bluuebunny/crossref_metadata_2025 huggingface dataset:
Wear Behavior of Rotary Shaft Seals in Grease Application
Authors: Du¨rnegger Wolfgang , Haas Werner
Published: March 2009

The desire for small maintenance costs and extended service intervals promotes the development of life time lubricated systems. Therefore consistent fluids (greases) are mainly used. Their limitations, represented in characteristic value (speed*mean bearing diameter) clearly increased up to 2,5*106 min−1*mm. However possibilities, potentials and limitations for radial working sealing systems are still unknown. The following shows a possibility for test arrangement and measurement to analyse wear concerning rotary shaft sealing systems in grease application.
Tribological Challenges in MEMS/NEMS Devices
Authors: Patton Steven T. , Voevodin Andrey A.
Published: March 2009

Microelectromechanical systems (MEMS) devices with contacting interfaces offer numerous tribological challenges, which need to be solved to enable wider use of the technology [1–7]. These challenges become even more acute as further miniaturization occurs with Nanoelectromechanical systems (NEMS) technology. Although considerable progress has been made in the understanding of tribological phenomena of microscopic contacts, MEMS designers often use alternate designs to avoid surface contact and the associated reliability issues. For example, bulky devices with large spring constants are used to overcome surface forces and/or redundancy is built in to allow for a limited number of failures in individual MEMS components. Such design approaches prevent the realization of the full potential of MEMS/NEMS technology. Tribological solutions are therefore becoming an enabling technology for miniature MEMS/NEMS made with more compliant structures, smaller size, and smoother surfaces.
Thermal Effects in an Elastohydrodynamic Line Contact Using a CFD Approach
Authors: Hartinger Markus , Gosman David , Ioannides Stathis , Spikes Hugh
Published: March 2009

Traditionally the problem of elastohydrodynamic lubrication (EHL) has been solved using the Reynolds equations for fluid flow. In this paper we explore the finite volume method (FVM) to model fluid behaviour in rolling-element bearing systems. We discuss the effects of temperature in an ehl line contact, which results in a non-uniform viscosity distribution across the film. Furthermore, the thermodynamic implications of using a Reynolds-condition like cavitation model are investigated.
Tribology of High Pressure Rotor Seals: Friction and Failure
Authors: Henzler Markus , Haas W.
Published: March 2009

Rotating unions for high oil pressure (30 MPa) are common in technique. For example they can be found in excavators between the turnable upper part and the stationary lower part or in the indexing tables of tool machines. These seals often cause problems. Due to the high oil pressure, their friction torque can rise up to one hundred Nm and the seals fail during operation. But with known failure pattern the user is able to judge and improve the seal and the surrounding construction. This paper summarizes the failure causes that were observed during experiments at the Institute of Machine Components over the last years.
An Investigation to the Design of Vacuum Preloaded Air Bearings With Respect to Reproducibility
Authors: van Beek Anton , van Ostayen Ron , Munnig-Schmidt Rob
Published: March 2009

Vacuum preloaded (VPL-) air bearings are generally designed by combining a collar bearing and a central area where vacuum is drawn (Figure 1). Sometimes the bearing area and vacuum area are separated by a groove which is connected to ambient pressure in order to prevent flow from the pressurized area to the vacuum ejected area. The collar bearing around the vacuum area is generally orifice compensated, compensated by a porous surface or by shallow grooves applied in the bearing surface. In this paper a study is presented towards the design of bearing configurations with the highest axial bearing stiffness that can be machined with good reproducibility. Various bearing configurations are analyzed analytically and numerically and the performance of the analyzed bearings are compared to each other.
Correlation Between Film Forming Ability and Rheological Properties of New and Aged Lowsaps Automotive Lubricants
Authors: Meunier C. , Mazuyer D. , Vergne P. , El Fassi M. , Obiols J.
Published: March 2009

The rheological behavior of fresh and aged diesel LowSaps 5W30 lubricant, is studied with both ElastoHydroDynamic tribometer, and low shear and high shear viscometers. The evolution of the film thickness in EHD contact, that varies between 1nm and 150 nm, displays two types of lubrication process according to rolling speed. On the one hand, a classical EHD behaviour, controlled by viscosity, may be observed beyond 35 nm with a significant shear thinning effect in the range of temperatures. On the other hand, below 35nm, a steep drop of film thickness indicates the unability of the viscosity improver polymer to form a thin film within the contact. These observations are closely related to rheological measurements carried out in a shear rate range from 10s−1 to 107s−1, and temperatures between 25°C and 150°C. Indeed, analysis of two rheological parameters, polymer relaxation time and hydrodynamic radius, may explain non newtonian and thin film effects in the EHD experiments. A rheological modelling based on the Cross model is developed to calculate these parameters. Then, the principle of time-temperature equivalence is used to map the characteristics of lubricants. Finally, the approach coupling EHD tribometer\Viscometer is applied to lubricants which have been degraded during a light duty diesel engine test.
Influence of Collar Deformations on Hydrodynamic Thrust Bearing Performance
Authors: Michal Wasilczuk , Michal Wodtke
Published: March 2009

