bluuebunny/crossref_metadata_2025 huggingface dataset:
A Better Understanding of the Surface Topography at the Stem-Cement Interface
Authors: Zhang H. , Brown L. , Blunt L.
Published: March 2009

The long term stabilization and durability of cemented total hip replacement (THR) depends on not only the bulk properties of the components but also the interfaces through which they interact. The stem-cement interface has been consistently considered as a weak link in the stem-cement-bone system, being a transitional zone between two materials with significantly different mechanical properties. Previous research concerning this interface has been limited to investigation of interfacial shear strength through in vitro test and finite element analysis (FEA). Until now, a deep insight into the contact characteristics at this interface, especially the interaction between femoral stems with various surface finishes and bone cement, has not been established. In addition, it is still an area of debate whether a permanent fixation can be achieved by utilizing a matt femoral stem, and furthermore it is another matter of concern that a matt femoral stem would cause much more damage to the cement mantle, resulting in an acceleration of aseptic loosening of the femoral stem. This present study investigated the surface topography of stainless steel rods and Simplex P bone cement obtained from a series of pull out tests in order to gain a better understanding of the interaction at the stem-cement interface.
Cooling Effect and Dynamic Characteristics of Oil Film of Partial Tilting Pad Bearing
Authors: Bang Kyung-Bo , Kim Jeong-Hun , Kim Cheol-Hong
Published: March 2009

In the present paper, we suggest a new type of tilting pad journal bearing to decrease oil film temperature and eliminate pad fluttering during operation. This bearing consists of tilting pad journal bearing at low casing and fixed arc type journal bearing at upper casing. Namely we changed a tilting pad bearing with a fixed arc type bearing at upper casing. To investigate the effects of changing the bearing shape, the static and dynamic characteristics were compared experimentally with conventional tilting pad journal bearing. For the static characteristics, oil film temperature, hydrodynamic pressure and oil film thickness were measured with the variation of rotating speed, bearing load and oil flow rate. The stiffness and damping coefficients of oil film were also obtained using the response subjected to harmonic external force to evaluating the dynamic characteristics. The results show that the suggested type of bearing has effect on reducing oil film temperature and increasing stiffness and damping coefficients of oil film.
Cutting Tool Wear and Mechanisms of Chip Formation During High-Speed Machining of Compacted Graphite Iron
Authors: Dlamini Niniza S. P. , Sigalas Iakovos , Koursaris Andreas
Published: March 2009

Cutting tool wear of polycrystalline cubic boron nitride (PcBN) tools was investigated in oblique turning experiments when machining compacted graphite iron at high cutting speeds, with the intention of elucidating the failure mechanisms of the cutting tools and presenting an analysis of the chip formation process. Dry finish turning experiments were conducted in a CNC lathe at cutting speeds in the range of 500–800m/min, at a feed rate of 0.05mm/rev and depth of cut of 0.2mm. Two different tool end-of-life criteria were used: a maximum flank wear scar size of 0.3mm (flank wear failure criterion) or loss of cutting edge due to rapid crater wear to a point where the cutting tool cannot machine with an acceptable surface finish (surface finish criterion). At high cutting speeds, the cutting tools failed prior to reaching the flank wear failure criterion due to rapid crater wear on the rake face of the cutting tools. Chip analysis, using SEM, revealed shear localized chips, with adiabatic shear bands produced in the primary and secondary shear zones.
Friction Coefficient as a Macroscopic View of Local Dissipation
Authors: Iordanoff I. , Richard D. , Renouf M. , Berthier Y.
Published: March 2009

This paper presents an overview of a Discrete Element Method approach used to study the dry friction (global scale) taking into account local discontinuity with the presence of third body at the contact interface. Three dimensional computer simulations have been carried out to show the influence of the third body properties (and more specifically its adhesion) on the resulting friction coefficient as well as the dissipated power profiles. The physics of the interface is described by a simple cohesive contact law which is set up to uncouple the key parameters governing the contact rheology. The model is validated through a global energy balance. As it is shown that dynamic friction coefficient can be explained in term of local energy dissipation, the work also emphasizes the fact that mechanism effects and third body rheology have important consequences on the energy generation and dissipation field. The friction coefficient cannot be considered the same way at the mechanism scale than at the contact one where the third body plays a non-negligible role despite the fact that it has been neglected for years in thermal approaches of the contact.
The Synergistic Antiwear and Frictional Properties of Organic Molybdenum Compound With Zinc Dialkyldithiophosphate
Authors: Hu Jian-Qiang , Dai Ge-Lin , Hu Yi-Qin , Fu Yan
Published: March 2009

