bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure and Shear Flow Factors Calculation for Orthotropic Rough Surfaces
Authors: Dragomir Ramona , Bonneau Dominique , Ragot Patrick , Robbe-Valloire Franc¸ois
Published: March 2009

In general, average Reynolds equation is defined in terms of shear flow factors in order to determine the effects of surface roughness on partially lubricated contacts. This paper is essentially devoted to the application of flow factors model to real shaft and bearing surfaces, obtained by metrological measures. Additionally, the average Reynolds equation is completed by “cross” flow factors. The “cross” flow factors may have an important role if model is applied on either longitudinally or transversely oriented surfaces (surfaces with directional patterns oriented with an angle).
Drainage of a Wetting Liquid: Slip Effect or Molecularly Organised Layers?
Authors: Cayer-Barrioz J. , Tonck A. , Mazuyer D. , Yamaguchi E.
Published: March 2009

A Surface Force Apparatus has been used to investigate the drainage of a blend of copolymer viscosity improver additive molecules in a base oil. A quasi-static squeeze of the interface is used to characterize the first repulsion layer and the confined adsorbed layer. Moreover, dynamical measurements enlighten a significant negative value of the immobile layer thickness (−50 nm). The occurrence of slip at the wall that may result in such effect, is discussed in terms of liquid-solid interface wettability, surface roughness and cleanliness, and friction experiments. As a consequence, a modeling of the interface consisting of two layers of different viscosity is proposed. This model of interfacial molecular organization allows us to explain the drainage behaviour of the wetting liquid.
Effect on the Film Pressure Distribution on a Hydrodynamic Tilting Pad Bearing Caused by the Coating of the Journal With DLC by Triboadhesion
Authors: Rodri´guez-Lelis J. M. , Vela-Arvizo D. , Abundez-Pliego A. , Reyes-Galindo S. , Navarro-Torres J. , Vargas-Trevin˜o M.
Published: March 2009

This work is concerned with the effect on the film pressure distribution caused on a hydrodynamic tilting pad bearing, by the change in surface properties of the journal. Here two identical journals, both manufactured with AISI 9840, were employed. One of them was coated with DLC by the triboadhesion process, and the second, was used as a reference without applying any coating. During tests, the tilting pad experienced a lower film pressure distribution when the journal coated with DLC was employed. This phenomena could readily be attributed to the different surface energies of the coated and uncoated journals, which in time causes that the fluid film characteristics to be modified by the reduction of the shear stresses at the wall, thus reducing the maximum film pressure measured and shifting the maximum pressure to the line of symmetry, drawn from the center of the journal to the pin of rotation of the tilting pad.
Oil Debris Detection Using Capacitance and Ultrasonic Measurements
Authors: Zhe J. , Choy F. K. , Murali S. V. , Sarangi M. A. , Wilfong R.
Published: March 2009

This paper aims at the use of a capacitance sensing approach using a RLC meter to detect oil debris contents and experimental results are compared to those obtained using an ultrasonic device. It was found that both capacitance and ultrasonic measurement can both detect particles as small as 4 mils (101 μm) in diameter. Experimental results show that the measured capacitance increases linearly with the increase of particle size while the ultrasonic wave amplitude decreases linearly with the increase of particle size. While some measurable differences can be detected by both capacitance and ultrasonic measurements between the ferrous and the nonferrous particles, a systematic difference between the data point cannot be developed. In addition, the existence of nonconductive particles cannot be readily detected using the capacitance measurements but their existence can be observed by the ultrasonic measurement.
Temperature Distribution of a Wave Journal Bearing: Comparison With Test Data
Authors: Ene Nicoleta M. , Dimofte Florin , Keith Theo G. , Handschuh Robert F.
Published: March 2009

An advanced three-dimensional model is developed to compute the temperature distribution in a wave journal bearing. The analysis takes into account the heat transfer between the film and both the shaft and the bush. The theoretical results are validated by comparison with experimental data.
Development of a Novel Green Lubricant for Sheet Metal Forming Operation
Authors: Kabir M. A. , Higgs C. F. , Lovell M.
Published: March 2009

The main purpose of the present investigation is to analyze a novel, green, and petroleum-free lubricant that is produced by mixing two environmentally benign components—canola oil and boric acid powder. To study the influence of boric acid crystal size and volume ratio on the proposed lubricants performance, computerized pin on disk experiments were conducted with spherical copper pins (radius 6.5 mm) and aluminum disks (Ra = 1.35μm). Friction coefficient measurements were taken at more than twenty distinct operating conditions while varying the lubrication condition (unlubricated, boric acid, canola oil, boric acid/canola oil mixture), boric acid volume fraction (3.5%, 7%, 10.5 and 21%), and boric acid crystal size (0–100 microns, 100–150 microns, 150–180 microns, 180–350 microns and 350–710 microns). Based on the experiments, it was determined that a 7% by volume boric acid powder in canola oil with 350–700 micron particles was the optimum green lubricant for minimizing the friction at the conditions tested. In addition, the results indicated that the boric acid/canola oil lubricant demonstrated excellent potential for use in industrial applications such as sheet metal stamping.
Mechanical and Environmental Degradation of Self-Assembled Monolayer Coatings for Microelectromechanical Systems
Authors: Timpe Shannon J.
Published: March 2009