Theoretical models of hydrodynamic thrust bearings do not usually consider thermoelastic deformations of the collar, while pad deformations are usually taken into account. In many cases the results of theoretical analysis differ much from experimental data despite of variety of effects being included in the TEHD models. In the authors’ research an attempt of including runner thermoelastic deformation in a bearing model was taken up. The results of calculations of a water turbine thrust bearing were compared for three cases — no runner deformation, elastic runner deformation and thermoelastic deformation. Including runner thermoelastic deformations resulted in improved agreement between theoretical results and available experimental data. However a detailed knowledge on runner design and boundary conditions is necessary for realistic evaluation of deformations, which is to a great extent individual design dependent and difficult to generalize.
Safe and Economically Efficient Use of Metal Working Fluids in Mechanical Processing of Magnesium Alloys
Authors: Joksch Stefan , Schwerin Rene´
Published: March 2009

Magnesium, a light-weight metal, has been used as a construction material since the early days of the 20th century. Excellent availability and low specific weight are the main benefits for applications in the aerospace and automotive fields. Because of a vast increase of Magnesium machining applications in the mobile equipment manufacturing industry over the last 10 years, there is an increasing demand for specially adapted cutting fluid systems for the machining of Magnesium parts. This paper will provide an overview on the latest research activities in Germany to develop new cutting fluid systems for a safe and economically efficient use of metal working fluids in mechanical processing of Magnesium alloys. Laboratory results and field applications with new innovative water-miscible cutting fluids are demonstrating that it is possible to control the huge problems of the past, such as hydrogen formation, emulsion split and corrosion. Based on experiences in the biggest european magnesium Machining project, the “Al/Mg Hybrid Crank Case” (Fig. 1), problems and solutions specific for large scale machining of Magnesium alloys with water-mixed cutting fluids are shown.
Approximate Closure Equations for Elastic Contact of Nominally Flat Rough Surfaces
Authors: Sepehri A. , Farhang K.
Published: March 2009

A hybrid interactive/optimization technique is used to derive in approximate closed form equations relating contact load to mean plane separation. Equations governing Hertz contact for the interaction of surface asperities are considered in which asperity shoulder-to-shoulder contact results in normal and tangential components of force. The normal component of asperity force is summed statistically to find total normal force between the two surfaces. The tangential component of asperity force, summed statistically, yields zero total force due to the symmetry of the distributed tangential force components. The tangential force over a half-plane corresponding to a select direction is found accounting for the directionality of the tangential component of asperity forces. Two sets of approximate equations are found for each of the normal and half-plane tangential force components. The simplest forms of the approximate equations achieve accuracy to within five (5) percent error, while other forms yield approximation error within 0.2 percent.
Effect of Process Conditions on Adhesion Between Stamp and Polymer Film Used in Thermal Nanoimprint Lithography
Authors: Kim K. S. , Kang J. H. , Kim K. W.
Published: March 2009

In this study, the adhesion characteristics between stamp and thermoplastic polymer film were studied in order to investigate the effect of process conditions on the adhesion between two materials. Imprint pressure, separation speed and coating of anti-sticking layer (ASL) were considered as the process conditions. A piece of fused silica without patterns on its surface was used as a stamp and the thermoplastic polymer film was made on Si substrate by the spin-coating of commercial polymer solution such as mr-I PMMA and mr-I 7020. The ASL was derived from (1H, 1H, 2H, 2H - perfluorooctyl) trichlorosilane (F13-OTS) and coated on the fused silica stamp in vapor phase. The adhesion force was measured in various process conditions when the polymer film was separated from the stamp. As a result, it is found that the adhesion force was changed according to the polymer materials and the adhesion reduction effect of ASL also appeared differently. In addition, the adhesion force did not depend on the imprint pressure in cases of the stamp coated with ASL while it increased as the imprint pressure increased in cases of the stamp without ASL. The dependency on separation speed appeared stronger in cases without ASL.
Comparison Between Plain and Herringbone-Grooved Aerodynamic Journal Bearings
Authors: Delhaes Guido M. J. , van Beek Anton , van Ostayen Ron A. J. , Munnig-Schmidt Rob H.
Published: March 2009

Aerodynamic journal bearings are commonly used to support high-speed rotors. In applications where the shaft rotates concentric, like turbines and high-speed spindles, grooved aerodynamic bearings are used because they can run concentric. Plain aerodynamic journal bearings are unstable in the concentric position and are therefore not used for these applications. The instability is caused by the 90° attitude angle of the plain bearing at low rotational speeds. However by increasing the rotational speed the attitude angle of the plain bearing approaches the attitude angle of the grooved bearing. Moreover up to a certain speed the load capacity of the plain bearing is higher than the load capacity found for grooved bearings. In certain circumstances plain bearings might be preferable, since the plain bearing is much easier to manufacture. In this work a comparison is outlined for the plain and herringbone grooved bearings.
Closure Equations for CEB Elastic-Plastic Contact
Authors: Sepehri A. , Farhang K.
Published: March 2009

