bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Conductance of Individual Single-Wall Carbon Nanotubes
Authors: Pettes Michael T. , Shi Li
Published: June 2009

This work presents an experimental study of phonon transport in individual suspended single-wall carbon nanotubes (SWCNTs). Through the use of a micro fabricated device consisting of two adjacent suspended membranes, each with a platinum resistance heater and thermometer, the thermal conductance of several individual SWCNTs has been directly measured over the temperature range of 100 to 490 K. The effects of Umklapp phonon-phonon scattering remain weak and the thermal conductance remains roughly proportional to the calculated ballistic conductance throughout the temperature range. The macroscopic thermal conductance increases with temperature throughout the temperature range indicating static scattering processes or contact thermal resistance dominate transport in this regime. These results are an order of magnitude lower than the predicted ballistic thermal conductance calculated for a defect-free (18,0) nanotube. The results contrast with thermal conductance measurements reported using a high-bias DC self heating method. The discrepancy is discussed in terms of the differences in the contact thermal resistance, defects, and measurement methods.
A Computational Study of Catalytic Platinum Nanoparticles With and Without OH Chemisorption During Reactions
Authors: Sekachev Mikhail , Lin Cheng-Xian , Hu Zhiyu , Dareing Don
Published: June 2009

In this paper, various energies and geometries of pure platinum nanoparticles and those of platinum nanoparticles with adsorbed OH were investigated. Ten different platinum clusters of up to 28 atoms were studied using spin-unrestricted density functional theory (DFT) with a double numerical plus polarization basis set. Three different shapes were presented, and the effect of cluster size on binding energy, total energy, and HOMO-LUMO energy gap was investigated. The same set of calculations was performed for selected clusters with OH adsorbate on the Pt(111) surface. The results show that the stability of both the pure clusters and the clusters with adsorbed OH molecule increases with an increase of cluster size. This fact indicates that direct influence of the size of Pt cluster on the reaction rate is possible, and the understanding of how cluster size would affect binding energy is important. The effect of cluster size on total energy of molecule was shown to be a linear function independent of cluster type, as expected. We also found that optimized (stable) Pt clusters were bigger in size than that of the initial clusters, or clusters with bulk geometry.
Photo- and Thermionic Emission From Potassium-Intercalated Single-Walled Carbon Nanotube Arrays
Authors: Westover Tyler L. , Franklin Aaron D. , Fisher Timothy S. , Reifenberger Ronald G.
Published: June 2009

Vacuum thermionic electron emission has been considered for many years as a means to convert heat or solar energy directly into electrical power. However, an emitter material has not yet been identified that has a sufficiently low work function and that is stable at the elevated temperatures required for thermionic emission. Recent theoretical models predict that photonic and thermal excitation can combine to significantly increase overall efficiency and power generation capacity beyond that which is possible with thermionic emission alone. Carbon nanotubes (CNTs) intercalated with potassium have demonstrated work functions as low as 2.0 eV, and low electron scattering rates observed in small diameter CNTs offer the possibility of efficient photoemission. This study uses a Nd:YAG laser to irradiate potassium-intercalated single-walled CNTs (K/SWCNTs), and the resultant energy distributions of photo- and thermionic emitted electrons are measured using a hemispherical electron energy analyzer for a wide range of temperatures. We observe that the work function of K/SWCNTs is temperature dependent and has a minimum of approximately 2.0 eV at approximately 600 K. At temperatures above 600 K, the measured work function K/SWCNTs increases with temperature, presumably due to deintercalation of potassium atoms.
Development of a Scanning Transient Harman Method for Thermoelectric Properties Characterization
Authors: Castillo Eduardo E. , Borca-Tasciuc Theodorian
Published: June 2009

Low-dimensional nanostructures and nano-composites may demonstrate a large enhancement of the thermoelectric figure of merit ZT, therefore measurements of their thermoelectric properties are of high interest. Techniques able to screen the thermoelectric properties of a large number of samples and also to measure the spatial distribution of thermoelectric properties in a specimen are needed. This work explores a scanning transient technique for thermoelectric characterization of thin films based on the Harman method. A one dimensional theoretical model was used to investigate the appropriate experimental setup and the effect of a scanning electrode/thermal probe contacting the top surface of the specimen. Results indicate that for micrometer thick films of ZT∼1 small current values of the order of mA and electrical contact resistance below 1 Ω are necessary to minimize the Joule heating effects and to take advantage of the Peltier effect when employing the bipolar technique. A proof of concept experiment was performed on an n-type Bi2Te3 pellet used in a commercial thermoelectric device. The experiment lays out the strategy to extract the thermoelectric properties. Seebeck coefficient of −241 μV/K and thermal conductivity of 1.48 W/m.K were obtained from the transient Harman method when the data reduction model included energy losses through the wire. These results prelude the feasibility of the scanning technique on thin film samples.
Thermal Rectification by Ballistic Phonons
Authors: Miller John , Jang Wanyoung , Dames Chris
Published: June 2009

