bluuebunny/crossref_metadata_2025 huggingface dataset:
Degradation of W-DLC Coatings in Rolling/Sliding Applications
Authors: Hua Diann Y. , Zhang Jian
Published: November 2008

W-DLC coatings have demonstrated the benefit to improve contact fatigue life in different applications. The understanding of coating degradation mechanism becomes important for coated component design. In this present study, FZG gear rig has been used to investigate coating wear. The testing procedure was designed to monitor coating wear with interruptions. Scanning Electron Microscope and surface profilometer were used to characterize coating wear. Cone-shaped micro particle pullouts were observed at low stress cycles. Fracture-based cohesive delamination is one form of coating wear associate with concentrated stresses. Another form of wear is characterized as polishing wear (or, sliding wear). The mechanism of polishing wear is complex and can be attributed to chemical or oxidation wear and abrasive wear. However, unlike fracture-based cohesive delamination, polishing wear results a smoother surface. The evolution of surface topography due to coating wear is demonstrated by profilometry measurements. Wear mode of W-DLC coating degradation is proposed as a combination of cohesive delamination and polishing wear.
Thermo-Electro-Mechanical Simulation of Aluminum-Steel Imperfect Electrical Contact With Extremely High Interfacial Temperature
Authors: Kim Wan-Sik , Liu Shuangbiao , Wang Q. Jane , Keer Leon M.
Published: November 2008

This paper introduces the frequency response function (FRF)-based continuous convolution and fast Fourier transform (CC-FFT) algorithm to simulate a periodically large contact area rather than the influence coefficient (IC)-based discrete convolution fast Fourier transform (DC-FFT). The former and the latter may be called as a periodic boundary condition (PBC) and a non-periodic boundary condition (nPBC) based on their periodicity. In the calculation, the contact pressure, surface displacement, and surface temperature are analyzed and compared by means of PBC CC-FFT and nPBC DC-FFT.
Gas Foil Bearings: Limits for High-Speed Operation
Authors: San Andre´s Luis , Kim Tae Ho
Published: November 2008

Commercial oil-free micro turbomachinery relies on gas foil bearings (GFBs) for reliable performance with improved efficiency. However, GFB modeling is still largely empirical, lacking experimental validation. An analysis of simple GFBs operating at large shaft speeds (infinite speed number) follows. The bearing ultimate load and stiffness coefficients are derived from simple algebraic equations for the gas film pressures at the equilibrium journal position and due to small amplitude journal motions, respectively. GFBs without a clearance or with assembly interference are easily modeled. The underlying elastic structure (bump foil strip) determines the ultimate load capacity of a GFB as well as its stiffnesses, along with the limiting journal displacement and structural deformation. Thus, an accurate estimation of the actual minimum film thickness is found prior to performing calculations with a complex computational model, even for the case of large loads that result in a journal eccentricity well exceeding the nominal clearance, if applicable. An initial assembly preload (interference between shaft and foil) increases the GFB static stiffness at both null and infinite rotor speeds. At infinite speed, cross-coupled stiffnesses are nil; and thus, GFBs are impervious to hydrodynamic whirl instability.
An Improved Fractal Contact Model With Special Emphasis on Surface Roughness, Elastoplastic Transition Deformation Zone, and Hardness Effects of Coating Film
Authors: Horng Jeng-Haur , Chan Yi-Jiu , Sheng Chang , Yu Joseph
Published: November 2008

In this work, fractal characterization of surface topography is applied to the study of contact mechanics between two coating film rough surfaces. Incorporating with MB model, the occurrence of elastic-plastic transition regime and the hardness effect of coating film are considered in the new contact model. Results show that the real contact areas predicted by this new model are larger than those predicted by MB model. For low fractal roughness parameter and fractal dimension of 1.5, up to 19% of difference can be found between the results from the new model and old model.
Friction Properties of Array Films of Amorphous Carbon Nanorods Prepared by Dual-Catalyst Growth on Porous AAO Membrane
Authors: Tu J. P. , Jv Y. , Xia Z. Z. , Guo S. Y.
Published: November 2008

The array films of amorphous carbon nanorods were prepared by thermal catalytic pyrolysis of acetylene at 650°C on a porous anodic aluminum oxide (AAO) membrane with Co-Ni catalysts. The morphology and microstructure of the array films were examined by scanning electron microscopy (SEM) and Raman spectroscopy. The friction properties of array films of amorphous carbon nanorods were investigated using a ball-on-disk tribometer and a friction force microscopy (FFM) in ambient air. The friction coefficients of the array films were influenced by the graphitization degree of the amorphous carbon nanorods. The amorphous carbon film with high graphitization degree showed low friction coefficient.
Tribological Property of WC Cermet Coatings Sprayed by Using an Improved HVOF Process
Authors: Ishikawa Y. , Kawakita J. , Kuroda S.
Published: November 2008