The CEB elastic-plastic contact of nominally flat rough surfaces based on conservation of volume during plastic flow was forwarded by Chang, Etsion and Bogy [1]. The CEB model presents contact force as integral functions of the mean plane separation. A closed-form approximate function providing an explicit relation between contact force and surface parameters and mean plane separation would be desirable for several reasons. First, it facilitates implementation of the contact relation in the dynamics of mechanical system and, second, it provides expediency and efficiency for calculation of contact force when repetitive computation of the contact force is required. This paper presents closed-form approximate equations expressing contact force explicitly as a function of critical interference and mean plane separation. Two alternative approximate equations are provided. The first equation, in simpler form, is shown to yield error within six percent (6%) of the exact integral equations. The second form of approximate equations provides contact force accuracy within 0.1 percent of the original integral equations.
An Investigation of Three Dimensional Elastic-Plastic Hemispherical Sliding Contact, Part I: Modeling and Validation
Authors: Moody John , Green Itzhak
Published: March 2009

This work presents a three dimensional (3D) finite element analysis (FEA) of an elastic-plastic hemispherical contact model for two hemispherical bodies sliding across each other with various preset vertical interferences. The boundary conditions, model simplifications, and the normalization scheme are presented. Sample results from this FEA investigation are compared to a semi-analytical solution to validate the methodology.
CFD Analysis of the Lubricant Flow in the Supply Groove of a Hydrodynamic Thrust Bearing Pad
Authors: Grzegorz Rotta , Michal Wasilczuk
Published: March 2009

Inlet temperature is one of the main inputs in all models for analysis of fluid film bearings performance. On the other hand inlet temperature distribution and also oil speed distribution at the inlet is the result of flow phenomena in the gap between bearing pads. These phenomena are complex and in many cases additionally affected by a special bearing design incorporating various arrangements of forced oil supply to the gap between pads. The reason for such arrangements is more efficient introducing of the lubricant cooled in an external cooling system to the oil film. Not much is known about flow phenomena in the gap between the pads and even less if the bearing is fitted with any kind of directed lubrication system. One of those special bearing arrangement is a leading edge groove (LEG) design described by Mikula [1] Experimental results showed that LEG lubricating system in comparison to flooded lubrication caused about 10–20°C drop in maximum temperature in high-speed bearings. But not much is known of potential benefits of using this lubrication method in large low-speed bearings applied in water turbines. There were no attempts of adaptation of this lubrication system to large size bearings. In this case modeling is necessary because of large cost of experiments. Contemporary computer codes of Computational Fluid Dynamics (CFD) enable one to study flow between bearing pads or in lubricating groove and even to build models of a whole hydrodynamic bearing within CFD systems. Some results of modeling lubricant flow in the gap in a bearing with a directed lubrication system are presented in the paper.
MEMS Lubrication by Tribochemical Reaction
Authors: Dugger Michael T. , Asay David B. , Ohlhausen James A. , Kim Seong H.
Published: March 2009

A means of providing replenishable lubrication to rubbing silicon surfaces is demonstrated. Alcohol at a small fraction of saturation vapor pressure is introduced in a nitrogen environment. Pin-on-flat sliding experiments in this environment reveal a friction coefficient near 0.2, and absence of wear above a critical alcohol concentration. This lubrication approach was also demonstrated in microfabricated silicon machines, where the devices operated at least a factor of 104 longer without failure when alcohol vapor was present in the nitrogen gas environment, compared to devices in dry N2 with a chemisorbed monolayer alone. When water vapor was added to the environment, vapor lubrication by alcohol was inhibited at concentration ratios of water:alcohol = 2.5:1.
Geometry Optimization of Hybrid Tilting-Pad Journal Bearings
Authors: Santos Ilmar Ferreira , Kristiansen Bo Uldall
Published: March 2009

Radial tilting-pad bearings under hybrid lubrication conditions are industrially used in heavy horizontal machines. One single orifice is normally designed and machined in the middle of the pad. Through such an orifice pressurized lubricant is injected and the rotor-bearing system is hydrostatically lubricated during start-up and run-up conditions. Nevertheless, at a pre-defined angular velocity the hydrostatic lubrication is turned-off and the rotor-bearing system operates under hydrodynamic condition. The main focus of the present work is to investigate the feasibility of using the hydrostatic lubrication as an auxiliary mechanism to improve rotor stability and increase damping reserve of rotor-bearing systems. The geometry of the bearing, namely number of orifices, their positioning over the pad surface and their diameters, are optimized using the damping factor of the rotor-bearing system as weighting functional. The dependency of the optimal parameters on the rotor angular velocity and injection pressure (operational conditions) is discussed and the limits of an increase in damping reserve via geometry optimization are elucidated.
Hardness and Frictional Properties of Alumina Coatings by AC Inverted Magnetron Sputtering Technique
Authors: Wang H. , Aryasomayajula A. , Zou M. , Gordon M. , Bhat D.
Published: March 2009

Alumina thin film coatings of 500 nm thickness were deposited on silicon substrates by AC inverted magnetron sputtering technique at 350°C. The effect of deposition power and oxygen partial pressure on the hardness and frictional performances of the alumina coatings were investigated using a nanoindenter. The film hardness varied with both the power and the oxygen partial pressure with the power had more pronounced effect. The maximum hardness of 22 GPa was obtained at an optimum power of 5 kW and oxygen partial pressure of 40%. The coefficient of friction decreased with the increase in hardness.
Air Bearing Surface Design for Improving Efficiency of Thermomechanical Actuation
Authors: Zhang Shuyu , Strom Brian , Lee Sungchang , Kim Dongman , Tyndall George , Ferber Joerg
Published: March 2009

