bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of Matt Surface Topography in Aluminium Pack Rolling
Authors: Utsunomiya Hiroshi , Sutcliffe Michael P. F. , Shercliff Hugh R. , Bate Pete S. , Miller Dan B.
Published: November 2008

Roughening of the matt surface of pack rolled aluminium foil has been modelled. The model is based on the finite element method using isotropic plasticity. A distribution in material properties has been used to simulate the distribution of orientations through the material. The predictions of roughness show good quantitative agreement with the experiments.
Tribological Applications of WS2 (MOS2) Inorganic Fullerene-Like Nanoparticles as Solid Lubrication
Authors: Rapoport L. , Fleischer N. , Tenne R.
Published: November 2008

Fullerene-like WS2 (MoS2) nanoparticles (IF) have been studied in the past [1–3] Their efficacy as additives for lubrication fluids has been demonstrated. [4–5] Recently, IF-WS2 nanoparticles were confined inside a porous and densified bronze-graphite matrix, prepared by powder metallurgy (PM) technique. Substantial reduction in both friction and wear, and an increase in the critical load were observed [6]. New applications of IF nanopartcles as development of polymer nanocomposites, burnishing and friction of ceramic materials under severe contact conditions are presented in this work.
Analyzing Oil Analysis: Part One
Authors: Poley Jack
Published: November 2008

Some years ago this author coined the term “After Test Support” to indicate the need to look more deeply into Condition Monitoring test results in order to glean maximum value from a sampling program, specifically test results for Oil Analysis. The Oil Analysis industry has burgeoned over the last four decades, adapting information technology to its processes on a steady, ongoing basis, and with noteworthy success. But most of the technology has been applied to instrumentation improvements and to data acquisition, storage and delivery. On the other hand, very little technology has been applied to data evaluation and interpretation beyond statistical limit and trend setting. In particular, there is little in the way of expert system development to render routine maintenance advisories, let alone to assess component wear and other complex condition scenarios. This presentation will explore the development of Oil Analysis and its somewhat misdirected emphasis on testing rather than data interpretation, wherein the Oil Analysis process has nearly become a commodity. Next data analysis will be discussed, along with a unique software approach to rendering highly nuanced scenario analyses and other after-test support concepts, thereby creating a platform for truly maximized return on the Oil Analysis investment.
Applications of Impact Dynamics to Assessment of Composite Erosion Resistance
Authors: Hussainova Irina , Schade Klaus-Peter
Published: November 2008

Surface damage or material removal during particle target collision is the result of material response to the contact stresses. Energy dissipation under two bodies collision may be estimated by means of the coefficient of velocity restitution and friction. Approach of impact dynamic and experimental study of dynamic coefficients has been applied to clarify the composite material behaviour under conditions of solid particle erosion. It has been shown that the level of energy dissipation during application and value of dynamic coefficient of friction can be a good guide for material selection for the use in conditions of dynamic loading.
Determination of Turboprop Reduction Gearbox System Fatigue-Life and Reliability From Computer Generated Tests
Authors: Savage Michael , Zaretsky Erwin V. , Lewicki David G.
Published: November 2008

Two computational models for the fatigue life and reliability of a turboprop gearbox are compared with each other and with field data. The two models are (1) Monte Carlo simulation of randomly selected lives of individual bearings and gears comprising a gearbox and (2) life analysis of the bearings and gears in the gearbox using the two-parameter Weibull distribution and the Lundberg-Palmgren life theory. These results were compared with field life results from 75 gearbox failures. Field data for the gearbox resulted in an L10 life of 2100 hrs. and a Weibull slope of 1.3. The Lundberg-Palmgren method resulted in a calculated L10 life of 1735 hours and a Weibull slope of 1.17. For the life estimation produced by the Monte Carlo method, the median L10 life approached 1775 hours and the Weibull slope approached a value of 1.21. There is reasonably good engineering correlation between the life results obtained from the field data and those predicted from the Lundberg-Palmgren analysis and the Monte Carlo simulation.
Tribology Without Friction: Limited Travel Solid State Design Elements
Authors: Rivin Eugene I.
Published: November 2008

Many mechanical systems have components performing limited displacements relative to other components. Examples: meshing motions between teeth of power transmission gears; compensation motions in universal joints and Oldham couplings; wedge mechanisms of clamping devices including friction-based shaft-to-sleeve connections. Typical features of such connections are: high contact force magnitudes; high stiffness in one direction and low resistance to motion in the perpendicular direction(s); high motion sensitivity (ability to perform very small motions under small motive forces while subjected to high contact loads in a perpendicular direction); maintaining no-backlash connection in case of reversal of contact forces requiring the connection to be preloaded; low friction losses; small size and low cost of the connection; high durability combined with low maintenance requirements.
On the Wear Measurement and Calculation in Ball on Disc Test
Authors: Iliev Christo
Published: November 2008

The pin on disc test configuration is widely used in laboratory friction and wear testing of materials. The variant configuration ball on disc offer an advantage of the ball being self-aligned with respect to disc. Also, usage of ball allows for higher accuracy of wear measurement compared to ball weight loss evaluation.
Effects of Laser Surface Texturing on the Microstructure and Frictional Characteristics of Zirconia Surfaces Under Liquid and Solid Lubrication
Authors: Blau Peter J. , Qu Jun , Riester Laura
Published: November 2008