An improved HVOF spray process called “Gas-shrouded HVOF” (GS-HVOF) has been developed over the past several years. By using an extension nozzle at the exit of a commercial HVOF spray gun, GS-HVOF is capable of controlling the oxidation of sprayed materials during flight as well as achieving higher velocity of sprayed particles. These features result in extremely dense and clean microstructure of the sprayed coatings. The process has been successfully applied to corrosion resistant alloys such as SUS316L, HastelloyC, and alloy 625 as well as cermets such as WC-Cr3C2-Ni. Wear properties of WC cermet coatings were measured by using a pin-on-disk wear tester. The specific wear rates of the coatings prepared by the GS-HVOF with a reducing (fuel rich) flame were close to that of chrome plating. The wear amount of the heat-treated GS-HVOF coatings could not be detected after testing. It is believed that transition to mild wear appeared early because of the increased surface oxidation due to the heat treatment.
Thickness and Distribution of the Transfer Film in Journal Bearing
Authors: Polak Adam , Grzybek Janusz
Published: November 2008

Paper presents investigations of the transfer film formation processes in tribological pair: steel journal–plastic bushing. Processes of transfer film formation were examined for different operating conditions of friction pair (pressure, sliding speed and temperature). Conducted tests and examinations enabled characterization of transfer film formation processes in dependence of operating conditions. Obtained results allowed, to determine dependencies between operating conditions and thickness and distribution of the transfer film.
Optimized Coatings/Substrate Combinations Under Contact Loadings Through a Combined Experimental and Numerical Methodology
Authors: Baietto Dubourg M. C.
Published: November 2008

For a long time the search of suitable coatings/substrate combinations was mainly based on empirical approaches using results issued from scratch, hardness, wear tests or extrapolating previous experiences to different configurations. There is an increasing need to understand and to be able to predict the performance of the coatings To reach these objectives a methodology encompassing the development of coatings, the complete characterization, the testing and the modeling must be carried out, requiring a multi-disciplinary approach implying collaborations. Concerning the characterization, the number of parameters to be addressed is huge, spanning from micro-structural, materials, physical, mechanical and surface properties to the behavior of complex coatings/substrate systems under representative loading conditions. Further these properties may be thickness dependant. In addition, there is a serious lack in fundamental resistance, fatigue data of the coatings and the interfaces. The choice is all the more difficult since many coating combinations are feasible, from single layer to multilayered coatings or graded coatings over a substrate. A review of the different 2D and 3D numerical models developed will be presented with some applications.
Sliding Friction of Polymers: The Complex Role of Interface
Authors: Bistac S. , Schmitt Marjorie , Ghorbal Achraf
Published: November 2008

The objective of this work is to analyse the influence of interfacial properties on the sliding friction of polymers. In order to change the nature of interface, two types of smooth and rigid substrates are used: a hydrophilic silicon wafer (hydroxylated by a piranha treatment) and a hydrophobic silicon wafer, obtained by a chemical grafting with a CH3 terminated silane. Both substrates exhibit identical stiffness and roughness and differ only by their surface chemical composition. Two different polymers are studied: crosslinked polydimethylsiloxane, PDMS (soft elastomer with a low glass transition temperature) and polystyrene (rigid thermoplastic polymer with a high glass transition temperature). Friction experiments are performed with a translation tribometer for different normal forces and friction speeds.
A Physics-Based Heat Transfer Analysis for Aerospace Ball Thrust Bearings
Authors: McCutchan Sean , Barnsby Roger M.
Published: November 2008

Component temperatures have a significant influence on ball bearing life and durability. Critical parameters such as internal clearance, contact stress and oil film thickness are influenced by the thermal characteristics of a bearing. Previous heat transfer analyses that predict bearing ring temperatures have been typically based on empirical data. A new physics-based analysis has been developed which is derived from fundamental heat transfer and fluid flow equations. Gyroscopic torque and churning forces are balanced by oil shearing contact traction, using recent developments in new life theory [1] and lubricant property models [2]. Bearing ring temperatures and heat generation calculated by the new analysis have been successfully correlated with test data over a wide range of bearing sizes and operating conditions.
Global Planarization Requirements for Wafer-Level Three-Dimensional (3D) ICs
Authors: Gutmann R. J. , McMahon J. J. , Lu J.-Q.
Published: November 2008

Planarization needs for integrated circuit (IC) technology focus on feature-scale (100nm–1μm) and die-scale (5mm-20mm) dimensions. As three-dimensional (3D) integration moves from die-by-die assembly to wafer-level integration to provide a higher density of low electrical parasitic vertical interconnects (or vias), wafer-level planarization needs to be considered. Planarization needs depend upon the 3D technology platform approach (such as (1) blanket bonding followed by inter-wafer interconnect processing or via-first processing followed by bonding and thinning to expose the vias and (2) the number of wafers in a 3D stack) and the processing conditions used in fabricating the wafers to be 3D integrated (in particular, the built-in stress levels and post-bonding thermal processing budget). This invited presentation includes a summary of the current interest in wafer-level 3D integration in both the academic and industrial research community. Wafer-level planarization issues with different technology platforms are presented, and the limited results presented in the literature to date are summarized. The importance of wafer-level planarization compared to bonding, thinning and wafer-to-wafer alignment is discussed.
Characterization of Fretting Damage at Ti-6Al-4V Interfaces in Point Contact
Authors: Neu R. W. , Huang X. , Zerayohannes T. , Wan S. L.
Published: November 2008