The synergistic antiwear and friction reducing properties of oils containing nor-sulfur nor-phosphoruorganic molybdenum compound (MC) with zinc dialkyldithiophosphate (ZnDDP) were evaluated by four ball tester. The results show that the combination of organic molybdenum compound and ZDDP exhibits good synergistic antiwear and friction reducing properties. Moreover, at the same concentration of ZDDP with different alkyl groups, there was an different optimum MC concentration for better antiwear and friction reducing properties. When MC concentration exceed this optimum valves, the antiwear and friction reducing properties of lubricants were not improved obviously. However, These properties were affected significantly by ZDDP type, while the effect of ZDDP type on these properties became small at higher MC/ZDDP ratios. Especially, the combination of MC with ZDDP containg primary C8 alkyl groups is very effective on tribological behaviours under lower dosage of MC added to oils. Finally, the surface analysis indicated that Mo, S atoms are distributed evenly on the wear scar, which contribute to improve the tribological properties of lubricants.
Elastohydrodynamic Film Thickness and Acoustic Emission for Meshing of Spur and Helical Gears
Authors: Raja Hamzah R. I. , Mba D.
Published: March 2009

This paper presents experimental evidence of the correlation between Acoustic Emission (AE) activity and the specific film thickness (λ) for operational spur and helical gears. Whilst recording AE activity for a range of test conditions the specific film thickness was varied during operation by spraying liquid nitrogen onto the rotating gear wheel. It was noted that the AE activity reduced significantly as the theoretically estimated specific film thickness increased. It is concluded that the measurements of AE activity may offer an opportunity to quantify the level of asperity contact for meshing gears under a range of operating conditions.
Study of Self-Locking Mechanism of Belt Friction
Authors: Imado Keiji
Published: March 2009

It is well know that the belt friction is expressed in an exponential function of a product μ and θ, the coefficient of friction and the angle of contact between the flexible belt and the cylindrical surface respectively. So the frictional force increases greatly with an increment of contact angle θ. Using this property, many kinds of buckles were developed to fasten belt. But the locking condition of belt is not obtained from the equation unless θ is of infinity. Their locking conditions were not clarified theoretically. In practice, the product of μθ is usually less than θ, so that the exponent of the product μθ is not so large. Then some slippage may occur in case of severe loading condition. This study is focusing on a self-locking mechanism of a simple buckle developed for flat belt. The belt in the buckle is partially wound again over the belt. According to the equation derived, the fraction of the tight side belt tension to the loose side belt tension is significantly affected by the angle of double-layered segment. With an increment of angle of doublelayered segment, the fraction increases to infinity, which means the occurrence of belt locking. The locking condition is determined by the geometry of the buckle and the coefficient of frictions. The frictional force is automatically generated by the tension of belt so that the self-locking mechanism is realized in the buckle. The equation derived was confirmed by the experiments.
Numerical Model of a Tandem Reciprocating Hydraulic Rod Seal
Authors: Yang Bo , Salant Richard F.
Published: March 2009

A numerical model of a tandem reciprocating hydraulic rod seal, consisting of two elastomeric U cup seals, has been constructed. The model consists of coupled steady state fluid mechanics, deformation mechanics and contact mechanics analyses, with an iterative computational procedure. The behaviors of the two seals are coupled through the pressure/density in the inter-seal region and through flow continuity. Results for a typical tandem seal are compared with those of a single seal and a double lip seal.
Tribological Behavior of AZ31B Magnesium Alloy Sheet During Sliding at High Temperatures
Authors: Hanna M. David , Carter Jon T. , Mahayotasanun Numpon
Published: March 2009

This investigation was undertaken to understand the interaction between steel tools and AZ31B magnesium alloy sheet during high-temperature forming. A new method of tribo-testing at high temperature, which involves reciprocating sliding of steel specimens against magnesium alloy sheet, was used to determine the effects of temperature and load. On the steel tool/magnesium sheet interaction. The coefficient of friction increased with increasing test temperature but decreased with increasing load.
In Situ and Real Time Optical Investigation of Junction Growth in Spherical Elastic-Plastic Contact
Authors: Ovcharenko Andrey , Halperin Gregory , Etsion Izhak
Published: March 2009

The contact area evolution during pre-sliding (junction growth) of copper spheres loaded against a hard sapphire flat is investigated experimentally. Tests are performed with a recently developed test rig for real-time and in situ direct measurements. The results provide a new insight of the junction growth mechanism showing new points of the sphere surface that are coming into contact with the flat. It is found that junction growth at sliding inception can cause up to 45 percent increase in the initial contact area that is formed under normal preload alone. Good correlation is found between the present experimental results and a theoretical model for medium and high normal preloads.
Marine Water Lubricated Stern Tube Bearings: Design and Operation Problems
Authors: Litwin Wojciech
Published: March 2009

Faculty of Ocean Engineering and Ship Technology of Gdansk University of Technology (Poland) co-operates with ship industry and some well known manufactures of water lubricated bearings. In the last few years, three various test stands for research work with water lubricated main shaft bearings were designed and built. They were used for many different tests with various kinds of bearings. The testing process helped to understand and prove some phenomena. Water lubricated stern tube bearings are often used on modern ships. This environmentally friendly bearing is much cheaper than popular oil lubricated one. The difference in price is a result of simplicity of the bearing unit and lower material costs. Unfortunately, there were many serious breakdowns associated with this kind of bearing. Sometimes the wear process was very rapid. It was mainly a result of problems with stability of the hydrodynamic film, poor material properties or unfavorable working conditions. Theoretically, water lubricated stern tube bearings operate in hydrodynamic regime. Loads are low because of high bearing length to shaft diameter ratio (L/D). Sliding speed depends on engine type, main gear ratio and ship size. Generally, the speed could be even higher than 3 meters per second, which should be sufficient for hydrodynamic lubrication. So why are there problems with this kind of bearings? There are three main groups of reasons — design flaws, ship specific problems and negative influence of sea environment.
Preliminary Study on Tribological Performance of Straw Based Bio-Fuel
Authors: Xu Yufu , Wang Qiongjie , Hu Xianguo , Chen Jinsi
Published: March 2009

