nanoscales
Authors: Kanaga Karuppiah K. S. , Bruck Angela L. , Sundararajan Sriram
Published: March 2009

In this work, we have compared the friction behavior of two different materials (a) mica and (b) ultra-high molecular weight polyethylene (UHMWPE) at two length scales. The friction experiments were carried out at the nanoscale with an atomic force microscope (AFM) and at the microscale, with a custom-built microtribometer. The material interface (Si3N4 probe) and the environmental conditions (RH < 10%) were kept the same at both the scales. The friction data obtained were analyzed for dependence on normal load or contact area, based on which, a coefficient of friction has been reported or an appropriate contact mechanics theory was applied and an interfacial shear strength value was calculated for the material pair. Friction between a silicon nitride and UHMWPE interface resulted in contact area dependence at both the length scales, for the applied load ranges of our experiment. Friction between silicon nitride and mica at the nanoscale showed an initial nonlinearity and then exhibited damage and linearity with normal load beyond certain loads. At the microscale, the mica-silicon nitride interface resulted in a linear friction behavior.
An Integrated Numerical Fluid/Solid Interaction Model for Finger Seals With a Padded Low-Pressure Laminate
Authors: Braun Minel J. , Li Hongmin
Published: March 2009

Finger seals, that contain padded low pressure laminates, are compliant seal configurations that can be designed to function as non-contacting seals. Unlike brush seals, due to the padded elements, they exhibit hydrodynamic lifting capabilities which allow non-contact sealing between stationary and rotating members. Through elimination of rub between the seal and the rotor, this configuration presents the user with the advantage of a potentially unlimited lifespan and reduced maintenance. The model presented here uses a commercial package CFD-ACE+ for the fluid calculations and a stress module combined with a mesh deformation module for the compliant solid calculations, respectively.
Studies on ZDDP Anti-Wear Films Formed Under the Different Conditions by XANES Spectroscopy, Atomic Force Microscopy and 31P NMR
Authors: Li Yue-Rong , Pereira Gavin , Kasrai Masoud , Norton Peter R.
Published: March 2009

Antiwear (AW) films, generated from a mineral base oil containing zinc dialkyl dithiophosphate (ZDDP) additive, were extensively studied. These films were formed at various conditions such as different temperatures, various loads and rubbing times. The surface morphology of these films was investigated using atomic force microscopy (AFM) and the surface roughness of these films has been calculated from the images. X-ray absorption near edge structure (XANES) spectroscopy has been used to characterize the chemistry of these films. The intensity of phosphorus K-edge was also used to monitor the thickness of these films. Phosphorus L-edge spectra show that these films have slightly variable chemical natures. 31P Nuclear magnetic resonance (31P NMR) was used to study the ZDDP components in the residue oils. The spectra show that the primary and secondary ZDDP decompose quite differently at the various conditions. Tribological characteristics of these AW films were probed by measuring the coefficients of friction and the wear scar width of the counter faces.
Non-Newtonian Response of EHL Film Temperature
Authors: Kaneta M. , Nishikawa H. , Okabayashi S. , Wang J. , Yang P.
Published: March 2009

The temperature and thickness of oil film in point EHL contacts between a rough stationary surface and a smooth moving surface are measured with infrared and optical interferometry techniques. The ridges and furrows of the roughness are aligned with the parallel direction to that of lubricant entrainment. The experimental results are compared with numerical simulations based on Eyring and Newtonian fluid flow models. Under certain conditions, the average film temperature across the oil film near the central contact region is higher at the furrow position than at the ridge position. It is revealed that this phenomenon is caused by shear thinning behavior of lubricant.
A Rapid Method of Numerical Calculation for Oil Film Temperature in Engine Bearings
Authors: Ashihara Katsuhiro , Hashimoto Hiromu
Published: March 2009