The aim of this study is to characterize the baseline fretting behavior of Ti-6Al-4V on Ti-6Al-4V in point contact. The displacement amplitudes span the partial slip, mixed fretting, and gross slip fretting regimes. Surface cracks are only observed when the displacement amplitude is near the transition between partial and gross slip regimes.
Tribological Characterization of Steels for Cutlery: A New Methodology to Access Cutting Edge Sharpness
Authors: De Mello J. D. B. , Ba´lsamo P. S. S.
Published: November 2008

In this work, the tribological behaviour of stainless steel used in cutlery is analysed. Professional knives were tested in well-controlled field conditions and the mechanism of cutting edge loss of sharpness was determined by using Scanning Electron Microscopy. It was determined that the mechanism which causes loss of sharpness in the cutting edge is plastic deformation whereas the edge life itself is mainly affected by abrasive wear during the resharpening process and the sliding wear that occurs while the knife is being used. A new methodology based on the energy that causes plastic deformation is proposed in order to access the bending resistance of the cutting edge. The proposed technique is very simple and cost effective. It reproduces to a great extent the field mechanisms that cause the loss of sharpness in the cutting edge and allows the ranking of different stainless steels usually used by the cutlery industry. Additionally, abrasive and sliding wear tests were carried out on martensitic and ferritic stainless steels. Although the chemical composition and heat treatment considerably modified the microstructure and hardness of the steels, they had no significant effect on abrasion resistance and friction coefficient. On the other hand the sliding wear rate was greatly affected by the chemical composition of the steel.
Gas Foil Journal Bearing Power Loss at High Ambient Pressure
Authors: Bruckner R. J. , DellaCorte C.
Published: November 2008

The National Aeronautics and Space Administration’s (NASA) Exploration Initiative requires the reliable availability of electrical power, on the order of hundreds of kilowatts, for operating spacecraft electric ion engines, on-board instruments, and communications. Foil gas bearing performance in Helium-Xenon (He-Xe) gas mixtures at high ambient pressures is a critical issue in the design of these power conversion systems. The work describe herein is a combined experimental and analytic approach to predicting bearing power loss at these conditions. A high pressure test chamber is used to test generation III foil journal bearings up to 47 atmospheres (∼700 psig). Data is then calibrated to classic Taylor-Couette flow to determine an appropriate power loss model for these bearings.
A Hybrid Signal Processing Technique for Bearing Defect Severity Estimation
Authors: Gao Robert X. , Yan Ruqiang
Published: November 2008

This paper presents a hybrid signal processing technique for bearing defect feature extraction and severity estimation. This is achieved by decomposing vibration signals measured on multiple bearings with different defect conditions into multiple sub-bands by means of the wavelet packet transform (WPT). Representative statistical features for each sub-band are then calculated. Subsequently, Principal Component Analysis (PCA) is performed on the statistical features to choose the best-suited representative features as inputs to a diagnostic classifier for bearing health diagnosis.
Objective Lifetime Design of Orthopaedic Joint Replacements: Are We There Yet?
Authors: Banks S. A. , Fregly B. J. , Harman M. K. , Hamilton M. A. , Sawyer W. G.
Published: November 2008

A computation methodology to objectively predict the lifetime of orthopaedic joint replacements has been developed over the past 5 years. This methodology relies on accurate definitions of the joint kinematics, loads, and contract pressure coupled with experimentally determined wear rates. The validation process makes use of a joint retrieval program at the BioMotion Foundation.
Perturbation Analysis of Texture Effects on Lubricated Devices
Authors: Buscaglia Gustavo C. , Jai Mohammed , Ciuperca Sorin
Published: November 2008

Given a bearing of some specified shape, what is the effect of texturing its surfaces uniformly? Experimental and numerical investigations on this question have recently been pursued, which we complement here with a mathematical analysis. Assuming the texture length to be much smaller than the bearing’s length, we combine homogenization techniques with perturbation analysis. This allows us to consider arbitrary, 2D texture shapes. The results show that both the load capacity and the friction force depend, to first order in the amplitude, just on the mean depth/height of the texture. The dependence of the friction coefficient is thus of second order.
Theoretical and Experimental Investigation of Frictional and Thermal Behavior in Oscillatory Sliding Line Contact
Authors: Mansouri M. , Khonsari M. M. , Hua D. Y.
Published: November 2008

A model is developed to predict the thermal behavior of two sliding bodies undergoing oscillatory relative motion. The thermal model is capable of predicting the temperature rise distribution within the pin-bushing pair and the housing. The bodies geometrically form a pin-bushing configuration and the Hertzian line contact theory is used to approximate the contact pressure and the width. A quasi- three dimensional temperature model is developed by averaging the temperature in the axial direction. The resulting dimensionless heat equations and proper boundary conditions are solved by the finite element method. A series of dimensionless equations for use at the design stage is presented. A test rig capable of inducing oscillatory motion under heavy loading condition is used for measuring friction and temperature. The measured coefficient of friction history, which is curve fit as a function of time, is used in the simulations. The description of the test rig, modeling aspects, and the future extension of the research comprise the contents of this paper.
Oxidation Chemistry of Primary and Secondary Antioxidants
Authors: Karis T. E. , Carter M. D.
Published: November 2008

