bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Air Ingestion vs. Dimensionless Parameters in Squeeze Film Dampers
Authors: Torres Jorge E. , Diaz Sergio E.
Published: February 2010

Ingestion and entrainment of air into the Squeeze Film Dampers (SFDs) with open end result in a bubbly mixture that affects their damping capacity. The industrial applications demand dampers with low pressure supply and operating high speed, it means, it exists a necessity of propose a model to predict the air ingestion in this kind of bearing. Diaz and San Andre´s reported results of an extend research to quantify the effect bubbly mixture in the performance of the SFDs. They also advanced an analytic model for short infinity bearings (L/D = 0) which estimate the air ingestion as function of non-dimensional number named by them feed squeeze flow number. Me´ndez et al. advanced the understanding of the effect air entrainment. They propose a new dimensionless map to estimate the air volume fraction in finite length bearings. Although, their results are immediate applicability, they do not have been validated. The present work looks for confirm the results presented by Me´ndez et al. To achieve this, it is solved a compressible Reynold equation with a different numerical method. The results indicate that is necessary another dimensionless number to estimate the entrapment air and the dimensionless map proposed by Me´ndez et al. is valid only to bearings with an eccentricity-clearing ratio of 0.5248.
Effects of Surface Roughness on the Fly-Ability of a Thermal Protrusion Air Bearing Slider
Authors: Hua Wei , Liu Bo , Yu Shengkai , Zhou Weidong , Gonzaga Leonard
Published: February 2010

A femto air bearing slider with thermal protrusion is studied based on three groups of surface roughness. It is observed that the air bearing force and the contact force are proportional to the value of average roughness in the minimum flying height region studied, while the intermolecular force or the electrostatic force is the smallest for the smoothest surfaces when the minimum flying height is above a certain value. As a result, the total force on the slider is the largest on the smoothest surfaces in a certain minimum flying height region. When the minimum flying height is designed in that region, the fly-ability of the slider is maximized.
Optimized Logarithmic Roller Crowning Design of Cylindrical Roller Bearings and Its Experimental Demonstration
Authors: Fujiwara Hiroki , Kawase Tatsuo , Kobayashi Takuji , Yamauchi Kazuto
Published: February 2010

A logarithmic profile is an essentially optimal geometry for rolling machine elements such as bearing rollers and raceways. Under most conditions of loading, it yields less stresses to give longer endurance. Lundberg first suggested the basic profile, and some researchers followed him by modifying it to satisfy engineering requirements. In this paper, the authors propose a mathematical optimization method for various profiles including a logarithmic one in roller bearing applications. Moreover, rolling contact fatigue life tests are carried out to make a comparison among logarithmically-crowned, standard partially-crowned and modified partially-crowned rollers. Results show that the logarithmic and modified partially crowned rollers are comparable in fatigue life, although the logarithmic rollers require less working effort to process the crowning.
Tribological Characteristics of Thin-Film Disks With and Without Mobile Lubricant
Authors: Kawakubo Youichi , Hayakawa Takahiro , Sugawara Yusuke , Ikeda Koji , Kitamura Osamu
Published: February 2010

Lubricant on thin-film magnetic disks is divided into two parts. One is bonded lubricant that is fixed on disk surface and remains on disk surface after solvent rinsing. The other is mobile lubricant that can move on disk surface and is removed by solvent rinsing. It has been believed that mobile lubricant is imperative to design reliable hard disk drives. However, mobile lubricant would also be a cause of high friction between heads and disks. We started our studies on disks without mobile lubricant to find the possibility of disks with only bonded lubricant. In this paper, tribological characteristics of disks with and without mobile lubricant at the same lubricant thickness were compared using our transparent pin-on-disk wear tests. The results showed that pin wear was smaller on disks without mobile lubricant than those on disks with mobile lubricant in low load or slow speed conditions. The reason of this was considered to be the contact force increase by meniscus force due to lubricant bridge.
Stresses in Bearing Liner of Misaligned Hydrodynamically Lubricated Journal Bearings
Authors: Elsharkawy Abdallah A. , Al-Fadhalah Khaled J.
Published: February 2010

A numerical study examined the combined effects of journal misalignment and hydrodynamic lubrication on the stress fields of bearing liner under steady state conditions. The oil pressure, obtained by solving Reynolds equation, is imposed on a finite element model of an elastic liner bearing to calculate its stress fields. It was found that large degree of misalignment increases remarkably the oil pressure, and consequently the stresses in the bearing liner become significantly higher.
Tribological Characteristics of the Aluminum-Silicon Alloy Impregnated Graphite Composite Under Insufficiently Lubricated Reciprocating Sliding Conditions
Authors: Goto Hozumi , Suciu Claudiu Valentin
Published: February 2010

