bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study of the Importance of Three Key Parameters on the Separation Modes of Adhering Microcontacts
Authors: Du Yan , Adams George G. , McGruer Nicol E. , Etsion Izhak
Published: March 2009

Three key parameters describing contacts with adhesion were identified in previous investigations. Here a series of finite element simulations of a single load/unload cycle of a contact are performed to study the impact of each of these parameters. The results show that one parameter (S) is most important in determining the separation mode, i.e. brittle or ductile separation. Smaller S leads to brittle separation while larger S gives ductile separation. The transition between the two separation modes occurs at about S = 1.2 which corresponds to the theoretical stress being somewhat greater than the hardness.
A Tribological Investigation of Carbon-Carbon Composites and the Effect of Roughness and Waviness Parameters on Friction Performance
Authors: Arico Alan , Ovaert Timothy C.
Published: March 2009

Friction tests for two types of carbon-carbon (C-C) composites were performed using a sub-scale aircraft brake dynamometer for 100 stops. Worn surface profiles were measured using a surface profilometer. Roughness and waviness parameters from the profilometry measurements were compared to weight loss, thickness loss, effectiveness, stop time, and torque for each C-C composite type. The results show that when roughness is analyzed, for an increase in torque and effectiveness and a decrease in stop time, there is a decrease in skewness and high spot count; and an increase in maximum valley depth, mean spacing of local peaks, and mean arithmetic wavelength. For waviness profiles, for an increase in torque and effectiveness and a decrease in stop time, there is a decrease in skewness; and an increase in high spot count, maximum valley depth, mean spacing of local peaks, and mean arithmetic wavelength. Furthermore, there are differences in both friction performance and surface topography between the CC composite types which can be attributed to the differences in fiber orientation and microstructure at the wear surfaces.
Effect of Adhesion on Wafer Separation Due to Trapped Particles
Authors: Pamp Andy , Adams George G.
Published: March 2009

Template-based high-rate nanomanufacturing and wafer bonding both rely on surface energy to bring the surfaces into intimate contact. In high-rate nanomanufacturing, unlike wafer bonding, the contacting surfaces must be easily separated after the pressure is removed. A common problem in wafer bonding and nanomanufacturing is particle contamination. Trapped particles cause a separation zone that will prevent the intimate contact required to transfer nanoscale devices from the template to the device wafer. This problem is examined here using two different methods. The first method examines the effect of a rigid particle trapped between elastic plates. The second investigates the effect of a plastically deforming particle trapped between two elastic half-spaces.
Nanomechanical and Nanotribological Properties of Nano- and Micro-Particle Filled Polymer Composites Used for Dental Restorative Applications
Authors: Devaprakasam D. , Hatton P. V. , Moebus G. , Inkson B. J.
Published: March 2009

The objective of this work is to quantify nanomechanical and nanotribological properties of nano- and micro-particles filled polymer composites used for the dental restorative applications. Nanotribological performances of the two polymer composites with different reinforcing particulates were investigated using advanced microscopy techniques. Both the polymer composites composed of same dimethacrylate based monomeric mixture, Bisphenol-A-glycidyldimethacrylate (Bis-GMA), triethylene glycoldimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), as matrix. It was found that the elastic modulus, hardness, particle size, shape, distribution and agglomeration significantly influence the friction and wear characteristics of the polymer composites. The results show that nanotribological performance of nanoparticle reinforced polymer composites is better than the microparticle reinforced polymer composites.
A Critical Investigation on the Nature of Material Dependency of Elastic-Plastic Contact Behavior
Authors: Malayalamurthi R. , Marappan R.
Published: March 2009

This work attempts to make an investigation on the nature of material dependency of elastic-plastic contact behavior through a more accurate contact analysis between a deformable sphere and a rigid flat by finite element method. Analysis is carried out beyond elastic limit, till the inception of plasticity for various materials with different radii. It is found those materials with Young’s modulus to yield stress (E/Y) ratio less than 300 show strikingly different contact phenomena. Equation for hardness in terms of E/Y ratio for these materials is presented. A proposal for fixing the point of attaining fully plastic state is suggested. Existing disagreement over the dependency of hardness on material properties is critically examined.
Rolling Friction in MEMS Ball Bearings: The Effects of Loading and Solid Film Lubrication
Authors: McCarthy M. , Hanrahan B. , Zorman C. , Ghodssi R.
Published: March 2009

The effects of loading and solid film lubrication on rolling friction in MEMS-fabricated ball bearing structures are investigated in this paper. An in-situ non-contact experimental procedure was used to measure the frictional forces transmitted through a linear ball bearing system. The test devices consist of two silicon plates with deep-etched rectangular trenches acting as the housing for 285μm diameter steel microballs. The dynamic friction is measured with respect to relative velocity for several normal loads and it is observed that the frictional force increases linearly with microball contact area. Additionally, test structures with a 1μm silicon carbide (SiC) film deposited in the trenches have been tested. A 70% reduction in rolling resistance is shown between the nonlubricated and the SiC-lubricated test structures under identical experimental conditions. This is attributed to the reduced sliding friction in the SiC-steel contact area during interfacial slipping. To the best of our knowledge this is the first reported characterization of dynamic rolling friction in a MEMS device using a solid film lubricant. It is assumed that all frictional forces measured in this work are due to the desired rolling motion as well as bulk sliding of the microballs.
Friction Characteristics and Topography of Tribofilms From Anti-Wear Additives Applied to Metal V-Belt Type CVT Fluids
Authors: Narita K. , Priest M.
Published: March 2009