Inhibition of oil oxidation is the key to long life of synthetic lubricants operating in thermal stress and boundary lubrication environments [1]. Bench-scale tests to screen oil formulations provide a rapid means for optimizing formulations prior to longer running verification tests done with the oil in the end-use application [2]. The ultimate goal of accelerated oil life tests is to link the sample combustion temperature, or induction time, at a given heating rate, or temperature, to the estimated lifetime under normal use temperatures. A first order reaction model has recently been employed to derive kinetic parameters from the heating rate dependence of the combustion temperature in the non-isothermal pressure DSC (NIPDSC) test by Adhvaryu et al. [3]. The first order reaction model [4] is also employed here, but we show that a more detailed scheme is needed to fit the heat flow during the combustion exotherm. The detailed kinetic model also provides the link between the NIPDSC test and the isothermal pressure DSC test, as well lifetime estimation at temperatures closer to the end-use conditions. Although isothermal PDSC is useful on grease [5], it does not provide a sharp exotherm for the unthickened base oil [6]. The NIPDSC test provides a reasonably sharp exotherm for formulated base oil in a relatively short amount of time. In the NIPDSC test, 10–12 mg of oil is placed in an open DSC pan. The sample chamber is pressurized with oxygen. The sample temperature is linearly increased with time until the occurrence of the combustion exotherm. The exotherm peak temperature and total heat flow did not exhibit any regular dependence on oxygen pressure between 0.55 and 3.4 MPa. The base oil was an (average) C7 ester of pentaerythritol. Primary antioxidants were hindered phenol and aromatic amines, and Zn-dialkyldithiocarbamate (ZDTC) and Zn-dialkyldithiophosphate (ZDDP) were used as secondary antioxidants. For some of the tests, soluble catalyst [2] was incorporated as iron (III) 2-ethylhexanoate. The reduced heat flow thermograms during the NIPDSC test on the base oil are shown in Fig. 1. The curves are normalized by the peak heat flow rate as Q/Qp, and the symbols denote curves from the first order reaction model, discussed below. The exotherm temperature increases and the exotherm sharpens with increased heating rate. At the 20 °C/min heating rates, the internal heating upon combustion noticeably skews the shape of the exotherm.
Effect of Lubricant Darkening on Wear Properties of White Metal Bearing in 2-Stroke Marine Diesel Engine
Authors: Ahn Yong-Hee , Kim Dae-Young , Kim Eun-Cheol
Published: November 2008

Effect of lubricant darkening on tribology characteristics of the tin-based white metal bearing in the 2-stroke marine diesel engine has been investigated. Through a reciprocating wear test, friction and wear characteristics were evaluated as a function of lubricant darkening. The darkness of the lubricant increased with wear test time even under the condition of less possibility of soot contamination. The principal cause responsible for darkening was found to be the very fine tin particles dispersed in the lubricant. The formation of these particles is attributed to the wear of the bearing. However the wear loss of the bearing metal obtained from the wear test with the darkened lubricant was similar to that with the initial clean lubricant. This means that the lubricant darkening is not a main factor responsible for the degradation of white-metal bearing durability.
Effects of Microscopic Spherical Particles Mixed in Lubricating Oil on Frictional Characteristics of Linear Slide Guide
Authors: Uehara Kazutake , Obata Fumio , Okamoto Hisaki , Inoue Kenichi
Published: November 2008

In order to develop a superior linear slide guide having friction coefficient independent of sliding velocity, the authors have proposed a method to supply microscopic spherical particles to hardened sliding surfaces finely finished by lapping. The frictional characteristics of a slide guide to which the method was applied were investigated using a model of machine tool’s slide guide. Experiments were carried out at the sliding velocity ranging from 1 to 6000 mm/min. Adding spherical particles with a 5 μm diameter to a vegetable lubricating oil having a viscosity of 215 mm2/s leaded to a constant friction coefficient excluding ultra-low sliding velocity range.
Improved Analysis of Unstable Bouncing Vibration and Stabilizing Design of Flying Slider in Near-Contact Regime
Authors: Ono Kyosuke , Yamane Masami
Published: November 2008

We proposed a design method of a flying head slider that can suppress the bouncing vibration in a near-contact regime, based on parametric study using an improved slider and contact models. At first, we numerically calculated the characteristics of contact force and adhesive force between air bearing pad and disk surface under the current small roughness conditions and found that the contact characteristics can be modeled by constant contact stiffness, a constant adhesion force and the separations of beginning and end of contact. Next we numerically computed the slider dynamics of a 2-DOF slider model by using these contact characteristics and nonlinear air-bearing stiffness. As a result, we could get the self-excited bouncing vibration whose general characteristics are more similar to the experimented results compared to our previous study. Parametric study shows that the frictional coefficient, attractive force and contact stiffness should be decreased and front and rear air-bearing stiffness and ratio of rear to front air-bearing stiffness should be increased in order to realize a stable flying slider in a smallest possible spacing. Moreover, we elucidated the effect of micro-waviness on the self-excited vibration of the slider.
A Method to Predict Temperature Fields During Frictional Welding by Introducing the Heat Input Coefficient and the Heat Input Surface Transfer
Authors: Ikeshoji T.-T. , Suzumura A. , Demura A. , Yamazaki T.
Published: November 2008