Tribological characteristics of Al-Si alloy impregnated graphite composite (ALGR-MMC) in contact with bearing steel were investigated under insufficiently lubricated reciprocating sliding conditions. Ball (JIS SUJ2 bearing steel) on disk (ALGR-MMC) type wear tests were conducted under unlubricated conditions, i.e., in air with high (70%) and low (≤ 1%) relative humidity (RH), under drop-feed lubrication, i.e., oil-drops were deposed on the disk surface before commencing the tests, and under immersion lubrication, i.e., the ball-on-disk contact was submerged in a oil (SAE30) bath. Reciprocating sliding movement was maintained, under a contact load of 40 N at a frequency of 3.3 Hz and amplitude of 3.5 mm, for 100,000 cycles. Tribological properties were continuously monitored. Variation of the kinetic friction coefficient (KFC) versus the number of reciprocating cycles (NRC) was obtained for various amounts of oil (lubrication conditions) and two values of the air RH. For drop-feed lubrication the KFC has at beginning the same value as that under immersed lubrication, but if breakdown of the oil film has occurred after a certain NRC, it increases towards the value corresponding to unlubricated conditions. Connected to the oil film breakdown, there is a certain transition range, expressible both in terms of the oil amount and NRC. Minimum quantity of oil to avoid the film breakdown was found. Due to its self-lubricating properties, ALGR-MMC was able to endure adverse lubrication conditions such as insufficiently lubricated reciprocating sliding.
Chip Clogging in Dry Drilling: Workpiece Temperature Effects
Authors: Qin Feng , Chou Kevin , Nolen Dustin , Thompson Raymond
Published: February 2010

This study investigates the chip clogging phenomenon which occurs in dry drilling of aluminum alloys and composites, and yet, is seemingly critical to the drill life. This issue must be resolved in order to facilitate dry drilling. A highspeed dry drilling test using common twist drills was conducted with the workpiece temperature pre-heated to a wide range, room to 265 °C. The drills after testing were then examined in terms of aluminum residue that strongly adheres with the flute surfaces. A possible transition temperature range that may result in severe aluminum build-up and chip clogging was identified under the tested condition.
UHMWPE Composites for Orthopaedic Applications: A New Paradigm
Authors: Plumlee Kevin G. , Schwartz Christian J.
Published: February 2010

The authors investigated the viability of UHMWPE composites for use in orthopaedic bearing applications as an alternative to crosslinking. Two composite systems were used, both based on a UHMWPE matrix: PtZr quasicrystals and Zr particle fillers. Through wear testing and impact toughness measurement it was shown that these two fillers produced composites that had high wear resistance and more impact toughness than the crosslinked polymer. These results suggest that further investigation into the use of composites for implant bearing surfaces is warranted and that appropriate criteria for filler materials must be developed to spur development of longer-lasting devices.
Characterization of Nano Crystalline Lubricating Coatings for Tribological and Nano-Mechanical Properties
Authors: Gitis Norm , Khosla Vishal
Published: February 2010

This paper presents the techniques used to comprehensively characterize the effect of current density on tribological, mechanical and adhesion properties of nanocrystalline coatings.
Evaluation of Oil Bearing Supported Rotors Coupled by Flexible Coupling
Authors: Kim Choong Hyun , Lee Kyeong Soo , Lee Yong-Bok
Published: February 2010

In this study, analytical evaluation of dynamic characteristics of the mechanical coupling and its effect on the coupled rotor-bearing system are presented. The results indicate that the oil film bearing supported rotor system may successfully be coupled by the flexible coupling.
Tribological Characteristics of Carbon Nanotube Thermoplastic Resin Composites
Authors: Kawakubo Youichi , Nagata Masaki , Yokoyama Takashi , Hayashi Yoshitaka , Arai Masahiro
Published: February 2010

Wear reduction by Carbon Nanotube (CNT) addition in composites with Ultra-High Molecular Weight Polyethylene (UHMWPE), Polyimide (PI), Polytetrafluoroethylene (PTFE), and epoxy resins have been reported separately. We studied Polypropylene (PP) and Polyamide (PA) composites and showed that with the addition of Multi-wall Carbon Nanotube (VGCF: Vapor Grown Carbon Fiber), wear decreased for PA composites but increased for PP composites. Differences in tribological characteristics of CNT composites with different resins were not well understood. In this paper, we compared tribological and mechanical characteristics of VGCF composites with PE, PP, and Polyacetal (POM) resins. Ball-on-Disk wear tests and mechanical strength measurements were performed. It was found that with the increase in VGCF content, specific wear amount (SWA) of VGCF-PE composite decreased while SWA of VGCF-POM composite stayed almost constant and SWA of VGCF-PP composite increased. On the other hand, with the increase in VGCF content, the tensile strength of VGCF-PE composite was increased but those of VGCF-PP and VGCF-POM composite were decreased. Decrease in SWA of VGCF-PE composite corresponded to the increase in tensile strength with VGCF content. We considered that the intermolecular force between side wall of VGCF and PE was strong enough to make both the SWA small and the tensile strength large.
Characterization and Design of Laser Textured Surfaces
Authors: Podgornik B. , Sedlacˇek M. , Vilhena L. , Vizˇintin J.
Published: February 2010