This study has investigated the metal-meal friction properties and the topography of tribochemical films derived from antiwear additives for application to metal-V-belt pushing type continuously variable transmission fluids (B-CVTFs). The influence of metal-metal tribological properties of various kinds of anti-wear additives were evaluated using a ball on plate tribometer, enabling lubricant film formation to be monitored during a reciprocating sliding test. In addition, contact mode atomic force microscope (AFM) was used to characterize the nature of the tribofilms at the namometre scale. For zinc-dithiophosphate (ZnDTPs), significant differences were observed in the friction coefficients and the topographic images between secondary and aryl type ZnDTP. The films derived from secondary type exhibit large solid pads, 5–30μm in length elongated in the sliding direction while the aryl type forms films in streaks on the ridges, with 8% higher friction coefficient than the secondary ZnDTP. Notably, the combination of over-based calcium sulphonate and hydrogen phosphite demonstrated a synergism with 8% higher friction coefficient and more stable film formation than the individual cases, providing a positive outcome for a BCVTF. Tribofilm species produced by a chemical reaction between hydrogen phosphite and over-based calcium sulphonate were densely deposited on the rubbing tracks, exhibiting rougher surfaces than those observed in the individual cases, consequently with a higher friction coefficient. These results suggest that the friction properties between metal-metal contacting surfaces strongly depend on the morphology of tribofilms derived from lubricant additives.
Performance Evaluation of Half-Wetted Hydrodynamic Bearings With DLC Coated Surfaces
Authors: Hunsberger Andrew Z. , Jahanmir Said , Heshmat Hooshang , Eryilmaz Osman , Erdemir Ali
Published: March 2009

In conventional liquid lubrication it is assumed that surfaces are fully wetted and no slip occurs between the fluid and the solid boundary. Under the “no slip” condition the maximum shear gradient occurs at the fluid-surface interface. When one or both surfaces are non-wetted by the fluid, boundary slip can occur due to weak bonding between the fluid and the solid surface, which reduces shear stresses in the fluid adjacent to the non-wetted surface. A thrust bearing tribometer was used to compare the performance of “no slip” hydrodynamic thrust bearings with bearings surfaces that were made to slip at the interface between the surface and fluid. Hydrophobic surfaces on both runner and bearing were achieved with the deposition of hydrogenated diamond like carbon (H-DLC) films, produced by plasma-enhanced CVD on titanium alloy surfaces. Hydrophilic surfaces were created through the surface modification of DLC. A mixtures of water and glycerol was used as the lubricant. The tests were conducted using different constant bearing gaps. The normal load and the torque or traction force between the rotating runner and hydrodynamic thrust bearing were measured with load cells. The experimental results confirmed that load support is still possible when surfaces are partially-wetted or non-wetted.
Friction and Wear Behavior of Ultra-High Molecular Weight Polyethylene as a Function of Polymer Crystallinity
Authors: Kanaga Karuppiah K. S. , Bruck Angela L. , Sundararajan Sriram
Published: March 2009

In this study the friction and wear behavior of medical grade ultra-high molecular weight polyethylene (UHMWPE) (GUR 1050 resin) were evaluated as a function of polymer crystallinity. Crystallinity was controlled by heating UHMWPE samples to a temperature above its melting point and varying the hold time and cooling rates. Degree of crystallinity of the samples was evaluated using differential scanning calorimetry (DSC). Quantitative friction experiments were conducted at two different scales. A custom-made microtribometer with commercially available spherical Si3N4 probes in dry conditions was used to test friction at the microscale. An atomic force microscope with commercially available Si3N4 probes under dry conditions was used for nanoscale experiments. A higher degree of crystallinity in the UHMWPE resulted in lower friction force and an increase in scratch resistance at both scales. Reciprocating wear tests preformed using the tribometer show that higher crystallinity also results in lower friction, as well as lower wear depth and width.
Anisotropic Diffusion of Large Neutral Solute in Cartilage
Authors: Zhang Le , Szeri Andras Z.
Published: March 2009

Articular cartilage is an avascular soft tissue that covers the ends of the bones in diarthrodial joints. Since there are no blood vessels, chondrocytes rely on solute diffusion to receive nutrients and remove waste products. Diffusive transport is thus essential to the operation and maintenance of cartilage tissue. Cartilage is composed mainly of interstitial water and extracellular matrix, which consists of collagen fibers and proteoglycan. The distribution of collagen fibers and proteoglycan impart an inhomogeneous and anisotropic microstructure to the cartilage.
The Dynamic Performance Analysis of Foil Journal Bearings Considering Coulomb Friction: Rotating Unbalance Response
Authors: Lee D. H. , Kim Y. C. , Kim K. W.
Published: March 2009