Self-assembled monolayer coatings have shown great promise for dramatically reducing the tribological forces of adhesion and friction in microelectro-mechanical systems (MEMS). However, monolayer coatings often display significant degradation when exposed to extreme environments, dynamic sliding contact, and dynamic impact loading. This degradation is coupled with a corresponding increase in the tribological properties. In this study, the degradation of tridecafluorotri(dimethylamino)silane is examined under the typical operating conditions of MEMS technology using a specialized microdevice designed for characterizing the tribological behavior surface micromachines. Results of friction and adhesion degradation under normal loading and sliding contact are interpreted in relation to the primary degradation mechanisms of self-assembled monolayers.
New Rig to Test Journal Oil Lubricated Wave Bearings
Authors: Dimofte Florin , Ene Nicoleta M. , Handschuh Robert F. , Keith Theo G.
Published: March 2009

A new rig to test journal fluid film bearings was designed, manufacture and installed at NASA Glenn Research Center in Cleveland, Ohio, USA. This rig can apply total radial loads to 133,000 N (30,000 lbs) and can rotate the shaft to speeds to 13,000 RPM. The test bearing has a diameter of 68 mm and is 38 mm long. Two such bearings are used to support the total load. The shaft is also supported by two fluid film bearings. The rig is well instrumented for measuring oil flow, oil inlet and outlet temperatures, bearing sleeve temperatures along its circumference and the oil temperatures in oil supply pockets. The shaft position is monitored by proximity probes. Vibration levels at four locations are also displayed and recorded. Preliminary tests of wave bearings at 8,000 RPM and loads to 20,000 N (4,500 lbs) show a good correlation between the test and prediction data.
Modeling a Porous Slider Bearing With an External Reservoir
Authors: Johnston Joshua D. , Braun Minel J. , Young Gerald W.
Published: March 2009

This work considers a porous slider bearing above an external reservoir. The bearing system consists of a lubricating film, porous medium, and a reservoir. The Darcy model is used for flow inside the porous medium. The moving slider bearing establishes a pressure profile that circulates fluid between the lubricating region and the reservoir. Simplifications are made to allow for a semi-analytical solution to be constructed that can be easily solved using a standard computational package. It is shown that the fluid is circulated inside the bearing to allow for a load-carrying capability as well as for no external lubricant supply.
An Investigation of Three Dimensional Elastic-Plastic Hemispherical Sliding Contact, Part II: Results
Authors: Moody John , Green Itzhak
Published: March 2009

This work presents the results from a three dimensional (3D) finite element analysis (FEA) of an elastic-plastic asperity contact model for two spherical bodies sliding across each other with various preset vertical interferences. Stresses, forces, contact areas, deformations, and net energy loss are presented for steel-on-steel and aluminum-on-copper contact.
Finite Element Analysis of Contact and Structural Phenomena of a Lab-Scale Electromagnetic Accelerator
Authors: Chung Bummo , Green Itzhak , Cowan Richard S.
Published: March 2009

This work presents a finite element analysis (FEA) of the initial armature-to-rail contact of a lab-scale electromagnetic accelerator (12.5 mm rail height) and a modal analysis of the armature. Structural results of the von Mises stress, the contact pressure, and the contact area are presented with the vibrational characteristics (frequencies and mode shapes) of the un-stressed and the pre-stressed armature.
A Finite Element Study of the Effect of Friction on the Deformations, Forces, Stress Formations, and Energy Losses in a Sliding Contact Between Aluminum and Copper Cylinders
Authors: Vijaywargiya Raghvendra , Green Itzhak
Published: March 2009

This work presents the results of a Finite Element Analysis (FEA) used to simulate two-dimensional (2D) sliding between two interfering elasto-plastic cylinders, one with material properties of a tougher material (copper alloy Glidcop) and the other of a relatively weaker material (aluminum alloy Al 6061-T651). Trends in the deformations, reaction forces, stresses, and net energy losses as a function of sliding distance are established. Results for both frictionless and frictional sliding are presented and comparisons are drawn. The effects of plasticity and friction on energy loss during sliding are isolated.
Air Bearing Flying Characteristics on Patterned Media
Authors: Peng Wei , Crone Robert M. , Esmenda Emil , Hsia Yiao-Tee
Published: March 2009

The air bearing steady-state flying characteristics on patterned media has been studied with a proprietary air bearing simulation code. Variation of minimum fly height with relative pattern-to-slider skew has been characterized at slider positions (ID, MD, OD). The results show that at the steady state minimum fly heights drop with introducing the pattern. Furthermore, the pattern-to-slider skew angle has a noticeable effect on the fly height drop, while the maximum fly height drop occurs on radial servo patterns.
On the Amount of Air Entrainment Into Finite Length Squeeze Film Dampers
Authors: Me´ndes Tilmer , Ciaccia Marco A. , Torres Jorge E. , Di´az Sergio E.
Published: March 2009