In analogy to the asymmetric transport of electricity in a familiar electrical diode, a thermal rectifier transports heat more favorably in one direction than in the reverse direction. One approach to thermal rectification is asymmetric scattering of phonons and/or electrons, similar to suggestions in the literature for a sawtooth nanowire [1] or 2-dimensional electron gas with triangular scatterers [2]. To model the asymmetric heat transport in such nanostructures, we have used phonon ray-tracing, focusing on characteristic lengths that are small compared to the mean free path of phonons in bulk. To calculate the heat transfer we use a transmission-based (Landauer-Buttiker) method. The system geometry is described by a four-dimensional transfer function that depends on the position and angle of phonon emission and absorption from each of two contacts. At small temperature gradients, the phonon distribution function is very close to the usual isotropic equilibrium (Bose-Einstein) distribution, and there is no thermal rectification. In contrast, at large temperature gradients, the anisotropy in the phonon distribution function becomes significant, and the resulting heat flux vs. temperature curve (analogous to I-V curve of a diode) reveals large thermal rectification.
Characterization of Contact Damping and Frequency in Elastic-Plastic Contact
Authors: Sepehri A. , Farhang K.
Published: June 2009

Elastic-plastic interaction of a block of rough surface with a smooth plane is considered in this paper. The nonlinear normal vibration response of the block is examined when subject to an external compressive load. Free vibration response of the block is studied. The vibration response corresponds to the application of a constant compressive external load and the study yields closed-form equations for the contact damping rate and contact natural frequency. It is shown that vibration decay rate is constant as opposed to the exponential decay rate for the linear vibrating systems. Closed form equations relating contact damping rate and contact natural frequency to the surface parameters are given.
Superlubricity of Steel Surfaces in Presence of Polyhydric Alcohols
Authors: de Barros Bouchet M. I. , Matta C. , Martin J. M. , Joly-Pottuz L.
Published: June 2009

Anomalous low friction of hydrogen-free tetrahedral hybridized carbon (ta-C) coated surfaces lubricated by pure glycerol was observed at 80°C. In the presence of glycerol, the friction coefficient is below 0.01 at steady state, corresponding to so-called superlubricity regime. This new mechanism of superlow friction is attributed to easy glide on tribo-formed OH-terminated surfaces. In addition to the formation of OH-terminated surfaces but at a lower temperature, we show here some evidence that superlow friction of polyhydric alcohols could also be associated with tribo-induced degradation of glycerol, producing a nanometer-thick film containing organic acids and water. Second, we show novel outstanding superlubricity of steel surfaces directly lubricated by a solution of myo-inositol in glycerol at ambient temperature (25°C). For the first time, under boundary lubrication at high contact pressure, friction of steel is below 0.01 in the absence of any long chain polar molecules. Mechanism is still unknown but could be associated with friction-induced dissociation of glycerol and interaction with steel surface.
Thermal Study of the Dry Sliding Contact With Third Body Presence
Authors: Richard David , Renouf Mathieu , Berthier Yves , Iordanoff Ivan
Published: June 2009

The objective of this paper is to highlight the influence of the rheology of a third body in dry sliding contact conditions. It has been shown that the local cohesion of the third body can create an asymmetric dissipative field through its thickness. The present study puts forward the consequences from a thermal point of view, overcoming the inherent experimental difficulties at this microscopic scale.
Tribological Performances and Mechanism of Bismuth Dialkyl-Dithiocarbamate Additive
Authors: Zhang Yi , Luo Yan , Hu Jian-Qian , Zhang Tao , Xu Yun-Yun
Published: June 2009

A four-ball tester was used to evaluate the tribological performance of bismuth diamyl-dithiocarbamate in mineral oil, and compared with same types of metal additives. The results show that it exhibits better load-carrying capacities than said organic metal additives. The surface analytical tools such as X-ray photoelectron spectrometer (XPS) and Scanning electron microscopy (SEM) were used to investigate the topography, the compositions contents and the depth profile of some typical elements on the rubbing surface of worn scar. Smooth topography of worn scar further confirms that the additive showed good antiwear capacities, the results of XPS indicated that tribochemical mixed protective films consists of bismuth compounds, sulfides, sulphates and metal oxides, which contribute to improve the tribological properties of lubricants. Particularly, a larger number of bismuth containing compounds play an important role in improving extreme pressure properties of oils.
Post-CMP Cleaning Applications
Authors: Khosla V. , Vinogradov M. , Gitis N. V. , Singh R. K. , Stockbower D. W. , Wargo C. R.
Published: June 2009

CMP process yield depends on effectiveness of a post-CMP cleaning, which should reduce roughness of the polished wafer and leave it defect-free, consistently removing particles, organic residues, and ionic contamination. This paper presents an overview of wafer cleaning attributes, challenges and opportunities. The cleaning effectiveness depends on the stability of brush PVA (Poly Vinyl Alcohol) properties, magnitude of brush-wafer frictional force, and the adhesion forces between the particle and wafer, and the particle and brush.
Modeling the Pressure and Temperature Dependence of Viscosity and Volume for Hydraulic Fluids
Authors: Bair Scott , Michael Paul
Published: June 2009

