bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulations for Nanoscale Meniscus Formation and Rupture by Using Molecular Dynamics
Authors: Ogata Susumu , Mitsuya Yasunaga , Zhang Hedong , Fukuzawa Kenji
Published: November 2008

To investigate the dynamic behaviors of nanoscale meniscus intervening between a solid surface and a probe tip of a scanning probe microscope in molecular scale, meniscus formation and rupture process were simulated by using molecular dynamics method. Lennard-Jones molecules were used to model both the lubricant film and the solid probe, and the techniques to analyze the normal force exerting between the film and the probe were introduced to identify the meniscus formation time and the meniscus elongation. We clarified that the meniscus formation time became longer for wider spacings between the film surface and the probe, and that the meniscus elongation became longer for larger probe retracting velocity.
Performance Evaluation of Magnetohydrodynamic Bearing
Authors: Hirani H. , Samanta P.
Published: November 2008

The present paper introduces a concept of hydrodynamic-permanent-magnetic hybrid bearing. The hybrid bearing uses repulsive force between permanent magnets and fluid force developed due to relative speed in a single assembly arrangement. Repulsive type passive magnetic levitation has advantage of minimum starting torque. Hydrodynamic lubrication mechanism has advantage of low friction at medium and high speed. This hybridization will be an attractive choice in commercial applications for its low cost, structural-simplicity and no metal-to-metal contact. An experimental setup is designed and developed to investigate the performance characteristics of proposed concept of hybrid bearing. Minimum film thickness, oil flow rate, and temperature rise are recorded at various speed- and load- conditions. Results are plotted to demonstrate the behavior of hybrid bearing arrangement.
Study of Microcontact Model for Hard Particles Between Rough Surfaces
Authors: Horng Jeng-Haur , Chern Shin-Yuh , Chen Chih-Hsien , Ku Ming-Yao
Published: November 2008

Particles are often presented at contact interfaces. In this study, a three-body microcontact model Considering of hard particles and rough surfaces is proposed in order to understand the effects of particles between surfaces on contact characteristics. Both transitional surface-to-surface and particle-to-surface two-body microcontact simulations can be obtained according to the simplification of this model. In the three-body contact situation, the curves of contact area ratio versus dimensionless load are located in the range between two straight lines. The surface-to-surface two-body contact situation is the upper bound and the particle-to-surface two-body contact situation is the lower bound. The contact situation will approach to the pure particle-to-surface two-body contact situation as the value of particle diameter over roughness value of surface increases. The total contact area ratio increases when particle size or particles density decreases, and contact load increases. Contrary to the results for contact area ratio, the dimensionless separation increases when particle density increases or contact load decreases.
Effects of Molecularly Thin Lubricant Films on Slider Touch-Down and Take-Off Hysteresis Behavior in Hard Disk Drives
Authors: Tagawa Norio , Sendo Hiroshi , Mori Atsunobu
Published: November 2008

This paper describes the effects of molecularly thin liquid lubricant films on slider hysteresis phenomena of touch-down and take-off process in hard disk drives. In the experiments, the tested lubricants were conventional Zdol and novel cyclotriphosphazene-terminated PFPE lubricant (A20H lubricant) with different molecular weight. As a result, it is found that the difference between the touch-down velocity and take-off one (hysteresis behavior) for novel A20H lubricant film is larger than that for Zdol. The LDV RMS values for novel lubricant, which indicate the slider bouncing vibration during the slider-lubricant contact, are also larger than that for Zdol. The effects of lubricant film thickness and molecular weight on slider hysteresis behavior as well as slider bouncing vibration are also clarified. In addition, the replenishment performances of test lubricants for depleted tracks due to slider touch down contact are investigated and discussed.
Wear Reduction by Functional Protein Boundary Film on Poly(Vinyl Alcohol) Hydrogel
Authors: Nakashima K. , Sawae Y. , Murakami T.
Published: November 2008

Poly(vinyl alcohol) (PVA) hydrogel is a candidate material for artificial cartilage of joint prostheses. From previous researches [1–4] it is shown that the wear of PVA hydrogel depends on the concentration of proteins in lubricants. Therefore it is considered that the adsorbed film formation by protein of albumin or γ-globulin influences upon the wear grade of PVA hydrogel. The remaining film of proteins on the glass plate was observed in fluorescence microscope. The adsorption condition of albumin and γ-globulin was different. The adsorbed film with effective reduction of the wear showed cooperative stratification of albumin and γ-globulin, but the condition of increased the wear showed separation of albumin and γ-globulin. Consequently, to reduce the wear of PVA hydrogel, cooperative stratification layers are effective.
Four Different Numerical Approaches of Calculating Strains and Stresses During Impact in Wheel-Rail Rolling Contact
Authors: Wiest Martina , Daves Werner , Fischer Franz D.
Published: November 2008