Squeeze Film Dampers (SFDs) are routinely employed to reduce vibration amplitudes and isolate structural components in gas jet engines, high performance compressors and, occasionally, water pumps. Most open-ended squeeze film dampers in practice present the phenomenon of air entrapment. It is generally accepted that the presence of air reduces the damping capability of the SFD, especially at large amplitudes and high frequencies of vibrations. Thus, there is a need for a reliable model of practical use in the analysis of high performance turbomachinery SDFs operating with air entrainment. Di´az and San Andre´s advance a model for estimation of air entrapped into the film lands. This model is based on a dimensionless number that relates geometric and operational parameters, but is strictly valid only for infinitesimal length bearings. The present research has by objective extending the previous work of Di´az and San Andre´s for prediction of air entrainment and entrapment on finite length bearings. The Reynolds lubrication equation for a homogeneous mixture is solved using the finite volume method. The results are shown in a map that allows determining air volume content in the film as a function of the dimensionless parameter created by Di´az and San Andre´s (Squeeze-Feed Flow Number, γ) and the length-diameter ratio (L/D). This work represents a significant step towards a better understanding of air entrainment in finite length Squeeze Film Dampers.
Fractal-Regular Surface Characterization Based on Experimental Data From Atomic Force Microscopy of Hard Disks
Authors: Sasikanth Anne , Wang Shao
Published: March 2009

Engineering surfaces should be characterized as fractal-regular surfaces since they possess both a macroscopic regular shape component and a random fractal component. In the present study, surface topography measurements were conducted for magnetic hard disks with an atomic force microscope (AFM). The power spectral density data obtained reveal a regular shape region and two fractal regions, indicating bifractal-regular behavior. By combining the AFM data with previous profilometer data, a complete description of the power spectral density behavior of the measured surfaces was obtained for a wide range of scales from 2 nm to 5 mm. The fractal dimension was found to be 1.935 and 1.186 for the upper fractal region and lower fractal region, respectively. Good agreement between the AFM data and profilometer data was observed in a range of overlapping scales. A multi-section modified Weierstrass-Mandelbrot function has been proposed to simulate bi-fractal surfaces with a power spectral density trend which matches that of experimental data.
Micro and Nanoscale Experiments and Finite Element Studies of Rail Steels
Authors: Lee Ki Myung , Polycarpou Andreas A.
Published: March 2009

Recently rail steel with bainite microstructure was developed that had higher hardness compared to conventional pearlite microstructure steels and was expected to exhibit improved wear performance. However, it showed worse wear performance than pearlitic steel, and it was shown that conventional pearlitic steel work-hardened significantly more than bainitic steel under severe stress conditions. As the effects from the wheel/rail contact are confined to the topmost contact surface and sub-surface, convenient micro and nanowear experiments may also be used to predict the wear performance of rail steels. Such experiments were performed on rail samples and subsequently, a finite element model was developed to simulate repeated sliding contact/wear.
An Approximate Analytical Solution for the Elasto-Plastic Contact of the Non-Isotropic Rough Surfaces
Authors: Moraru Laurentiu , Keith Theo G.
Published: March 2009

The contact mechanics models incorporate various integral expressions that involve the probability density functions of the asperity heights. These integrals can be calculated numerically with the desired accuracy, however, in the practical applications of the contact mechanics, the computations are already quite time consuming. Consequently, various authors have proposed approximate solutions, mostly for the isotropic contact mechanics models. The current paper presents an approximate solution for the non-isotropic elasto-plastic model proposed by Horng. The probability density of the asperity heights is approximated, so the integrals that describe the elastic contact, as well as the integrals that describe the plastic contact, can be obtained as closed form expressions. Finally, the plastic supported load and the elastic supported load for the non-isotropic roughness are expressed using the gap, the spectral moments of the roughness and the plasticity index.
An Extension of CEB Elastic-Plastic Contact Model
Authors: Sepehri A. , Farhang K.
Published: March 2009

Three dimensional elastic-plastic contact of two nominally flat rough surfaces is by developing the equations governing the shoulder-shoulder contact of asperities based on the Chang, Etsion and Bogy (CEB) model of contact in which volume conservation is assumed in the plastic flow regime. Shoulder-shoulder asperity contact yields a slanted contact force consisting of both tangential (parallel to mean plane) and normal components. Each force component comprises elastic and elastic-plastic parts. Statistical summation of normal force components leads to the derivation of the normal contact force for the elastic-plastic contact akin to the CEB model. Half-plane tangential force due to elastic-plastic contact is derived through the statistical summation of tangential force component along an arbitrary tangential direction.
Three Dimensional Elastic-Plastic Contact of Nominally Flat Rough Surfaces: Approximate Closed-Form Equations
Authors: Sepehri A. , Farhang K.
Published: March 2009