Viscosity and compressibility have a major impact upon the efficiency and dynamic response of fluid power systems. The viscosity and compressibility of five hydraulic fluids have been measured for temperatures to 150 C and pressures to 350 MPa. A new correlation of viscosity with temperature and pressure based on the thermodynamic scaling rule of Roland et al is offered. This correlation provides a means to extend the accuracy of fluid power system models to higher pressures.
Wear Between Human Cartilage Surfaces
Authors: Verberne Gabi , Merkher Yulia , Halperin Gregory , Maroudas Alice , Etsion Izhak
Published: June 2009

The present paper describes wear tests performed using human cartilage on cartilage under various working conditions. Wear was assessed by determining the concentration of proteoglycans (PG) and hydroxyproline in the lubricating solution.
Effect of Temperature on the Spreading Characteristics of Molecularly Thin Liquid Lubricant Films in Hard Disk Drives
Authors: Tagawa Norio , Mori Kenta , Mori Atsunobu , Ikegami Masako
Published: June 2009

In this study, the effect of temperature on the spreading characteristics of ultra-thin liquid lubricant films in hard disk drives (HDD) was investigated by using three types of lubricants, namely, Zdol2000, Ztetraol2000, and A20H2000. The apparent diffusion coefficient of individual lubricants was evaluated and compared by varying the temperature of disk substrates. As a result, it was found that the mobility of each lubricant increases with the temperature. However, the rate of mobility increase is different for each lubricant, depending on the lubricant material. Furthermore, there exists no quantitative correlation between the mobility increase for ultra-thin liquid lubricant films and the viscosity decrease in bulk lubricant materials due to a rise in the temperature. It was also found that among the test lubricants, A20H2000 has the highest robustness for temperature change. In addition, it could be observed that the evaporation of the mobile fraction of lubricants occurred remarkably over a temperature range of 50– 80 °C.
Lubricating Film Thickness Measurements on Bovine Serum
Authors: Mavraki A. , Cann P. M.
Published: June 2009

In this paper lubricant film thickness for bovine serum (BS) was measured in a ball-on-disc optical device under steady-state rolling and sliding. Tests were carried out for a range of BS concentrations and substrate materials (M52100 steel and chromium coatings) in both low (MPa) and high-pressure (GPa) configurations. The results show that BS forms films 2–50 nm thick over the speed range although this depends on the contact pressure. However there was significant scatter in these results, possibly due to the inherent nature of the fluid, which is an inhomogeneous biological sample. Clearly this will contribute to scatter in wear results. In some cases thick (up to 100nm) films were formed at low speeds under both sliding and rolling conditions, this behaviour was considered representative of high-viscosity surface layers rather than solid films. However residual films of 13–17nm were also measured under static loading. These are attributed to the adsorption of protein molecules and will provide surface protection during stance or on initiation of gait. A small number of results at under low pressure sliding conditions indicated that much thicker films were formed than at high pressures. One interesting aspect of the results is that they are not representative of a simple Newtonian fluid and thus have considerable implications for the development of predictive film thickness models.
Theoretical Effects of Contaminant Particles on the Lubrication Considering Particle Rotation
Authors: Han Haiyan , Zhang Youyun , Zhong Zhenyuan
Published: June 2009

The model of a lubrication problem involving a Newtonian fluid with the contaminant particle smaller than the minimum film thickness is developed. The interaction of fluid and particle is considered in the model. The behavior of a particle in the lube oil is also studied. The lube oil is regarded as the continuum phase, and the lubrication problem is solved by the modified Reynolds equation to determine the film pressure and velocity. The dynamics of a particle in the lubricant are studied using Newton’s second law to determine the particle velocity, angular velocity and displacement. The effects of the particle motion including translation and rotation on lubrication characteristics are analyzed. The effect of relative velocity between particle and oil on the pressure is also discussed. The results indicate that the particle motion has a significant effect on the film pressure distribution. When the particle velocity is lower than the film velocity, the motion of particle causes a significant pressure increase. This high pressure only lasts a short time if the particle rotation is neglected. However, when considering the particle rotation, the high pressure will last a much longer time.
Cyclic Loading of an Elastic-Plastic Adhesive Contact
Authors: Kadin Y. , Kligerman Y. , Etsion I.
Published: June 2009

A numerical simulation is presented for several loading-unloading cycles of an adhesive contact between an elastic-plastic sphere and a rigid flat. The main goal of the simulation is to study the plastic deformation evolution in a contact bump material — the microscopic electrode found in a MEMS micro-switch for providing a good electric contact. This bump is subjected to a cyclic contact interaction with a harder substrate and cyclic plasticity of the bump material can lead to its wear and as result to a failure of the whole MEMS device.
Synthesis, Characterization, and Tribological Applications of Nanomaterials
Authors: Liang Hong
Published: June 2009