Increased requirements for improved performance and reliability of mechanical systems dictate the use of new advanced materials and surface engineering techniques, which would increase efficiency and reduce energy losses. Already with a small change in surface roughness or topography lubrication mechanism can be change, thus leading to substantial improvement in tribological behaviour of contact surfaces. One of the ways of altering surface topography, known as surface texturing is by introducing small dimples or channels at the contact surface. Surface texturing is already successfully used in different applications, however, they are mainly based on trial and error approach. The aim of this investigation was to identify surface roughness parameters which could be used as a design parameter when preparing textured surfaces and to determine the effect of texturing parameters on roughness and tribological properties of boundary lubricated surfaces. Results of this investigation show that textured surfaces can be treated as an ordered roughness, with skewness and kurtosis parameters showing good correlation with the change in tribological behaviour of contact surfaces. Negative skewness and high kurtosis values, which can be achieved through wedge-shaped dimples, reduced dimple size and increased dimple spacing, were found to result in lower friction.
Development of an Interferometric Technique to be Used in Measuring Micron Level Clearances Filled With a Lubricant
Authors: Yıldırım Murat , Dursunkaya Zafer , Okutucu Tuba
Published: February 2010

The aim of this study is to develop an interferometric technique to measure micron level clearances occurring in small piston-cylinder arrangements; such as hermetically sealed compressors. A Cartesian model of the piston cylinder arrangement is manufactured and lateral and vertical motions are generated via a step motor, and micrometers, respectively, to simulate the piston motion and the change of clearance during the motion. Experiments are conducted in air and a lubricant. Measurements show the important effect of surface waviness of the mirror and the effect of the motion of the carriage at micron level measurements.
Effects of Lattice Orientation and Size on Molecular Asperity Contact Models
Authors: Polchow J. Robert , Huang Wei , Jackson Robert L.
Published: February 2010

Surface asperities can range widely in size. Therefore it is important to characterize the effect of size and scale on the contact mechanics. This work presents a molecular model of asperity contact in order to characterize small scale asperity contact. The effects of lattice orientation and radius (number of particles) are examined. It appears that lattice orientation has a noticeable effect, but nominally may not be important in the contact of asperities and rough surfaces. The size appears to be important until a certain minimum size is achieved.
The Effect of Machining Induced White Layer on Frictional and Wear Performance at Dry and Lubricated Sliding Contact
Authors: Waikar R. A. , Guo Y. B.
Published: February 2010

A white layer on a machined surface is often produced at abusive machining conditions. However, the effect of white layer on frictional and wear performance has received little attention. This study has shown that the existence of a turned white layer slightly decreases the coefficient of friction (COF), while a ground white layer significantly increases COF at dry conditions. At lubricated conditions, the turned white layer only slightly increases COF while the ground white layer slightly reduces it. The third body wear debris may act as solid lubricants leading to reduced friction.
Effects of Altitude on the Thermal Flying Height Actuation
Authors: Zheng Jinglin , Bogy David B. , Zhang Shuyu , Yan Wentao
Published: February 2010

Thermal flying-height control (TFC) is now a key technology used in hard disk drives (HDD) to push the magnetic spacing to sub-5nm. The precise control of the flying height (FH) actuation is a major consideration in improving the read/write capability as well as increasing the reliability. In this paper, we investigate the response of TFC sliders to altitude change with a focus on the actuation efficiency variation with altitude. Numerical and experimental results both indicated an increase in the actuation efficiency at higher altitudes. Simulations are conducted which disclose that increased protrusion and less pushback near the transducer contribute to the efficiency increase at higher altitudes. This study is of practical importance for improving the heater and ABS designs to reduce HDD sliders’ sensitivities to altitude changes.
Transient Thermomechanical Contact Between a Sphere and a Moving Flat
Authors: Ovcharenko Andrey , Yang Min , Chun Kaynam , Talke Frank E.
Published: February 2010

Transient thermo-mechanical contact between a sphere and a moving flat is investigated using finite element analysis. Both the sphere and the flat are treated as elastic plastic bodies with isotropic hardening. Friction is related to heat generation at the contact interface. Strain and temperature distributions of the contacting bodies are obtained. For conditions corresponding to contact between a slider and a disk in a hard disk drive, plastic deformation and high temperatures are found to occur at the interface.
Partial Contact Head-Disk Interface With Thermal Protrusion
Authors: Chen Du , Bogy David B.
Published: February 2010

A new partial contact head disk interface (HDI) with thermal protrusion is proposed for magnetic recording with densities of 1 Tbit/in2 and above. This HDI has the advantage of maintaining light contact between the slider and the disk, so that both the bouncing vibration amplitude and the contact force are small compared with a traditional partial contact HDI. The slider’s dynamic simulations are carried out to analyze the effect of various factors within the HDI on the slider’s dynamic performance, including the friction and adhesion between the slider and the disk, the track profile morphology of the disk and the air bearing design. It is found that the bouncing vibration amplitude can be reduced to the level of the flying height modulation (FHM) of a non-contact air bearing slider without thermal protrusion.
Stress Field Induced by a Stringer of Inhomogeneities in a Half Space
Authors: Zhou Kun , Keer Leon M. , Wang Q. Jane , Ai Xiaolan , Sawamiphakdi Krich , Glaws Peter
Published: February 2010