Approximate closed-form (closure) equations governing the shoulder-shoulder contact of asperities are derived based on a generalization of Chang, Etsion and Bogy (CEB). The work entails the consideration of asperity shoulder-shoulder contact in which volume conservation is assumed in the plastic flow regime. Shoulder-shoulder asperity contact gives rise to a slanted contact force comprising tangential and normal components. Each force component comprises elastic and elastic-plastic terms, which upon statistical summation yields the force component for the elastic and elastic-plastic force for the contact of two rough surfaces. Half-plane tangential force due to elastic-plastic contact is derived through the statistical summation of tangential force component along an arbitrary tangential direction. Two sets of closure equations are found. In the first set of equations the functional forms are simpler and provide approximation of contact force to within nine percent (9%). The second set of closure equations are closed form equations of more complicated form but with accuracy to within 0.2 percent (0.2%).
Friction Due to Elastic-Plastic Contact of Rough Surfaces
Authors: Sepehri A. , Farhang K.
Published: March 2009

A three dimensional model based on CEB elastic-plastic contact leads to the derivation of two force components due to the shoulder-shoulder interaction of the asperities. A normal force component is resulted that upon summation of all possible interactions, in a statistical sense, obtains the normal force between the two surfaces. A second component of asperity force would be along the tangential plane (mean plane). When there is not net applied tangential force the tangential component of force on an asperity due to all its interactions would vanish. Upon impending motion, however, the tangential force can no longer cancel since the existence of a net tangential applied load would disrupt the symmetry of loading in the tangential direction. A three dimensional elastic-plastic model then furnishes a half-plane tangential elastic-plastic force term that would exist when relative movement of one surface on another occurs along an arbitrary axis in the tangential plane. This paper addresses an account of friction due to the elastic-plastic interaction of two surfaces by recognizing that the tangential half-plane elasto-plastic force term is the resisting force when two surfaces in elastic-plastic contact are made to slide.
Chemical Mechanical Polishing Friction Measurements With Silica Atomic Force Microscope Tips
Authors: Choi Joo Hoon , Lee Yangro , DeMarco Louis E. , Leveille Richard T. , Levert Joseph A. , Korach Chad S.
Published: March 2009

The feature sizes on Integrated Circuits (ICs) continue to decrease to provide higher device densities and smaller chip designs. To accomplish this, current fabrication and processing technology must be advanced to achieve these goals. In particular, Chemical Mechanical Polishing (CMP), which is used for planarization of wafers and logic circuit components during IC fabrication, can cause severe surface damage to components in the form of delamination or distortion of surface features. CMP utilizes polishing particles suspended between a polymeric pad and the substrate to be polished. To control the process with higher precision the fundamentals of friction between CMP surfaces need to be analyzed. To investigate the friction contributions of the polishing particles in the CMP process, individual CMP abrasive particles are modeled by a silica atomic force microscope (AFM) probe with a radius of curvature on the order of 200 nm that is utilized in a scanning probe microscope (SPM). Lateral forces are measured that occur in simulated polishing of silica substrates and polyurethane pad material in a liquid environment. Results are obtained as a function of pH and environment and are compared with macroscopic friction results obtained using a high precision tribometer with a glass ball.
Prediction of Dissipation in Joints Subject to Oscillating Force
Authors: Farhang K. , Segalman D. , Starr M.
Published: March 2009

Energy dissipation in mechanical joints occurs as a result of micro-slip motion between contacting rough surfaces. An account of this phenomenon is especially challenging due to the vast differences in the length and time scales between the macro-mechanical structure and the micron-scale events at the joint interface. This paper considers the contact between two nominally flat surfaces containing micron-scale roughness. The rough surface interaction is viewed as a multi-sphere elastic interaction subject to a periodic tangential force. It combines the Mindlin’s formulation [1,2] for the elastic interaction of two spheres with the Greenwood and Williamson’s [3] statistical approach for the contact of two nominally flat rough surfaces so as to develop a model for multi-sphere problem in which sphere radii, contact load and the number of spheres in contact can only be known in a statistical sense and not deterministically.
Nanotribology, Nanomechanics and Materials Characterization Studies Using Scanning Probe Microscopy
Authors: Bhushan Bharat
Published: March 2009

At most solid-solid interfaces of technological relevance, contact occurs at numerous asperities. A sharp atomic/friction force microscope (AFM/FFM) tip sliding on a surface simulates just one such contact. However, asperities come in all shapes and sizes which can be simulated using tips of different shapes and sizes. AFM/FFM techniques are commonly used for tribological studies of engineering surfaces at scales ranging from atomic- to microscales. Studies include surface characterization, adhesion, friction, scratching/wear, boundary lubrication, and surface potential and capacitance mapping1–5. AFMs and their modifications are also used for nanomechanical characterization, which includes measurement and analysis of hardness, elastic modulus and viscoelastic properties, and in-situ localized deformation studies. State-of-the-art contact mechanics models have been developed and are used to analyze dry and wet contacting interfaces. Experimental data exhibit scale effects in adhesion, friction, wear, and mechanical properties, and a comprehensive model for scale effects due to adhesion/deformation and meniscus effects has been developed. Generally, coefficients of friction and wear rates on micro- and nanoscales are smaller, whereas hardness is greater. Therefore, micro/nanotribological studies may help define the regimes for ultra-low friction and near zero wear. New lubrication strategies such as the use of self-assembled monolayers promise to be very versatile and effective at these scales. To improve adhesion between biomolecules and the silicon based surfaces, chemical conjugation as well as surface patterning have been used. In the area of biomimetics, surface roughness present on lotus and other leaves has been measured and the surface films are characterized to understand the mechanisms responsible for superhydrophobicity (high contact angle). A model for surface-roughness-dependent contact angle has been developed and optimum distributions have been developed for superhydrophobic surfaces.
Tribo-Diagnostics of Nanoparticle Coated Smart Surface Using Phase Fluctuation Based Processor
Authors: Veeregowda Deepak H. , Sharma Jagdish P. , Wagstaff Ronald A. , Wang Qian J.
Published: March 2009