A method to predict the time evolution of temperature fields during the frictional welding of stainless steel bars is proposed. The features of the proposed method are the introduction of the heat input coefficient and the transfer of the heat generating plane proportional to the shortening of the work. The heat input coefficient is the multiplication of the heat conversion efficiency of mechanical work and the dynamic friction coefficient. The values of heat input coefficient are decided experimentally. The frictional welding experiments were conducted for the austenitic stainless steel bars with welding conditions. The measured temperature at several points on the surface of the stator agrees with the calculated temperature. Despite the welding conditions, the heat input coefficient shows little difference. Therefore, using the proposed method, by deducing the heat input coefficient from several experiments, the time evolution of temperature fields for work with other diameters might be able to be predicted precisely.
Effect of Intermolecular Forces on the Dynamic Response of a Slider
Authors: Deoras Saurabh K. , Talke Frank E.
Published: November 2008

As the spacing between the slider and the disk approaches atomic distances, near range intermolecular forces start to act at the slider-disk interface. Wu and Bogy have numerically predicted that intermolecular forces become of importance when the slider-disk spacing is lower than 5nm [1]. Thornton and Bogy have proposed that it may not be possible for a slider to fly at a very low flying height without “snapping” and without having slider disk contacts [2; 3]. According to their calculations, a slider would “snap” (get pulled very close) to the disk surface, as a result of attractive intermolecular forces, when the flying height is lowered below a certain “critical” flying height. However, the question arises whether a slider is likely to “snap” at flying heights greater than the “critical” flying height due to its dynamic response.
Friction and Wear Behavior of Boronized Chromium for Biological Applications
Authors: Ribeiro R. , Ingole S. , Juan O. , Liang H. , Usta M. , Bindal C. , Ucisik A. H.
Published: November 2008

Enhanced corrosion and wear resistance are crucially important to prolong the service life of biomaterials. Boronizing has been reported to enhance the wear resistance of pure chromium. In this research, we investigate friction and wear behavior of boronized chromium. Pin-on-disc tribometer was used to conduct the wear and friction tests. Experiments were conducted in dry conditions as well as in simulated body fluid (SBF). Fundamental aspects of wear mode and lubrication behavior were studied using surface characterization techniques such as TEM, and X-ray diffraction. Results showed evidence of tribo-chemical interactions between SBF and work piece materials.
Major Breakthrough in Load Capacity, Speed and Operating Temperature of Foil Thrust Bearings
Authors: Heshmat Hooshang
Published: November 2008

This paper describes major breakthroughs in foil thrust bearings achieving a thrust load capacity in excess of 570 kPa (83 psi), supersonic tip speed of 625 m/s (2050 ft/s) and temperature capability of 815 °C (1500 °F). Compliant foil bearings surpass many of the inherently show-stopping and debilitating features of rolling element bearings. Foil Bearings not only provide an environmentally-friendly, oil-free system of support, but are also well suited for high speed and extreme temperature applications such as gas turbines, compressors, turbochargers, cryogenic-turbopumps, turboexpanders, high speed motors and others. Modern foil bearings have demonstrated stable operational capabilities at super-critical speeds due to their tribodamping intrinsicality and ability to operate with any process fluid (gas or liquid). Recent developments have allowed increased operating temperatures, soaring to 815 °C and above, thus, providing a broader operational temperature range from deep cryogenic to extreme high temperatures. Foil journal bearings received more research and development attention in the past, achieving load capacity of 670 kPa (97 psi), reported by Heshmat in 1994. Foil thrust bearings’ load capacity at that time was in the range of 150 kPa to 200 kPa (20–30 psi) and their temperature capability was ambient to 150 °C (300 °F). This paper discusses a recent major breakthrough in the improvement of the load capacity, high speed capability of compliant foil thrust bearings, as well as extending their operating temperature range to 815 °C. Applying the available analytical tools and newly developed coatings, new thrust bearings have been designed with improved bearing geometry and structural compliancy. The advancement in solid lubricant coatings provided excellent tolerance to intermittent high-speed rubs, thus, making the bearings more robust against shock and extreme loadings. These advanced bearings, with outer diameters ranging from 90 mm to 230 mm, demonstrated a load capacity of 570 kPa (82.7 psi) at 200 m/s runner tip speed. This achievement constitutes two-fold improvement over any state-of-the-art hydrodynamic foil thrust bearings ever reported in the literatures and significantly expands the envelope of possible bearing applications. Improving the bearing load capacity at speeds near Mach 1.6 and higher is also discussed, as well as hydrodynamic operation of a foil thrust pad at 815 °C.
Frictional Properties of Silicon and Self-Assembled Monolayers as a Function of Surface Roughness, Chemical Composition and Sliding Condition
Authors: Bregliozzi G. , Conte´ N. , Ahmed S. I.-U. , Randall N. X. , Steinmann P.-A.
Published: November 2008