This paper presents the study of a stringer of inhomogeneities in an isotropic half space under prescribed load. It shows that the presence of stiff inhomogeneities causes the increase in the stresses in the regions where they are formed. Stress concentration generally occurs within the inhomogeneities, particularly near their edges or corners, and increases as the location of the inhomogeneities approaches the material surface and as the friction force increases.
Including Friction and Spin Rules in the Lattice-Based Cellular Automata Approach to Model Granular Flows
Authors: Marinack Martin C. , Jasti Venkata K. , Higgs C. Fred
Published: February 2010

Granular flows have been proposed as an alternative lubrication mechanism to conventional liquid lubricants in sliding contacts due to their ability to carry loads and accommodate surface velocities. Their load carrying capacity has been demonstrated in the experiments of Yu and Tichy [1]. Alternate lubrication techniques are becoming necessary due to the failure of conventional liquid lubricants in extreme temperature environments, and their promotion of stiction in micro-/nanoscale environments. Yet, understanding granular behavior has been difficult due to its non-linear and multiphase behavior. Cellular Automata (CA) has been shown to be a viable first order approach to modeling some complex aspects of granular flow. Previous work by the authors successfully modeled granular shear with a CA model [2]. Additional work combined CA computational efficiency with particle dynamics to effectively model collision events. This work builds upon and modifies the prior CA modeling approaches by adding friction modeling and spin of particles. This modification maintains the computational efficiency of CA, while increasing accuracy of the predicted granular flow properties, such as speed, solid fraction, and granular temperature. The current work compares the CA model with friction and spin physics relations to the authors’ prior CA model which neglected friction. Both CA models are also evaluated against experimental data to quantify the benefits of including friction and spin in the CA modeling approach for granular flows.
Thermohydrodynamic Lubrication Analysis of Slider Bearings With Steps on Bearing Surface
Authors: Ogata Hideki
Published: February 2010

This study focuses on the thermohydrodynamic lubrication analysis of fluid film bearings with step on the surface such as a Rayleigh step bearing. In general, the Reynolds equation does not satisfy the continuity of the fluid velocity components at steps. This discontinuity results in the difficulty to solve the energy equation for the lubricants, because the energy equation needs the velocity components explicitly. The author has solved this problem by introducing the equivalent clearance height and the equivalent gradient of clearance height at steps. These parameters remove the discontinuity of velocity components and the energy equation as well, so that one can solve these equations on all of the bearing surfaces including the step region by finite differential method (FDM). The numerical results of pressure and temperature distributions by the proposed method for a Rayleigh step bearing were compared with the results obtained by a commercial CFD package. These results showed good agreement with each other. This method is extended to 2D unequal grid problems.
Numerical Analysis on Dynamic Characteristics of Flying Magnetic Head With Ultra Thin Spacing
Authors: Yao Hua-ping , Chen Yang-zhi , Ping Huang
Published: February 2010

Numerical analysis of the dynamic characteristics of a magnetic head with ultra-thin spacing is presented. The dynamic response of the air film is analyzed with the momentum equations and the time-dependent modified Reynolds equation based on the FK-Boltzmann modified model. The pressure distribution is numerically calculated by using an up-wind scheme for a very large bearing number with the finite difference method, and a harmonic average method is used for calculating the flux factor with abrupt change of film thickness. Then, the dynamic characteristics are analyzed in time domain. The numerical results show that under an external motivation the significant vibration is produced in the height direction and in the pitch direction, but the slider is capable of returning to the equilibrium position very quickly.
Investigation Into the Wear Films Formed on Certain Superalloys Between 20 and 600°C During Rotation in an Unlubricated Bearing
Authors: Wood P. D. , Evans H. E. , Ponton C. B.
Published: February 2010

The tribological behaviour of Stellite 6, Tribaloy 700 and Tribaloy 400C have been studied during self-mated unlubricated rotational sliding between 20 to 600°C, at 3ms−1 for 1 hour using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Testing was conducted using a specially designed wear rig in which bearings and shafts of the materials were machined and tested within a furnace. Tribaloy 700 exhibited high bearing wear rates for all temperatures. Tribaloy 400C and Stellite 6 bearing wear rates generally decreased with temperature until very low wear rates were recorded at 600°C. The bearing wear rates appeared to be related to the formation of wear resistant oxide films often known as ‘glazes’. Adherent ‘glazes’ formed on Tribaloy 400C and Stellite 6 at 450°C and 600°C. However, ‘glazes’ formed on Tribaloy 700 showed poor adherence to the substrate causing high wear rates.
Effect of Body Lateral Extension Upon the Elastic Contact
Authors: Glovnea Marilena , Diaconescu Emanuel
Published: February 2010