Nanomaterials play important roles in tribolgy and manufacturing. This lecture provides an opportunity for us to review and learn the knowledge and techniques that have been involved in nanomaterials and nanotribology areas. Targeting tribological applications, a brief history of nanoparticulates, dated back more than 2500 years, will be given briefly. The classification and synthesis of nanoparticles will be followed by nanomaterils and nanocomposites, their characterization techniques, and mechanical, tribological, chemical, and physical properties. Discussion ends with summary of applications.
Frictional Heating Effect on the Propagation of Surface Crack Under Hertzian Contact Loading
Authors: Kim Sang-Woo , Kim Seock-Sam
Published: June 2009

In this paper frictional heating effect on the propagation of surface crack under Hertzian contact loading based on the fracture mechanics is investigated. For theoretically analyzing this effect, we estimated stress intensity factor of surface crack-tip in shear mode under Hertzian contact sliding friction. Theoretical results showed that thermal load (Th), Peclet number (Pe) and crack angle (β) are very important factors on the propagation of surface crack under Hertzian contact loading. When thermal load (Th) and Peclet number (Pe) are constant, maximum variable range of stress intensity factor, ΔK II, is located in the range of surface crack angle 130°∼150°.
An Adhesive Wear Model of Fractal Surfaces in Normal Contact
Authors: Yin X. , Komvopoulos K.
Published: June 2009

A generalized adhesive wear model was derived for three-dimensional fractal surfaces in normal contact. A criterion for wear particle formation was derived based on the critical asperity contact area for fully plastic asperity deformation, taking into account the contribution of the adhesion force to the total normal load applied at the contact interface. The analysis yields a relationship of the adhesive wear coefficient in terms of total normal load (global interference), fractal parameters, elastic-plastic material properties, surface energies, material compatibility, and interfacial adhesion characteristics of the contacting rough surfaces. Numerical results of the wear coefficient of representative engineering material systems illustrate the roles of global interference and interfacial adhesion conditions (lubrication effect) in adhesive wear of surfaces in normal contact.
Evaluation of Rayleigh Plesset-Based Cavitation Models for Squeeze Film Dampers
Authors: Gehannin Je´roˆme , Arghir Mihai , Bonneau Olivier
Published: June 2009

This work is intended to evaluate a cavitation model based on the complete Rayleigh Plesset (RP) equation for use in squeeze film damper (SFD) calculations. The RP equation governs the variation of the radius of the cavitation bubbles at rest, surrounded by an infinite incompressible fluid and subject to an external pressure. This equation is obtained from the momentum equation and it takes into account the ensemble of the phenomena related to the dynamics of the bubbles (surface tension, damping, inertia). All the terms in the RP equation will be taken into account in the present work. Numerical results will be compared with experimental data obtained by Adiletta and Pietra [1]. The results then underline the influence of the effects contained in the RP equation on the pressure field.
Improved Tribological Performance of Tribo-Pairs by Optimization of Sliding Speed: Implications for Hot Forming Processes
Authors: Franetovic Vjekoslav
Published: June 2009

The tribology of hot forming processes is highly critical for the quality of formed aluminum panels and the cost-effectiveness of hot forming. In this report a flat-on-flat experimental technique for tribological evaluation of a single stroke was used to investigate the effect of sliding speed on the operative friction coefficient (FC) and tribological failure of the tribo-pairs used in Quick Plastic Forming (QPF) and warm forming processes.
Modification of Surface and Tribological Properties of DLC Films by Adding Silver Content
Authors: Zhang H.-S. , Endrino J. L. , Anders A.
Published: June 2009

The incorporation of silver into the diamond-like carbon (DLC) coatings has shown excellent potential in various applications; therefore the surface and tribological properties of silver-containing DLC thin films deserve to be investigated. In this study we have deposited silver-containing hydrogenated and hydrogen-free DLC coatings by plasma immersion ion implantation and deposition (PIII-D) methods. Atomic force microscopy (AFM) and nano-scratch tests were used to study the surface and tribological properties. The silver incorporation had only slight effects on hydrogenated DLC coatings. However, the incorporation of silver has significant effect on hydrogen-free DLC of smoothing the surface and increasing the surface energy. Those effects have been illustrated and explained in the context of experimental results.
An Investigation to the Effect of Elastic Deformations of the Bearing Surface of EP Air Bearings
Authors: van Beek Anton , van Ostayen Ron , Munnig Schmidt Rob
Published: June 2009

In this paper a study is presented towards the effect of elastic deformation of the bearing surface of axial externally pressurized centrally pivoted modular air bearings. To this purpose shallow pocket, tapered and grooved air bearings are selected, which look the most promising to apply in small dimensions and with very small film thickness. The elastic deformation is calculated numerically by simultaneously solving the 2D-Reynolds equation for compressible fluids and the 3D-elasticity equation. The effect of the elastic distortion on the bearing performance is visualized in graphs presenting the load capacity and flow as a function of the film thickness. The results obtained from numerical calculation are verified experimentally.
Numerical Analysis of Contact Mechanics Between Spherical Slider and Disk Due to Intermolecular Forces
Authors: Ono Kyosuke
Published: June 2009