This paper reports on the frictional properties in a ball and flat configuration of silicon and two different self-assembled monolayers (SAMs). Such studies are relevant, in part, for microsystems affected by the poor tribological properties of silicon. This report differs from previous studies in that it also considers the case when both contacting surfaces are SAM-coated. In this case it was found that friction is reduced the most. In the case when only one tribopair is SAM-coated, different frictional behavior occurs depending on whether the ball or the flat is coated. Furthermore, SAMs coated on surfaces with very rough topographies exhibit high friction coefficients.
Molecular Design of Durable Hydrophobic Film
Authors: Cha Kum Hwan , Hsu Stephen M.
Published: November 2008

The demand for long durable hydrophobic surface is rising as more and more devices are coming to market. Nanotechnology promises more micro- and nanoscale devices for biomedical, aerospace, transportation purposes. Hydrophobicity can be imparted by a thin layer of low surface energy molecules or a densely-packed hydrocarbon film. Because of heterogeneous surface energy and surface defects, very few films can stay defect-free for an appreciate period of time. Eventually, moisture penetrates into the film through pin holes or defects created by surface reconfiguration. This paper describes a novel hydrophobic film design combining geometric stacking concept with self-healing mobile molecules and an polymeric canopy of cross-linking top layer to prevent evaporation of organic molecules, all within two nanometer thick suitable for most micro- and nanodevices applications.
Adhesion/Stiction and Friction Studies of Nano/Micro-Textured Surfaces Produced by Crystallization of Amorphous Silicon
Authors: Wang Hengyu , Cai Li , Yang Dehua , Wyrobek Thomas , Zou Min
Published: November 2008

This paper reports a new method of nano/micro surface-texturing and the results of systematic studies of adhesion/stiction and friction properties on the textured surfaces produced by this method. Nano/micro-textured surfaces with various roughnesses were produced by low temperature aluminum-induced crystallization of plasma enhanced chemical vapor deposited (PECVD) amorphous silicon. Adhesion/stiction experiments on these nano/microtextured and non-textured surfaces were performed using two diamond tips under predefined displacement profiles with different maximum indentation displacements. Friction experiments on the textured and non-textured surfaces were conducted using the same tips under various normal contact forces. The adhesion/stiction forces and coefficients of friction (COF) of the textured surfaces were found to be much smaller than those of non-textured surfaces.
Nano-Scale Tribology Study of Organic Adlayer-Metal Interface Using Quartz Crystal Microbalance Combined With Scanning Tunneling Microscopy
Authors: Lee Sang M. , Abdelmaksoud M. , Krim J.
Published: November 2008

A quartz crystal microbalance combined with scanning tunneling microscopy (STM-QCM) was used to investigate the interactions between organic adlayers (C6H6 and C6H5I) on Cu surfaces and a metallic STM tip. STM images of C6H6 covered Cu surface improved when the QCM was simultaneously oscillated during the imaging. In contrast, STM images of C6H5I covered surfaces became noisy when the sample was oscillated. The two systems moreover exhibited frequency changes of opposite signs in response to STM tip contact, indicative of different physical phenomena at the surface. The dependence of the STM image quality and the frequency shift were interpreted in terms of the adsorbate-substrate chemical and physical interactions, and different levels of frictional heating at the interface.
Dental Materials and Teeth: Testing Demands and Performance Challenges (Keynote)
Authors: Rekow D. , Thompson V.
Published: November 2008

Contact fatigue plays a critical role in performance of dental materials. Both naturally occurring materials (e.g., the tooth itself) and restorative materials, particularly ceramics are vulnerable to contact fatigue-induced and fatigue-exacerbated damage. Normal chewing functions are complex and unless accurately mimicked by test methods, do not reproduce clinically relevant failure modes. Without this, development of new material systems cannot proceed on a rational basis and will continue to rely on patients serving as the testing ground.
Approaches to Dynamic Tribosystem Modelling
Authors: Druet Krzysztof
Published: November 2008

Predictive models for friction and wear are among the most important issues setting guidelines for tribological research [5]. The analysis of published models of tribological phenomena reveals, that the achievement of satisfactory predictive accuracy of the proposed models is still problematic [10, 12]. Practically speaking the mathematical models mentioned have a limited usability for the purpose of designing new machines. Two groups of models used in tribology can be distinguished: design practice oriented and fundamental [10]. The model belonging to the first group is built so it calculates the expected behaviour of the tribological system on the basis of input data. The core of the model is a ‘black box’ the characteristics of which is based on experience. Data gathered in laboratory and field experiments is used by the designer to predict friction and wear on the design stage of a real life tribosystem. Such a model will nowadays have a form of a computer program allowing to calculate wear rates etc. Whereas the fundamental model quantifies various physical processes influencing friction and wear in the analysed system.
Tribological Properties of Ground Surfaces
Authors: Babic Miroslav
Published: November 2008