Half-space contact theory cannot be applied when either contacting bodies are thin or they possess small transversal dimensions. The former situation is often dealt with, but the latter seems to be neglected. This paper investigates the effect of outer radius of cylindrical bodies upon the contact stress field. The method consists in adding supplementary displacements and stresses to the half-space solution in order to fulfill the boundary conditions and the force balance equation on load direction. It is found that the half-space theory is applicable if transversal radius exceeds contact radius.
Contact Stress State in Elastic Layers
Authors: Spinu Sergiu , Diaconescu Emanuel
Published: February 2010

This paper presents the discrete counterpart of an existing continuous formulation for an elastic layer loaded symmetrically. The influence coefficients based numerical approach allows for computing contact stresses induced in the elastic layer by arbitrary shaped indenters. The newly developed code is validated against existing pressure distributions in layer contact for quadratic form punches.
A Model on the Motion of Wear Particles in the Synovial Fluid of an Artificial Hip Joint
Authors: Jhurani Sunny M. , Higgs C. Fred
Published: February 2010

Improvements in surgical procedures, installation techniques and properties of materials have resulted in a remarkable reduction in the failure of artificial hip joints (AHJ) due to infection. However, the durability of these replacements is greatly limited by premature osteolysis and eventual joint loosening, caused by macrophage activity in response to the release of submicron particles of ultra-high molecular weight polyethylene (UHMWPE) cup material [1–4]. The wear debris is mainly due to wear between the bearing surfaces, and these wear rates are known to be accelerated by the third body action of polymethylmethacrylate (PMMA) bone cement particles and metallic fragments of the femoral head material scattered within the synovial fluid lubricant [5]. This study is focused on development of a model that simulates the motion of UHMWPE particles in the synovial fluid between the AHJ bearing surfaces during articulation.
A Simple Method to Calculate Contact Factor Used in Average Flow Model
Authors: Meng F. M. , Wang Q. Jane , Hua Diann , Liu Jordan
Published: February 2010

The average flow model proposed by Patir and Cheng offers a great convenience for the analysis of rough surfaces in lubrication. The contact factor introduced by Wu and Zheng helps to solve a difficulty in local film evaluation using the average flow model. This paper reports a simple method to calculate the contact factor. Method validation is demonstrated by the comparison of the contact factors for Gaussian surfaces obtained with the present method and the fitting formula of Wu and Zheng. The proposed method can not only easily compute the contact factor values for Gaussian surfaces, it can also be used for those of non-Gaussian and measured surfaces, especially those with unknown probability density distribution of the roughness height.
Analytical Results for the Resolution-Dependent Progression of Contact Area in a Multi-Scale Contact Model
Authors: Goedecke A. , Jackson R. L. , Mock R.
Published: February 2010

This work presents an analytical solution of a multi-scale contact model for nominally flat rough surfaces. Based on an extension of the multi-scale model of Jackson and Streator incorporating certain fractal properties, the model investigates the resolution-dependent contact area as a function of load. The progression of contact from full contact to clusters of contact regions, and from elastic to plastic asperity behavior is described in a concise, analytical formulation. Moreover, using an appropriately defined dimensionless scale number, this progression is found to be essentially independent of the roughness. The latter, however, determines how fast the progression is traversed. In a comparison with previous models, e.g. the Persson diffusion model, the present model is found to show good quantitative and qualitative agreement in spite of its more simplistic construction.
A Model and Simulation of the Actuation of a CNT-Based Nanoswitch
Authors: Wu Yu-Chiao , Adams George G.
Published: February 2010

Carbon nanotubes (CNTs) are the subject of extensive research in nanoelectromechanical devices due to their excellent mechanical and electrical properties. This study focuses on modeling the actuation of a CNT-based nanoswitch. The CNT is simulated as a wire with negligible bending stiffness. The distributed force due to the applied voltage difference between it and the electrode causes the CNT deflect toward the electrode. The 2nd order nonlinear ordinary differential equation (ODE) is first solved by the finite difference method (FDM) with fixed point iteration. However, this result is only found in a portion of the stable domain. The second method algebraically reduces the governing equation to a 1st order ODE. After removing the singularity, a numerical integration method is applied without iteration. This method gives complete results in the stable and unstable domains that coincide with the results by FDM in its convergent range.
Tribological Properties of Si3N4 Sliding Against Bearing Steel Under Different Conditions
Authors: Tong Yongxing , Wang Liqin
Published: February 2010

The friction and wear behaviors of Si3N4/GCr15 were studied on the pin-on-disk machine under three different lubrication conditions. The results showed that both the friction and the wear were significantly lower in glycol than in deionized water and kerosene. The steady friction coefficient was 0.02 in glycol, 0.05 in deionized water and 0.20 in kerosene. Scanning electron microscopy revealed that formation and dissolution of the film may occur in deionized water and glycol. The main wear mechanisms were tribochemical and abrasive wear in deionized water, fretting wear for tribochemical film by esterification of oxidized surface of Si3N4 in glycol, corrosive and adhesive wear in kerosene.
Effect of Cu Content on the Tribological Performance of Cr-N Coatings at High Temperatures (840°C)
Authors: Polychronopoulou Kyriaki , Rebholz Claus , Demas Nicholaos G. , Polycarpou Andreas A. , Gibson P. N.
Published: February 2010