The production of dimple patterns in surfaces by laser surface texturing (LST) has received considerable interest. The current research characterized the effects of LST on the near-surface microstructures in transformation-toughened zirconia (TTZ) and investigated how dimpling can affect reciprocating frictional behavior under both liquid and solid lubrication. Microstructural characterization included scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning acoustic microscopy (SAcM), and nanoindentation testing. Fine-scale micro-cracks were observed in both the rims and bottoms of dimple craters. Most of the laser-affected zone is composed of very fine grains with diameters 125∼150 nm, but no grain structure was observed nearest the rim edges. The distribution of residual stresses around the dimples, induced by LST, was revealed by SAcM. Nanoindentation tests of TTZ indicated no significant differences in hardness or elastic modulus between the material near the dimples and in the bulk. Counterface materials in the flat-on-flat reciprocating sliding tests included silicon nitride and a galling-resistant stainless steel. Friction tests were conducted under both liquid (mineral oil) and solid (fine graphite powder) lubrication. Dimpling did not show measurable improvement on frictional behavior under the applied test conditions, although they were supposed to function as lubricant reservoirs and debris traps.
Widening Classical Wear Laws to the Concept of Third Body
Authors: Fillot N. , Iordanoff I. , Berthier Y.
Published: November 2008

During the second part of the twentieth century, many efforts have been done to model wear. Particularly, Archard proposes in 1953 [1] one of the first wear law, which is often written on the following form: dW/dt=K.P.V(1) with dW/dt the mass of detached particles from the rubbing materials per unit time, P the applied pressure, V the sliding speed and K the “wear rate”.
Integrated Design of Highly Loaded Sliding Surfaces of a Huge Ball-Joint
Authors: Samyn Pieter , Van Paepegem Wim , De Baets Patrick , Degrieck Joris , Leendertz J. S. , Suister Eric , Van Schepdael Ludo
Published: November 2008

The surfaces of a ball-joint (diam. 10 m and weight 680 tons) used for the rotation of two retaining walls of a storm surge near Rotterdam are initially covered with a sliding spray of MoS2 and PTFE, but suffer wear. Lubricants in heavy-loaded constructions should most likely be avoided, implying a new design of the sliding surfaces by incorporation of polymer discs into holes (diam. 250 mm and depth 32 mm) tapped onto the back-scales of the joint. This study comprises theoretical and practical analysis of the contact situation, using FEM and full-scale test equipment for verification of the local static and dynamic behaviour of the polymer parts.
Fluorocarbon Films Deposited by Deep Reactive Ion Etching for Stiction Minimization of MEMS Structures
Authors: Zhuang Yan Xin , Menon Aric K.
Published: November 2008

Fluorocarbon films, which can be used to minimize stiction of silicon microstructures, have been deposited by passivation process in deep reactive ion etching tool. The wettability, surface energy, nano-scale adhesive force, and thermal stability have been investigated by contact angle measuring system, atomic force microscopy (AFM) and ellipsometry. The fluorocarbon films are good for anti-stiction applications due to their high water contact angle (110°), low surface energy (14.5mJ/m2), low nano-scale adhesive force (33 nN) and high thermal stability up to 300°C.
Bearing Performance Limits With Grease Lubrication
Authors: Cann P. M. , Lubrecht A. A.
Published: November 2008

This paper has examined the influence of bearing design and operation in controlling lubricant supply to the contact zone. Grease lubricated contacts are liable to starvation and as a result the film thickness is reduced, this can result in surface damage or premature bearing failure. It is of obvious importance to know when starvation occurs and the effect of grease type, bearing design and operation on lubrication replenishment. The aim therefore is to develop a starvation parameter capable of predicting the operating limits for a particular bearing/grease system. A number of bearing design parameters are examined in the paper, these include cage design, ball spin and bearing size. Ball spin and cage effects can be efficient mechanisms for maintaining the lubricant supply to the track. Increased bearing size, line contact geometries and high load result in reduced lubricant replenishment of the contact. Using this analysis it will be possible to establish operating limits for families of bearings.
Tribological Properties of Boron Nitride Based Composites
Authors: Hussainova Irina , Kommel Lembit , Kybarsepp Jakob , Kimmari Eduard
Published: November 2008

Tribological properties of lightweight cubic boron nitride (c-BN) based composites under conditions of dry sliding and slurry erosion in sodium solution were studied. It was shown that c-BN based composite has a higher wear resistance as compared to WC-CoNi hard metals, TiC-Ni cermets and B4C-Al composites. This material was produced by SHS method followed by hot compaction. Binder phase consists of Ti, Fe, Cr, Ni and C. Within a stainless steel (FeCr25Ni11) binder phase, a secondary hard phase of TiC was found to be formed during production. Those ultra-fine sized spherical particles (up to 600 nm in diameter) were supposed to have a great influence on the tribological behavior of composite.
Tribological Properties of MEMS Materials Measured on a Small-Scale Device
Authors: Williams J. A. , Faszer K. L. D.
Published: November 2008