This paper presents the results of tribometric investigations of ground surfaces machined with different combinations of grinding regime. Though they belong to the same class of surface roughness, they show significant differences in tribological properties. This is a consequence of differences in the state of material in the surface layers, which arise from the machining regime parameters variation. These results emphasize the essential importance of correct definition of tribological criteria for contact surface states in the design phase.
Optimization of Groove Dimensions in Spiral-Grooved Journal Bearings for Spindles of Precision Equipments
Authors: Hirayama Tomoko , Yamaguchi Naomi , Sakai Shingo , Hishida Noriaki , Yabe Hiroshi
Published: November 2008

Spiral-grooved bearings have lately attracted considerable attentions as better substitutions for current ball bearings, especially in motor spindles of precision equipments such as hard disk drive systems. Their high stiffnesses and high damping abilities can realize good run-out characteristics even for such small-sized equipments. Regarding the groove dimensions of the spiral-grooved journal bearings, it seems that we usually design them according blindly to a traditional standard aiming for maximizing the direct bearing stiffness. It is also the fact that the bearings designed according to this standard can realize comparatively good bearing performances. On the other hand, there have been considerably few discussions on optimum designs of the groove dimensions specialized for a reduction of amplitude of the operating run-out, which is a major characteristic for applications to precision equipments. The optimization of groove dimensions of the spiral-grooved journal bearings is, then, discussed in this paper. The subjects for optimizations are: 1) reduction of rotor displacement against a static load, 2) reduction of amplitude of the operating repeatable run-out (RRO) due to an unbalanced rotor mass, and 3) reduction of amplitude of the operating non-repeatable run-out (NRRO) against an external impulse load.
Transient Behavior of Near Frictionless Carbon Films in Reciprocating Microtribometery in Low Humidity Inert Environments
Authors: Dickrell P. L. , Erdemir A. , Sawyer W. G.
Published: November 2008

Microtribological measurements of near frictionless carbon (NFC) films in controlled gaseous environments show that water vapor plays a role in the friction coefficient. These experiments also show that the NFC films initially have high friction in argon, which then decreases. This high friction does not reform over extended periods of exposure to Ar and low partial pressures of H2O and O2. Tests varying water vapor pressure show that under certain humidity conditions the friction coefficient can increases to values seen after extended periods of environmental exposure.
The Narrow Groove Analysis Revisited
Authors: Pan Coda H. T. , San Andre´s Luis
Published: November 2008

The narrow groove analysis (NGA) as pioneered by Whipple [1] is a two-scale formulation with an infinitesimal micro-scale. Its shortcomings include: ambiguity in minimum required number of grooves, implied assumption of local incompressibility, violation of end conditions and omission of local squeeze effect. Alternative numerical computation methods of the finite-element or finite-volume type [2][3] to treat the problem with a finite number of grooves are at best very expensive because good designs tends to require a large number of grooves. In view that interest in inclined groove gas lubricated devices has intensified [3], a new two-scale formulation is presented here to consider a small but finite micro-scale. Cross-pattern profiles of pressure and induced transverse flux are presented for the entrance condition of a typical thrust bearing with eighteen spiral-grooves.
Oil Film Temperature Distribution of Cylindrical Journal Bearings With Variable Axial Profile
Authors: Strzelecki S. , Ghoneam S. M. , Someya T.
Published: November 2008

Misaligned shaft affects the bearings characteristics and significantly diminishes the range of safe bearing operation and it generates the mixed friction and transient conditions of unstable operation. Misalignment of journal bearing can be caused by position errors too. Journal bearings with. hyperboloidal profile extend the bearing operation range without the stress concentration on the edges of bush and the load can be carried without application of self-aligning bearings.
Reliability Analysis Based on Crosstabulation: A Novel Method
Authors: Ahlroos T. , Parikka R.
Published: November 2008

By choosing the critical components, the maintenance and service operations can be directed to the most relevant parts of a facility or a process. Traditionally in definition of critical components reliability techniques, such as fault mode effect analysis, fault mode effect and criticality analysis or fault tree analysis, have been used. The disadvantage of these methods is laborious of the analysis and deficient available statistic data. The determination of critical components can be carried out by new reliability analysis method developed by VTT Technical Research Centre of Finland, which is based on the self-evaluation by the operation personnel and crosstabulation of the affecting factors in a similar manner as a decision matrix.
Chaotic Dynamics of Rotor Supported on Tilting-Pad Journal Bearing (TPJB): A Review and Current Work
Authors: Abu-Mahfouz Issam
Published: November 2008

The use of tilting-pad journal bearing (TPJB) has increased in the recent past due to their stability effects on the rotor bearing system. The first part of this paper presents a review of the state of the art work on rotor response when supported on TPJB. Only few published work presented results relating to the strongly nonlinear behavior, especially chaos, resulting from the use of these types of bearings. In the second part of this paper, three loading mechanisms capable of producing instabilities in terms of sub-harmonic and chaotic motions are suggested. The first one is that of a centrally loaded pad with small rotor unbalance excitations. The second one is when the load is applied between two pads. And, the third represents a concentric rotor (zero static load) acted upon by centering sprigs and unbalance excitation. After a quite extensive numerical experimentation, the resulting response shows, for certain parameters, sub-harmonic, quasi-periodic and chaotic motions.
Brittle Fracture Generated by Abrasion Wear in Borided Low Carbon Steel
Authors: Castillo Marti´n , Vite Manuel , Herna´ndez L. H. , Villa G. , Urriolagoitia G.
Published: November 2008