Smart material surfaces/interfaces are playing important role in making hybrid nano particulate coated sensors and smart composite structures for applications in space, defense, infrastructure and biological system. The reliability and performance of these coatings on the smart surface depends upon the stability and life of their nano/micro-structures and interface properties. Atomic Force Microscopy is used extensively to study friction, wear and surface forces. In this paper a tool has been developed to have an insight of signals associated with friction and tribo-acoustics. This research aims to develop a combination of tools using High Speed Data Capture tools used in conjunction with the AFM to collect the frictional signal at the frequency of 500 kHz for 500 ms and phase fluctuation processor for study of friction signal. Friction signal from the AFM has poor information on the interfacial material properties like the stick-slip, plastic deformation of the contact surface. Clearer, information can be attained using the phase fluctuation based processor. This method provides friction signal and generation of the tribo-acoustics due to surface plastic deformation with excellent signal to noise ratio.
Advanced Experimental and Numerical Analysis of the Pressurized Air Wave Bearings
Authors: Sescu Adrian , Dimofte Florin , Sescu Carmen , Afjeh Abdollah A. , Handschuh Robert
Published: March 2009

Experimental, analytical, and numerical investigations have been done in the field of gas lubrication, but few people focused on details of fluid flow between the sliding surfaces. In this work the entire pressurized wave bearing is analyzed in detail. The numerical study using a three-dimensional commercial code and a two-dimensional finite difference code gives information about the flow at many levels. The numerically computed flow rates using the commercial code are compared with experimental results determined at NASA Glenn Research Center on an experimental rig. The calculated discharge coefficient is used in the finite difference code which solves the Reynolds equation. The holes effect is considered as a source term, instead of applying hybrid type boundary conditions on the holes contours. Data from experimental tests, commercial three-dimensional code, and two-dimensional code are reported and compared to each other. Good agreement was found between numerical study and experiment.
A Parametric Experimental Investigation and Performance Comparison of Four Finger Seal Embodiments
Authors: Smith Ian M. , Braun Minel J.
Published: March 2009

For the finger seal, the compliance, combined with the non-contacting characteristic (not available in a brush seal), allow both axial and radial adjustment of the seal to the rotor excursions, without losing physical integrity, or diminution of seal worthiness. Four finger seal configurations are being investigated. Three models feature a padless high pressure laminate and a padded low pressure laminate, and a fourth one incorporates a novel third and interlocking padded layer. This additional layer’s role is to further reduce leakage and increase lifting capability. The finger seal lifting properties and its structure compliance are evaluated through the performance of a set of parametric studies where the seal upstream pressure is held at 10 psi, and the rotor angular velocity is increased to 15 krpm.
Hydrodynamic Pressure Generation Caused by Surface Roughness or Texture
Authors: To̸nder Kristian
Published: March 2009

It is well established that roughness or texture on bearing surfaces may generate hydrodynamic pressures exceeding those generated by smooth surfaces of the same nominal macro-geometry. The effect is often attributed to the local positive pressure excursions being larger than the negative ones. It is shown that this interpretation is erroneous, and that the effect of cavitation plays a very minor role. Similarly, solutions based on the Navier-Stokes equations indicate that asymmetric pressure profiles that may be generated at very steep edges of surface micro-profile excursions, usually have little effect. It is concluded that the increased pressure is essentially caused by the changes in flow impedance.
A New Approach to Improving Oil Lubricity
Authors: Levchenko V. A. , Ignatieva Z. V. , Buyanovsky I. A. , Matveenko V. N.
Published: March 2009

A new approach to oil lubricity improving is considered. It bases on changes in molecular structural ordering of adsorbed oil boundary layers governed by a highly oriented solid substrate. Among diamond-like coatings with varying structure there are some ones (with monocrystalline or polycrystalline structures) having orientation effect on molecular ordering of lube oils what leads to decrease in friction coefficient. It is shown that orientating and adsorption effects of carbon coatings can be intensified by additional active centers creation on their surfaces, particularly by nitrogen atoms doping. The tribotests had shown better antifriction properties of nitrogen doped coatings at various contact loads both under dry friction and under friction in lube oils as compared with that of amorphous carbon coating and uncoated steel.
Friction of Aromatic Thiols in Contacts of Different Adhesive Strength
Authors: Ruths M. , Yang Y.
Published: March 2009