Four different numerical approaches to calculate strains and stresses in the contact zone are investigated. The examination is performed considering as example the transition process of a wheel passing a crossing. A dynamic, a quasi-static, a static and a Hertzian model are available. The four elasto-plastic models for rolling contact are evaluated and the results are compared.
Experimental Study of Bouncing Behavior of Spherical Sliders on Stationary Magnetic Disks
Authors: Ono Kyosuke , Nakagawa Kenji
Published: November 2008

This paper presents experimental study of measuring dynamic contact force and meniscus force from the bouncing motion of hemispherical sliders on stationary magnetic disks. Two hemispherical sliders of 1.0mm and 2.0mm radii and test disks with 1, 2, 3 nm thick lubricants with/without UV treatment are used for the experiment. Typical data of displacement, velocity and acceleration of bouncing motion shows a clear adhesion force by formation of a meniscus bridge at the end of impact. It is found that the maximum contact force versus penetration depth can be estimated by Hertzian contact theory. The maximum dynamic adhesion force is close to the static meniscus force.
Tribological Characteristics of Newly Synthesized Multi-Functional PFPE Lubricants
Authors: Chiba Hiroshi , Oshikubo Yukiko , Watanabe Keiji , Tokairin Takeshi , Yamakawa Eishin
Published: November 2008

We have successfully synthesized a multi-functional PFPE lubricant in which extra polar groups exist in the middle of molecule. This was achieved by combining several PFPE molecules that contain hydroxyl end groups. The multifunctional molecule was fractionated using supercritical fluid of carbon dioxide then identified using NMR methods, which showed that average three to five hydroxyl groups are contained in one molecule depending on each fraction. This paper presents lubricant spreading properties and first monolayer thickness determined by means of half-dip coat method. It was found that resulting first monolayer thickness shows does not increase significantly; rather it was almost the same as that of the parent molecule.
Deterministic Model for Rubber-Metal Contact Including the Interaction Between Asperities
Authors: Deladi E. L. , de Rooij M. B. , Schipper D. J.
Published: November 2008

Rubber-metal contact involves relatively large deformations and large real contact areas compared to metal-metal contact. Here, a deterministic model is proposed for the contact between rubber and metal surfaces, which takes into account the interaction between neighboring asperities. In this model, a description of the actual micro-contact is used instead of a summit which is a local maximum at the surface. Linear viscoelastic behavior, modeled by a three-element mechanical model, is assumed for the rubber. In the present model, the equations regarding the deformation due to a Hertzian pressure inside and outside the contact area have been modified for the viscoelastic case. The deterministic case is compared with the statistical one. Besides this, the deformation of the bulk material beneath the asperities is taken into account. The results reveal that the bulk deformation has a significant effect at higher nominal pressures.
An Investigation of Fretting Wear Behaviour of a Ternary (Zr,Hf)N Coating
Authors: Atar Erdem , Cimenoglu Hu¨seyin , Kayali E. Sabri
Published: November 2008

In this study, the wear behaviors of ZrN and (Zr, 21wt.% Hf)N coatings, deposited on hardened AISI D2 cold work tool steel by a arc-physical vapor deposition (PVD) technique were examined by a fretting wear tester. Wear tests were conducted by rubbing Al2O3 and steel balls on the surfaces of the coatings under dry sliding condition. Characterization tests showed that, the hardness and the surface roughness of the examined coatings were almost the same. However, addition of 21wt.% Hf to ZrN improved the adhesion between the coating and the substrate. Fretting wear tests conducted by rubbing both Al2O3 and steels balls revealed that, addition of 21wt.% Hf achieved an increment in the wear resistance of the ZrN coating. Steel ball encouraged oxidative wear, while wear of the coatings by Al2O3 ball progressed by coating removal.
The Stress of Sliding Vanes in a Rotary Compressor
Authors: Huang Yuan Mao , Li Chien Liang
Published: November 2008

A rotary sliding vane compressor was redesigned with extended rods on both edges of each vane and guide slots on both cover plates to improve its performance. The governing equations were derived to obtain loads acting on vanes and the stress of vanes. The finite element method is used with a generated computer program to determine the stress of vanes based on the calculated loads and the measured loads acting on the vanes. The results were compared and show good agreement with those obtained by using an existing software IDEAS.
Appling Micro Devices to Scanning Probe Microscopes for Micro/Nano Tribology Study (Keynote)
Authors: Ando Yasuhisa , Naoki Shiraishi
Published: November 2008

We have designed and fabricated two kinds of micro devices. The mechanisms of the micro devices and some experimental results using the micro devices are described in this paper. The first device is a three-dimensional (3D) microstage and the other is a lateral force sensor. Each device was fabricated on an SOI (silicon on insulator) wafer using MEMS (micro electromechanical systems) technology. We applied these devices to an SPM (scanning probe microscope) and conducted tribology tests.
Elliptical Contact Area Between Elastic Bodies Bounded by High Order Surfaces
Authors: Diaconescu Emanuel N.
Published: November 2008