This work is related to failure as a consequence of brittle fracture by abrasion wear. The experimental evidence showed that this situation depends on the size and shape of the abrasive particles and their velocity when they are interacting against the abraded surface. The particle morphology determines the type of failure, in which the crack may propagate. This can be in a lateral and radial direction. Also this situation is observed in low carbon steel (AISI 8620) which has been borided previously. In accordance with the results, the strength is improved by: developing phases, varying thickness of the borided layer and increasing the hardness. At the same time, a hardness analysis of the borided steel and the abrasive surfaces was carried out. The hardness is the principal characteristic which increases the abrasion resistance and the borided improved resistant to wear. However, it has different behaviour according to the type mechanism of abrasion wear (two or three bodies). In the case of three bodies, it is necessary to take into account the superficial characteristic, because over rough surfaces, the hard particles deteriorate the surface of the specimen. On the other hand, on smooth borided surfaces, generally the particles slip without several damage.
Design of Abrasion Resistant Surfaces by Textures on Macroscopic Size
Authors: Badisch E. , Geiderer P. , Polak R. , Franek F.
Published: November 2008

Although abrasive wear is a predominant type of wear in almost all fields of industry, it is particularly relevant to the field of mining and mineral processing. This wear mechanism is mainly influenced by the abrasive particle (e.g. hardness, size, shape, mass), the wear kinematics (impact angle, impact velocity), and also by the worn material itself (e.g. surface, structure, hardness). Today, a lot of work is done to develop systems which are resistant against wear caused by mineral abrasives. One goal for higher abrasion resistance is the use of macroscopic surface textures which hinder the abrasive particles from hitting unprotected surface areas (especially for dry, coarse abrasives) or force the formation of surface adherent mineral embedment which leads to a self-protection effect (especially for fine, wet type of abrasives). However, there is a serious lack of systematic and scientific knowledge for the design of abrasion resistant surfaces. The aim of this study was to evaluate the efficiency of macroscopic surface textures on their ability of minimizing abrasive attack, finally with the purpose to establish design rules for abrasion resistant surfaces. Profile geometry, profile distribution and surface arrangements were investigated on the wear protecting properties. It could be observed that the surface protection factor against abrasion can be adjusted by distribution and surface coverage. A strong influence of the grain size of the abrasives used on the wear behavior was observed.
A Generalized Analytical Model for the Elastic Deformation of an Adhesive Contact Between a Sphere and a Flat Surface
Authors: Schwarz Udo D.
Published: November 2008

A new method to calculate the elastic deformation of a sphere on a flat surface is presented. The model considers the influence of short-range as well as long-range attractive forces both inside and outside the actual contact area. In contrast to earlier models, this theory describes the nature of these deformations in the intermediate regime between the so-called JKR and DMT limits by simple analytic expressions. Equations for the calculation of the contact radius, the deformation, and the pressure distribution are given. In all equations, the critical force that might vary between the limiting values found in the DMT and the JKR model acts as transition parameter.
Some Numerical Simulations and an Experimental Investigation of a Finger Seal
Authors: Braun Minel J. , Pierson Hazel M. , Li Hongmin
Published: November 2008

Finger seals (FS) are compliant seal configurations. Unlike brush seals, they exhibit hydrodynamic lifting capabilities which allow non-contact sealing between stationary and rotating members. The compliance combined with the non-contacting feature allows both axial and radial adjustment of the seal to the rotor excursions without endangering the integrity of the former. The embodiment of a two-layer finger seal with high pressure (1c) and low pressure (1b) laminates is shown in Figure1. In this paper we shall analyze the thermo-hydraulic and mechanical performance (axial and radial deformations and displacements) of a representative repetitive cell that contains four high pressure and four low-pressure fingers arranged axially in a staggered configuration, and subject to rotation and an axial pressure drop. We shall also present experimental results pertaining to the seal deformation under axial pressure differential and rotation.
Single Asperity Atomic Force Microscope Studies of the CMP of Silicate Glasses
Authors: Langford Stephen C. , Stevens Forrest , Dickinson J. Thomas
Published: November 2008

The Atomic Force Microscope (AFM) allows one to examine the effects of applying highly localized stress to a surface. In the presence of solutions, tribochemical wear can be investigated. We present results of fundamental studies of the simultaneous application of chemical agents and mechanical stress involving a model single asperity and a solid surface. We show the consequences of combining highly localized mechanical stress (due to contact with the AFM tip) and exposure to aqueous solutions of known pH. The experiment simulates many features of a single particle-substrate-slurry interaction in CMP. We show that linear scans and rastered scans display significantly different material removal rates. Quantitative models are presented to explain the observed nanometer-scale surface modifications. This work complements recent observations of tip-induced wear and growth in a number of inorganic surfaces in aqueous solution.