In the design and analysis of engine bearings for automobiles, the elastic deformation of bearing surface due to high pressure and temperature of oil film affects significantly on the bearing characteristics. Thermo-elasto-hydrodynamic lubrication analysis (TEHL) is usually used to consider such effects, but a large amount of calculation time is needed to obtain the numerical solution of oil film temperature by solving the conventional type of 3-dimensional energy equation in TEHL. This paper describes a rapid method of numerical calculation of oil film temperature in engine bearings. In this modeling, it is assumed that the temperature distribution in the oil film thickness direction takes the parabolic form. Under such an assumption, averaging the 3-dimensional energy equation over the film thickness, the 2-dimensional energy equation is newly obtained. The numerical solutions of oil film temperature based on the 2-dimensional model are compared with the solutions based on the 3-dimensional model. It is confirmed that the calculation time is remarkably reduced to obtain the oil film temperature with an allowable accuracy. Moreover, the predicted oil film temperature by the 2-dimentional model is compared with measured data, and the good agreement is seen between them.
Instability of Herringbone Grooved Aerodynamic Floating Bush Bearings Flexibly Supported by Foils With Hemispherical Bumps
Authors: Yoshimoto Shigeka , Miyatake Masaaki , Nagata Katsuya
Published: March 2009

In this paper, a herringbone grooved aerodynamic floating bush bearing is proposed and the instability of a rigid rotor supported by the proposed bearings is investigated, numerically and experimentally. The proposed floating bush bearing is flexibly supported by three- or four-layered foils with hemispherical bumps. Accordingly, it is expected that the rigid rotor supported by the proposed bearings will be able to rotate stably at higher speeds compared with conventional herringbone grooved bearings which are rigidly mounted on housing. It was found that the proposed floating bush bearing with 6 mm in diameter can stably support a rotor at more than 0.6 million rpm.
A MEMS Device for Studying the Friction Behavior of Sidewall Surfaces
Authors: Wu Jie , Wang Shao , Miao Jianmin
Published: March 2009

A MEMS device for friction characterization was designed and fabricated with single-crystal silicon. This testing device consists of two orthogonal electrostatic comb actuators. A sensor plate for sliding contact was connected with a normal comb actuator via two supporting flexures. Opposite to the sensor plate, a driving plate with two bumps designed for the Hertzian contact was integrated with a tangential comb actuator. The contact regions were in the elastic regime on the scale of the bumps. By applying a DC voltage to the normal comb actuator, the sensor plate was brought into contact with the driving plate under a normal loading. Subsequently, a trapezoidal waveform was applied to the tangential comb actuator to generate a periodic sliding motion. The measurement was performed at the sidewall surfaces of singlecrystal silicon and a quasi-static stick-slip model was developed. With an image processing technique developed, experimental displacement data were extracted from the captured video frames. Analytical expressions were derived to determine the coefficients of static and kinetic friction from the displacement data for the driving and sensor plates.
The Problems of Application of PVD/CVD Thin Hard Coatings for Heavy-Loaded Machine Components
Authors: Szczerek Marian M. , Michalczewski Remigiusz , Piekoszewski Witold
Published: March 2009

The authors developed test methods for investigation of heavy-loaded coated machine elements: scuffing and pitting. Results of their investigation indicate the very positive role of coatings for increasing resistance to scuffing. The authors stated that the role of usually toxic lubricating additives can be taken over by the thin coating. The crucial problem is pitting. Comprehensive research indicates that steel components with typical PVD coatings (eg. TiN, CrN) usually do not exhibit a satisfactory fatigue life. However the results of experiments performed by the authors for new coatings are encouraging.
Analysis of High-Speed Cylindrical Roller Bearing With Flexible Rings Mounted in a Squeeze Film Damper
Authors: Defaye Cyril , Nelias Daniel , Bon Florence
Published: March 2009