Hertz theory fails when contacting surfaces are expressed by a sum of even polynomials of higher powers than two. An alternative analytical solution implies the knowledge of contact area. In the case of elliptical domains, there are some published proposals for the correlation between pressure distribution and surface normal displacement. This paper identifies the class of high order surfaces which lead to elliptical contact domains and solves a contact between fourth order surfaces.
Classification of Wear Particles Based on Qualitative Morphological Features
Authors: Chang R. H. , Kong Hosung , Yoon Eui-Sung , Choi Dong-Hoon
Published: November 2008

Wear debris morphology is closely related to the wear mode and mechanism occurred. Image recognition of wear particles is, therefore, a powerful tool in wear monitoring. An algorithm of classification of wear particles is proposed based on qualitative morphological features. The standard classes are presented as a set of vectors of coded ratings. Descriptions of the standards are based on the knowledge-base of experts. A distance between the particle and the standard classes in the multidimensional space of features showed rating of the similarity. The classification of particles is determined by identifying the closet standard. The coding of the semantic features of the morphological feature of wear particles was demonstrated to be useful for classification with statistical methods. The results showed that the presented method was satisfactory in solving practical problems.
Effects of Adhesion and Friction on the Pattern Transfer in Nanoimprint Lithography: A Molecular Dynamics Simulation
Authors: Kang Ji-Hoon , Kim Kwang-Seop , Kim Kyung-Woong
Published: November 2008

Due to the direct contact between the stamp and polymer film during the nanoimprint lithography (NIL) process, the adhesion and friction are unavoidable. To investigate the effect of adhesion and friction on the pattern transfer, molecular dynamics (MD) simulation of NIL is performed. As the simulation results, the adhesion and friction forces between the stamp and polymer film are calculated and the effects of the adhesion and friction on the pattern transfer are studied.
Evaluation of Wear Resistance of Cross-Linked Ultra-High Molecular Weight Polyethylene for Joint Prostheses in the Multi-Directional Pin-on-Plate Apparatus
Authors: Sawano T. , Murakami T. , Sawae Y.
Published: November 2008

Gamma irradiation is used as a sterilization method for joint prosthesis. For this procedure, gamma irradiation causes crosslinking of UHMWPE. Crosslinked UHMWPE molecules connect each other strongly. However gamma irradiation causes the reduction in mechanical properties such as tensile strength and elongation because primary chain scission occurrs. Therefore, excessive irradiation would cause some problems. We suggest the existence of the optimum dose for minimum wear and moderate reduction in tensile strength and elongation. Furthermore we indicate a mechanism of wear resistance of gamma irradiated UHMWPE.
New Insights on Superlow Friction Mechanisms of Hydrogenated Amorphous Carbon
Authors: Fontaine Julien
Published: November 2008

Some hydrogenated amorphous carbon (a-C:H) films have the peculiarity to exhibit coefficients of friction in the millirange, known as “superlow friction”, under inert environments like dry nitrogen or high vacuum. However, this “superlubricity” is only observed for some coatings and sometimes for very short duration. The role of tribofilm in the superlow friction regime observed on various a-C:H films sliding against steel pins has been investigated by performing experiments in ultra-high vacuum and hydrogen ambient. Tribofilm build-up appears to be controlled by interactions with oxide layers. Then, evolutions of the tribofilm will depend both on the composition of a-C:H film and on interactions with environment, through tribochemical reactions. Furthermore, the mechanical properties of the films are correlated with the achievement of superlow friction. All these results suggest that surface rheological properties are of critical importance in reaching superlow friction regime with a-C:H films.
Experimental Investigations Upon Fatigue Life of Circular Contacts With Transversal Furrow
Authors: Cerlinca Delia F. , Diaconescu Emanuel N.
Published: November 2008

Rolling contact fatigue depends essentially on both surface and subsurface populations of defects. First, this paper describes experimental results obtained in rolling contact fatigue tests in the presence of a furrow oriented transversally to the race-way. Then an attempt to predict theoretically the effect of geometric parameters of the furrow upon contact fatigue life is described.
Active Lubrication for Eliminating Instability Problems in Rotating Machines
Authors: Santos Ilmar F.
Published: November 2008

When the hydrostatic and the hydrodynamic lubrication are simultaneously combined in a journal bearing, with the aim of reducing wear between rotating and stationary parts, one refers to the hybrid lubrication, which offers the advantages of both lubrication mechanisms. When part of the hydrostatic pressure is also dynamically modified by means of hydraulic control systems, one refers to the active lubrication. By the combination of fluid power, electronics and control theory, the active lubrication makes feasible the reduction of wear and the attenuation of rotor instabilities. Significant reduction of resonance peaks is demonstrated in a test rig, specially designed with the aim of experimentally exploring the potential of the active lubrication. Experiments are led in the frequency domain.
Sliding Induced Nanocrystals on Si
Authors: Guruzu Srinivas , Liang Hong
Published: November 2008

Our previous research has shown that Ga pin sliding again Si induces nanometer length scale crystals. In this research, we continued on with an In pin with one stroke slides on Si substrate. Applied load was varied for sliding Surface characterization was conducted using an atomic force microscope. Results showed that triangular-shaped nanocrystals were formed on Si surfaces. The height and side length of these nanocrystals depend on test conditions. In this paper, we report our findings in crystal structures and boundary properties.
Multi-Physics Modeling of Tribological Processes Using Cellular Automata
Authors: Vick Brian
Published: November 2008