A numerical method for analyzing the elastic contact mechanics due to intermolecular forces between a spherical slider and a disk is presented and typical results for a 1-μm radius sphere (which simulates a roughness asperity), 2-mm radius sphere (test slider), and 10–30-mm radius spheres (magnetic head sliders) are given. A numerical method for evaluating intermolecular forces at contacting asperities is also presented.
Application of Degradation-Entropy Generation Theorem to Dry Sliding Friction and Wear
Authors: Bryant Michael D. , Khonsari Michael M.
Published: June 2009

The Entropy Generation Theorem recently formulated by Bryant, Khonsari and Ling [1] relates any form of degradation to the irreversible dissipative processes germane to the degradation mechanism. The theorem was formulated and proved [1] based on the first and second laws of thermodynamics In this article, dry sliding wear will be related to dry sliding friction through application of the theorem. The result reproduces the Holm-Archard wear law, but with a wear coefficient based on measurement of temperatures and wear volume lost.
Flying Clearance Distribution With Thermo-Mechanical Actuation of Hard Disk Drive
Authors: Lee Sung-Chang , Tyndall George W. , Suk Mike
Published: June 2009

Flying clearance distribution with thermo-mechanical actuation is characterized. Especially, what factors contributing to variation of flying clearance are identified based on thermo-mechanical actuation profiles taken from burn-in process of hard disk drives and Gage R&R test of touch down repeatability. In addition, the effect of static temperature compensation scheme on flying clearance distribution is investigated and disadvantages of static adaptation to temperature change are identified. In order to avoid catastrophic early HDI failures due to poor static temperature compensation, we need to dynamically adjust flying clearance whenever environmental change is detected. Otherwise we need to utilize individual temperature sensitivity values of each flying head to adjust thermo-mechanical actuation amount accordingly with temperature change.
Rolling-Sliding Laboratory Tests of Friction Modifiers in Leaf Contaminated Wheel-Rail Contacts
Authors: Arias-Cuevas Oscar , Li Zili , Lewis Roger , Gallardo-Hernandez Alberto
Published: June 2009

Leaf-related low adhesion problems have been present in many railway networks all over the world in the last decades. One of the counter measures adopted by many railway networks is the use of friction modifiers. However, the effectiveness of these friction modifiers is not well proven yet due to the lack of research in controlled conditions. In this paper, a laboratory study of a widely used friction modifier is presented together with another adhesion enhancer designed for wet wheel-rail contacts due to rainfall. A twin-disk roller rig has been used to investigate their performance in leaf contaminated contacts. The adhesion characteristics of both friction modifiers were examined for different slip ratios. The constituents of the friction modifiers are identified and their suitability for leafy contacts is evaluated.
Alternative to ZDDP Additive: Study of Zinc Dialkylphosphate Lubricant Properties
Authors: Minfray Clotilde , le Mogne Thierry , Martin Jean-Michel , Tsujimoto Teppei , Igarashi Jinichi
Published: June 2009

The friction and wear behavior of ZP additive is investigated as an alternative to ZDDP (poisonous for catalyst-based emission control systems). The effect of temperature (25°C and 100°C), of load (200 N and 320 N) and the wear kinetics (5 min and 60 min experiments) were studied. Physico-chemical characterization of the wear tracks were performed by XPS. A protection against wear even at ambient temperature was found. This feature was attributed to the presence of zinc polyphosphate in the tribofilm.
Marine Water Lubricated Stern Tube Bearings: Calculations and Measurements of Heavy Loaded Bearings
Authors: Litwin Wojciech
Published: June 2009

Water lubricated bearings are often used to support propeller shaft of modern ships. These environmentally friendly bearings are less expensive than those oil lubricated because of simplicity of the bearing unit and lower material costs [1].
Modeling of Flexible Tilting Pad Journal Bearings With Radial Oil Injection
Authors: Haugaard Asger M. , Santos Ilmar F.
Published: June 2009

The static and dynamic properties of tilting-pad journal bearings with controllable radial oil injection are investigated. The tilting pads are modelled as flexible structures and their dynamics are described using a three dimensional finite element framework and linear elasticity. The oil film pressure and flow are considered to follow the modified Reynolds equation, which includes the contribution from controllable radial oil injection. The Reynolds equation is solved using a two dimensional finite element mesh. The rotor is considered to be rigid. The servo-valve flow is governed by a second order ordinary differential equation, where the right hand side is controlled by an electronic input signal. The constitutive flow pressure relationship of the injection nozzles is that of a fully developed laminar velocity profile and the servo-valve is introduced into the system of equations by a volume conservation consideration. The Reynolds equation is linearized with respect to displacements and velocities of the nodal degrees of freedom. When all nodal points satisfy the static equilibrium condition, the system of equations is dynamically perturbed and subsequently condensed to a 2 by 2 system, keeping only the lateral motion of the rotor. As expected, rotor stability is heavily influenced by the control parameters.
Systems Development of Lubricated Multi-Disc Clutch Systems With Advanced Ceramics
Authors: Albers A. , Bernhardt J. , Ott S.
Published: June 2009