A significant advantage of foil journal bearings is their superior dynamic performance in rotor systems. However, the evaluation of their dynamic characteristics is still not enough because of the mechanical complexity of the foil structure and the strong nonlinear behavior of friction force. This work presents a nonlinear transient analysis method to predict dynamic performance of foil bearings considering Coulomb friction. In this method, the time dependent Reynolds equation is used to calculate pressure distribution and a finite element method is used to model the bump foil structure. Using this method, the hysteretic behavior of bump foil resulting from the unbalance excitation is observed. And, a number of parametric studies are performed to evaluate effects of design parameters on the unbalance response. The parameters are friction coefficient, bump half wavelength, amount of mass unbalance and number of bump foil strip.
Contact Stress, Frictional Torque and Lubrication in Articulating Pin Joints
Authors: Dwyer-Joyce R. S. , Beke A.
Published: March 2009

Pin joints are used in many items of industrial machinery where two structural members are required to articulate. A pin is assembled between typically four bushes. As the members articulate the pin rotates relatively slowly inside the bushes. A hydraulic test machine has been developed to load and articulate a 56 mm diameter pin held in four bushes, typical of that found in earth moving machinery and aircraft landing gear. The rig is capable of applying realistic loads and speeds of articulation, whilst measuring torque and angular displacement. The test machine design and operation is described. The pin joint is lubricated with mineral oil based grease. Joint rotation is relatively slow and hydrodynamic calculations predict that the joint operates in the boundary regime. During a single cycle the torque remains largely constant, with a static friction peak at the beginning and end of the cycle. Measurements of the torque during articulation demonstrate friction coefficients varying from 0.02 to 0.12 depending on the rotational speed. The contact stress distribution between the pin and bushes was estimated by an ultrasonic method. An ultrasonic pulse was sent through the hollow pin and reflected back from the pin-bush interface. High contact pressures causes conformity between the pin and bush and so the wave passes through. The proportion of the sound wave reflected was used to estimate the contact stress distribution. The results showed how the stress is maximum in the outer bushes and over a 60° arc of the pin. The results of the study can be used to understand how pin joints function and how they may be optimised.
Experimental Study and Analysis on Incipient Stage of Cavitation Erosion
Authors: Wang Jiadao , Liu Shihan , Qin Li , Chen Darong
Published: March 2009

Cavitation erosion has been studied for over one hundred years, but its mechanism is still uncertain. It has been found in this research that the existence of micro particles is an important factor to induce cavitation erosion. Experiments in rotating disk equipment were performed, and there is no obvious damage on sample after 5 minutes test in deionzed water, while the one tested in deionzed water with 500nm particles is eroded. Wear debris analysis technique was applied to study the particulates formed in the experiments, and results showed that many debris several micro-meters in size were yielded, which agreed with the scale of the cavitation pits on the sample. It was demonstrated that the mechanical action induces the cavitation erosion.
Friction and Wear Properties of DLC/UHMWPE Composite Film
Authors: Minn M. , Sinha Sujeet K.
Published: March 2009

In this work, we focus on the advantages of soft (ultra high molecular weight polyethylene, UHMWPE) and hard (diamond like carbon, DLC) composite film over either soft or hard film alone for tribological performance. Thin hard tetrahedral amorphous carbon, ta-C (DLC) is deposited onto Si substrate. Micron scale thin soft UHMWPE is coated onto Si and Si/DLC films by simple dip coating method. In order to get higher tribological performances, perfluoropolyether (PFPE) is coated onto Si/UHMWPE and Si/DLC/UHMWPE. The friction and wear tests are carried out using a custom-built high speed tribometer at a constant speed of 500rpm. A 4mm diameter silicon nitride ball under a normal load of 4g is used as counterface. The nanoscratch tests show that the load carrying capacity of Si/DLC/UHMWPE film is superior to that of Si/UHMWPE. The coefficients of friction of UHMWPE film on Si and Si/DLC are 0.18 and 0.13, respectively. After applying PFPE on UHMWPE, the coefficients of friction drop to 0.06 and 0.07 for Si/UHMWPE and Si/DLC/UHMWPE respectively. Hard DLC film can provide high load carrying capacity, high hardness, high penetration resistance and low contact area for the soft polymer film. The wear durability of Si/DLC/UHMWPE is approximately five times higher than that of Si/UHMWPE. Overcoating of PFPE further extends wear durability by approximately five times for Si/UHMWPE and three times for Si/DLC/UHMWPE (experiments stopped). This study shows that the combination of soft and hard composite film is better than either soft or hard film alone for tribological properties.
Study of Hydrostatic Mechanical Face Seals Operating in Turbulent Rough Flow Regime
Authors: Brunetie`re Noe¨l , Tournerie Bernard
Published: March 2009