Tribology is in every sense of the word multidisciplinary. A multitude of different physical processes can occur simultaneously, often over widely varying time and length scales. The contact region between sliding bodies is a particularly interesting area, where thermal, mechanical, chemical, and electrical affects all play a role and interact in complex ways. Often our understanding of these phenomena is limited by the lack of a convenient methodology to model and solve such complex problems. The objective of this paper is to describe a new modeling and solution method that is relatively simple yet powerful enough to handle complex, multi-physics problems.
Thermal Analysis of Sliding Contact in Systems With Rotary Motion
Authors: Vick Brian , Furey Michael J.
Published: November 2008

Many devices involve sliding contact where a rotating component slides over a stationary component. Examples include disk brakes, cam/valve lifters, and laboratory pin-on-disk machines. An essential feature of these devices is that a wear track forms on the rotating component that is cyclically exposed to frictional heating, temperature fluctuations, and enhanced chemical film formation. The objective of this paper is to develop a theoretical model and solution methodology to examine the thermal effects produced by friction between sliding contacts in systems with rotary motion. A new methodology based on a combination of control volume finite difference and the cellular automata concepts is developed. The method involves a cascading sequence of simple, explicit rules of evaluation, rather than complicated partial differential equations. Results using the general model developed in this study are presented in dimensionless form to show the importance of critical operating parameters. Implications for applications such as disk brake and cam/valve lifters are suggested.
Crank-Angle Resolved In-Cylinder Friction Measurements With the Instantaneous IMEP Method
Authors: Leustek M. E. , Sethu C. , Bohac S. , Filipi Z. , Assanis D.
Published: November 2008

The instantaneous IMEP method is used to measure crank-angle resolved in-cylinder friction force in a series production spark ignition engine as a function of design parameters and operating conditions. An improved telemetry system, which continues to provide data after 50+ hours of operation at speeds as high as 2000 rpm, is presented. Primary sources of error associated with the technique will be presented. These include intra-cycle engine speed fluctuations, the effect of thermal shock on pressure transducers, the effect of connecting rod force calibration and measurement error. The instantaneous IMEP method is used to measure crank-angle resolved in-cylinder engine friction as functions of engine speed and coolant (oil-film) temperature. Both crank-angle resolved and cycle-integrated results are compared.
Influence of Deformation Effects on a Misaligned Plain Journal Bearing
Authors: Bouyer J. , Fillon M.
Published: November 2008

Bearings nowadays are often subjected to misalignment. Both theoretical and experimental misaligned bearings have been previously studied, it being found that the minimum film thickness is the parameter which is most noticeably affected. However, other work has showed that both thermal and deformation effects have to be considered when a bearing is subjected to severe operating conditions. The present work analyzes the influence of thermal effects, as well as the effects of mechanical and thermal deformation on misaligned bearing performance.
Magnetically Suspended Rotary Blood Pump (Keynote)
Authors: Heshmat Hooshang , Walton James F. , Tomaszewski Michael J. , Jahanmir Said
Published: November 2008

MiTiHeart™ LVAD is a rotary centrifugal blood pump with a hybrid passive/active magnetic bearing support system. It exhibits low power loss, low vibration, and high reliability under transient operating conditions. Unique features of the design include a simple and direct flow path for both main and washing blood flows, non-contact pump rotor, i.e., no rubbing surfaces, and relatively large clearances between the pump rotor and housing. The first prototype was constructed from medical grade polycarbonate. To reduce the possibility of thrombosis, the internally exposed surfaces were coated with a biocompatible polymer. Hemolysis test results showed a low normalized index of hemolysis of 0.01 mg/dL. An acute animal test was successfully completed at the Hershey Medical Center. During the test, the pump was implanted in a calf and operated in parallel with the heart. Following the acute test a chronic 200-hour implant study was completed. A second prototype was constructed using a titanium alloy for all blood contacting surfaces and incorporating a redundant hydrodynamic thrust bearing. This prototype was successfully evaluated in two chronic implant studies in a calf animal model for a total of 130 hours.
Low-Friction Wear Resistant Coatings for High-Temperature Foil Bearings
Authors: Heshmat Hooshang , Hryniewicz Piotr , Walton James F. , Willis John P. , Jahanmir Said
Published: November 2008