Thermomechanical actuation (TMA) at the transducer region of the air bearing surface (ABS) protrudes the transducers toward the recording media, yet also results in greater air bearing slider lift. The ratio of these two effects is defined as the TMA efficiency. An expression based on dimensional analysis is introduced to describe the changes of air bearing forces due to TMA protrusion. A framework is proposed that facilitates optimization of ABS design for improved TMA efficiency. On the basis of the theory presented, several ABSs are designed to have different TMA efficiency. Numerical solutions of these air bearings respect to the protrusion shows agreement with the proposed theory.
An Experimental and Numerical Investigation of Flow Regimes in Narrow Gaps
Authors: Deng D. , Braun M. J.
Published: March 2009

A comparison between the experimental and numerical results of the torque-speed graph is presented. There is a good agreement between the numerical and experimental data in the Couette, Taylor and Pre-wavy regimes. In the wavy regime, the numerical data are larger than the corresponding measured torques but the difference is confined to below 14%. The calculated critical speeds for the onset of Taylor vortex and Pre-wavy flows are slightly larger than the experimentally measured ones. Flow patterns in the longitudinal cross section view of the fluid between two cylinders are also presented. Experimental results show that Taylor vortex flow is replaced by a new equilibrium flow, which is defined as Pre-wavy flow. The major characteristic of the Pre-wavy flow is the appearance of zones of particle accumulation in the areas near the inner cylinder. These zones correspond to the low pressure regions. Except for the flow patterns in the Pre-wavy regime there is good agreement between the numerical simulation and the experimental results.
Influence of Surface Roughness on Friction and Contact Resistance in Sliding Electrical Contacts
Authors: Bansal Dinesh G. , Streator Jeffrey L.
Published: March 2009

An experiment is conducted to investigate the role of surface roughness on the coefficient of friction and contact resistance of sliding electrical contacts. A hemispherical pin is sliding along both smooth and rough 2-meter rail surface. Tests are performed at both low and moderate sliding speed and for a range of electrical current densities, ranging from 0 to about 12 GA/m2. It was found that surface roughness had a significant influence on the coefficient of friction, with the smoother surfaces exhibiting higher coefficients of friction. Contact resistance, on the other hand, did not show as strong an effect of surface roughness, except for a few parameter combinations. At the higher current densities studied (>10 GA/m2), it was found that the contact resistance values tended to be on the order of 1 mΩ, independent of load, speed and roughness. This convergence may be due to presence of liquid metal film at the interface, which established ideal electrical contact.
On the Wear of Carbide and Cermet Tools in Machining of Compacted Graphite Iron (CGI)
Authors: Varghese K. Philip , Balaji A. K.
Published: March 2009

This work presents an extension of a previous investigation [1] conducted on gaining an understanding of the critical tribological issues encountered in the machining of compacted graphite iron (CGI) using different cutting tool materials. As part of this study, wear tests were conducted on flat-faced coated and uncoated carbide tools and coated and uncoated cermet tools. The machining tests were conducted under dry condition. Performance assessment of the cutting tools was made using a comparative analysis of the measured cutting forces and post machining scanning electron microscopy (SEM) of used tools. The results reveal the interaction of selected cutting conditions and tool substrate material and coatings on the tribological performance and wear behavior of tools during CGI machining.
Effects of Water Environment on Tribological Properties of DLC Rubbed Against Brass
Authors: Uchidate M. , Liu H. , Iwabuchi A. , Yamamoto K.
Published: March 2009

The effects of water environment such as temperature and dissolved ions on tribological properties of DLC against brass were studied for development of the water-lubricated hydraulics, valves and cylinders based on metal. A ball-on-disk type rotating tribotester was used for detailed examination of above mentioned factors. DLC was deposited on the disk by the unbalanced magnetron spattering system. Pure water and quasi-tap water were used to study the effects of dissolved ions. The results show that temperature and dissolved ions have major impact on the wear of DLC. EPMA, XPS and AES indicate that tribo-layer on the metal surfaces, consists of carbon and the base metal and some element from water, plays important role for the phenomena.
Biological Contact Systems With Enhanced Adhesion: What Can We Learn From Evolution?
Authors: Gorb Stanislav N.
Published: March 2009

Biological hairy attachment systems demonstrate their excellent adhesion and high reliability of contact. The structural background of this functional effect is discussed in the present paper. It is demonstrated here how comparative experimental biological approach can aid in development of novel tribological materials and systems.
Improved Hot Aluminum Forming Tribology by Anodization
Authors: Franetovic Vjekoslav , Schroth James G.
Published: March 2009