More and more attention has been paid to alternative fuel in internal combustion engine. One of alternative fuels is to convert straw biomass to biomass fuel. Various methods and apparatuses used for converting straw biomass to bio-fuel were invented and developed. However, alternative fuel from biomass can not be used well in internal combustion engine. The reason is complicated and relative with the separation technology of bio-fuel and corrosion, wear, lubrication and combustion chemical reaction between bio-fuel and the surface of combustion room. It is necessary to study the tribological properties of bio-fuel in order to instead the current gasoline or diesel oil in internal combustion engine in the future. In the present study, the straw based bio-oil obtained by liquidizing process was chosen to evaluate its lubrication by MQ-800 fourball tribometer, in which extreme pressure and friction coefficient and wear resistance were measured respectively. The experimental results showed that the extreme pressure of the bio-fuel was up to 392 N, and the extreme pressure of diesel oil was 333 N. The frictional coefficient of bio-fuel varies between 0.08 and 0.11. The wear scar diameter increased with load slowly in 30min. SEM images indicate that lots of thin and dense belt-like ploughs were presented on the rubbed ball surface. The chemical compositions of the worn zone on the ball surface were analyzed by XPS, the thermal property and variation of chemical compositions of bio-fuel before and after friction and wear tests were studied by TGA and GC-MS, respectively. It was shown that the rubbing surface film was composed of FeS, FeSO4 and organic compounds with C-C, −COH and −COOH groups.
Dissolved Wear Metal Monitoring in Lubricating Fluids
Authors: Discenzo Fred M. , Kania Steven A. , Liu Chung-Chin , Dudik Laurie , Vasser Aleksandr , Ward Benjamin
Published: March 2009

Lubricating fluids play a critical role in the operation of many machines in commerce, industry, and the military. Failure of a lubricant often results in accelerated metal wear and the release of wear debris in the lubricant. Early detection of abnormal metal wear is important for fault detection and failure prevention. An electrochemical cell can be operated in a lubricating fluid in such a way that the operating characteristics of the cell can provide an indication of the chemistry of the fluid. For example, certain ions in the fluid, such as wear metal ions, will react to particular potential values applied to electrodes in the electrochemical cell. By applying a changing potential across the electrodes in an electrochemical cell and observing the resulting current it is possible to detect and identify the ionic species present in the lubricating fluid. The objective is to provide real-time monitoring of lubricating fluids using an in situ sensor to detect and diagnose conditions leading to machinery failure. A series of experiments have been conducted to confirm the ability of an electrochemical cell to detect wear metal ions in lubricating fluids extracted from machinery. Additional tests have been conducted to test the hypothesis that the presence and amount of wear metal ions corresponds to the type and amount of wear particles in the fluid. Initial laboratory tests have established a positive correlation with wear particles detected in used lubricating oil with ion presence determined using ion chromatography. The results reported indicate that a small, real-time multielement sensor with an electrochemical cell will be able to detect wear metal ions and provide an early indication of unusual material wear. This capability may provide an early warning of atypical wear patterns and provide a cue to an operator or service engineer indicating the type of fault occurring and the specific component experiencing wear or early failure.
Changes in Friction Properties of Monolayer Lubricant Films Induced by Development of Molecules’ Bonding
Authors: Zhang H. , Mitsuya Y. , Fujikawa Y. , Fuwa A. , He Y. , Fukuzawa K.
Published: March 2009

Functional perfluoropolyether (PFPE) films consisting of bonded and mobile molecules are widely used for lubrication of magnetic disk. To clarify the effect of film composition (mobile/bonded) on tribological performance, we measured the time-dependent friction properties of two types of monolayer PFPE films (functional Zdol2000 and nonfunctional Z03) under lightly loaded (loading force: 0–1 mN) and quasi-static (low rotational speed: 2.1 mm/s) conditions. The friction force of Z03 remained unchanged with time and it increased linearly with external loading force. In contrast, induced by the development of molecules’ bonding with time, the friction force of Zdol2000 increased and transited to a nonlinear increase with external loading force as the time proceeded.
A New Foil Bearing Dynamic Structural Model
Authors: Le Lez Se´bastien , Arghir Mihai¨ , Frene Jean
Published: March 2009