Compliant foil bearings offer many advantages over rolling element bearings in high-speed and high-temperature applications. However, implementation of foil bearings in these applications requires development of solid lubricant coatings that can survive the severe operating conditions encountered at high speeds and high temperatures. The objective of this paper is to present results on development of an advanced coating system for use with compliant foil bearings that permits higher operating speeds and temperatures. In order to evaluate the coating performance and to select the best coating combination for implementation, a number tests were conducted using a high-temperature, high-speed tribometer up to 810 °C. Inconel test substrates, representative of a portion of a foil bearing, were coated with several different Korolon™ coatings. The counterface disks were coated with four different hard coatings. The test results confirmed the excellent tribological behavior of Korolon™ coatings for high-speed high-temperature foil bearing applications. While the tribological behavior of Korolon™ coatings were determined to be a function of temperature, in most cases a maximum coefficient of friction less than 0.1 was observed during startup/shutdown periods. Subsequently, a foil journal bearing was designed and a composite Korolon™ coating was applied to the bearing top foil; and a dense chrome coating was applied to the journal surface. The foil bearing was installed in a turbojet engine and operated successfully to 54,000 rpm for over 70 start-stop cycles.
Friction-Induced Phase Transformations of Cu-Al During Severe Wear
Authors: Ingole Sudeep , Liang Hong
Published: November 2008

Surface modification and performance depend largely on the properties of surface atoms and structures. Fundamental investigation of friction was conducted in a Cu-Al sliding system. Deformation, wear, and transfer were studied. Detailed study was focused on friction-induced phase transformations. Surface characterization was carried out using an atomic force microscope (AFM). The debris analysis was done using a transmission electron microscope (TEM). Results showed that debris formed during sliding were amorphous. On the wear track, there is indication of surface melting and hardening. This presentation will discuss wear mechanisms involved in oxidation and property-performance of metallic materials.
Tribological Properties of Nanocrystalline Diamond Films With Different Nanoscale Morphology and Bonding Characteristics
Authors: Winfrey A. L. , Reising S. E. , Bilbro L. S. , Nemanich R. J. , Chromik R. R. , Wahl K. J.
Published: November 2008

The morphology and bonding characteristics of nanocrystalline diamond films prepared with different Ar:H ratios have been studied and are correlated to tribological performance. A coating made with high Ar:H ratio displayed low friction of 0.05 and very minimal wear, while the low Ar:H film showed high friction (> 0.2), rapid wear, and complete failure after 50 cycles. As both films had the same rms roughness, their different tribology appears to stem from a change in morphology.
New Generation of Smart Sensors
Authors: Murphy M. , Leigh-Jones C. , Kent T. , Baldwin A.
Published: November 2008

Advanced warning from arrays of on-line sensors to trigger more in-depth laboratory testing is now possible because the development phase of “smart” sensors has matured. There has been a need to develop reliable, affordable on-line instrumentation (sensors) that provides information on both lubricant and machinery condition (wear) supports critical systems requirements, addresses remote applications that are difficult to physically sample routinely, and that reduces manpower needs. The monitoring of specific oil related parameters like, alkalinity, acidity, and contaminants such as ferrous and non-ferrous debris, water, coolant and soot, with no human involvement, will be reviewed in this paper. Sensor technology includes Magnetometry and TAN Delta. They have been evaluated on test rig and on-engine trials to assess the improvement of sensitivity, insulation, electronics, connectors, and specialised software with interpretive algorithms to suit specific applications. Sensors will supplant some, but not all routine testing, thereby changing the Oil Analysis landscape.
The Effects of Stress State in Dental Biocontacts
Authors: Frunza M. C. , Frunza G.
Published: November 2008

The present paper approaches the tribological aspects of the oral cavity, emphasizing stress state in dental biocontacts. Stress state influences the biomechanical fatigue microcrack propagation mechanism, which is finally manifested over a very small area on tooth interface. The cracks can be nucleated on the surface, on the subsurface, or both, depending on the quality of dental materials, restoration accuracy, physiological or pathological conditions, as well as on the initial and interface stresses. The groups of stresses that act upon a nucleate crack on the dental biocontact surface are contact, interface, and initial stresses. While tribological processes in natural biocontacts take place in conventional conditions that are controlled by the biosystem in which they are integrated, things are not the same in biocontacts between a natural and an artificial material, which constitutes the subject of this paper.
Fiberscopic Visualization of Total Knee Replacement Contact Kinematics During In Vitro Simulation
Authors: DesJardins John , Gustafson Lisa , Benson Lisa , LaBerge Martine
Published: November 2008

Optimization of total knee replacement (TKR) design and wear behavior requires the study of bearing contact mechanics. In this study, a novel fiberscopic imaging method was developed and combined with dynamic TKR simulation to visually quantify dynamic TKR contact areas in vitro. Contact areas between transparent TKR tibial inserts and metallic femoral components were captured using opaque lubricant media and a fiberscopic high-speed video camera within the simulator. Walking and stair descent loading patterns were characterized. Centroid location and contact pathways were calculated to determine pathway velocity and cross-shear characteristics. Overall, contact velocities ranging from 0 to 233mm/sec and crossing angles ranging from near 0 to 90 degrees were found during this study. These results provide a basis for wear testing and cross-shear modeling of TKR materials, leading to more accurate predictions of wear behavior in these implants.
Nanoscale Surface Force Measurement
Authors: Yang Seung Ho , Hsu Stephen M.
Published: November 2008