The process of Quick Plastic Forming (QPF) developed by General Motors involves hot aluminum forming at ∼450°C, and has formability advantages over conventional stamping of aluminum or steel. However, there are still no fully satisfactory solutions for the problem of local interaction/sticking between the aluminum blank and the tool, and the eventual transfer of some aluminum to the steel tool after repeated forming cycles. In this paper we show that the process of anodizing aluminum prior to forming greatly diminishes the interaction of aluminum with steel at QPF forming temperatures. Significantly improved tribological behavior of the aluminum surface after anodization as compared to lubricated aluminum was shown on a laboratory scale with flat-on-flat reciprocating experiments.
Influence of Environmental Humidity on Wear Behavior of Aluminum Alloy Impregnated Graphite Composite Under Insufficient Lubrication
Authors: Goto Hozumi , Shibuya Yusaku
Published: March 2009

Wear characteristics of an Al-Si alloy impregnated graphite composite containing 56 vol% graphite and its matrices in contact with bearing steel were investigated under insufficient lubrication. Pin-on-disk type wear tests in air were conducted at various levels of relative humidity (RH) under dry sliding and drip feed lubrication (0.005 to 0.02 cm3) before each test by using base oil for engines. Changes in friction and wear were continuously monitored during the tests. Four types of wear mode for the composite were obtained: steady wear with a low rate (Type 1), high wear after a lubricating oil shortage (Type 2), no wear after pin lifting (Type 3) and steady wear with a high rate (Type 4). Type 1 appears over the whole range of RH (5 to 80%). Type 2 is found at low RH levels of 5 and 10%. Type 3 occurs at a frequency of 30 percents between 10 and 35% RH. Type 4 is seen over the whole RH range under dry sliding. The appearance of each wear mode at a specified RH depends on wear behavior of the matrices associated with RH under drip feed lubrication.
Oil Temperature Analysis of Brush Seals
Authors: Duran E. Tolga , Aksit Mahmut F. , Dogu Yahya
Published: March 2009

Due to their superior performance and stable leakage characteristics, brush seals are one of the dynamic seals used in oil and oil mist applications in aero-engines and turbines. The viscous medium between the high speed rotor surface and brush seal bristles generates a hydrodynamic lifting force that determines seal clearance and leakage rate in oil sealing applications. The analytical solution to bristle lifting force can be obtained by using Reynolds formulation. However, there is a strong dependence on oil temperature and viscosity. This work presents a solution to oil temperature using nonlinear pressure distribution. Starting with continuity and Navier Stokes equations, temperature and nonlinear pressure distribution is derived by solving the thermal energy and reduced continuity equations simultaneously. Results of oil temperature estimates using nonlinear pressure analysis are compared with the results of a previous work using linear pressure assumption. Findings indicate that for low rotor surface speeds oil temperature distribution is almost the same for both linear and nonlinear pressure cases. Difference in oil temperature estimates increases with increasing rotor surface speeds.
Analysis of Residual Stresses Impact on Fatigue Life of Rolling Contacts
Authors: Cretu S. , Benchea M.
Published: March 2009

The values of residual stresses resulting from a heavily stressed contact are numerically evaluated by employing a three-dimensional strain deformation analysis model. The model is developed in the frame of the incremental theory of plasticity including the von Mises yield criterion, Prandtl-Reuss equations, and Ramberg-Osgood stress-strain equation. Two groups of cylindrical specimens were subjected to rolling contact fatigue, one as the reference group and the other with an induced residual stresses state. To obtain theoretical lives of the tested groups the von Mises equivalent stress is used in Ioannides-Harris rolling contact fatigue model. Both, the experimental data and theoretical analysis reveal more than two times greater fatigue life for the group with induced residual stresses versus the life of the reference group.
Rolling Stream Trails: An Alternative Cavitation Analysis
Authors: Pan Coda H. T. , Kim Tae Ho , Rencis Joseph J.
Published: March 2009

The Rolling Stream Trails (RST) model introduces new interpretation of photographic data of the cavitation process in an eccentric journal bearing gap. It stipulates a 3-D flow structure for transition from the Filled Fluid Film (FFF) to a cross-void fluid transportation process. The transition starts as a two-component composite rupture front and becomes an Adhered Film (AF) that is masked by rolled-on stream trails, which are drawn from the rupture front. The AF moves with the journal surface across the void to feed the FFF at the formation boundary. The rupture front comprises a first component of periodic streamers separated by a second component of interspersing wet pockets. Olsson’s Equation for flow continuity relative to a moving cavitation boundary (OEM) [1] yields a moving speed of the rupture front that is proportional to the reciprocal of the width fraction of the wet pockets multiplied into the FFF pressure gradient. Both rupture and formation boundaries move with finite speeds. The formation boundary speed in RST is determined by overall mass conservation in the bearing gap. RST formulation of the cavitation of a journal bearing fluid film yields an initial value time-dependent problem for the fluid flow in the bearing gap. The latter includes both the FFF and the AF that are joined at rupture and formation boundaries. The initial fluid content in the void span is bracketed between a dry void and a freshly cavitated wet void. As time progresses, transportation of AF across the void space and boundary motions form a coupled evolution process. Formulas for the boundary motions indicate that the formation boundary would become stationary simultaneously as the rupture boundary approaches the Swift-Stieber (SS) condition [2, 3]. Sample 1-D RST calculations illustrate temporal evolutions of the FFF pressure profiles, cavitation boundary locations and fluid content in the void span (AF profile). Resulting asymptotic pressure profiles are substantially different from published ECA calculations.
Effect of Tribochemical Interactions on Friction and Wear of Highly Hydrogenated DLC Films
Authors: Eryilmaz O. L. , Erdemir A.
Published: March 2009