Micro-electro-mechanical systems, MEMS, is a rapidly growing interdisciplinary technology within the general field of Micro-Systems Technology which deals with the design and manufacture of miniaturised machines with major dimensions at the scale of tens, to perhaps hundreds, of microns. Because they depend on the cube of a representative dimension, component masses and inertias rapidly become small as size decreases whereas surface and tribological effects, which often depend on area, become increasingly important. Although MEMS components and their areas of contact are small, tribological conditions, measured by contact pressures or acceptable wear rates, are demanding and technical and commercial success will require careful measurement and precise control of surface topography and properties. Fabrication of small numbers of MEMS devices designed to test potential material combinations can be prohibitively expensive and thus there is a need for small scale test facilities which mimic the contact conditions within a micro-machine without themselves requiring processing within a full semiconductor foundry. The talk will illustrate some initial experimental results from a small-scale experimental device which meets these requirements, examining in particular the performance of Diamond-Like-Carbon coatings on a silicon substrate.
Finite Element Analysis on Critical Conditions for Heat-Induced Demagnetization in Head/Disk Sliding Continuous Contact
Authors: Liu Jinyi , Diao Dongfeng
Published: November 2008

A finite element analysis of head/disk sliding continuous contact was performed to investigate the fields of temperature rise and thermal stress due to friction heat, and to develop the critical conditions for heat-induced demagnetization of the disk. Sliding contact was continued for a sufficient time to attain a relatively constant maximum temperature magnitude. The characteristic temperature increasing with whole sliding time was presented under various operating conditions. The demagnetization map for hard disk was developed by combining the simulated results together with available demagnetization temperature, a critical temperature magnitude at which occurrence of demagnetization is observed.
Carbon Nanotubes and Onions as Lubricant Additives
Authors: Joly-Pottuz L. , Martin J. M. , Dassenoy F. , Vacher B. , Mieno T. , Ohmae N.
Published: November 2008

Most of lubricant additives used as friction modifier and anti-wear agents are mainly organic compounds containing sulphur and phosphorous. Their lubrication mechanism is based on a tribochemical reaction leading to tribofilm formation but also the formation of some harmful by-products. Inorganic nanoparticles (nanotubes, fullerenes, onions...), because of their unique morphology and very small size, could be envisaged for the replacement of such organic additives. The purpose of this work is to study and compare the tribological properties of different kinds of nanoparticles added and dispersed as additives to a lubricating base oil. Here, we are particularly interested in carbon nanotubes and graphite onions which were then tested and compared. Added to a poly-alpha-olefin (PAO) base oil, all nanoparticles tested show a reduction of both friction and wear of steel counterfaces. The detailed study of the concentration effect in PAO shows that 1wt% of nanotubes is sufficient to obtain good tribological properties. A structural modification of nanoparticles during friction was clearly evidenced by analytical TEM. In the case of nanotubes, flake-like wear debris made of amorphous carbon have been observed [1].
Inorganic Fullerene-Like Nanoparticles as New Lubricant Additives: A Drug Delivery Mechanism
Authors: Joly-Pottuz L. , Martin J. M. , Dassenoy F. , Schuffenhauer C. , Tenne R. , Fleischer N.
Published: November 2008

When dispersed in a synthetic polyalphaolefin (PAO) base oil, inorganic fullerene-like (IF-MS2) nanoparticles of metal dichalcogenides (IF-MoS2, IF-WS2, IF-NbS2) lead to a significant reduction of both friction and wear under boundary lubrication. The effect of the contact pressure on the tribological properties of IF nanoparticles is particularly interesting. Results show that the higher is the pressure, the lower is the friction coefficient. The effect of the concentration shows that, even used at a low concentration (0.1%wt), IF-MS2 is able to decrease friction (0.05) compared to base oil only (0.08). A steady state friction coefficient of 0.04 was reached with IF-WS2 at 1%wt in PAO. Friction-induced transformation of the IF-MS2 nanoparticles into H-MS2 single sheets was evidenced by High Resolution Transmission Electron Microscopy (HRTEM). Some of these superimposed sheets are found in incommensurate positions, thus possibly explaining the very low friction coefficient of 0.04 obtained with IF-WS2. In-situ Raman spectroscopy was performed during a friction test to follow this structural modification. The lubrication mechanism of IF-MS2 is very similar to a “drug delivery system”. A very low concentration of additives is sufficient and the activation is obtained by the opening of the nested structure, like in certain micellar structures. Furthermore, no chemical reaction is required to obtain interesting properties. Thus, fullerene-like nanoparticles are active at the very beginning of the test and even at ambient and low temperature.
Effect of Surface Textures in Highly Loaded Grease Lubricated Reciprocating Sliding Contacts
Authors: Jacobson S. , Ka¨lvesten E. , Pettersson U.
Published: November 2008