The aim of this paper is to present a turbulence model that allows turbulent rough flows to be dealt with. This model is then applied to a hydrostatic mechanical seal with roughness on one face, operating in non-laminar flow. As expected, the wall roughness leads to a decrease in leakage rate.
Effects of Hydrogen Atmosphere on Wear Behavior of PTFE Sliding Against Austenitic Stainless Steel
Authors: Sawae Y. , Yamaguti A. , Nakashima K. , Murakami T. , Sugimura J.
Published: March 2009

The tribological characteristics of polytetrafluoroethylene (PTFE) sliding against austenitic stainless steel was evaluated under dry condition by using a pin-on-disk wear tester coupled with an environmental test chamber, and effects of gaseous hydrogen were examined. Results indicated that the wear behavior of unfilled PTFE was affected by the counterface roughness, the chemical composition of the stainless steel and also the type of gaseous environment within the test chamber. Especially, the specific wear rate of PTFE slid against 316L stainless steel became significantly smaller in the hydrogen environment compared with that in dry air and argon. Microscopic observation revealed that the formation of the PTFE transfer film on the stainless steel surface was enhanced in the hydrogen environment. The dense PTFE film formed in hydrogen had a preferable lubricating property and might be effective to reduce the PTFE wear amount in the sliding surface.
Experimental Studies on Flexure Pivot Tilting Pad Gas Bearings With Pad Radial Compliance
Authors: Sim Kyuho , Rimpel Aaron , Kim Daejong
Published: March 2009

This paper presents experimental studies on imbalance responses of a rotor supported by two flexure pivot tilting pad gas bearings with radial compliance. The radial compliance was aimed to accommodate large rotor centrifugal growth inherent with high speed operation. Frequency-dependent rotordynamic force coefficients calculated from developed software were used to predict critical speeds and onset speed of instability and compared with experimental results. Two results show very good agreement.
Analysis of the Tribofilm Formation on the Friction Drive Surfaces of a Piezoelectric Motor
Authors: Olofsson J. , Jacobson S. , Johansson S.
Published: March 2009

Piezoelectric motors typically have a friction drive system to transfer the movement. The miniaturized motor type investigated here has a friction drive system consisting of two drive pads that transfer the oscillating movement of the piezoelectric elements to a linear drive rail. The pads and rail consist of alumina. Tests have shown that the friction coefficient in this type of systems varies between 0.2 and 0.7, depending of wear of the surfaces and the formation of the tribofilm. This study further investigates the friction coefficient and its dependence of the pad oscillation frequency as well as the wear and the structure and of the tribofilm formed. Scanning electron microscope studies of the friction surfaces showed how the tribofilm forms as a function of numbers of cycles and frequency. To further investigate the nature of these tribofilm plateaus, cross section samples were produced with a Focused Ion Beam. Apparently the tribofilm plateaus were formed gradually by sintered/deformed wear debris. The practical implications of these findings for the possibilities to give this type of motors a stable driving force and speed as well as a long lifetime are discussed.
Internal Contact of Cylindrical Geometries: A New Approach
Authors: Pereira C. , Ambro´sio J. , Ramalho A.
Published: March 2009

Most of the models available in the literature describing the contact between cylindrical geometries express the contact force as an implicit function of the indentation. As a result, a numerical iterative technique is required to evaluate the contact force at each integration time step, during the solution of the dynamics of a system, which represents a numerical difficulty when implementing it in a computational program [1]. An analytical model that explicitly defines the indentation as a function of the contact force is more efficient for implementation in a computational code for impact simulation of dynamical systems. A new analytical model for cylindrical contact that in which the force is an explicit function of the indentation, still providing a force-indentation curve similar to that of the Johnson model [2], is proposed and discussed here. The new force contact law expresses the contact force as a function of the indentation and of geometric and material parameters for the contacting cylinders. The new analytical force model parameter identification is based on a sensitivity analysis of the response of the model against the response of the Johnson model [2] for specific contact geometries of the cylinders and Young modulus and Poisson coefficients of the materials of these elements. A comparative study is established to evaluate the performance of the new model with respect to the model presented by Johnson. Considering moderate load values, the force-indentation results show that the new model has always differences lower than 10% from the Johnson model for all geometries and materials, i.e., for a wide range of cylinder diameters and metallic materials properties. Nevertheless, the new model inherits some of the foundations of the Johnson model, which in turn is based on the Hertz non linear contact theory. The Hertz elastic contact theory includes several assumptions that limit its application is restricted to non-conformal contact situations [2]. Therefore, the applicability of the Hertz theory to describe the contact of internal cylinders, in particular for very low clearances, is questionable, to say the least. To show the performance of the new proposed model for internal contact of cylinders with low clearance numerical and experimental studies are performed. The comparative evaluation of results of the experimental studies with those resulting from the analytical model proposed by Johnson and from the new model is presented. The experimental and numerical results using the new model, for cylindrical contact with similar clearance values, show differences smaller than 3%. The experimental results difference with respect to the Johnson model reaches values of 15%. Finally, it can be concluded that not only for a wide range of large clearance values but also for very small clearance/external radii ratios, both the Johnson model and the new model are perfectly suitable to describe the contact between cylindrical bodies.
Tribochemical Interactions of Moly Dimer and ZDDP Additives With CrN Coating and Bearing Steel While Sliding Against Cast Iron in Boundary Lubrication Conditions
Authors: Neville Anne , Haque Tabassamul , Morina Ardian
Published: March 2009