A dynamic model of the bump-type foil bearing structure is presented in this paper. This model is an extension of a static model that considers the corrugated foil as a multidegree of freedom system. The system of differential equations describing the dynamic displacements is obtained by considering the global stiffness matrix of the structure and the typical Coulomb damping of the corrugated foil. By using a regularization technique, the friction forces are described in a continuous way over the whole process of motion. The results of the model are presented first for a single bump and then for a complete strip. Good correlations are obtained between the model and both finite element simulations and experimental data issued from the literature.
Elastohydrodynamic Lubrication of Rough Surfaces Under Oscillatory Line Contact With Non-Newtonian Lubricant
Authors: Mongkolwongrojn Mongkol , Wongseedakaew Khanittha , Kennedy Francis E.
Published: March 2009

This paper presents the analysis of elastohydrodynamic lubrication (EHL) of two parallel cylinders in line contact with non-Newtonian fluids under oscillatory motion. The effects of transverse harmonic surface roughness are also investigated in the numerical simulation. The time-dependent Reynolds equation uses a power law model for viscosity. The simultaneous system of modified Reynolds equation and elasticity equation with initial conditions was solved using multi-grid multi-level method with full approximation technique. Film thickness and pressure profiles were determined for smooth and rough surfaces in the oscillatory EHL conjunctions, and the film thickness predictions were verified experimentally. For an increase in the applied load on the cylinders, the minimum film thickness calculated numerically becomes smaller. The predicted film thickness is slightly higher than the film thickness obtained experimentally, owing to cavitation that occurred in the experiments. For both hard and soft EHL contacts, the minimum film thickness under oscillatory motion is very thin near the trailing edge of the contact, especially for stiffer surfaces. The surface roughness and power law index of the non-Newtonian lubricant both have significant effects on the film thickness and pressure profile between the cylinders under oscillatory motion.
The Calculation Model of Boundary Lubrication Under Point Contact
Authors: Wang Weizu , Huang Ping
Published: March 2009

A calculation model of boundary lubrication under point contact is established according to some hypothesises. Then, a modified model is developed by the theory of adsorption heat. Tests are carried out on a self designed ball-on-disk machine in a stearic acid (dissolved in petroleum ether) bath. Disks have surface roughness values (Ra) of 0.2 μm and 0.4 μm. The comparison of the calculation results and the experimental results shows a pretty good coincidence. The influence of temperature and sliding speed on the friction coefficient is analyzed base on the calculation model.
Contact Mechanics Study in Biotribology: A Tissue Engineering Example
Authors: Jeng Yeau-Ren , Mao Chien-Ping , Lin Tsung-Ting , Shieh Dar-Bin
Published: March 2009

The study of biotribology attracts increasingly attention because it holds great promise to have profound impact on the way people live their lives. This study presents two cases of contact mechanics study on tissue engineering: one in soft tissue and the other one in hard tissue. In the study of soft tissue, we conducted a theoretical investigation into the effect of particle on the adhesion of a biological nanostructure system. Based on a three-body contact model and JKR theory our results show that geckos’ spatulas provides robust adhesions even with trapped particles in the interface. In the case of hard tissue, we utilized nanoindentation technique to characterize the mechanical property and tribology behavior of calcium fluoride-like deposits on human tooth. The low nanohardness and high nano-wear depth characteristics of the surface deposits identified in this study account for the natural loss of the surface deposits days or weeks after topical fluoride treatment as a result of daily brushing and mastication.
Influence of the Cross-Hatched Surface Texture on a Starved Hydrodynamic Linear Contact
Authors: Organisciak M. , Cavallaro G. , Lubrecht A. A.
Published: March 2009

Surface roughness and topography are two important parameters that influence the film thickness and friction of a lubricated contact. In many industrial applications, these parameters are imposed by the manufacturing process. This has been the case for the cylinder liner: the honing process creates a specific cross-hatched groove pattern on the cylinder liner surface. Laser surface texturing can produce surfaces with the same type of micro-geometry, but with an increased precision and control. Thus a better compromise between friction losses and oil consumption can be found. For this, it is necessary to understand the effects of the cross-hatched grooves on the film thickness and friction. This paper describes a transient model of a starved hydrodynamic linear contact based on the Reynolds equation. A deterministic description of the surface cross-hatched grooves is used. The results show that the introduction of a surface pattern always reduces the mean film thickness compared to a smooth surface. This reduction depends on parameters like cross-hatch angle and groove density. An appropriate cross-hatched angle can reduce the frictional losses.
Thermo-Mechanical Wear Mechanisms of Ceramic Materials
Authors: Kim Sang-Woo , Lee Seung-Hun , Park Jun-Seok , Kim Seock-Sam
Published: March 2009

This paper was investigated the thermo-mechanical wear mechanisms of ceramic materials under lubricated sliding condition based on the fracture mechanics. Thermo-mechanical wear model for ceramic materials was proposed, and non-dimensional parameter T for evaluation of ceramic materials was also proposed. Non-dimensional parameter T is consist of thermal load (Th) and Peclet number (Pe).
Ductile Separation and Its Role in the Evolution of Gold Contacts
Authors: Chen Lei , Du Yan , McGruer Nicol E. , Adams George G.
Published: March 2009