The influence of surface textures on the friction and surface damage of grease lubricated ball on flat fretting and short stroke reciprocating sliding has been investigated. The tested steel and DLC coated steel specimen were given eight different texture patterns and were compared with untextured ground and polished surfaces. The objective is to find optimum treatment of fretting surfaces to endure vibratory contact without suffering severe surface damage, by introducing lubricant supply between the surfaces within the area of contact. The friction evolution was continuously recorded. The friction and surface damage behaviour is discussed.
Nano-Objects and Their Influence on Properties of Motor Oils
Authors: Beklemyshev V. I. , Bolgov V. Ju. , Letov A. F. , Makhonin I. I. , Filippov K. V. , Aptekman A. G.
Published: November 2008

Results of researches of various nature nano-objects and tribotechnical researches of the motor oils containing nano-sized particles were examined.
EHD Contacts in Low-Amplitude Oscillatory Motion
Authors: Glovnea Romeo P. , Spikes Hugh A.
Published: November 2008

In some practical applications such as spline couplings or constant velocity joints, the machine components are subjected to a low amplitude lateral motion, very often oscillatory, so that conditions for a full elastohydrodynamic film to form are not completely realized. The questions that arise are what mechanism of lubricating takes place in such contacts and what is the influence of working parameters and lubricant properties on such mechanism? In the present study, a EHD contact formed between a flat and a ball is subjected to oscillatory-motion of amplitude ranging between one half to one contact diameter. High speed ultra-thin film interferometry is used to monitor the gap between the two solid surfaces. The influence of parameters such as load, frequency and amplitude of motion are investigated.
Effect of Graphite Content on Wear of Thermostable Graphite-Reinforced Plastics
Authors: Sytar V. I. , Burya A. I. , Burmistr M. V. , Danilin D. S. , Kabat O. S.
Published: November 2008

This article contains the examination of graphite-filled systems based on an aromatic copolyamide (poly-m-,-n-phenylen isophthalamide) - phenilon C1. Used as fillers are natural colloidal graphites ELP-B, B-1 and C-1 contained at the amount of 5 to 30 mass %. The results of investigations allowed to state that the type and content of filler has a substantial effect on tribotechnical properties of graphite-reinforced plastics. It has been found that phenilon containing 15–20 mass % of graphite C-1 possesses the best tribotechnical characteristics.
Nanoscale Fretting Study by Scanning Probe Microscopy (Keynote)
Authors: Varenberg Michael , Etsion Izhak , Halperin Grigory
Published: November 2008

Nanoscale fretting can be studied by using scanning probe microscopy (SPM) and a newly proposed “slip index” which provides unified approach to fretting on different scales. Various relevant issues such as production of colloidal probes and SPM calibration will be presented. Partial and gross slip nanoscale fretting tests with displacement amplitude from 5 to 500 nm and normal load from 15 to 28 μN will be described. Experiments show a substantial increase of the friction at the transition from partial to gross slip and a significant difference of damaged surfaces in the two fretting regimes.
Influence of Surface Modification on Aqueous Lubrication of Elastomers
Authors: Lee S. , Spencer N. D.
Published: November 2008

Water is generally not an efficient lubricant for most tribosystems due to its extremely low pressure-coefficient of viscosity. This barrier is less important, however, when elastomers are employed as tribopairs, since a low-pressure, conformal contact is readily achieved under these conditions, and thus the isoviscous-elastic lubrication (or soft elastohydrodynamic lubrication, “soft EHL”) mechanism can be activated. Isoviscous-elastic lubrication does not necessitate the increase of viscosity under pressure. The aqueous lubrication of elastomers, however, requires a careful control of surface properties of tribopairs since hydrophobic interactions between the sliding surfaces in water can result in the failure of lubricating films to form at low sliding speeds. In this context, we have investigated the influence of surface modification of an elastomer, poly(dimethylsiloxane) (PDMS), on its aqueous lubrication properties. A dramatic reduction in frictional forces has been observed upon hydrophilization by oxygen-plasma treatment when PDMS was slid against PDMS in an aqueous environment. A similar effect was also observed when the PDMS surface was coated with a variety of copolymers that possess amphiphilic characteristics. This effect is attributed to the removal of the strong hydrophobic interaction between PDMS surfaces in water, thereby enabling the soft EHL mechanism to predominate. This study demonstrates the significance of surface modification in allowing effective soft EHL of an elastomer to take place.
Tribological Study of Various Graphite Powders Sliding Against Steel
Authors: Schmitt M. , Bistac S.
Published: November 2008

With its high resistance, good hardness and electrical conductibility in the basal plans, graphite is used for many years in various tribological fields such as seals, bearings or electrical motor brushes, and also for applications needing excellent lubrication and wear-reducing properties. But thanks to its low density, graphite is at the moment destined for technologies for which the combination of the possibility of reducing the weight of the components, and the ability of enhancing their efficiency is a fundamental asset. This is especially the case in the aeronautical industry where composites containing carbon, and more particularly graphite, are more and more widespread. In this context, the friction and wear of industrially produced graphite powders were evaluated in order to identify promising tribomaterials for braking use. Six different powders (natural and synthetic) having various grains sizes, were tested when sliding against steel, under various applied normal loads. The morphological and structural modifications of the graphites were observed by Scanning Electron Microscopy and AFM, and analysed by Raman spectroscopy. A classification of the various graphite powders could thus be realised; the determining of the friction and wear mechanisms for the different materials, according to their own characteristics, as well as to the applied normal load, was also achieved.
The Thermoelastic Behavior of Thrust Washer Bearings Considering Boundary Lubrication and Asperity Contact
Authors: Jackson Robert L. , Green Itzhak
Published: November 2008