In this paper, we attempted to elucidate the nature and extent of tribochemical interactions between sliding surfaces of highly-hydrogenated diamondlike carbon (DLC) films (containing about 40 at.% hydrogen) and correlated these findings with their friction and wear behaviors in dry and humid nitrogen environments. For the tribochemical studies, we used a time-of-flight secondary ion mass spectrometer (ToF-SIMS) in 2- and 3-D imaging modes, while for tribological tests, we used a ball-on-disk machine that was operated under a 5 N load and at sliding velocities of 0.2 to 0.3 m/s. In dry nitrogen, the DLC films provided a friction coefficient of ≈ 0.007, but in humid nitrogen, the friction coefficient 3 to 4 times higher. 3-D surface profilometry and optical microscopy did not reveal much wear on sliding ball and disk surfaces after the tests regardless of the test environment, but the 2- and 3-D ToF-SIMS images of the same surfaces revealed very rich tribochemistry for films tested in humid nitrogen but not much chemistry for those films tested in dry nitrogen. Complementary x-ray photoelectron spectroscopy of these sliding surfaces showed similar results further confirming extensive tribo-oxidation (in the forms of both C-O and C=O) of DLC surfaces tested in humid nitrogen but no major chemical changes in DLC films tested in dry nitrogen. Based on the results of surface analytical and tribological studies, we concluded that superlow friction behavior of highly hydrogenated DLC films was perhaps due to the hydrogen termination of their surface carbon atoms, while the much higher friction coefficients observed in humid nitrogen was primarily due to tribo-oxidation and/or oxygen termination of these surfaces.
Plastification of Adhesive Micro-Spherical Contact During Jump-In Neck Formation
Authors: Kadin Y. , Kligerman Y. , Etsion I.
Published: March 2009

Approach between two deformable micro-spheres in the presence of adhesion is sometimes accompanied by discontinuous change of the surface profile at the narrow region near their summits (jump-in phenomenon or neck formation). The main goal of the current work is to show that neck formation can involve local plastification. The adhesive traction acting on the sphere’s surface is evaluated by the Lennard-Jones potential. The theoretical strength rather than the engineering yield strength of the material is used in the von Mises (VM) local yielding criterion. The results show that adhesion between deformable micro-spheres may cause elastic to plastic transition during the neck formation for specific combinations of geometrical and physical properties of the spheres.
In-Situ Vapor Phase Lubrication of MEMS Devices
Authors: Kim Seong H.
Published: March 2009

The basic principles, potentials, and challenges of the in-situ vapor phase lubrication will be addressed in the MEMS panel discussion.
Effects of Gas Adsorption in Nanotribology and Demonstration of In-Situ Vapor Phase Lubrication of MEMS Devices
Authors: Asay David B. , Dugger Michael T. , Kim Seong H.
Published: March 2009

This paper discusses the important role of gas adsorption in nanotribology and demonstrates in-situ vapor phase lubrication of microelectromechanical systems (MEMS) devices. We have elucidated the molecular ordering and thickness of the adsorbed water layer on the clean silicon oxide surface and found the molecular-level origin for the high adhesion between nano-asperity silicon oxide contacts in humid ambient. The same gas adsorption process can be utilized for continuous supply of lubricant molecules to form a few Å thick lubricant films on solid surfaces. Using alcohol vapor adsorption, we demonstrated that the adhesion, friction, and wear of the silicon oxide surface can significantly be reduced. This process made it possible to operate sliding MEMS without failure for an extended period of time.
Scale-Dependent Contact Deformation of Layered Media Due to Multi-Wavelength Surface Roughness Effects
Authors: Komvopoulos K.
Published: March 2009

In view of the self-affinity property exhibited by many engineering surfaces, multi-scale roughness leads to scale-dependent deformation of asperity contacts. Therefore, it is necessary to incorporate real surface topographies and local constitutive models of the deformation mode of interacting asperities in contact mechanics analyses. A theoretical treatment based on multi-wavelength surface topography description and asperity deformation models is presented and its applicability is demonstrated for layered media with fractal surfaces.
Polyethylene Wear Debris Produced in a Knee Simulator Model: Effect of Crosslinking and Counterface Material
Authors: Williams Paul A. , Brown Cindy M. , Tsukamoto Riichro , Nakamura Takashi , Clarke Ian C.
Published: March 2009

Polyethylene (PE) debris has been examined in total hip replacements from clinical retrievals and laboratory simulator studies, but little is known about PE debris from total knee replacements. In this study we investigated the effects of crosslinking PE and the counterface material. Mildly and highly crosslinked PE were studied in combination with CoCr and Zirconia femoral components. Wear was determined by gravimetric measurements and the wear debris was isolated and morphologically characterized. Although the zirconia counterface with 7 Mrad PE did not exhibit measurable wear, wear debris was found. This indicated that wear occurred below the limits of the gravimetric approach. This study showed that the amount of crosslinking of PE and the counterface material were important factors in the wear of PE in a knee simulator model.
Regulation of Cell Adhesion and Proliferation by Physicochemical Surface Modification and Protein Enhancement Due to Mechanotransduction
Authors: Komvopoulos K.
Published: March 2009