In recent years, use of low friction non-ferrous coatings under boundary lubrication condition has become a challenge to meet the increasing demand of fuel economy in automotive applications. In this study, chromium nitride (CrN) was chosen as a non-ferrous coating and experiments were performed in a pin-on-plate reciprocating tribotester to produce the tribofilm. An atomic force microscope (AFM) was used to record high resolution topographical images while chemical analysis of the tribofilm was performed using X-ray photoelectron spectroscopy (XPS). Both AFM and XPS analyses give evidence of the formation of ZDDP and Moly Dimer derived tribofilm. This paper will also focus on the synergistic or antagonistic effect of ZDDP with Moly Dimer additive in the tribological performance of CrN coating.
Mini-Traction-Machine Tests to Assess the Effect of Base Oil and Additive Interactions on Surface Charge and Friction
Authors: Booth J. E. , Nelson K. D. , Harvey T. J. , Wood R. J. K. , Martinez J. G. , Powrie H. E. G.
Published: March 2009

Electrostatic condition monitoring was implemented on a MTM to examine the influence of additive adsorption from three base oils. Statistical analysis (ANOVA) indicates significant affects on measured charge and friction levels for both additive and base oil type.
Surface Separation and Contact Resistance Considering Elasto-Plastic Multi-Scale Rough Surface Contact
Authors: Wilson W. Everett , Jackson Robert L. , Angadi Santosh , Streator Jeffrey
Published: March 2009

The current work considers the multiscale nature of surface roughness in a new model that predicts the real area of contact and surface separation, all as a function of load. By summing the distance between the two surfaces at all scales, a model of surface separation as a function of dimensionless load is also obtained. The model is also able to make predictions for thermal (and electrical) contact resistance. In striving for a more realistic model, the multi-scale model accounts for the effects of a rough surface geometry ranging from macro down to the nano scale. A previous rough surface contact model was based on stacked elasto-plastic spheres. This work uses stacked 3-D sinusoids to represent the asperities in contact at each scale of the surface. The results are also compared to several other existing rough surface contact models and experimental results.
Overview of Analytical Methods for Lubricated Engine Components
Authors: Shi Fanghui
Published: March 2009

Engine designs require better fuel economy, lower NVH, and longer durability. Consequently, the understanding, analysis and design for lubricated engine components that have relative moving surfaces play an important role in this objective. As the GM corporate standard analytical tool for these components, FLARE has been under continuous improvements and validations since its first rollout from GMR in the late 80s. It has also been benchmarked with the best features available in the commercial software package and research literature. There are currently more than 20 standard work procedures directly involving FLARE as solver and its applications span over: • Rod, crank, cam and balance shaft journal bearings; • Connecting rod structure; • Piston structure and scuffing; • Engine mechanical friction; • Load calculation for engine block structural analysis; • Lube system analysis; • Noise analysis. There are three levels of analysis based on requirements. Namely, level one is used in initial design stage that finds solution by interpolating the curve-fitted equations. It requires the least information about the design and runs in seconds. In level 2, a more detailed solution can be obtained by solving mixed mass-conserving lubrication governing equations using FEM with the assumption of rigid bounding surfaces. Heat transfer can be taken into account in this level and above. Level 3 has the full capability, in addition to the features in level 2, the solution is coupled with the elasticity of surface/structure which can be obtained through offline structure FEM analysis. Higher level of analysis captures more physics but requires better understanding of the input parameters and careful interpretation of the results. The unique strength of FLARE is its detailed component level analysis capability. This presentation is an overview of the latest development on FLARE technology. It includes the physics captured in FLARE, integrated solution technique and some selected results for crankshaft bearings, floating piston pins, and piston/liner impact under partial film lubrication.
Influence of Soap Fiber Structure on Frictional Property of Lithium Soap Grease
Authors: Yokouchi Atsushi , Yamamoto Yuji
Published: March 2009

The authors have reported on results from a sliding test, which was conducted using a ball-on-disk type point-contact sliding test apparatus under gradually increased loading. Under slow sliding conditions where formation of an oil film is not expected, friction-resistant properties of grease are better than those of base oil. This result indicates that the soap fibers in grease work to protect the rubbing surface. Grease with long soap fibers shows better frictional resistance properties and offers greater protection against friction at the rubbing surface than grease with short soap fibers. In this paper, we examined factors that influence different frictional resistance properties according to soap fiber structures in the grease. Evaluation results of the friction-resistant properties of soap fibers alone, and the evaluation results of conditions of entraining grease into the rubbing surface area, show that friction-resistant properties vary according to the soap fiber structure in grease as a result of the conditions of introducing grease into the rubbing surface area.
Tangential Interactions Arising When a Circular Rigid Punch Slides Over an Elastic Half-Space
Authors: Diaconescu E. N. , Glovnea M. L.
Published: March 2009