The behavior and life of a tilted flat thrust washer bearing is modeled by a comprehensive numerical code. The goal is to investigate the conditions that distress thrust washer bearings through numerical techniques. This work includes thermo-mechanical deformations (which have been neglected in previous studies). The thrust washer bearing supports non-axisymmetric loads within the planetary gear sets of automatic transmissions and consists of flat-faced washers placed between an idle helical gear and its contacting face. Various coupled numerical schemes model sliding friction, boundary lubrication, asperity contact, thermo-mechanical deformation, thermo-viscous effects, and full film lubrication. The model provides predictions of frictional torque, bearing temperature, hydrodynamic lift and other indicators of bearing performance. The experimental and numerical results show that the bearing is very susceptible to the mechanism of thermoelastic instability (TEI). Theoretical predictions indeed predict that the washer may operate in the range of TEI.
An Atomic Force Microscopy Indentation Study of Biomaterial Properties
Authors: Berger E. J. , Tripathy S. , Vemaganti K. , Kolambkar Y. M. , You H. X. , Courtney K.
Published: November 2008

Atomic force microscopy (AFM) is a powerful and increasingly common modality of biomechanical investigation, including imaging, force spectroscopy, and microrheology. AFM indentation of biomaterials requires use of a contact model for data interpretation and material property extraction, and a large segment of the scientific community uses the Hertz model or a close relative for small-scale indentation of thin, soft materials in high strain applications. We present experimental results and analytical/numerical modeling which lead to two main conclusions: (i) Hertzian mechanics are useful in a surprisingly large parameter range, including scenarios in which the underlying assumptions are seemingly violated, and (ii) the Hertz solution serves as a useful base from which power-series type solutions can be derived for a variety of non-Hertzian effects.
A Thermoelastic Investigation of Friction Phenomena
Authors: Berger E. J. , Deshmukh D. V. , Mackin T. J. , Xue X.
Published: November 2008

We have studied dynamic friction phenomena using a variety of experimental measurement approaches. We have combined thermoelastic stress analysis (TSA) and optical microscopy to measure both the stress field and the interface slip displacement in a model frictional contact. We use a plane stress, fiber pullout-type geometry to produce a line contact interface. The interface operated in the partial slip regime with no gross sliding. The stress field and slip displacement information allow us to construct a friction constitutive relationship directly from experimental data. We also use complementary interface modeling to physically interpret the experimental observations. The results suggest that the interface slip zone size is a nominally linear function of pullout force, while the interface slip displacement responds as a second-order function of distance along the interface. When combined, these observations suggest a scaling law for per-cycle energy dissipation of the form E ∼ Fo3, where Fo is the forcing amplitude. Experimental and modeling results are presented to support this conclusion.
Tribological Properties of Embedded Solid Lubricant Coatings Fabricated by Patterning Methods
Authors: Krzanowski James E. , Nunna Dyumani
Published: November 2008

In this work we have investigated the tribological properties of embedded solid lubricant coatings and compared them to monolithic and alloy films of the same constituents. Lithographic patterning methods were used to create two-component coatings in which columns of MoS2 were embedded in a Ti matrix. Coatings were deposited using rf sputter deposition, and co-deposition of MoS2 and Ti was used to deposit the alloy coatings. A pin-on-disk (POD) test was used to examine the frictional behavior and mechanical stability of the coatings, and was carried out in both low and high humidity conditions. Optical and scanning electron microscopy (SEM) was used to examine the morphology of the wear track after the POD test. Coatings of MoS2 alone were found to perform well under low-humidity conditions, but poorly under high humidity. Alloying of MoS2 with Ti was found to provide some improvement under high humidity. The patterned film, which consisted of 2 μm diameter pillars of MoS2, spaced 10 μm apart and embedded in a Ti film, was found to exhibit friction and wear properties superior to either Ti or MoS2 alone. The coatings investigated here have potential applications for cutting tools and metal forming dies that will enhance tool life and reduce the energy expended due to frictional forces.
Contact and Surface Problems in Adhesion, Friction, Indentation, and Cavitation Erosion Related to Space and Aeronautics Lubrication
Authors: Miyoshi K. , Street K. W. , Vander Wall R. L.
Published: November 2008