We have used friction force microscopy to study the boundary friction of thiophenol and 2-napthalenethiol monolayers on gold. The strength of the adhesion was altered by working in dry N2 gas or in ethanol. A contact mechanics model developed by Sridhar, Johnson and Fleck1,2 (SJF) for a thin, compliant elastic film confined between stiffer substrates was used to evaluate the data in systems with higher adhesion.
Homogeneous Approach for Composite Under Dynamic Contact With Friction
Authors: Peillex Guillaume , Baillet Laurent , Berthier Yves
Published: March 2009

An explicit dynamic 2D finite element model of a composite under dynamic tribological loading is proposed. The software used for this kind of application manages contact conditions thanks to the Lagrange multipliers. The kind of contact is a deformable against rigid surface one. First of all due to ill-posedness of the classical Coulomb friction law, a regularized Coulomb friction law that allows local and global convergence of the models even under the presence of contact instabilities is proposed. This friction law is experimentally motivated and is similar to the simplified “Prakash-Clifton” law. In a second time the dynamic tribological behavior of the composite is studied by the mean of different models where the heterogeneities of the material are explicitly introduced. Those heterogeneous models stand for a description of the microscopic scale of the composite. A comparison is made between the results given by these heterogeneous models and the results obtained by the analysis of a homogeneous model. The elastic properties of the homogeneous model are obtained through classical homogenization process which is suitable here because the scale separation, difference between the size of the heterogeneities and the wavelength of the loading, is sufficiently important. The homogeneous model represents the macroscopic scale of the composite. Equivalence between heterogeneous models and the homogeneous one is straightforward if the contrast of Young’s modulus between the heterogeneities and the matrix is sufficiently low and if the local contact dynamic is stable. This equivalence has been observed for different contact instabilities like slip-separated, and stick-slip-separated ones. When the equivalence between the models is not ensured, because of high contrast of elastic properties for example, an adaptation of the dynamic parameter of the friction law is necessary to retrieve this equivalence. Finally the determination of the stresses and their evolution along the time in the heterogeneities and in the matrix is performed thanks to the relocalization process. This process is mixing dynamic analysis of the homogeneous models and fast static calculations on heterogeneous model. This process has already been applied to structures submitted to static loading but to our knowledge this is the first attempt to use it for dynamic contact problems. So this work highlights a full multi-scale approach for composite under dynamic contact with friction loading.
Effect of Lubricant Scarcity on the Film Formation in an Inlet Zone During High Speed Cold Rolling Process
Authors: Singh Prahlad , Pandey R. K. , Nath Yogendra
Published: March 2009

Effective lubrication during the cold rolling is vital in achieving desirable tolerance and surface quality over the metallic sheets. However, in the process of cold rolling, it has been established that the lubricant’s viscosity drastically reduces (viscosity thinning) due to huge viscous heat dissipation in the lubricating film at the elevated rolling speeds. Thinning of lubricant viscosity increases the escaping tendency of the lubricant from the inlet zone. Thus, scarcity (starvation) of lubricant prevails in the inlet zone of roll and strip interface. Based on the present investigation, it is observed that the existence of starvation seems to be beneficial in terms of reduced temperature rise and less quantity of lubricating oil required provided there is a continuous film at the strip-roll interface.
Improving Cylindrical Pin Cage Bearing Performance in Mill Applications Using Dynamic Modeling and Space Filling Design
Authors: Pederson Bradley M. , Rhodes Jerry
Published: March 2009

A dynamic cylindrical bearing model was modified to analyze large bore cylindrical mill bearings with pin cages. A factor-response methodology was coupled to the dynamic modeling input and output variables in order to generate a suitable transfer function for predicting bearing performance. Response optimization of the transfer function indicated that a traction-based parameter was determined to have the greatest effect on reducing roller slip and improving bearing performance.
Experimental Analysis of Journal Bearings Undergoing Oscillatory Motion
Authors: Lu Xiaobin , Khonsari Michael M.
Published: March 2009

A series of experiments is carried out on a grease-lubricated, heavy loaded journal bearing undergoing oscillatory motion to examine its thermal field. The history of temperature measurement and the friction coefficient are monitored. The finite element method is employed using ANSYS to simulate the temperature history with input of the friction coefficient result. Experiment and simulation show good agreement.
Tribochemical Interactions Between Lubricant Additives and Low Hydrogen Containing DLC Coating Under Boundary Lubrication Conditions
Authors: Haque Tabassamul , Morina Ardian , Neville Anne
Published: March 2009