At nanoscale, surface forces often dominate or exert significant influence on contact interfaces. Adhesion and stiction in micro- and nanodevices are important technological challenges in nanotechnology and they are closely linked to our ability to control the surface forces. Yet our understanding of surface forces in nanoscale contacts is lacking, especially the interplay between surface roughness, material properties, contact geometry and the environment. Traditional means of measuring surface forces use a macrocontact with atomically flat mica surfaces and the forces measured by laser interferometry. Semiconductor and insulator materials cannot be measured by this technique. We have developed a preliminary AFM-based technique using colloidal probes capable of directly measure the surface forces at nanoscale. The difficulties are surface roughness control, force sensitivity of the cantilevers, the control of snapon, and the size of the probe tip. We have demonstrated that all these issues can be controlled to a large extent and reasonable surface forces can be measured between a probe tip and a flat surface down to a nanometer distance to the surface.
Granular Flow Lubrication: A Lattice-Based Cellular Automata Modeling Approach
Authors: Jasti V. K. , Higgs C. F.
Published: November 2008

Liquid lubricants break down at extreme temperatures and promote stiction in micro/nano-scale environments. Consequently, using flows of solid granular particles as a “dry” lubrication mechanism in sliding contacts was proposed, because of their ability to carry loads and accommodate surface velocities. Granular flows are highly complex flows that in many ways act similar to fluids, yet are difficult to predict because they are not well understood. Granular flows are composed of discrete particles which display fluid and solid lubricant behavior with time. This work describes the usefulness of employing lattice-based cellular automata (CA) as a tool for modeling granular flows in tribological contacts. The granular kinetic lubrication (GKL) continuum modeling approach has been successful at predicting trends gleaned from experiments conducted with granules in a couette shear cell. These results are used as a benchmark for determining the effectiveness of the CA modeling results. While the CA model was constructed entirely from rule-based mathematics, velocity and solid fraction results from the simulations were in good agreement with those from the GKL model benchmark results.
CMP and Nano-Characterization of Magnetic Head Wafer Films
Authors: Garcia Jonathan , Terrell Elon , Higgs C. Fred
Published: November 2008

Similar to the semiconductor sector improving processing power by decreasing device sizes, the information storage sector has been working to decrease device sizes in read/write heads. Chemical mechanical polishing (CMP) is a critical enabling technology for terabyte storage systems and other systems consisting of nanotechnology. A commercial CMP polisher was used, and the experimental material removal rates (MRR) are presented. Since the MRR is a function of the load, relative speed, and film hardness, a nano-indention technique was employed to characterize mechanical properties of the permalloy (NiFe) films. A basic MRR model was developed to compare to the experimental results.
Analysis of EHL Circular Contact Start Up: Comparison With Experimental Results
Authors: Zhao Jiaxin
Published: November 2008

In this paper, the start up condition in elastohydrodynamic lubrication was studied on a steel ball on glass disc contact lubricated with a mineral oil, using a previously developed mixed phase lubrication contact model. The numerical simulation demonstrated the contact geometry change in the transition from initial solid contact to final fully lubricated contact, as well as the load sharing variation between lubricated and solid contacts during the start up. The numerical results of contact geometry was then compared with an experimental study of the same start up situation published by Glovnea and Spikes [1]. The film thickness variations and the propagation of the solid-lubricated contact interface during the start up were compared. Furthermore, an analytical result of the propagation of the solid-lubricated contact interface was also generated by assuming the dominance of the wedge and squeeze terms in the Reynolds Equation, and was also compared with the numerical and experimental results. Good agreement exists among the analytical, numerical and experimental results. The good agreement proves the numerical model as a valid tool in studying the start up condition in elastohydrodynamic lubrication as the transition from solid contact to lubricated contact is of great importance when investigating the start up process and its effects on the overall lubrication performance.
Self-Replenishing, Self-Repairing Solid Lubrication: Modelling and Experimentation
Authors: Wornyoh E. Y. A. , Higgs C. F.
Published: November 2008

Several pellet-on disk and pad-on disk tribometer tests were conducted to study the lubrication characteristics of third-body particles of MoS2 powder. The tests consisted of simultaneous pellet-on disk and pad-on disk sliding contacts. Results from the tests show the self-repairing, self-replenishing, oil-free lubrication mechanism of MoS2. A theoretical control-volume fractional coverage model was developed to predict (1) the friction coefficient at the pad/disk interface and (2) the wear factor for the lubricated pellet/disk sliding contact. The fractional coverage varies with time and quantifies the amount of third body film covering the disk asperities. Results from the model capture the tribological behavior of the experimental sliding contacts reasonably well.
Characteristics and Nanotribological Applications of Scanning Wear
Authors: Yang Dehua , Stromberg Ryan , Nay Richard , Wyrobek Thomas
Published: November 2008

For the first time, a new method of scanning wear has been developed to expose and observe microstructural features of heterogeneous materials, and is presented in this paper. Experimental results of scanning wear of two computer hard disks with DLC protecting layers are also reported. These two applications have proven that scanning wear, as a unique format of wear caused by raster scanning a probe against its counterpart surface under controlled light load, is a very useful and powerful tool for tribological and microstructual investigations of materials at micro/nano scales. The further exploration and application of scanning wear is recommended.
First Observation of Elastic Plowing in Nanofriction
Authors: Ying Z. Charles , Hsu Stephen M.
Published: November 2008