This paper presents fundamental studies and observations of the adhesion, friction, deformation, and fracture behavior of solid surfaces undergoing solid-to-solid contact and liquid-to-solid contact. Emphasis is on the basic material and structural characteristics, as well as the surface effects, in the tribological phenomena. First, the adhesion and friction behaviors of smooth, atomically clean surfaces of solid-solid couples in a clean environment are presented, and the friction mechanisms are described in terms of surface energy and ductility. The roles of interface species (dispersed carbon nanotubes as well as contaminant and oxide layers) are also considered. The importance of surface analytical techniques used both to understand the phenomena and mechanisms of adhesion, friction, deformation, and fracture and to define the associated problems is addressed. Secondly, deformation behavior of single crystals, such as MgO, subjected to hardness indentation and cavitation erosion is discussed. How the deformation behavior relates to crystal orientation and distribution of dislocations is explained. Thirdly, crack patterns in ceramics, such as diamond, generated by spherical indenters under normal loading are discussed in relation to the structures, impurities, and properties of the ceramics.
Characterization of Wear of a Soft Coating Deposited on Titanium Alloy During Fretting
Authors: Lee H. , Mall S. , Sanders J. H. , Sharma S. K.
Published: November 2008

Fretting behavior of Cu-Al coating on Ti-6Al-4V substrate was investigated with and without fatigue load. Soft and rough Cu-Al coating resulted in abrasive wear and a large amount of debris remained at the contact surface which caused an increase in tangential force during the fretting test under gross slip condition. Fretting in the partial slip condition also showed the wear of coating. To characterize wear, dissipated energies during fretting were calculated from fretting loops and wear volumes were obtained from worn surface profiles. Energy approach of wear analysis showed a linear relationship between wear volume and accumulated dissipated energy. This relationship was independent of fatigue loading condition and extended from partial slip to gross slip regimes.
Molecular Dynamics Simulations of Nanocomposite Diamond-Like Carbon
Authors: Gao G. T. , Schall J. D. , Van Workum K. , Mikulski P. T. , Harrison J. A.
Published: November 2008

A constant tension and constant temperature molecular dynamics simulation method was used in the calculations of the elastic constants of the nanocomposite systems. The nanocomposite systems contain a core of sp3 diamond structure surrounded by an amorphous carbon network. The simulation results show that the elastic properties of nanocomposites of diamond-like carbons are closely related to the size of the sp3 diamond core; the bigger the core, the larger the elastic constants, and the system becomes more anisotropic.
A Material Removal Rate Model Considering Interfacial Micro-Contact Wear Behavior for Chemical Mechanical Polishing
Authors: Jeng Yeau-Ren , Huang Pay-Yau
Published: November 2008

Chemical Mechanical Polishing (CMP) is a highly effective technique for planarizing wafer surfaces. Consequently, considerable research has been conducted into its associated material removal mechanisms. The present study proposes a CMP material removal rate model based upon a micro-contact model which considers the effects of the abrasive particles located between the polishing interfaces, thereby the down force applied on the wafer is carried both by the deformation of the polishing pad asperities and by the penetration of the abrasive particles. It is shown that the current theoretical results are in good agreement with the experimental data published previously. In addition to such operational parameters as the applied down force, the present study also considers consumable parameters rarely investigated by previous models based on the Preston equation, including wafer surface hardness, slurry particle size, and slurry concentration. This study also provides physical insights into the interfacial phenomena not discussed by previous models, which ignored the effects of abrasive particles between the polishing interfaces during force balancing.
Study of Lubricant Viscosity From Diesel Engine Operating on Various Percentages of Coconut Oil Blended Fuel
Authors: Varman M. , Faizul M. S. , Masjuki H. H. , Kalam M. A. , Mahlia T. M. I.
Published: November 2008

In this study, the lubricant viscosity from a diesel engine operating on various percentages of coconut oil blended fuel is investigated to determine the suitable mixture appropriate for a diesel engine. The coconut oil was blended with conventional diesel fuel at an amount varying from ten to fifty percent. The lubricant used in this study is the conventional commercially available lubricant (SAE 40). After proper blending of diesel with coconut oil, the blended fuels are loaded into the fuel tank. The engine is operated at half throttle setting running at 1600 rpm for 100 hours. At every ten hour interval, one lubricant sample was collected and analyzed using a viscometer at 100 °C and 40 °C. The results show that the viscosity for all the blended fuel remain about constant throughout the 100 hours test. However, fifty percent coconut oil blended fuel at 40 °C shows slightly lower viscosity level in comparison to other percentages of blended fuel system. It is expected this is due to high fuel dilution in lube oil. As a result, ten to thirty percent coconut oil blended fuels seems suitable for diesel engine because it’s able to prolong lubricant life span by maintaining its viscosity.
Numerical Analysis on Fatigue Failure of Sleeve in Oil-Film Bearing
Authors: Wang Jian-Mei , Huang Qing-Xue , Yang Shi-Chun
Published: November 2008

Due to the three-segment loop-like damage axially along inner surface of bearing sleeve under rolling loadcases, to quantitatively analyze damage mechanism, a mathematical model of oil-film bearing in the process of roll was developed by 3-D elastic contact boundary element method. A program of automatically creating 3-D surface grid model has been developed to check data and display deformation, the properties of stress and deformation fields have been analyzed, the rules of 3D contact pressure distribution among contact areas have been quantitatively described, which provided an effective way to decrease wear and adhesive damage of sleeve, and to increase load capacity of oil-film bearing and its service life as well.
Adhesive Component of Friction Between Rough Surfaces
Authors: Goryacheva I. G. , Makhovskaya Yu. Yu.
Published: November 2008