Diamond Like Carbon (DLC) coatings are becoming very popular for automotive tribo-components as they can offer excellent tribological properties resulting in improved fuel economy and reducing dependence on harmful components of existing additives. The tribochemical interactions of low hydrogen containing DLC coating with lubricants, basically customised for ferrous materials, are yet to be well understood. In this work, an experimental study has been performed to understand the synergistic and antagonistic effects of low friction and antiwear additives on a 15 at. % hydrogen containing DLC coating. Surface sensitive analytical techniques, such as atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to perform physical and chemical characterization of the tribofilms.
An Efficient Elastic Deformation Analysis Procedure for Simulating Conformal-Contact Elastohydrodynamic Lubrication Systems
Authors: Xiong S. W. , Wang Q. Jane , Lin Chih , Wang Yansong , Liu W. K.
Published: March 2009

A compliance operator is often utilized to evaluate the elastic deformation during simulation of elastohydrodynamic lubrication of conformal-contact systems. The values of the compliance operator represent the elastic deformations of all nodes when only one node is under a unit external load. The accuracy of compliance operator values, computational cost, and storage size are important issues. It is found that values only in a small region surrounding the loading node should be used and those in other regions can be discarded. Moreover, the mesh refinement in thickness direction is found to be more important than that along the longitudinal and width directions. A simple formula is suggested as the relationship between the values of a compliance operator and refinement steps. These two approaches enable an efficient elasticity procedure for the simulation of conformal-contact Elastohydrodynamic lubrication systems.
Relations of Microstructure, Piezoelectricity, and Surface Forces at Nanoscale
Authors: Lee Hyungoo , Cooper Rodrigo , Mika Bartosz , Liang Hong
Published: March 2009

In small devices such as micro-electro-mechanical systems (MEMS) and nano-electro-mechanical systems (NEMS), adhesion and friction forces make them less reliable with unacceptable performance [1]. These forces need to be completely understood to make advances in the systems. In our previous research, it has been proven that using a functional material, polyvinylidene fluoride (PVDF), both stiction and friction could be modified or turned on-off. The phase of the polymer affects the adhesion and friction forces. β phase contents reduced the adhesion forces due to its less electrostatic forces. With higher phase difference, higher roughness of the polymer surface got higher friction forces. In this research, we continue our investigation in understanding microstructure aspects of the PVDF, its dipole structure, and piezoelectricity on surface adhesion and friction. Doing so, we used an atomic force microscope (AFM) with an external potential to study the piezeoelectrical behavior. The effects of the electrical potential on adhesion and friction force were tested. It was shown that when the electrical potential increases, the surface roughness increases under the AFM, however not with a profilometer. Changes were also found in adhesion. This paper discusses the mechanisms of nanoscale adhesion and friction of the PVDF with an AFM tip along with the microstructures and dipole structures. This article contributes to understanding in fundamental adhesion and friction forces at a nanometer length scale.
A Lumped Parameter Model for Prediction of Temperature in Disk Pair in Dry Friction Contact
Authors: Elhomani A. , Farhang K. , Krkoska M.
Published: March 2009

In applications involving substantial friction, surface failure is an inevitable phenomenon. Friction induced failure typically involves the generation of considerable heat. Existence of significant frictional force leads to relatively high interface temperature as a result of dynamic nature of flash temperatures at the contact areas. A first step in predicting friction induced failure is to develop an accurate thermomechanical model of the friction system. A thermo-mechanical model is developed in this paper based on a lumped parameter representation of a two-disk brake. A disk is viewed as consisting of three main regions, (1) the surface contact, (2) the friction interface, and (3) the bulk. The lumped parameter model is obtained by dividing a disk into a number of concentric rings and stacked layers. The friction layer contains both the interface and contact elements, each include the equivalent thermal capacitance and conductive resistance. The contact capacitance and resistance are described in terms of the elastic contact interaction between the surfaces of the two disks. Therefore they are obtained using the Greenwood and Williamson model for contact of rough surfaces. Each is described as a statistical summation of the micron-scale interaction of the surfaces. The model is shown to provide accurate prediction of bulk temperature using a dynamometer test on a carbon composite disk pair.
Running-In of Sidewall Friction in Bulk-Fabricated Microtribotester
Authors: Meng Yonggang , Guo Zhanshe , Wu Hao
Published: March 2009

Sidewall friction is of great significance for many MEMS devices such as micromotors, microgears and microhinges. Because sidewalls in MEMS devices are different from in-plane surfaces both chemically and topographically, friction and wear occurring on sidewalls are expected to have its own characteristics. A microtribotester has been developed with the bulk-fabrication technology to measure the sidewall friction and wear, and static friction and dynamic friction measurements have been reported previously. In this paper, experiment results of the microtribotester for a testing period of 55 hours are presented. It is found that the coefficient of dynamic friction reduces gradually with the increase in rubbing cycle, being similar to most macroscale tribopairs. The morphology and chemical components of the wear debris generated in the testing process were analyzed on scanning electron microscope and EDX. From the analysis results, it is concluded that the silicon sidewalls undergoes oxidation during the test.
Analysis of the Multiple Flying Height States in the Load/Unload HDD Systems Using the 4-DOF Suspension Model
Authors: Khan P. , Hwang P.
Published: March 2009