Accurate friction measurement at nanoscale is critical in reliable micro- and nano-device design. Different values of coefficient of friction (COF) have been reported in the literature for the same material when different instruments and tip sizes were used [1–3]. We have conducted a series of experiments to delineate the effects of different tip sizes and shapes on friction as a function of load and found that friction force values under the elastic contact regime for various tips can be unified when plotted against the tip cross-sectional area in the direction of sliding. This observation implies a volumetric dependence of friction that has not been reported before in the elastic regime.
Selective Surface Nano/Micro-Texturing by UV Assisted Low Temperature Crystallization of Amorphous Silicon
Authors: Wang Hengyu , Cai Li , Yang Dehua , Wyrobek Thomas , Zou Min
Published: November 2008

This paper presents a novel selective surface-texturing method as well as adhesion/stiction and friction studies of the selectively-textured surface. The selective surface-texturing was accomplished by ultraviolet (UV) assisted low temperature crystallization of amorphous silicon. Adhesion/stiction experiments on the nano/micro-textured and non-textured surface areas were performed using a diamond tip under controlled displacement profiles with different maximum indentation displacements. Friction experiments on the textured and non-textured surface areas were conducted using the same tip under various normal contact forces. The adhesion/stiction forces and coefficients of friction (COF) of the textured surface areas were found to be much smaller than those of non-textured surface areas.
Some Analytical Approximations and Numerical Solutions of EHL Problems for Non-Newtonian Fluids Fatigue
Authors: Kudish Ilya I.
Published: November 2008

Plane steady isothermal and non-isothermal EHL problems for non-Newtonian lubricants in a line contact are considered. Two cases of lubricant rheologies are studied. Namely, lubricants for which (a) the shear stress is any explicitly given nonlinear function of the shear strain and (b) the shear strain is any explicitly given nonlinear function of the shear stress are analyzed. The isothermal EHL problem is reduced to solution of a nonlinear equation for the sliding shear stress f, generalized Reynolds equation for pressure p, and the equation for gap h as well as the classic balance and boundary conditions. The non-isothermal EHL problem is reduced to solution of the above mentioned nonlinear equations and the nonlinear equations for temperatures of the lubricant T and of the contact surfaces Tw1 and Tw2. The EHL problems are considered in the case of heavily loaded contact when the rolling shear stress in lubricant is much smaller than the lubricant sliding shear stress [1–7]. Therefore, the problems contain a small parameter represented by the ratio of the characteristic rolling and sliding shear stresses. That leads to the opportunity to use the perturbation methods for simplifying the EHL problem formulations.
Foil Bearings Makes Oil-Free Turbocharger Possible
Authors: Heshmat Crystal A. , Heshmat Hooshang , Valco Mark J. , Radil Kevin C. , Della Corte Christopher
Published: November 2008

This paper describes an oil-free, 150 Hp turbocharger that was successfully operated with compliant foil bearings in a range of pitch and roll angles, including vertical operation, thereby demonstrating its viability for aircraft applications. On a gas test stand the turbocharger was operated to 120,000 rpm, under extreme conditions. In addition, the compliant foil bearing-supported turbocharger successfully tolerated shock and vibration of 40 g. Advanced technologies have been applied to the second generation of this turbocharger, shown in Figure 1, including self acting, compliant foil hydrodynamic air bearings with advanced coatings capable, of operation above 815 °C (1500°F). Journal foil bearings with maximum load capacity up to 670 kPa (97 psi) were used in conjunction with thrust foil bearings capable of maximum loads to 570 kPa (83 psi). Bearing component development tests demonstrated 30,000 start stop cycles at 815 °C (1500°F) with a newly developed, solid lubricant coating, KOROLON™. KOROLON™ exhibits a coefficient of friction of less than 0.1 at a wide range of temperatures. Current-designed foil bearings with KOROLON™ have immensely decreased turbolag, allowing acceleration from rest to over 100,000 rpm in less than 2 seconds. Advanced bearing stiffness maintained rotor total axial end-to-end motion within 100 microns (0.004 inch). Total radial static and dynamic motion was controlled within 25 microns (0.001 inch). Development of this high speed turbomachine included bearing and solid lubricant component development tests, rotor-bearing dynamic simulator qualification and gas stand tests of the assembled turbocharger. Gas stand and simulator test results revealed stable bearing temperatures, low rotor vibrations, good shock tolerance and the ability of the rotor bearing system to sustain overspeed conditions beyond 120,000 rpm. This combination of component and integrated rotor-bearing system technology addresses many of the issues associated with application of compliant foil bearings to industrial compressors, blowers, and gas turbine engines, overcoming many of the inherently show-stopping and debilitating features of rolling element bearings, i.e., speed and temperature limitations.
Effects of Contact Load on Fretting Wear of Al-Si Alloy Impregnated Graphite Composite
Authors: Goto H. , Amamoto Y.
Published: November 2008