In the field of mechanical engineering there is a constant demand of shorter development cycles combined with increasing requirements concerning product quality and costs. To meet these demands, which can be seen as a main success factor of industrial enterprises, suitable development processes are needed. The main goal of the IPEK is to provide tools, methods and processes to support the development of complex technical systems. Representative for high loaded frictional systems with low pressure and high sliding speed, a lubricated multi-disc clutch is used as a demonstrating system. With this demonstrating system the functionality of the developed methods is validated. For this reason a prototype of a lubricated multi-disc clutch system with ceramic friction materials has been developed and built up. Experimental investigations confirmed the potential concerning power density resulting from the use of ceramic friction materials in combination with a ceramic suitable systems design.
Plane EHL Problems for Pre-Critical Heavy-Loaded Contact: Stable Numerical Solutions
Authors: Kudish Ilya I.
Published: June 2009

The paper is aimed at considering the classic isothermal plane EHL problem for heavy-loaded contacts lubricated by Newtonian and non-Newtonian fluids. The analytical analysis of the problem is based on matched asymptotic expansions. For pre-critical lubrication regimes asymptotic equations for pressure and gap are derived and solved numerically in the inlet and exit zones. The number of input parameters in asymptotic equations is reduced. The numerical solutions are stable. Formulas for lubrication film thickness for Newtonian and non-Newtonian fluids for pre- and over-critical regimes are derived based on the asymptotic analysis.
Simulating Synchroniser Stick-Slip Behaviour for Superior Gearbox Performance
Authors: Smith O. , Gelder A. , Durham J. , Saccomando D. , Walker G.
Published: June 2009

OEMs strive to obtain greater mechanical efficiency from their transmissions. It is widely accepted that this can be achieved by reducing the bulk viscosity of the transmission fluid, which reduces the churning losses responsible for a considerable amount of the inefficiency. There is ever-increasing demand on the transmission fluid to maintain or even increase the durability of the transmission components. However, the resulting loss of film thickness due to the lower viscosity fluid produces ever more arduous operating conditions for the transmission components, which rely on strong multifunctional additive packages not only to maintain durability but also to control the contact mechanics. This paper describes the development of a novel bench-top, friction screening test used to gain valuable fundamental knowledge and guide the formulation of manual transmission fluids (MTF) with tailored and controlled frictional performance.
A Generalized Thermal EHL Model for Point Contact Problems
Authors: Liu Yuchuan , Wang Q. Jang , Zhu Dong , Shi Fanghui
Published: June 2009

A generalized thermal elastohydrodynamic lubrication (TEHL) model for point contact problems is developed based on an isothermal generalized Newtonian elastohydrodynamic (EHL) model recently developed. The thermal model couples FDM for lubricant energy equation and the DC-FFT method for surface temperature integration. A generalized Reynolds equation is derived considering the change of viscosity with respect to temperature, pressure and shear in three dimensions. Numerical cases are conducted to verify the model.
An Efficient Elastic Deformation Analysis Procedure for Simulating Conformal-Contact Transient Elastohydrodynamic Lubrication Systems
Authors: Xiong Shangwu , Wang Q. Jane , Lin Chih , Wang Yansong
Published: June 2009

A compliance operator, Eji, is often utilized to evaluate elastic deformation in the simulation of transient and steady state elastohydrodynamic lubrication of conformal-contact systems. The values of the compliance operator represent the elastic responses of all nodes when only one node is under a unit load. The accuracy of compliance operator values, computational cost, and storage size are important issues. Based on our previous study on steady-state conformal-contact elastohydrodynamic lubrication systems, an advanced method of selective-fine-mesh with selective storage is suggested, and a special technique of combined selective-fine-mesh with selective storage mapping is proposed. These two techniques enable an efficient elasticity procedure for the simulation of transient conformal-contact elastohydrodynamic lubrication systems.
A Model for Optimizing Material Removal Rate in Low-Pressure CMP: Effects of Pad Porosity and Abrasive Concentration
Authors: Bozkaya Dinc¸er , Mu¨ftu¨ Sinan
Published: June 2009

The necessity to planarize ultra low-k (ULK) dielectrics [1], and the desire to reduce polishing defects leads to use of lower polishing pressures in chemical mechanical polishing (CMP). However, lowering the applied pressure also decreases the material removal rate (MRR), which causes the polishing time for each wafer to increase. The goal of this work is to investigate effects of pad porosity and abrasive concentration on the MRR.
Tribological Analysis of Alumina Nanocomposites for Orthopedics Applications
Authors: Morillo Carlos , Sawae Yoshinori , Murakami Teruo
Published: June 2009

In this study the tribological analysis of Al2O3 nanocomposites/Al2O3 pair; proposed as a candidate material to fabricate hip prostheses was carried out. Nanopowders of Al2O3 (AKP 50, 300 nm), TiO2 (PS-25, 50 nm) and Co metallic powder (Nilaco, 28 nm) were mixed and hot pressed. Wear test was carried out in a pin-on-plate tribometer, with a frequency of 1 Hz, a load of 49 N, for 4h; the counterface used was Al2O3. Mechanical properties as Vickers hardness, fracture toughness and Young’s modulus were estimated using the indentation method. Distilled water and fetal bovine serum solution (FBSS) were used as environment. It was found that the specific wear rate of Al2O3 nanocomposites was about 10−8mm3/N*m and the coefficients of friction were around 0.3–0.5 for FBSS. Worn surfaces were observed using SEM.
Experimental Piston Ring Tribology for Marine Diesel Engines
Authors: Klit Peder , Vo̸lund Anders
Published: June 2009