The 4-DOF suspension model is employed in order to analyze the multiple flying height states of the coupled air bearing – suspension system. The results are compared with previously presented results for the simpler suspension model.
A Multi-Physics Particle-Augmented Mixed Lubrication Modeling Approach for Studying CMP
Authors: Terrell Elon , Higgs C. Fred
Published: March 2009

An integrated multi-physics approach was taken in order to model the complex physics behind chemical-mechanical polishing (CMP). This model, known as the particle-augmented mixed lubrication model, accounts for the important mechanical interactions in CMP—namely, fluid mechanics, particle dynamics, contact mechanics, and wear—and incorporates all of them into an integrated algorithm. The compiled model is then simulated over a series of time steps in order to form a predictive tool for CMP.
Nonlinear Thermal Protrusion and Slider Disk Contact Forces
Authors: Knigge Bernhard , Moser Andreas , Juang Jia-Yang , Baumgart Peter
Published: March 2009

Some of the recently shipped hard disk drives have a new technology to actively control the flying height between slider and disk. The slider to disk spacing is controlled by thermal protrusion actuation using a small heater coil which is located close to the read write element at the trailing end of the slider. By applying an electric current to the heater coil, the slider’s trailing end protrudes towards the disk and can be driven into contact with sufficiently high heating power. The contact force and the thermal protrusion efficiency is mainly controlled by air bearing design. In this paper we want to discuss the trade offs in air bearing design to achieve low contact force and high thermal actuation efficiency. We have done both numerical simulation and experimental measurements to investigate contact force and air bearing stiffness. Typically a softer air bearings will produce less contact force but usually exhibit worse flying height tolerances. We have found a nonlinear clearance change with applied heater power. At closer spacings, the pressure peak increases dramatically leading to reduced actuation efficiency. The actuation efficiency may also vary at different skew angles. For calibration purpose slider to disk touchdown requires contact. Due to different actuation efficiencies at different radii different contact forces are estimated.
Finite Element Modeling of Measured Rough Surfaces for the Prediction of Thermal Contact Resistance
Authors: Thompson M. K. , Thompson J. M.
Published: March 2009

Surface topography has long been considered a key factor in the performance of many contact applications. However, essentially all analytical and numerical contact models either neglect surface topography or make simplifications and assumptions about the nature of the surface which limit the quality of the models. This work presents a method for creating surface geometry by importing surface metrology data into a commercial finite element program. The measured surface geometry is then combined with a multi-scale thermal/structural finite element model to demonstrate the impact of geometric surface assumptions on the prediction of thermal contact resistance.
Part Repairing Using a Hybrid Manufacturing System
Authors: Ren Lan , Eiamsa-ard Kunnayut , Ruan Jianzhong , Liou Frank
Published: March 2009

At present, part remanufacturing technology is gaining more interest from the military and industries due to the benefits of cost reduction as well as time and energy savings. This paper presents the research on one main component of part remanufacturing technology, which is part repairing. Traditionally, part repairing is done in the repair department using welding processes. However, the limitations of the traditional welding process are becoming more and more noticeable when accuracy and reliability are required. Part repairing strategies have been developed utilizing a hybrid manufacturing system in which the laser-aided deposition and CNC cutting processes are integrated. Part repairing software is developed in order to facilitate the users. The system and the software elevate the repairing process to the next level, in which accuracy, reliability, and efficiency can be achieved. The concept of the repairing process is presented in this paper, and verification and experimental results are also discussed.
Forming of Porous Micro-Features Using Hot Compaction
Authors: Chen Peng , Kim Gap-Yong , Ni Jun
Published: March 2009

Porous metallic micro-scale features are becoming important in the modern industry. However, a mass production of such features is a challenge when robustness, cost-effectiveness, and high productivity requirements are considered. In this study, the fabrication of such porous micro-features using hot compaction was investigated. A hot compaction experiment setup was designed and fabricated, which was capable of high temperature operation (up to 700 °C), quick heat-up, and avoiding oxidation of workpiece and tools. A 3D thermal simulation of the experiment setup was conducted to understand the heat transfer characteristics of the system, which was used as a reference for the experiment. The effects of compression loading force and temperature on the compact quality in terms of powder consolidation strength and porosity were studied.
High Precision Hybyid Technology Using Dual-Stage of Linear Motor and Piezo-Actuator for Milling Machine
Authors: Chung B. M. , Yeo I. J. , Ko T. J. , Park J. K.
Published: March 2009

High precision machining technology has become one of the important parts in the development of a precision machine. Such a machine requires high speed on a large workspace as well as high precision positioning. For machining systems having a long stroke with ultra precision, a dual-stage system including a global stage (coarse stage) and a micro stage (fine stage) is designed in this paper. Though linear motors have a long stroke and high precision feed drivers, they have some limitations for submicron positioning. Piezo-actuators with high precision also have severe disadvantage for the travel range, and the stroke is limited to a few microns. In the milling experiments, the positional accuracy has been readily achieved within 0.2 micron over the typical 20 mm stroke, and the path error over 2 micron was reduced within 0.2 micron. Therefore, this technique can be applied to develop high precision positioning and machining in the micro manufacturing and machining system.