Cr-N and Cu-Cr-N coatings with Cu content between 3–65 at.%, Cu/Cr ratios in the 0.04–4.5 range and 21–27 at.% N, synthesized by twin e-beam Physical Vapor Deposition (EBPVD) at 450°C, were investigated. Using X-ray photoelectron spectroscopy (XPS), glancing angle X-ray diffraction (GAXRD) and scanning electron microscopy (SEM), in combination with nanoindentation mechanical property measurements and laboratory controlled ball-on-disc sliding experiments, it is shown that Cu-Cr-N coatings with low Cu content (3 at.%) possess sufficient wear resistance for high temperature demanding tribological applications.
An Explicit Finite Element Model to Study the Influence of Rake Angle on the Discontinuous Chip Formation During Orthogonal Metal Cutting
Authors: Menezes Pradeep L. , Lovell Michael R. , Lin Jeen-Shang , Higgs C. Fred
Published: February 2010

Understanding the tribological aspects of machining processes are essential for increasing the dimensional accuracy and surface integrity of products, as well as gaining a better control of tool wear, chip handling and power consumption. The objective of this investigation is to develop numerical models that accurately predict the chip formation and stress profiles in the work-piece during orthogonal metal cutting using the explicit finite-element method (FEM). In our simulations, a damage material model was utilized to capture the work-piece chip separation behavior and the simultaneous breakage of the chip into multiple fragments. In the simulation, the rigid steel cutter of different rake angles was moved at different velocities against a stationary aluminum work-piece at constant friction for a cutting depth of 1 mm. Overall, the results indicate that the explicit FEM is a powerful tool for simulating metal cutting and discontinuous chip formation. The rake angle had a significant effect on the formation of chip during metal cutting. The formation of discontinuous chip along the contact interface was hypothesized to be due to the internal crack initiation and propagation in front of the tool and above the cutting edge, rather than from the free surface.
A Multi-Physics Computational Framework to Predict Dishing and Erosion in Patterned Wafers
Authors: Mpagazehe Jeremiah N. , Thukalil Geo A. , Higgs C. Fred
Published: February 2010

The prediction of dishing and erosion caused by CMP is desired as they adversely affect the electrical properties of interconnects in integrated circuits. For a model to properly capture these phenomena, it must account for the time dependent surface evolution in CMP. This work employs the previously introduced Particle-Augmented Mixed Lubrication (PAML) model to predict dishing and erosion in CMP. By using PAML to model the polishing of a patterned wafer, it is possible to predict the dishing and erosion experienced during CMP.
Friction and Wear Performance of Candidate Surface Treatments for Wind Turbine Gearbox Bearings in High Slip Contacts
Authors: Evans Ryan D. , Hager Carl H. , Logsdon Roger D.
Published: February 2010

Ring-on-ring rolling/sliding contact tests were conducted to evaluate the impact of ground, black oxided, isotropically finished (ES20), and tungsten carbide-incorporated amorphous hydrocarbon coated surfaces (ES322) on friction and wear in high slip contacts relevant to wind turbine gearbox bearings. The testing was performed in three phases, including Stribeck testing, adhesive wear testing, and cyclic acceleration testing. Results indicated that neither black oxide treatment nor ES20 had long-term adhesive wear protection benefits. However, ES20 exhibited the lowest traction coefficients in boundary lubrication during run-in as compared to the other test surfaces. Only the contacts containing the ES322 hard-coated surface consistently survived the harshest slip and boundary lubrication conditions.
Adhesive Contact Between Atomistic Surfaces Using a Continuum Analysis
Authors: Medina Simon , Dini Daniele , Olver Andrew V.
Published: February 2010

We have previously shown that, for non-adhesive conditions, an atomic scale contact can be adequately represented by a continuum analysis despite the physical shortcomings at this scale. Here we have extended the approach to include effects of the adhesive forces that become significant at this level of contact. Adhesive forces are obtained directly from the surface separation across the contact rather than through a total surface energy approach; this allows a complete representation of local surface features. The pull-off characteristics and pressure profiles have been obtained for several different atomistic AFM tip profiles and compared to those obtained from molecular dynamics simulations presented in the literature [1].
Frictional Shakedown in Contact Problems of Layered Systems
Authors: Reina Saverio , Dini Daniele
Published: February 2010

This article presents an investigation of frictional shakedown for layered systems subjected to periodic contact loading. The term shakedown is here referred to as the possibility of developing interfacial residual stresses at the layer/substrate interface such that frictional slip, originally activated by the applied external contact load, ceases after a few loading cycles. The two-dimensional elastic problem of an elastic strip uniformly pressed against an elastic half-plane and subjected to a concentrated oscillating tangential force is studied. A quadratic programming technique which enables to resolve interfacial micro-slip adopting the distributed dislocation technique is proposed to analyse the behaviour at the layer/substrate interface. The solution to the problem is first validated against classical solutions and subsequently used to map the interfacial behaviour of layered systems undergoing different loading scenarios.
Film Thickness Study of Lubricated, Compliant Contacts
Authors: Myant C. , Spikes H. A.
Published: February 2010