A very important condition for describing the frictional behavior of a piston ring correctly is knowledge about the amount of lubricant present. It is often assumed that piston rings operate under fully flooded conditions, but this is not the case in real life operation. In large two-stroke engines the cylinder oil is supplied periodically to the bearing at discrete locations on the cylinder liner. The shifting in lubrication regimes and the non-uniform oil distribution opens for the possibility of starved conditions for the piston ring bearing. Therefore it is important to measure the oil distribution on the liner as a function of the operating conditions. The amount of lubricant available is reflected in the friction absorbed in the bearing. The paper describes an investigation of the tribological condition between a piston ring and cylinder. A test apparatus is used to study the interaction between a piston ring and a cylinder liner.
Towards an Appropriate Modeling of Energy Balance in Molecular Dynamics Simulations of Confined Lubrication Films
Authors: Berro H. , Fillot N. , Vergne P.
Published: June 2009

We propose a new approach to the study of friction in molecularly thin films. The instantaneous occurrence of both momentum and thermal kinetic energy diffusions in the film requires a sophisticated energetic approach. This can be done by identifying the energetic terms which are due to thermal agitation or shearing rather than globally thermostating the system. With this approach, it becomes possible to quantify the energy loss due to friction and to describe the local mechanisms of its dissipation inside the liquid and through the interfaces. Implemented, the method can give more accurate results in molecular dynamics simulations of confined films.
Analysis of Thermo-Mechanical Distortions in Sliding Components: An ALE Approach
Authors: Owczarek P. , Geijselaers H. J. M.
Published: June 2009

A numerical technique for analysis of heat transfer and thermal distortion in reciprocating sliding components is proposed. In this paper we utilize the Arbitrary Lagrangian Eulerian (ALE) description where the mesh displacement can be controlled independently from the material displacement. A stationary and a moving component are modeled respectively as Lagrangian (mesh displacement equals material displacement) and Eulerian (mesh is fixed in space and material moves through the mesh). The description of the contact between both components accounts for frictional heating and heat exchange.
Elastic/Plastic Oblique Impact Analysis for Head Disk Interface Operational Shock
Authors: Katta Raja R. , Polycarpou Andreas A. , Hanchi Jorge V. , Crone Robert M.
Published: June 2009

Investigation of the slider corner/disk impact process at the Head Disk Interface was carried out using a dynamic elastic-plastic finite element model of a sphere obliquely impacting a thin-film disk. The effect of slider corner radius and impact velocity on critical contact parameters was examined. To characterize the energy losses due to the operational shock impact damage, the coefficient of restitution for oblique elastic-plastic impact was studied using the finite element model. A method to use a physics-based elastic-plastic oblique impact model in conjunction with an analytical normal impact model was proposed to accurately predict coefficient of restitution for a rigid sphere impacting a half-space. This analytical model results compared favorably to the FEA results for the whole range covering low impact angles (primarily normal impacts) to high impact angles (primarily tangential impacts).
Influence of Scratches on the Performance of a Partial Journal Bearing
Authors: Dobrica Mihai B. , Fillon Michel
Published: June 2009

In this paper, the influence of circumferential scratches on the thermohydrodynamic performance of a partial (lobe) journal bearing is studied. The bearing damage is characterized by four factors: the area of the scratched region, the density of the scratches within the affected area, the relative position of the scratched region and the relative depth of the wear defects. The bearing performance is characterized by minimum film thickness, average oil temperature, maximum pressure, friction torque etc., at imposed magnitude and direction of the load. A numerical hydrodynamic model with global thermal effects is used for studying the influence of the different wear related parameters on the bearing performance. The results permit to predict the overall performance loss due to the circumferential wear marks, for different wear profiles. The types of wear profiles that can lead to the bearing destruction (characterized by a critical minimum film thickness) are also investigated.
FEM-DEM Dialogue for Tribological Understanding
Authors: Saulot Aure´lien , Renouf Mathieu , Berthier Yves
Published: June 2009