In this paper, we study the role of ductile separation on the evolution of gold-on-gold micro-contacts. A specially designed SPM contact test station has been used to conduct the cycling tests. The evolution of contacts is studied by monitoring the characteristics of the pull-off force. The magnitude of the pull-off force, the force vs. displacement curves, and the rate-dependent pull-off force are sampled during cycling. It is found that ductile separation causes significant and random modification of the contact surfaces. The magnitude of the pull-off force also changes due to the variation of surface morphology. Significant plastic deformation during ductile separation can form a plateau region in the force-displacement curve which is characteristic of ductile separation. This deformation can also contribute to a higher pull-off force when the contacts are cycled at 300Hz compared with cycling at 0.5Hz. The difference between these rate-dependent pull-off forces can be used to indicate the degree of plastic dissipation during each separation.
Frictional Properties of Antimony Nanoparticles: The Influence of Contact Area, Structure, and Surface Contamination
Authors: Schwarz Udo D. , Ritter Claudia , Stegemann Bert , Heyde Markus , Rademann Klaus , Dietzel Dirk , Schirmeisen Andre´ , Fuchs Harald
Published: March 2009

We performed experiments where the frictional resistance of antimony nanoparticles with varying contact areas is measured in ambient conditions as well as in ultrahigh vacuum while they are pushed by the tip of an atomic force microscope (AFM). Two different procedures have been used in independent studies to investigate the frictional properties of these particles during dislocation using the AFM operated in the contact mode or dynamic (tapping) mode, respectively. Both experimental approaches revealed a linear dependence of the frictional properties on contact area. Moreover, both methods detect a sudden and distinct increase in frictional resistance at around 15000 nm2 particle size, which coincides with a structural transition of the particles from an amorphous to a crystalline core state and confirms our earlier data showing the same result. Possible reasons for this effect are discussed in terms of both the atomic structure of the antimony particles as well as the interface structure. Some of the observed frictional behaviour of the particles may be explained considering the influence of sample contamination.
Application of Nanofluids in Minimum Quantity Lubrication Grinding
Authors: Shen Bin , Shih Albert , Tung Simon
Published: March 2009

This research project investigated the wheel wear and tribological characteristics in wet, dry and minimum quantity lubrication (MQL) grinding of cast iron. Water-based Al2O3 and diamond nanofluids were applied in MQL grinding process and the results were compared with those of pure water. During the MQL grinding using nanofluids, a dense and hard slurry layer was formed on the wheel surface and could benefit the grinding performance. Experimental results showed that G-ratio, volume of wear of the grinding wheel vs. the volume of material removed, could be improved with high concentration nanofluids. Nanofluids showed the benefits to reduce grinding forces, improve surface roughness, and avoid workpiece burning. Compared to dry grinding, MQL grinding could significantly reduce the grinding temperature.
Effect of Stiff Coatings on EHL Film Thickness in Point Contacts
Authors: Liu Yuchuan , Wang Q. Jane , Zhu Dong
Published: March 2009

This study investigates the influences of coating material properties and coating thickness on lubricant film thickness based on a point-contact isothermal EHL model developed recently by the authors. The results present the trend of minimum film thickness variation as a function of coating thickness and elastic modulus under a wide range of working conditions. Numerical results indicates that the increase in minimum film thickness, Imax, and the corresponding optimal dimensionless coating thickness, H2, can be expressed in the following formulas: Imax=0.766M0.0248R20.0296L0.1379exp(−0.0245ln2L)H2=0.049M0.4557R2−0.1722L0.7611exp(−0.0504ln2M−0.0921ln2L) These formulas can be used to estimate the effect of a coating on EHL film thickness.
Influence of Surface Roughness in TEHL With Non-Newtonian Liquid/Solid Lubricants Under Sudden Load Change
Authors: Mongkolwongrojn Mongkol , Aiumpornsin Chatchai
Published: March 2009

This paper describes the influence of surface roughness on thermoelastohydrodynamic (TEHL) lubrication characteristics of a sliding line contact under sudden load change. The surface roughness is a harmonic wave in the transverse direction. The time-dependent Reynolds equation with non-Newtonian liquid-solid fluids has been formulated using a power law model. The constitutive equation of the liquid-solid lubricants was formulated based on experimental data. The simultaneous systems of modified Reynolds, elasticity and energy equations with initial conditions were solved numerically. The static and dynamic characteristics of the thermoelastohydrodynamic line contact with rough surfaces under sudden load change have been investigated numerically to determine the distribution of pressure, film thickness and temperature. The transient response of the lubricated line contact between a infinitely long cylinder surface and a flat plate was simulated under a heavy step load function. This simulation showed a significant effect of surface roughness and solid particles on thermoelastohydrodynamic lubrication under sudden load change.
On the Modeling of Friction in Micromachining Processes
Authors: Lovell M. R. , Cohen P. H. , Shankar R.
Published: March 2009