An Al-Si alloy impregnated graphite composite (ALGR-MMC) containing a large amount of graphite (56 vol%) has been newly developed to improve the friction and wear characteristics of machine components such as clutches under dry sliding and journal bearings under lubricated sliding. The ALGR-MMC has the same self-lubricating performance as graphite in moist environments. It has good properties of thermal expansion, heat resistance and wear resistance. The objective of this study is to investigate the friction and wear of the ALGR-MMC under fretting conditions. Ball-against-disk type fretting wear tests for the ALGR-MMC (flat) in contact with bearing steel (ball) were conducted at various contact loads in moist air under unlubricated conditions. The friction coefficient was monitored during the tests. The area and depth of wear scars were measured after the tests or in the interrupted tests. From the friction and wear data, the effects of contact load on the fretting wear characteristics of the ALGR-MMC were evaluated with SEM observations of wear scars and EPMA analyses of wear surfaces.
Contact Stiffness of New and Worn Surfaces
Authors: Soom A. , Serpe C. I.
Published: November 2008

The presence of surface texture/roughness on engineering surfaces results in contacts between surfaces being considerably more compliant than if the interfaces were smooth and flat. The inclusion of a local contact stiffness can be critical to the accurate analytical or computational modeling of mechanical contacts. We present measurements of contact stiffness for five pairs of freshly prepared and worn of steel surfaces. The wom surfaces variously contain surface glazes, oxide layers, subsurface cracks, inclusions and wear particles. Contact resonance frequencies between sample interfaces are measured at various applied pressures. With known modal masses, the contact stiffness is easily calculated and presented on a per unit area basis. For a given contact pair, the contact stiffness is nonlinear, increasing with nominal pressure and decreasing with increasing surface roughness. We compare these results with the Greenwood-Williamson (G-W) Theory of rough surface contact. The expected pressure and summit height dependencies are observed in the measured data. When there are wear particles within the contact, the stiffness is reduced when the underlying surfaces are very smooth. If the underlying surfaces are rough, the presence of wear particles have little effect on the contact stiffness.
Tribological Studies of Compressor Surfaces in the Presence of Carbon Dioxide Under Extreme Environmental Pressure Conditions
Authors: Demas Nicholaos G. , Polycarpou Andreas A.
Published: November 2008

The refrigeration industry has shown an inclination towards the use of carbon dioxide (CO2) as a refrigerant in some applications. While extensive thermodynamic studies exist, tribological studies with CO2 are limited and tribological testing has further been restricted to low environmental pressures up to 1.38 MPa (200 psi) due to limitations in equipment capabilities. In this work, experiments were performed using an Ultra High Pressure Tribometer (UHPT) that was custom designed and built for tribological testing of compressor contact interfaces at very high environmental pressures up to 13.8 MPa (2000 psi). These tests demonstrate the possibility of testing at very high pressures similar to the internal pressures of CO2 compressors.
Micro/Nano Scale Wear Behavior of Pearlitic and Bainitic Rail Steels
Authors: Lee Ki Myung , Polycarpou Andreas A.
Published: November 2008

To develop rails with higher hardness and thus better durability and longer life, alternative microstructures have been suggested, since conventional pearlitic rail steels have reached their hardness limit. Such a newly developed material has a fine bainite microstructure (coded J6 bainitic steel) and showed higher initial hardness but poorer on-site wear performance, compared to conventional pearlitic steels. This was explained by the fact that pearlitic steels show significant work hardening under severe stress conditions, even though their initial hardness was lower. In this work, the wear behavior of pearlitic and J6 bainitic rail steels was investigated at the micro/nano scale, using the nanoscratch technique. It was found that pearlitic steel shows better wear performance at the micro scale as well, in agreement with large scale rail field tests.
Analysis of Impact-Induced Head Disk Interface Damage During Op-Shock
Authors: Yu Ning , Polycarpou Andreas A. , Hanchi Jorge V.
Published: November 2008

Hertzian impact theory is used to analyze impact-induced head disk interface (HDI) contact damage. Contact parameters including penetration (media damage), contact force, contact radius, impact duration, maximum and mean contact pressure are given at different normal impact velocities and slider corner radii in the form of contour plots. The results clearly suggest that the decrease of impact velocity or the increase of corner radius could both reduce the possibility of plastic deformation due to slider (head) disk impact contact.
Micro Undulated Contact Surfaces on the Contact Behavior of a MEMS Switch
Authors: Shi Yong , Kim Sang-Gook
Published: November 2008

A novel direct contact micro-device has been developed with periodically micro-grooved lateral metal contacts on the sidewall of the MEMS relay. The uniqueness of the design lies in the self-cleaning mechanism of the microgrooved lateral metal contacts. The concept-proving device is fabricated by integrating a high aspect ratio polymer beam structure with lateral metal contacts. The long lifecycle test shows that the contact resistance has been maintained below 0.1 ohm over 10 billion cycles. The switch design is compatible to the surface micromachining processes and can be readily integrated into a fully functional MEMS relay. Our design opens the possibility of direct contact MEMS switch for both high power and low cost wireless applications.