For high-precision mechanical systems such as gas-turbine engines, which operate under extreme conditions, it is particularly important to accurately predict the behavior of the mainshaft rolling bearings. This prediction includes, among others, the load distribution, stiffness and power dissipation. Although shaft speeds tend to increase, rings and shaft walls are becoming thinner due to size and weight constraints. Thus, bearing behavior is no longer independent of the housing and ring stiffness. Furthermore, since forty years, the use of squeeze film damper is largely widespread in gas-turbine engines to significantly reduce the vibratory levels. Due to the flexibility of the ring providing the interface between the roller bearing and the fluid film, it appears an elastic coupling which modifies the behavior of the bearing-squeeze film damper system. This paper presents first a squeeze film damper model with a flexible inner ring (i.e. outer ring of the roller bearing). An analytical stop model is introduced to reproduce the interference between the inner ring of the squeeze film damper and its housing. In a second part, an elastic coupling between the presented squeeze film damper model and an existing roller bearing model is proposed. Finally, the results presented show that this coupling has a first order influence on the behavior of the bearing-squeeze film damper system. It is also shown that the coupling between a roller bearing and a squeeze film damper when linked by a flexible ring introduces a dissymmetry of the load distribution with respect to the applied load direction. Moreover, in certain cases, the position of the bearing in its housing can reach eccentricities larger than the radial clearance of the squeeze film damper.
Ball Motion and Sliding Friction in an Arched Ball Bearing
Authors: Leblanc Alexandre , Nelias Daniel , Plona Daniel
Published: March 2009

An analysis of double arched ball bearing which considers centrifugal forces and gyroscopic effects is performed. Based on operating conditions of a 5 DOF inner ring and Coulomb friction model, the conventional bearing theory is extended from 2 to 3 or 4 contact points. The commonly control criterion of ball bearing by the inner or outer raceway is debatable and is known to fit with difficulty with experimental data. In addition when more than two contact points are involved it becomes obsolete. The paper presents a mathematical model to describe the complex ball bearing internal kinematics under the effect of the external working conditions. Lubricant thickness is taken into account in geometrical equations and the non-linear system of this quasi-static model is solved by a Newton-Raphson method. The 3D model is first validated through comparisons with published data for conventional or single arched ball bearings. Results are also compared to those provided by the commercial software RBL4. The analysis of a double arched ball bearing is finally performed and the complex motion of the ball highlighted.
Texturing Effects in Plane-Inclined Slider Bearings
Authors: Dobrica Mihai B. , Fillon Michel , Pascovici Mircea D. , Cicone Traian
Published: March 2009

Surface texturing has been shown to have friction reducing / load capacity increasing effects in parallel sliders, as well as in cylinder-liner contacts and in hydrodynamic seals. However, if texture is to be regarded as the sole mean of hydrodynamic lift in parallel sliders, or as a way of improving hydrodynamic performance in slider, thrust and journal bearings, several issues have to be addressed, such as optimal texturing parameters and corresponding performance gains. This paper deals with these issues in the case of a plane inclined textured slider. Parametric studies are conducted to determine optimal texturing extents, dimple depth and texturing density, as well as the influence of the operating conditions on these optimal texturing parameters.
Influence of Crystallographic Orientation on Energy Dissipation During Sliding
Authors: Dawkins Jeremy J. , Neu Richard W.
Published: March 2009

This work presents the results of a finite element study of the sliding contact of interfering cylindrical asperities. One asperity is modeled as elastic with steel properties, while the other asperity is modeled as elastic-plastic copper. The simulations were run using two different plasticity models for copper, conventional J2 plasticity describing an initially homogeneous material and a continuum crystal plasticity model that can capture the influence of crystallographic orientation on the deformation response. The use of the crystal plasticity model and frictionless contact enables us to study the dependence of plastic deformation and energy dissipation as a function of crystal orientation and vertical interference. The relative trends predicted using crystal plasticity are consistent with classical experiments showing the dependence of friction with crystal orientation when plastic deformation is the primary energy dissipation mechanism.
Soluble Phosphorus-Based Compounds as Anti-Wear Additives for Perfluoropolyethers Lubricants
Authors: Di Meo Antonella , Riganti Fabio , Vezzulli Graziano , Picozzi Rosaldo
Published: March 2009

New soluble additives were synthesized to act as anti-wear for perfluoropolyether oils. The tribological properties of the formulations of these phosphorus-containing compounds in different base oils have been evaluated by a Falex four ball test machine and by an Optimol SRV oscillating friction and wear tester. The results obtained, object of the present work, clearly show that these additives are able to significantly reduce the wear of PFPE oils (up to 50% reduction).