When machining miniaturized components, the contact conditions between the tool and workpiece exhibit very small contact areas that are on the order of 10−5 mm2. Under these conditions, extremely high contact stresses are generated and it is not clear whether macroscopic theories for the chip formation, cutting forces, and the friction mechanisms are applicable. For this reason, the present investigation has focused on creating a basic understanding of the frictional behavior in micro machining processes so that evaluations of standard macro-scale models could be performed. Specialized machining experiments were conducted on 70/30 brass materials using steel tools over a range of speeds, feeds, depths of cut and tool rake angles. At each operating condition studied, the friction coefficient and the shear factor, τk, were obtained. Based on the experimental results, it was determined that standard macroscopic theory for analyzing detailed friction mechanisms was insufficient in micro machining processes. An approach that utilized the shear factor, in contrast, was found to be better for decoupling the physical phenomena involved. Utilizing the shear factor as an analysis parameter, the parameters that significantly influence the friction in microscale machining process were ascertained and discussed.
Hybrid Magnetic Bearings for a Centrifugal Blood Pump
Authors: Ren Zhaohui , Jahanmir Said , Heshmat Hooshang , Walton James
Published: March 2009

A hybrid passive/active magnetic bearing system was designed for a rotary centrifugal blood pump being developed for long-term circulatory support for heart failure patients. This system consists of two axially spaced bearing combinations for complete magnetic levitation of the rotor using only a single-axis active control. Each bearing combination comprises a pair of axially oppositely polarized permanent magnet rings on the rotor and a similar pair in the stator housing for both radial support and axial bias flux, and an electromagnetic coil to actively control the rotor axial position. The design permits a relatively large radial clearance between rotor and stator, and provides sufficient radial/axial stiffness, active controllability over the desired axial travel of the rotor. The bearing characteristics were evaluated by electromagnetic finite element analysis. The prototype pump was fabricated and levitated using a PID controller with zero-force balance algorithm to stabilize the rotor in the thrust direction and minimize the power draw. The experimental results confirmed the efficacy of the proposed magnetic bearing design and associated control algorithm.
Device and Reliability Physics of Capacitive MEMS
Authors: Gusev Evgeni
Published: March 2009

Micro-electro-mechanical systems (MEMS) and its younger “brother” nano-electro-mechanical systems (NEMS) are fast growing fields. In fact, in many areas, it is now at a turning point from the initial phase of device concept research and prototyping to volume manufacturing. To large extent, this transition is due to better general understanding of MEMS devices, materials and processes, major advances in packaging methods, and, as a result, significantly improved reliability characteristics up to billions of operation cycles.
Shear Strength and Durability of Self Assembled Monolayer
Authors: Masuko Masabumi , Miyamoto Hiroya , Suzuki Akihito
Published: March 2009

A well-defined self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) on a very smooth Si wafer or glass disk was prepared and the tribological performance was studied using a glass ball and a steel ball as a counter specimen. Shear strength and durability of OTS-SAM were discussed considering a difference of the surface roughness of specimen couples.
Detection of the Asperity Contact Between Sliding Surfaces by Monitoring the Excitation of Resonant Oscillation Using the Fiber Wobbling Method
Authors: Itoh Shintaro , Fukuzawa Kenji , Hamamoto Yuya , Zhang Hedong , Mitsuya Yasunaga
Published: March 2009

In the head disk interface (HDI) of a magnetic recording system, lubrication caused by a monolayer thick lubricant film is necessary to achieve stable relative motion between a magnetic disk and a magnetic head. Viscoelastic properties of lubricant films should be clarified for improvement of lubrication performance, however, measurement methods have not been established yet. In this study, we present a new method precisely detecting the starting point of asperity contact of sliding solid surfaces in order to measure viscoelastic properties of the molecularly thin lubricant film on the magnetic disk.
Depletion of Moleculary Thin Lubricant Under Flying Head in Hard Disk Drives
Authors: Yanagisawa Kenji , Kawakubo Youichi , Yoshino Masato
Published: March 2009

In Hard Disk Drives, lubricants are very important materials to reduce head and disk wear. Therefore, it is necessary to know the lubricant depletion under flying heads. Lubricant depletion due to flying heads has been studied experimentally. We developed simulation program to calculate numerically the change in lubricant thickness under a flying head on a thin-film magnetic disk from 10nm thick lubricant film. In recent HDDs, the lubricants thickness has become molecularly thin and polar lubricants have been used. In this paper, we took account of thickness-dependent lubricants diffusion and viscosity in our simulations to calculate a 1.2 nm thick polar lubricant film used in recent HDDs. The simulated results considering the thickness-dependent diffusion and viscosity showed that depletion was small in molecularly thin lubricant films. We considered it necessary to include thickness-dependent diffusion and viscosity in lubricant depletion simulation.
Tribological Characteristics of Materials for MEMS/NEMS by Using Chemically Modified AFM Tip
Authors: Heo J. C. , Kim K. S. , Kim K. W.
Published: March 2009