Adhesion forces associated with molecular attraction have substantial influence on the characteristics of contact and the friction force between highly smooth and chemically pure surfaces. Bodies coated by surface liquid films can also experience significant adhesive attraction due to capillary pressure in liquid menisci formed in the gap between such surfaces.
Finite Element Simulation of Metal Matrix Composites: Effective Coefficients of Friction and Temperature Fields Under Frictional Loading
Authors: Huber Christopher O. , Kremmer Sascha , Pettermann Heinz E.
Published: November 2008

Computational predictions on the tribological behavior of metal matrix composites (MMCs) are carried out. The influence of particle volume fraction and clustering of particles is investigated at different length scales. Finite Element simulations are performed on unit cells utilizing approaches from the field of ‘continuum mechanics of materials’. Models are based on the work of Segurado et al. [1], who used homogeneous, randomly distributed inclusions in a matrix phase with 30% particle volume fraction. In addition, the present work introduces modified unit cells with 10% volume fraction, with both homogeneous random and clustered distribution (Fig. 1). These modifications are derived from the original cell by either randomly removing inclusions in the first case, or from a predefined area in the second case.
Correlation Study of Functional Surface Parameters Based on Micro-Contact Analyses
Authors: Wang P. , Hua D. Y.
Published: November 2008

As well recognized, a functional surface finish can determine how well the surface wears, transmits heat, and distributes a lubricant. Among the large number of surface parameters available to describe surface finish requirements, the arithmetic mean of surface roughness, Ra, is the most specified surface finish parameter across most industries and applications. However, Ra may not fully describe the functional requirement of the surface. This study is focused on the selection of surface parameters based on local contact pressure, an important indicator of friction and wear. Surface parameters are obtained from measured or generated three-dimensional topographies. Surface performance responses, evaluated by local contact pressures, are calculated from micro-contact analysis based on the rough surfaces. The analysis of correlation, indicated by Pearson correlation coefficient that is a measure of correlation strength of linear relationship, is performed among these surface parameters and between surface parameters and responses. A set of functional parameters is identified to properly specify a surface evaluated by local contact pressure.
Identification of Bearing Force Coefficients in Flexible Rotors: Extensions to a Field Method
Authors: San Andre´s Luis , De Santiago Oscar
Published: November 2008

Rotor-bearing system characteristics, such as mode shapes and their associated natural frequencies and damping ratios are essential to diagnose and correct vibration problems during system operation. Of the above characteristics, reliable identification of fluid film bearing force parameters, i.e. stiffness and damping coefficients, is one of the most difficult to achieve, in particular during field operation. Results of an enhanced method to estimate support force coefficients in flexible rotor-bearing systems based on imbalance response measurements obtained near the bearing locations are presented herein. The procedure can be conducted on site with minimal instrumentation. A test flexible rotor mounted on two-lobe hydrodynamic bearings is used to validate the identification procedure. Imbalance response measurements for various imbalance magnitudes are obtained near the bearing locations and also at rotor mid-span. At shaft speeds around the bending critical speed, the displacements at rotor mid span are an order of magnitude larger than the shaft displacements at the bearings. The identification procedure renders reliable bearing force coefficients for shaft speeds between 1 krpm and 4 krpm. The sensitivity of the method and derived parameters to noise in the measurements is also quantified.
Wear Mechanisms in Dry Sliding Friction Tests of Copper Versus Steel
Authors: Enders S.
Published: November 2008

Dry sliding wear tests were performed using a ring-on-block configuration for copper sliding against steel. The wear mechanisms of this pair were investigated under different load ranges and sliding velocities. During the tests, the bulk temperature in the near-surface contact region was continuously recorded. The results of scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDS) and nanoindentation tests on the worn surfaces and the debris reveal a commanding role of the steel in the wear mechanisms of the pair. Additional tests of steel-steel pairs corroborate this assumption. It will be shown that the different wear mechanisms, which the steel experiences over the test range, markedly influence copper wear rates. Metallographic investigations on cross sections of copper samples show the formation of recrystallized layers on the worn surface at high sliding speeds. The onset of recrystallization is accompanied by extrusion of wear debris.
The Influence of Residual Stress on Micromachine Stiction of a Stiff Circular Plate
Authors: Wong Ming-Fung , Wan Kai-Tak , Kogut Lior
Published: November 2008

The notorious coupling of adhesion and residual membrane stress on the bridge of a MEMS-RF-switch and its effects on stiction failure are investigated. The previous model [1] of a thin flexible circular membrane with zero stiffness is here extended to thick stiff plate under bending. The mechanics of a film delaminating from a substrate is rigorously constructed based on an energy balance.
Transfer Film Lubrication for Ceramic Pairs at a Temperature of 800°C and a Pressure of 1300 Pa
Authors: Suzuki Mineo , Aoki Yoshio
Published: November 2008

Tribological performance of two types of Si3N4 pairs and one SiC pair was examined at a pressure of 1300 Pa and a temperature of 800°C. Prior to friction tests, a transfer film was formed from a self-lubricating composite in atmospheric environment. Test results showed that the transfer film acted effectively as a lubricant to prevent surface damage and lower friction for Si3N4 pairs, but it was not effective for the SiC pair. This result confirms that transfer film lubrication is one of promising candidates of lubrication methods for re-usable space vehicles, in which operation at high temperature in low vacuum is required.
Experimental Study of High-Speed Contact at Head-Disk Interface in a Magnetic Hard Disk
Authors: Bai Mingwu , Hsu Stephen M.
Published: November 2008