The mechanism of surface interaction in dry sliding is attributed either to a constant friction coefficient or to a constant friction shear stress. This paper investigates these assumptions in the case of circular rigid punches sliding against the elastic half-space bounding plane. Normal displacements generated by these interactions are calculated. It is found that these do not comply with front surface of the punch in the case of a constant friction coefficient, whereas a perfect agreement arises when a constant friction shear stress is assumed.
The Numerical Calculation of Static Performance of Multi Wound Foil Bearing and Experimental Validation
Authors: Feng Kai , Kaneko Shigehiko
Published: March 2009

Multi wound foil bearings (MWFB), as a kind of foil bearings with simple structures, are supposed to be one of the best candidates of supporting component for turbo-machineries because of their design simplicity, reduced weight and size, high speed and temperature capability, and easy maintenance. In this study, a theoretical model of MWFB taking account of the effect of the foil deformation is developed to predict its static performance. Reynolds’ equation is solved using Finite Difference Method (FDM) to yield air pressure distribution, while the elastic deformation equation is solved by Finite Element Method (FEM) to predict the deformation of the foil. Then, the above two equations are coupled by several iterations until the convergence criterion is reached. Based on the calculations, static characteristics of MWFB such as film thickness, load capacity and torque are presented. Finally, an experimental apparatus is built up to measure the load of MWFB at different operation condition, which are used to validate numerical calculation results.
New Materials and Coatings for Superlubricity and Near-Wearless Sliding
Authors: Erdemir A. , Martin J.-M.
Published: March 2009

Superlubricity is defined as a new sliding regime in which friction or resistance to sliding almost vanishes. Because of its enormous implications for a wide range of transportation and manufacturing systems, it has attracted increasing interest in recent years from both the research and industrial communities (see a recent book on this subject in Ref. 1). From a practical point of view, development and uses of new materials, coatings, and/or lubricants that can enable superlubricity in moving mechanical systems will have huge positive impact on saving energy and reducing emissions. The annual cost of friction- and wear-related losses in some of the highly industrialized nations is currently estimated to be more than 5% of their gross national products. Hence, achieving superlubricity in moving mechanical systems will also have a huge positive impact on the economical well-being of all nations. In this presentation, an overview of recent progress in superlubricty research in general and novel superlow friction coatings and solid/liquid lubricated systems in particular is provided and the prospects for achieving superlubricity in real life applications are highlighted.
Critical Conditions for Liquid Mediated Collapse of Two-Dimensional Rough Surfaces
Authors: Streator Jeffrey L. , Jackson Robert L.
Published: March 2009

Small-scale devices are particularly vulnerable to adverse effects of adhesion because of large surface-area-to-volume ratios. Additionally, small gaps can be easily bridged at high humidity or when there are other contaminant liquids present. The bridging of a portion of the interface by a liquid droplet of given volume, tends to pull surfaces in closer proximity due to the sub-ambient pressures that arise. In turn, regions spanned by the bridge will increase in size and lead to a greater adhesive force. In the present work we develop a model for these effects in the presence of surface roughness. The influence of asperities on the surface is treated by means of a recently-developed multi-scale model that considers the full range of wavelengths comprising the surface profile. In the simulations, two nominally flat rough surfaces with profiles that vary only in one direction are brought together under a prescribed load. A liquid bridge of given volume (per unit depth) is then introduced into the contact, assuming an initial areal coverage. The interface configuration is then iterated until one is found that satisfies the equations of elasticity and capillarity for a given liquid volume. As a result of the simulation, critical values are found for combinations of parameters that delineate stable and unstable conditions.
Diesel Engine Turbocharger Rebuild and Experimental Testing
Authors: Kirk R. Gordon , Sterling John , Utara Ryan , Biggins Gray , Hodge David , Johnson Stephen , Dean Jason , Mastropieri Brett , Fernandez Leopoldo , Mehta Rumeet , Miles Thomas , Chen Feng , Johnson Andrew , Ko Henry , Riggs Aaron , Price Matthew , Cerni Andrej
Published: March 2009

The objective of the 2006–07 Virginia Tech Turbocharger Project was to obtain and analyze vibrations data from different bearing designs. The supporting tasks were divided amongst various sub-teams; a turbocharger team, an engine test operating team, a dynamometer team, and an ADRE software team. The turbocharger team has successfully developed a procedure for disassembly and reassembly of the turbocharger. A consistent and well-documented assembly procedure has ensured turbocharger operation free from human error. Consistency in the rebuild process is vital to properly compare vibration data with the different shaft bearings. The most important aspect of this reassembly is the torque applied to the tie-bolt nut. This torque causes the tie-bolt to stretch, and this stretch must be accounted for because it is a measure of preload force on the compressor wheel. The team designed and made a stand to carefully apply this torque on the tie-bolt nut without creating a bending moment. The original stock bearings were used for the first turbocharger rebuild to see if the rebuild procedure would lead to similar data. Two other bearings have been tested and analyzed. This paper will give a brief overview of the results to date.
Spherical vs. Cylindrical Engine Bearings
Authors: Booker J. F. , Boedo S.
Published: March 2009