Obtaining lubricant film thickness values within a compliant contact is a challenging problem for several reasons [1]: • Lubricant film thickness covers a wide range of values. • The required measuring range is from fractions to hundreds of microns. • Contact area is considerably large when compared to “hard”, metallic contacts. • Many soft components have a high roughness compared to surfaces usually investigated with established techniques.
Microstructural Evaluation of Wheel Steel Using Simulated Service Thermal Loads
Authors: Dedmon Steven
Published: February 2010

The service thermal history of a wheel is often unknown. With today’s high braking energies, knowing the thermal history can make analysis of a failure a simpler process. These histories can also provide thermal input data for process simulations to assist an investigator in understanding the complex interactions in developing residual stresses. This investigation provides a semi-quantitative tool to evaluate the degree of thermal exposure to which a wheel has been exposed by simulating temperature exposures and how they affect microstructure.
Root Cause of Undesired Hose Separations and a Solution
Authors: Jimenez Edgardo , Hua Lin , Monear Michelle , Nilson Kevin
Published: February 2010

Hose separations remain a significant problem for the class 1 railroads. They average about six thousand undesired hose separations a year. There are a lot of facts that the railroads are aware of, but lack good explanations. Why do more separations happen in the winter than in the summer? Why are old end hoses more prone to separation? Why does replacing the gaskets more frequently lead to a lower separation rate? Substantial research has been done to figure out the root cause of the undesired separation problem and to answer the above questions. The data analyzed from the class 1’s has shown that the trolley arrangement accounts for 52% of the undesired separations. The force to move the end hose in a cushioned car trolley arrangement is sometimes greater than the force required to pull apart the gladhands. It is probable that misalignment of the gladhands, coupled with an end of car (EOC) cushioning arrangement that hinders smooth movement of the end hose, will lead to an undesired hose separation. Research points to the fact that if there is a way that the force required to pull apart the end hose connections is kept greater than the force required to move the shackle on a trolley, then this will lower the frequency of undesired hose separations. By changing various characteristics of the gladhand gasket, it can be ensured that the pull-apart force is always around the 600lb range. These changes have been incorporated into the design of a double wide lip gasket and are currently in field testing. By reducing the occurrence of undesired emergency (UDEs) separations, the amount of time a train is stopped can be greatly reduced.
Strategy for Alternative Occupant Volume Testing
Authors: Carolan Michael , Muhlanger Michelle Priante
Published: February 2010

This paper describes plans for a series of quasi-static compression tests of rail passenger equipment. These tests are designed to evaluate the strength of the occupant volume under static loading conditions. The research plan includes a detailed examination of the behavior of conventional equipment during the 800,000-pound buff strength test. The research will also include a demonstration of an alternative static test that is designed to load and test the occupant volume at a location other than the buff lugs. The alternative test will demonstrate a testing and evaluation method for the occupant volume strength of passenger rail cars that accounts for the collision load path through the occupant volume. Per current Federal Railroad Administration (FRA) regulations, all passenger cars must support an 800,000-pound static load applied to the car’s line of draft without undergoing permanent deformation. However, more operators are looking to introduce equipment built to foreign standards. Many international manufacturers are implementing alternative designs that make use of crash energy management design features, articulated truck designs that span two cars, and low floor designs. These changes in the form and function of the designs require alternative means of applying a compressive load to assess occupant volume strength. FRA has reviewed several proposed alternatively designed equipment under requests for waivers for specific corridors of operation. Because the number of requests has increased significantly, FRA is trying to establish reasonable alternative means for assessing adequate and equivalent occupant volume strength to conventional equipment. This paper proposes an alternative static test procedure that will provide a means of evaluating a similar level of occupant volume integrity and passenger protection during a collision. The test will allow for greater design variation for newer rail cars and cars built to foreign standards. For the alternative test, the load may be introduced through the available structure at the floor level and at the roof level. These loading locations will enable the load to be applied directly into key longitudinal members in the load path of collision loads through the occupant volume. Finite element models are used before testing to determine appropriate alternative load levels and locations. The test article is a modified Budd Pioneer car. No significant modifications are planned for the longitudinal members of the car, or for the occupant volume.
New Typical Assembly Models of MEMS on Passive and Initiative Manipulations
Authors: Kang Xiaoyang , Tian Hongchang
Published: February 2010