In many mechanisms, global dynamics resulting from operating conditions act as external solicitations for bodies in contact. As a consequence, dynamic instabilities occur in the contact and lead to particle detachments, usually called 3rd body and wear flow. Obviously, once detached, these particles play an important role in the evolution of the local friction coefficient and thus the local contact dynamics. As the contact is a confined area, experimental investigations have mostly been unsuccessful to locally describe both contact dynamics and material flows. To balance this lack, two numerical methods can be used to solve independently each part of the problem. From a global point of view, local contact dynamics is considered as a local condition for the two 1st bodies described as continuous media. From a local point of view, the discontinuity of the interface should be taken into account to describe material flows, considering effect of two bodies as boundary conditions. To model continuous aspects, a semi-implicit dynamic Finite Element (FE) method is used taking into account the elasto-plastic behaviour of the two bodies in contact. To model discontinuous effects, a non conventional Discrete Element (DE) method is used, called the Non Smooth Contact Dynamic (NSCD) method coupled with Cohesive Zone Models (CZM) to describe the behaviour of the 3rd body particles. To give a reliable description of the behaviour of bodies in contact, a coupling of scales is required on both local conditions and boundary conditions which are respectively inputs coming from DE and FE methods. The aim of the present paper is to gather these two complementary approaches by creating a numerical dialogue between DE and FE methods acting respectively at the 3rd and 1st bodies scales. After a brief description of each numerical model, the dialogue methodology will be detailed and applied to a reference example where dynamic instabilities occur in the contact. A comparison between results obtained with “classical” FE simulation and “coupled” FE-DE simulations is presented. As a conclusion, this numerical dialogue is a first step toward a better taking into account of the 3rd body behaviour in continuum model and its consequences on local contact dynamics.
Wear of Highly Crystalline Ultra-High Molecular Weight Polyethylene
Authors: Van Citters Douglas W. , Levack Ashley E. , Kennedy Francis E.
Published: June 2009

Highly crystalline ultra-high molecular weight polyethylene (UHMWPE) has historically experienced little success as a bearing material in total joint arthroplasty due to oxidation related fatigue failures. Recent sterilization and treatment advances have reduced or eliminated the risk of oxidation, allowing for a renewed interest in this particular material. The current study investigates the wear resistance of a highly crystalline UHMWPE in comparison to clinically relevant control materials. The highly crystalline material exhibits a wear rate superior to never irradiated material, and similar to irradiated material. The wear rate reduction is attributed to the larger crystallites’ ability to slow subsurface crack growth.
Tribological Characteristics of AlMgB14 and Nanocomposite AlMgB14-TiB2 Superhard Coatings
Authors: Qu Jun , Blau Peter J. , Zhu Dong , Cook Bruce A. , Elmoursi Alaa A.
Published: June 2009

This study investigated the friction and wear characteristics of two super-hard coatings on M2 steel. One was AlMgB14, produced by pulsed laser deposition (PLD), and the other was a nanocomposite of AlMgB14-TiB2, produced by physical vapor deposition (PVD). Tests were conducted under unidirectional and reciprocating sliding against AISI 52100 bearing steel in both dry and oil-lubricated conditions. The AlMgB14 coating exhibited an encouraging but short-lived low friction stage (μ = 0.2) in dry sliding. The AlMgB14-TiB2 coating reduced the wear rates by one order of magnitude relative to the M2 steel and three orders of magnitude for the counterface in dry sliding. This nanocomposite coating also demonstrated significant extension (>2.5X) of the low friction (non-scuffing) stage when sliding under starved lubrication.
Linking Rigid and Flexible Multibody Systems via Thin Fluid Films Actively Controlled
Authors: Estupinan Edgar A. , Santos Ilmar F.
Published: June 2009

This work describes in details the steps involved within the mathematical modelling of multibody systems (rigid and flexible) interconnected via controllable thin fluid films. The dynamics of the mechanical components are described with help of multibody dynamics and finite element method. In this paper, the methodology is applied to reciprocating machines such as hermetic reciprocating compressors and internal combustion engines. In previous studies [1], it has been shown that for a light duty vehicle, the friction losses may reach until 48% of the total energy consumption of an engine and from that, almost 30% are coming from bearings and crankshaft. Therefore, considering that the dynamics of the fluid films in the journal bearings can be actively controlled by means of different types of actuators, allowing significant reduction of wear and vibrations, one of the aims of this paper is to study the feasibility of applying active lubrication to the main journal bearings of reciprocating machines. In this framework the paper gives a theoretical contribution to the combined fields of fluid-structure interaction and active vibration control. The hydrodynamic pressure distribution for an active lubricated finite journal bearing dynamically loaded can be calculated by numerically solving the modified Reynold’s equation [2], by means of finite-difference method and integrated over the pressure area in order to obtain the dynamic reaction forces among components. These forces are strongly nonlinear and dependent on the relative kinematics of the system. From the point of view of active lubrication and specifically considered the case of a dynamically loaded journal bearing, the injection pressure should be controlled in the time domain. However, taking into account that the pressures and reaction forces in a reciprocating machine have a cyclic behaviour, the fluid film thickness of the main bearings may be modified by controlling the oil pressure injection, depending on the crank angle and the load bearing condition. It can be mentioned that the pressure and flow may be controlled by mechanical cam systems, piezoelectric nozzles [3] [4] or servovalves [5] [6], therefore, an adequate control strategy has to be defined. The fluid film forces are coupled to the set of nonlinear equations that describes the dynamics of the mechanical system. Such a set of equations is numerically solved giving some insights into the following parameters: a) maximum fluid film pressure, b) minimum fluid film thickness, c) maximum vibration levels and d) viscous frictional forces. The behaviour of such parameters is investigated when the system operate with conventional hydro-dynamic lubrication, passive hybrid lubrication and controlled hybrid lubrication.