Friction and adhesion tests were conducted in order to investigate the tribological characteristics of materials for MEMS/NEMS using AFM. AFM Si tips were chemically modified with self-assembled monolayer (SAM) derived from trichlorosilane like OTS and FOTS, and various materials such as Si, Al, Au, Cu, Ti, PMMA and PDMS were prepared for the tests. The friction and adhesion forces between AFM Si tip modified with SAM and MEMS/NEMS materials were measured and compared to those forces when AFM tip was uncoated. According to the results, however, the effect of SAM on the reduction of friction and adhesion could be changed with counterpart materials. After coating OTS on Si tip, the friction and adhesion forces on most of materials decreased while the friction and adhesion forces on PDMS rather increased than decreased. In case of the coating of FOTS, the friction and adhesion forces on PMMA540k and PDMS increased. Therefore, the adequate application of SAM would be required to effectively reduce friction and adhesion on each material for MEMS/NEMS.
Instrumentation of a Rolling Bearing With a Thin Film Piezo Coating for Oil Film Measurement
Authors: Dwyer-Joyce R. S. , Zhang J. , Drinkwater B. W. , Elgoyen J. , Kirk K. J.
Published: March 2009

This paper describes a novel design of oil-film monitoring sensor capable of measuring oil-film thickness in concentrated contacts. The approach is to use a thin (approx. 4 μm) sputtered coating of piezoelectric material, such as Aluminium Nitride. When correctly electroded this acts as an ultrasonic sensor with a usable bandwidth from 20–350 MHz. This sensor allows the interrogation of the small lubricated region between the ball and raceway without any special focusing requirements. Typically the dimensions of the contact region is less than a millimeter wide. This sensor system is then demonstrated experimentally on a deep groove ball bearing with the piezoelectric thin film on the external surface of the bearing outer raceway. The interaction of ultrasound with the oil-film is modeled using a quasi-static spring model and this allows properties such as film thickness to be extracted. The measured thicknesses are shown to agree well those obtained from classical elastohydrodynamic lubrication theory for the high bearing loads and low speeds where several data points can be collected from the contact during a ball passage. Measurement of oil film thickness in the region of 0.1–1 μm is demonstrated.
Tribology of Ultra-Thin Polymer Films Covalently Bonded to Silicon Surface: Effect of Molecular Structure
Authors: Satyanarayana N. , Sinha S. K.
Published: March 2009

The primary objective of the present study is to investigate the influence of the molecular structure (linear or with bulky side groups) of polymer films (of few nanometers thickness) covalently attached to Si surface on tribological properties. PE (polyethylene) and PS (Polystyrene) were selected to test the objective where PE has simple linear molecular structure while PS also has linear molecular structure but contains bulky benzene groups located at the side of the linear chain. PE and PS contains maleic anhydride groups and are chemisorbed onto the APTMS (3-aminopropyltrimethoxysilane) modified Si surface. AFM (atomic force microscopy), XPS (X-ray photoelectron microscopy) and water contact angle measurements are used to identify and characterize the polymer films. A micro-tribometer is used to identify the tribological properties in a sliding test using 4 mm diameter Si3N4 ball as the counterface. PE film has shown very low coefficient of friction and high wear durability when compared to PS film and moreover PS film did not show any improvement in the tribological properties when compared to bare Si surface. This study proves that even in film form polymer with linear molecular structure without the bulky side groups show good tribological properties and hence such polymers can be used as thin-films for reducing friction and wear of substrates, Si or other materials. The chemisorbed PE film may be able to find applications in micro-components made from Si surface as anti-stiction and anti-wear coating.
Leakage Studies With Seals for Solid-Oxide Fuel Cells
Authors: Green Christopher K. , Streator Jeffrey L. , Haynes Comas , Lara-Curzio Edgar
Published: March 2009

This research seeks to characterize the gas leakage of a mica-based compressive seal assembly in planar solid-oxide fuel cells through modeling and experiment. In particular, it is of interest to assess how certain physical parameters (i.e., seal material composition, compressive applied stress, and surface finish) affect leakage rates. Finite element analysis is used to determine the macroscopic stresses and deformations in the sealing interface, while a microscale contact mechanics analysis is employed to model the role of surface roughness on the mean interfacial gap at the interface. An averaged Reynolds equation from mixed lubrication theory is applied to model the leakage flow across the sealed interface, which is of nanometer to micrometer dimensions in the vertical direction. In conjunction with the mathematical modeling, leakage results are reported. For these tests, an annular Inconel tube was pressed against a stainless steel substrate, creating an annular sealing zone. The inside of the tube is pressurized with a test gas, the mass of which is monitored during the leakage experiment. Test results are compared to model predictions.
A Study of Antiwear Additive Film Build Up Using the MTM (Mini-Traction Machine)
Authors: Smeeth Matthew , Hamer Clive , Spikes Hugh A.
Published: March 2009

The measurement of lubricant film thickness under elastohydrodynamic (EHL) contact conditions is well established and a variety of experimental techniques have been used, the most accurate and widely used of which is optical interferometry. This lends itself particularly well to the study of the all-important mixed and boundary regimes, since the films are of the same order of magnitude as the wavelength of light. The vast majority of these studies have been made under pure rolling conditions, since the necessary optical coatings preclude the use of high sliding speeds within the critical thin fluid film regime. These conditions are however precisely those required to activate ZDDPs and other antiwear additives, making accurate ‘in situ’ optical studies of additive film build-up difficult. A modification to the existing MTM (mini-traction machine) has allowed steel on steel contacts to be run under high sliding speed conditions, thereby allowing antiwear additive reactions to occur. By optically measuring the film thickness of these reaction films as they form, in tandem with friction measurements, a full picture of both friction and reaction film build-up can be made. Using a novel LED (light emitting diode) light source and accurate calibration procedures, the film thickness of the whole contact area can be measured down to a few nanometres. This paper presents a study of the behaviour of standard additive combinations under realistic operating conditions and describes the rig in detail.
Rolling Fatigue Life and Reliability of Ball Screws
Authors: Shimoda Hirokazu , Shimizu Shigeo , Tosha Katsuji , Otani Yushi
Published: March 2009