In parallel with the development of new technologies that predicting and testing the performance and the reliability of MEMS, there has arisen a growing need for computer simulation. Besides the quality of the available data, such as temperature, the nonlinearities and the time-dependence of the materials properties etc., the accuracy of the simulation results depends substantially on the models for the simulation. The first part here is dedicated to the mathematical and physical models for the simulation of some typical MEMS assemblies. As part of this work, some typical assemblies as well as suitable models for their graphics and numerical representation are demonstrated. In the presentation, the results of the simulations of most of the relevant properties are reported. These assembly manipulations comprise aligning and inserting under typical service conditions. What’s more, new understandings of some manipulation are presented, which is very important to simplify the simulation of assembly. And a new model of MEMS numerical simulations is built in the degree of μm. These assembly manipulations will be divided into passive and initiative actions, which can never be divided in the MEMS assembly systems. The corresponding models for graphics and numerical simulations will be shown. Furthermore, the procedures to predict the performances of MEMS assemblies and interconnections are regarded. By using the typical assembly manipulations and the new understandings, it will be demonstrated that how these models can be utilized in designing MEMS.
A Multi-Objective Design Optimization of a Smart Magneto-Rheological Prosthetic Knee
Authors: Gudmundsson Ketill H. , Jonsdottir Fjola , Thorsteinsson Freygardur
Published: February 2010

Magneto-rheological (MR) fluids have been successfully introduced to prosthetic devices. One such a device is a biomechanical prosthetic knee joint that uses a MR fluid to actively control its rotary stiffness while an amputee walks. The knee is a synergy of artificial intelligence, advanced sensors and MR actuator technology. The MR fluid has response time in the order of milliseconds, making it possible to vary the knee’s stiffness in real-time, depending on sensors data. The focus of this paper is on the design of the magnetic circuit of the actuator and on the geometry of the fluid chamber. The paper describes the function of the MR rotary actuator and shows how design optimization techniques can aid in the development of the actuator. The design is optimized, with respect to three important design objectives. These objectives are: the maximum obtainable field-induced braking torque, the minimum obtainable rotary damping in the absence of a magnetic field, and the weight of the actuator. Multi-objective design optimization techniques are presented and applied to the prosthetic knee actuator design problem. Trade-offs between design objectives are investigated giving valuable information on the development of the actuator. Maximizing the field-induced braking torque is important for the knee to be capable of supporting heavy amputees. Minimizing the off-state stiffness is important for fast movements of the knee, in load-free movements. Furthermore, minimizing the weight of the actuator is important for allowing heavy components like batteries to be installed. It is realized that these design objectives can not be addressed separately and to some extend, the design goals are contradictory. Mathematical models are presented that describe the design objectives as a function of selected design parameters. Determining the field-induced braking torque requires a magnetic finite element analysis, to evaluate the magnetic flux density in the MR fluid, and the shear-yield stress curve of the MR fluid. Evaluating the off-state stiffness requires the off-state viscosity of the MR fluid, along with friction in bearings and oil seals. The models are based on rheological measurements of the MR fluid employed in the knee. Evaluating the weight of the actuator requires the geometry of the actuator and the density of its materials. The optimization is restricted by practical manufacturing design constraints. Mapping the dependency between the maximum torque, the minimum damping, and the weight of the MR actuator gives valuable insight into the design of the prosthetic knee actuator.
Bidisperse Perfluorinated Polyether (PFPE)-Based Magneto-Rheological Fluids in a Prosthetic Knee
Authors: Jonsdottir Fjola , Gudmundsson Ketill H. , Thorsteinsson Freygardur , Gutfleisch Oliver
Published: February 2010

Regaining biomechanical function, comfort and quality of life is a prime consideration when designing prosthetic limbs. Recently, microprocessor-controlled prosthetic knees, which rely on magneto-rheological (MR) technology, have become available and have the potential to meet these needs. One of these promising products is a prosthetic knee manufactured by the company Ossur Inc. The knee is a synergy of artificial intelligence, advanced sensors and MR actuator technology. A critical factor in the success of the prosthetic knee is the composition of the MR fluid. In the prosthetic actuator, the fluid is used in shear mode in a micron-sized fluid gap. The characteristics of the MR fluid, such as, the off-state viscosity, the field-induced shear yield stress, the post-yield viscosity, and the particle sedimentation rate, determine the properties of the prosthetic knee. This paper describes a novel perfluorinated polyether (PFPE)-based MR fluid with properties that are tailored for the requirements of the prosthetic knee actuator. Rheological measurements of monodisperse and bidisperse PFPE-based fluid mixtures are presented. The monodisperse fluid consists of micron-sized carbonyl iron particles and the bidisperse mixture contains micron- and nano-sized particles. A few different concentrations of nano particles are investigated; first by holding the total solid concentration constant, and then by increasing the total solid concentration, to exceed that of the MR fluid containing only micron-sized particles. An MR fluid composition is sought that has a suitable balance between field-induced strength, off-state viscosity and sedimentation rate, for the proposed application. This balance is determined by desired qualities of the prosthetic knee and relate directly to the MR fluid. The field-induced shear stress of MR fluid samples is measured as a function of the magnetic flux density along with the off-state viscosity as a function of the shear-rate. The shear stress and off-state viscosity at high-shear rates are of particular interest, since the working shear rate in the prosthetic knee is high, due to the micron-sized gap between the blades in the fluid chamber of the actuator. Mathematical models are presented that describe how the MR fluid properties relate to the behavior of the prosthetic knee. The paper shows how a tailored design of an MR fluid can further the success of the MR prosthetic knee.