Spherical bearings have been used successfully in engines for some years. The spherical bearing geometry allows a simplified axisymmetric piston design; gradual rotation of the piston and rings results in axisymmetric sidewall wear, temperature distribution and thermal expansion. A previously-described concept engine design incorporating a spherical joint piston was based on an existing production engine with a conventional cylindrical piston pin. Previously-developed finite element lubrication analysis methods are applied to both designs and predictive comparisons made.
A Three-Dimensional Deterministic Model for Rough Surface Line-Contact EHL Problems
Authors: Ren Ning , Chen W. Wayne , Zhu Dong , Liu Yuchuan , Wang Q. Jane
Published: March 2009

This paper reports the development of a novel three-dimensional (3D) deterministic model for rough surface line-contact mixed-EHL problems. This model is of great importance because line contacts are found in many mechanical components. The macro aspects of a line-contact problem can be simplified into a two-dimensional (2D) model, but the topography of contacting rough surfaces, micro asperity contacts, and lubricant flows around asperities are often 3D. The present model is based on Hu and Zhu’s unified mixed EHL model [1] and the mixed FFT-based approach formulated by Chen et al [2]. It is numerically verified through comparisons with results from conventional 2D line-contact EHL theories. Numerical examples involving sinusoidal roughness and digitized 3D machined surfaces are analyzed.
Elastohydrodynamic Lubrication Analysis of a Radially Adjustable Partial Arc Bearing Using Fluid Structure Interaction
Authors: Bhat Praveen , Shenoy B Satish , Pai Raghuvir
Published: March 2009

Conventional method of performing Elasto-hydrodynamic Lubrication (EHL) analysis on a partial arc bearing involves simplification of actual physical model and developing complex codes. This paper presents the overall EHL analysis of a radialy adjustable single 60° partial arc bearing using the sequential application of Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD). Here the coupled field analysis uses the capabilities of commercially available Finite Element Software ANSYS/FLOTRAN and the technique of Fluid Structure Interaction (FSI). The pressure field has been obtained using CFD considering the flow to be laminar. Stress distribution and deformation in the pad due to resulting pressure force is obtained using Finite Element Method (FEM), satisfying the boundary conditions. The stress distribution indicates the critical points in the pad. In this paper the static characteristics of radialy adjustable single 60° partial arc bearings are predicted for different eccentricity ratios and length to diameter (L/D) ratios. The results show reasonable agreement in general.
The Effect of Microstructure on Chemical Mechanical Polishing Process of Thin-Film Metals
Authors: Bonivel Joseph , Biltz Sarah , Terrell Elon , Ozdoganlar Burak , Higgs C. Fred
Published: March 2009

Chemical mechanical polishing (CMP) is a critical nanomanufacturing process used to remove or planarize ultrathin metallic, dielectric, or barrier layers on silicon wafers. The CMP process is a vital interim fabrication step for integrated circuits and data storage devices. One of the major shortcomings of existing CMP models is that they do not account for crystallographic effects of the thin film metal materials when predicting material removal rates. This work investigates the effect of the microstructure on the CMP of copper and metal thin films on silicon wafer. Nanoindentation tests were conducted to measure the hardness variations across a wafer surface due to the crystallography of the metal films. Spatial variation of mechanical properties was also input into an existing multi-scale CMP model. Nano-characterization and CMP experimental results are presented and compared to an existing CMP wear model.
The Behavior of the Liquid Like Adsorbed Film on Air Bearing Surfaces
Authors: Zhang Bo , Nakajima Akira
Published: March 2009

The behavior of the liquid-like adsorbed film on two types of air bearing surface with three dimension geometry was investigated by using the pumping effect with the Langmuir adsorption. The results shows that the contaminant tends to accumulate on the recession area of the air bearing surface. The viscosity of the adsorbed film will change the adsorbed film thickness distribution greatly.
Shock Response of a Small Form Factor Hard Disk Drive With Air Bearing Interface Fully Coupled
Authors: Peng Jih-Ping , Lee Yu-Min
Published: March 2009

The present paper investigates the shock response of a small form factor hard disk drive (HDD). Both the air bearing and the entire HDD structure are considered in the model. The air bearing is described by the compressible Reynolds equation. The HDD structure is modeled by the finite element method. The Guyan reduction method is used to reduce the number of degrees of freedom to manageable size. CML Dynamic Simulator is used to solve the coupled structure equations and air bearing Reynolds equation.
Numerical Investigation of Bouncing Vibrations of a Partial Contact Slider
Authors: Chen Du , Bogy David D.
Published: March 2009