Tribological performance of the head-disk interface will have significant impact on the performance and durability of the hard disk drive. A high-speed contact test method has been developed for the purpose of evaluating nanometer-thick lubricant film/carbon overcoats materials on hard-disk surfaces. Four different thickness overcoats were used in high speed contact experiments. High speed contact force was calculated based on the calibration of acoustic emission signal by proposed ball dropping tests. Acoustic emission analysis, frequency spectrum analysis, and surface morphology imaging were used to analyze the deformation and fracture at high speed contacted area. The availability of an experimental technique enables effective screening of different material chemistries and lubricant combinations to improve the level of protection for hard disk technology.
Characteristics of Powder Lubricated Finite-Width Journal Bearings: A Hydrodynamic Analysis
Authors: Tsai Hung-Jung , Jeng Yeau-Ren
Published: November 2008

In this paper, the average lubrication equation for grain flow is solved using a control volume method to analyze the performance of hydrodynamic journal bearings. The grain particle size effect was investigated. The nondimensional load and friction coefficient are demonstrated in terms of eccentricity ratios under various diameter-to-width ratios. The results demonstrate the performance of powdered lubricated journal bearings, and also accord with the results experimented by Heshmat and Brewe.
Wear of Crosslinked UHMWPE in a Hip Joint Simulator
Authors: Galvin A. L. , Ingham E. , Fisher J.
Published: November 2008

Crosslinking has been extensively introduced to reduce the wear of UHMWPE. In this study the wear rates and wear surfaces of UHMWPE with different levels of crosslinking were compared in a hip joint simulator. The UHMWPE was either non-irradiated, gamma irradiated in air (2.5MRad), or highly crosslinked (7.5 and 10MRad). The intentionally cross-linked materials showed a significantly lower volume change compared to the non-crosslinked UHMWPE. The results of the surface topography of the acetabular cups showed that the highly crosslinked materials became smoother than the other materials as the test progressed. This would benefit the crosslinked materials in aiding lubrication. Finite wear rates have been recorded for the first time in simulator studies with highly crosslinked polyethylene. The wear rates and wear surfaces compare with those found in clinical studies.
Testing and Comparative Evaluation of Space Shuttle Main Engine Flowmeter Bearings
Authors: Hissam D. Andy , Leberman Mike , McLeroy Rick
Published: November 2008

This paper provides a summary of testing of Space Shuttle Main Engine (SSME) flowmeter bearings and cage material. This testing was conducted over a several month period in 2004 at the Marshall Space Flight Center (MSFC). The test program’s primary objective was to compare the performance of bearings using the existing cage material and bearings using a proposed replacement cage material. In order to meet the test objectives for this program, a flowmeter test rig was designed and fabricated to measure both breakaway and running torque for a flowmeter assembly. Other test parameters, such as motor current and shaft speed, were also recorded and provide a means of comparing bearing performance. The flowmeter and bearings were tested in liquid hydrogen to simulate the flowmeter’s operating environment as closely as possible. Based on the results from this testing, the bearings with the existing cage material are equivalent to the bearings with the proposed replacement cage material. Therefore, the new cage material is a suitable replacement for the existing cage material.
Biotribology: The Wear Resistance of Repaired Human Articular Cartilage
Authors: Steika Nils A. , Furey Michael J. , Veit Hugo P. , Brittberg Mats
Published: November 2008

Normal, mature articular cartilage does not spontaneously repair itself back to hyaline cartilage after an injury or degenerative disease (e.g., osteoarthritis)—problems of increasing importance in an aging population. A promising new approach is to repair damaged cartilage by a method known as Autologous Chondrocyte Implantation (ACI)—a technique pioneered and further developed by the Cartilage Research Unit at Goteborg University in Sweden. However, the tribological properties of the repaired cartilage, including the important property wear-resistance, are unknown. How durable is the repaired cartilage? How long will it last? One of the co-authors, Dr. Mats Brittberg, has provided 16 samples of 2mm diameter human biopsies from the knees of eight Swedish patients for testing in our biotribology device. This paper presents results of wear experiments on cartilage repaired by Brittberg’s ACI technique and, for comparison, two other methods. Four of these samples (2 pairs) were from patients who had undergone the ACI procedure while another four were from those who had other methods of repair. A pair consists of a biopsy from the repaired area of the joint along with a sample from nearby “healthy” cartilage from the same joint. Thus, each pair allowed for a direct comparison of the tribological properties of the repaired cartilage to those of “normal” cartilage from the same joint. The results of this study show that the ACI method of cartilage repair gave substantially less wear than that of normal cartilage while spontaneous repair and abrasion arthroplasty produced higher wear. Friction levels were in the boundary lubrication regime and, in line with our previous experience, had no correlation with wear. Results obtained with cartilage from the remaining patients will be discussed in future papers.