Cell adhesion and proliferation and protein expression on surfaces possessing different topographies and chemical characteristics are examined in the presence of mechanical stress. Results from earlier studies illustrate the significance of surface roughness and chemistry modification on endothelial cell adhesion and spreading on untreated and plasma-treated polyethylene surfaces. Furthermore, changes in the friction characteristics of bovine articular cartilage resulting from mechanotransduction are correlated with variations in the near-surface expression of a glycoprotein secreted from the chondrocytes in the superficial layer of the cartilage. Recent work indicates that this glycoprotein plays a crucial role in the formation of a sacrificial boundary layer that effectively lubricates the cartilage surface, protecting it from mechanical wear.
Investigations on Mechanical and Abrasive Wear Behaviour of Carbon and Glass Fabrics Reinforced Vinyl Ester Composites
Authors: Suresha B. , Jayaraju T. , Siddaramaiah  , Shivakumar Kunigal N.
Published: March 2009

The aim of the research article is to study the mechanical and abrasive wear behaviour of carbon and glass fabric reinforced vinyl ester composites. The measured wear volume loss increases with increasing load/abrading distance. However, the specific wear rate decreases with increase in abrading distance and load. The results showed that the highest specific wear rate is for glass fabric reinforced vinyl ester composite with a value of 8.96 × 10−11 m3/Nm and the lowest wear rate is for carbon fabric reinforced vinyl ester composite with a value of 5.84 × 10−11 m3/Nm. Mechanical properties were evaluated and obtained values compared with the wear behaviour. The worn surfaces were examined using scanning electron microscopy (SEM).
Tribogyr: A New Test Rig for High Spinning EHL Large Size Contacts
Authors: Dormois H. , Fillot N. , Dalmaz G. , Querry M. , Vergne P. , Ioannides E. , Morales G.
Published: March 2009

Only few studies have been published on EHD contacts that experienced simultaneously rolling, sliding and spinning motions. This paper describes a new test rig especially designed to simulate such operating conditions while imposing normal load and speeds as those found in real life mechanisms. Then, experimental results are presented and discussed.
Performance of Two Lobe Multirecess Hybrid Journal Bearing Compensated With Capillary Restrictor
Authors: Kushare Prashant , Sharma Satish C. , Jain S. C. , Basavaraja J. Sharana
Published: March 2009

Multirecess hydrostatic/hybrid journal bearings are being used in many applications owing to their excellent characteristics. The Noncircular journal bearing configurations too are quite frequently used in high speed machinery as they are efficient, less costly and provide better shaft stability. The Two lobe bearing (elliptical bearing) are among the commonly used noncircular journal bearing configuration. The multilobe multirecess hybrid journal bearings have been developed to combine the features of noncircular and circular hybrid journal bearing configurations. In the present work a theoretical investigation of a two lobe multirecess hydrostatic/hybrid journal bearing system have been carried out. The multilobe journal bearing configuration is designed as an arc of the circle with the centre points placed on the symmetry line of the single lobe. The journal offset has been accounted by defining an offset factor ‘δ’. The finite element method has been used to solve the Reynolds equation governing the flow of lubricant in the clearance space of the journal bearing system. The bearing static and dynamic performance characteristics have been presented for the various values of the offset factors (0.75, 1, 1.25 and 1.50) for hybrid mode of operation of the bearing. The simulated results of the studies reveals that, a two lobe recessed hybrid journal bearing provides an improved performance in respect of fluid film stiffness and damping coefficients as compared to that of circular recessed journal bearing. It has been observed that for a multilobe bearing having offset factor more than one has a favourable effect on the dynamic performance characteristics of the two lobe bearing.
Dynamics of the Formation of the Subambient Pressure Distribution During Chemical-Mechanical Polishing
Authors: Osorno A. , Tereshko S. , Yoon I. , Danyluk S.
Published: March 2009

Chemical-Mechanical Polishing is used to polish silicon wafers in the manufacturing of integrated circuits. Wafers are pressed, electronics side down, onto a rotating pad that is flooded with a slurry containing abrasive particles. The slurry is entrained in the interface and the abrasive particles slide against the silicon and polish it. Our previous work has shown that subambient pressures develop at the silicon/pad interface and we have measured this pressure and its distribution over the wafer surface (1). However, our experiments have been limited to those conditions where the pad rotates and the wafer slides on the pad but the wafer itself does not rotate. Our experiments showed a skewed pressure distribution. This paper describes experiments and pressure distribution measurements where the wafer, as well as the pad/platen is rotated (2). Specifically-designed wireless electronic transmitters and receivers were built and used to measure the interfacial pressures at the silicon/pad interface. Subambient stress maps and temperatures have been measured and Figure 1 shows an example of a skewed pressure distribution when the silicon is not rotated and Figure 2 shows the pressure distribution for the same wafer while it is rotating. The subambient pressures develop over a 2 second time period from when the rotation started. The pressure distributions are symmetric in spite of the lean and tilt of the wafers. The rotational speed and other variables have a big influence on the polishing rate and this will be discussed in the talk.
Acidification of Gas Engine Oils: Characterisation by Sensors
Authors: Doerr N. , Schneidhofer C.
Published: March 2009