The experimental formula based on Lundberg-Palmgren theory has been used for the calculation of basic dynamic load rating of ball screws because its contact state resembles that of angular contact ball bearings. However, the compatibility between the theoretical and the actual rating life of ball screws has not been yet confirmed by life tests and probability theory. The inherent properties of ball screws are also not considered in this formula. In this paper, the authors deal with the development of ball screw life test machine and fatigue life test for ball screws with a total number of 31 test samples. Type and occurrence location of the initial failure of each sample are investigated. The fatigue life test data are analyzed with two and three parameters Weibull distribution functions. The basic dynamic load rating of the ball screws are also estimated from the life test data. The results are summarized as follows: (1) Initial failures are generated at the surface of the balls and the nut raceway as a spalling. (2) The life distribution of the test data fairy well fits three parameters Weibull distribution function. (3) Basic dynamic load rating, which is estimated by the life test, is approximately in agreement with that of manufacturer’s catalog.
Effect of the Nature of Nitride Phases on the Micro Abrasion of Plasma Nitrided Sintered Iron
Authors: De Mello J. D. B. , Binder C. , Deme´trio V. B. , Klein A. N.
Published: March 2009

In the present investigation, the effect of plasma nitriding on the micro abrasion behavior of sintered unalloyed iron is investigated. Plasma nitriding was carried out using two different sets of operative parameters in order to produce microstructures composed of different dominant iron nitrides, e.g. Fe4N (γ) and Fe2–3N (ε), phases. Micro abrasive wear tests were carried out in a “free ball” micro abrasion tester using SiC slurries. The tribological parameters were kept constant during the tests. The ε phase microstructures presented a superior abrasion resistance.
The Failure of an Electric Engine Caused by the Seizure of the Porous Bearing
Authors: Krol A. , Giemza B. , Kaldonski T.
Published: March 2009

In the article, the investigative results of the elements of the electric engine, after failure, are described. A preliminary inspection showed that the engine breakdown was caused by the seizure of one of the porous bronze bearings mounted in the electric motor. The analysis of the results showed that the probable reason for the seizure was the presence of brown dust. The seizure process occurred only in bearing No. 2 and it was connected to its location within the structure of the air conditioner.
Biotribological Investigation of Multi-Tube Foot for Application in Medical Micro-Robot
Authors: Kim Y. T. , Kim D. E.
Published: March 2009

In recent years, efforts to develop micro-robots for medical applications have been expanding. One of the key design issues in such micro-robots is to attain adequate frictional interaction between the robotic foot and the organ tissue. Particularly, it is important to generate the necessary frictional force without damaging the tissue. In this work, a design for the robotic foot was developed based on the frictional behavior of a tube structure. Fundamental experiments were initially performed to understand the bio-tribological behavior of a single tube. Then the design was modified to a multi-foot structure to achieve adequate friction. Bio-tribological investigation of a multi-tube foot in contact with a small intestine specimen of a pig was conducted. Friction tests were conducted using a pin-on-reciprocator type bio-tribotester. It was found that the multi-tube foot shows stick-slip behavior when slid against the small intestine specimen. The major mechanism behind the stick-slip behavior was due to interlocking between the tubes and the surface structures of the intestine specimen. Results of this work may be utilized for optimum design of frictional surface of medical micro-robots and other biological devices.
Contact Failure Mechanisms in Ohmic-Type MEMS Switches
Authors: Adams George G. , McGruer Nicol E. , Chen Lei , Du Yan , Guo Z. J.
Published: March 2009

In this paper, we present some current research issues in contact failures in ohmic RF MEMS microswitches. Such experimental and modeling research encompasses contact mechanics (including elastic, plastic, and adhesive contacts) and the related phenomena of brittle and ductile separation. Furthermore the contact interface is not static, but rather is known to evolve over the lifetime of the switch. Also discussed are contamination failures.
Effects of Tooth Width on Gas Labyrinth and Windback Seals Operating at Low Pressure Ratios
Authors: Morrison Gerald L. , Lim Chae Hwan
Published: March 2009

The difference in leakage rates for labyrinth and windback seals is studied. It is determined that the leakage under the teeth of a windback seal is within ± 3% of a labyrinth seal with the same cavity/tooth design. The windback leaks an additional amount due to fluid passing through the long conduit composed of the continuous screw thread like channel. At low pressures and low differential pressures across the seal, the effect of tooth width upon the leakage in labyrinth and windback seals is opposite to the normal accepted standard of thinner teeth leak less.