A nonlinear dynamic model is developed to analyze the bouncing vibration of a partial contact air bearing slider, which is designed for the areal recording density in hard disk drives of 1 Tbit/in2 or even higher. In this model the air bearing with contact is modeled using the generalized Reynolds equation modified with the Fukui-Kaneko slip correction and a new second order slip correction for the contact situation [1]. The adhesion, contact and friction between the slider and the disk are also considered in the model. It is found that the disk surface roughness, which moves into the head disk interface (HDI) as the disk rotates, excites the bouncing vibrations of the partial contact slider. The frequency spectra of the slider’s bouncing vibration have high frequency components that correspond to the slider-disk contact.
Integrated Hybrid Micro/Nano-Machining
Authors: Rahman M. , Asad A. B. M. A. , Masaki Takeshi , Wong Y. S. , Lim H. S.
Published: March 2009

There is a growing demand for industrial products with not only increased number of functions, but also of reduced dimensions, higher dimensional accuracy and better surface finish. Micro/nano-machining is the most promising technology for the production of such miniaturized parts and components. Components for MEMS are basically produced using processes from semiconductor technology which impels the fabrication process to be limited to a few semiconductor materials like silicon and their compounds, or requires expensive facilities. Hybrid micromachining processes that combine conventional and non-conventional micromachining have the capability to fabricate high-aspect ratio microstructures with paramount dimensional accuracy. In order to achieve meaningful implementation of micro/nano machining techniques, our research efforts seek to address three important areas; namely (a) development of machine tool capable of hybrid micromachining, (b) process control and (c) process development to achieve necessary accuracy and quality. An integrated effort in these areas has resulted in successful fabrication of micro structures that is able to meet the miniaturization demands of the industry. This paper presents a few tool-based approaches integrating micro-EDM, micro EDG, micro-turning and micro-grinding to produce miniature components. This paper also describes the features and aspects of miniaturized multi-process machine tool that provides the capability of hybrid micromachining.
Precision Printing of Cells and Biomaterials Onto 3D Matrices
Authors: Boland Thomas , Cui Xiaofeng , Chaubey Aditya , Burg Timothy C. , Groff Richard E. , Burg Karen J. L.
Published: March 2009

The long term goal of our work is to develop a fabrication technique that allows precision placement of cells inside biomaterial constructs. Such spatial and temporal control of the chemistry and pattern geometry can provide new insights into fundamental aspects of cell-surface interactions. For example, cellular development can be dramatically effected by constraining cells to spread over a specific cell-surface contact area. The cell and biomaterial printing techniques developed here may prove particularly useful for exploring the interactions of anchorage-dependent cells with their environment in vitro. Our recent studies addressed the simultaneous printing of endothelial cells and biomaterials. The studies further demonstrated that cells can be printed onto polymer scaffolds or fibers without significant loss of cell activity. A combination of these methods may result in the construction of vascularized tissue with mechanical properties approaching those of native tissue.
Manufacture and Characterisation of Bioceramic Tissue Engineering Scaffolds Produced by Selective Laser Sintering
Authors: Xiao K. , Dyson J. A. , Dalgarno K. W. , Genever P. , Wood D. J. , Goodridge R. D. , Ohtsuki C.
Published: March 2009

Currently there is no adequate bone replacement available that combines a long implant life with complete integration and appropriate mechanical properties. This paper reports on the use of human mesenchymal stem cells (MSCs) to populate porous bioceramic scaffolds produced by selective laser sintering (SLS) to create bespoke bioactive bone replacement structures. Apatite-wollastonite glass ceramic was chosen for use in this study because of its combination of excellent mechanical and biological properties, and has been processed using an indirect SLS approach. Process maps have been developed to identify process conditions for the SLS stage of manufacture and an optimised furnace cycle for the material has been developed to ensure that the required material phases for bioactivity are present in the manufactured scaffold. Results from tissue culture with the MSC’s on the scaffolds (using confocal and scanning electron microscopy) show that MSCs adhere, spread and retain viability on the surface, and penetrate into the pores of apatite wollastonite (A-W) glass ceramic scaffolds over a 21 day culture period. The MSC’s also show strong indications of osteogenesis, indicating that the MSC’s are differentiating to osteoblasts. These results indicate good biocompatibility and osteo supportive capacity of SLS generated A-W scaffolds and excellent potential in bone replacement applications.
Analysis of the Scale Effect for Microscale Machine Tools
Authors: Park Hyung Wook , Liang Steven Y.
Published: March 2009

Miniaturization of conventional machine tools has been initiated due to inherent technical and economical advantages. To support further development in this area, a systematic design scheme must be developed on a quantitative basis to reduce the subjective design of miniaturized machine tools. The present work is the size optimization of the miniaturized milling machine on the basis of the proposed design strategy. This design strategy includes individual mathematical computations of key parameters such as volumetric error, machine working space, static, thermal, and dynamic stiffness. This mathematical modeling is established by using analytical methods followed by experimental validation. Individual computations based on the mathematical modeling are carried out to produce the penalty function of the miniaturized milling machine which is then used to find out the optimal dimension. In addition to this, the sensitivity of weighing factors is discussed to find out which weighing factor is more effective to an optimal solution. This study will eventually contribute to the development of more precise miniaturized machine tools.