Recently, a number of sensor principles to measure physical and chemical properties of lubricating oils were investigated. The crucial property of lubricating oils for some applications is the degree of acidification as there is a correlation to corrosive wear of engine components. Corrosiveness is of particular importance for biogas engines due to the fact that bio-fuels are forming more aggressive components during the combustion process as in comparison with conventional fuels. Recent research showed that the corrosiveness of oil cannot be described sufficiently by conventional oil parameters such as total acid number and neutralization number. We propose a sensor concept using the effect of material loss of a thin metal film due to corrosion. The signal of the sensor being immersed in used gas engine oils with corrosive compounds showed good correlation with selected oil properties determined in the laboratory.
Behavior of a Fluid Filled Subsurface Crack Under Moving Hertzian Loading
Authors: Jin Xiaoqing , Keer Leon M. , Wang Qian
Published: March 2009

Cracking of a fluid filled subsurface crack is studied by the distributed dislocation technique within the framework of two-dimensional linear elastic fracture mechanics. The opening volume of the horizontal Griffith crack is fully occupied by an incompressible fluid. In the presence of friction, a moving Hertzian line contact load is applied at the surface of the half plane. The induced hydrostatic fluid pressure inside the crack is calculated through an iterative scheme with the restriction that due to the fluid incompressibility there is no change of the crack-opening volume (COV). The stress intensity factors at the tips of the fluid filled crack are analyzed and the effective quadrature formulae are given for the evaluation of the COV. A hypothesis is introduced that the crack propagation is initiated when the elastic strain energy release rate reaches the critical fracture toughness and is arrested when the energy release rate is below the arrest toughness. Based on the energy criterion, predictions will be attempted for determining the load position where the crack propagation/kink commences as well as the growth increment of the branch crack before it is arrested. A step-by-step crack path is constructed for various loading conditions.
Friction Force Calculation in a Quasi-Static Sliding Process Based on the Energy Principle
Authors: Ding Lingyun , Huang Ping
Published: March 2009

A method based on the energy principle is introduced to calculate the friction force in a quasi-static sliding process with two flat elastic surfaces of the same metal. The energy dissipation mechanism during the process is analyzed with IO model. The results show that the friction force is proportional to the standard interfacial potential energy barrier and the real contact area. The numerically calculated friction force is also compared with the experimental data.
Micro-Tribology of Flow-Induced Load on a Surface Asperity Using Lattice Boltzmann Method
Authors: Cheng W. , Hua D. , Farhang K.
Published: March 2009

In this paper flow around a single roughness, known as asperity, is examined using Lattice Boltzman Method. Elliptical asperity cross section is used for this study. Asperity of various aspect ratios, defined as width-over-thickness ratios are studied using two flow conditions. The flow conditions correspond to parallel (Poisuelle) flow and pressure-driven flow. Results show that negative gage pressure occurs under both flow conditions, in the first due to the flow vortices and in the latter due to emergence and growth of boundary layer. Asperity aspect ratio is shown to give rise to the pressure drop potentially leading to cavitation condition.
Microstructure, Mechanical and Tribological Properties of Reactive Magnetron Sputtered Titanium Carbide Coatings
Authors: Polychronopoulou Kyriaki , Rebholz Claus , Demas Nicholaos G. , Polycarpou Andreas A. , Theodorou Lefki , Bo¨bel Klaus
Published: March 2009

This study describes the correlation between the microstructure, mechanical and tribological properties of Ti1−xCx coatings (with x being in the range of 0–0.5), deposited by reactive magnetron sputtering from a Ti target in Ar/C2H2 mixtures at ∼200 °C. The mechanical and tribological properties were found to strongly depend on the chemical composition and the microstructure present. Very dense structures and highest hardness and elastic modulus, combined with low wear rates, were observed for films with chemical composition close to TiC. X-ray diffraction (XRD) studies showed that the coating deposited at high C2H2 flow rates composed of randomly oriented TiC crystallites. Morphological investigations by scanning electron microscopy (SEM) indicate that the morphology is strongly dependent on the carbon content of the coating. Coatings composition and bonding environment was investigated using X-ray photoelectron spectroscopy (XPS). Both the mechanical properties and tribological performance of the coatings were found to be dependent on carbon content.
A Statistical Account of Asperity Heating in a Rough Surface Contact
Authors: Farhang K. , Elhomani A.
Published: March 2009

When two rough surfaces are in sliding contact an asperity on a surface would experience intermittent temperature flashes as it comes in momentary contact with asperities on a second surface. The frequency of the flash temperatures, their strength and duration depend, in addition to the sliding speed, on the topology of the two surfaces. In this paper a model is developed for the work-heat relation with a consideration of the above-mentioned intermittent nature of contact. The work of friction on one asperity is derived in integral form and closed-form equations. The rate of generation of heat is found due to a single asperity. Using the statistical account of asperity friction heat generation, rate of heat generation between two rough surfaces is obtained both in statistical integral form and in the approximate closed form.