bluuebunny/crossref_metadata_2025 huggingface dataset:
Tool Heat Transfer in Orthogonal Metal Cutting
Authors: Ostafiev V. , Kharkevich A. , Weinert K. , Ostafiev S.
Published: February 2008

This paper analyzes heat flux transfer in the cutting tool in steady state orthogonal cutting. The method involves an iterative procedure to determine temperature distributions in the tool from varying heat flux transfer conditions. The temperature distributions determined from this procedure were compared with those obtained experimentally. A coincidence of the experimental and theoretical temperature distributions implied that the chosen heat flux model was appropriate. The experimental temperature distributions were obtained using a split carbide tip with special thermosensitive paint net. This prevented any split effect on the contact surfaces by films of any size and type. The investigation has provided two main insights. Firstly, it was apparent that the average temperatures determined from temperature models can be at large variance with those determined based on experimental observations. Thus, these models have to consider the effect of heat flux transfer peculiarity in the cutting tool if accurate predictions are desired. Secondly, it pointed to the necessity to account for such factors as heat flux reflection from tip sides, dependence of thermal properties on temperature and rise in temperature of the workpiece if accurate predictions are desired. It is demonstrated how the most accurate representation of heat transfer processes in the cutting tool can be determined through analyses based on accurate and reliable experimental temperature distributions.
Analytical Prediction of Stability Lobes in Ball End Milling
Authors: Altıntas¸ Y. , Shamoto E. , Lee P. , Budak E.
Published: February 2008

The paper presents an analytical method to predict stability lobes in ball end milling. Analytical expressions are based on the dynamics of ball end milling with regeneration in the uncut chip thickness, time varying directional factors and the interaction with the machine tool structure. The cutting force coefficients are derived from orthogonal cutting data base using oblique transformation method. The influence of cutting coefficients on the stability is investigated. A computationally efficient, an equivalent average cutting force coefficient method is developed for ball end milling. The prediction of stability lobes for ball end milling is reduced to the solution of a simple quadratic equation. The analytical results agree well with the experiments and the computationally expensive and complex numerical time domain simulations.
Stability Analysis in Face Milling Operations, Part 2: Experimental Validation and Influencing Factors
Authors: Jensen S. A. , Shin Y. C.
Published: February 2008

This paper presents rigorous experimental validation results of the stability algorithm as developed in the Part I. The two experiments which will be presented here focus on; first, a workpiece whose vibrational modes constitute the weakest part of the overall system, and second, a machine tool whose vibrational modes are the weakest part of the system. Next, it discusses some of the influencing factors that affect the onset of chatter in face milling processes. The factors considered include cutting conditions, entry and exit angles, axial dynamics, cutter geometry, material properties and structural dynamic parameters. Lastly, it presents the effect of structural dynamic change under operating condition on stability lobes.
Grinding Mechanisms and Energy Balance for Ceramics
Authors: Hwang T. W. , Malkin S.
Published: February 2008

An investigation is reported of the mechanisms and associated energy for grinding of ceramics. SEM observations of grinding debris indicate material removal mainly by brittle fracture. However, microscopic examination of the ground surfaces reveals extensive ductile flow with characteristic plowed grooves along the grinding direction. From an order of magnitude analysis it is shown that the energy expended by brittle fracture can comprise only a negligible portion of the total. Virtually all of the grinding energy is attributed to ductile flow by plowing. For a number of ceramic materials ground over a wide range of conditions, the grinding power is found to be nearly proportional to the rate o plowed groove area generated, which suggests a constant energy per unit area of plowed surface Js. Values obtained for Js are much bigger than the corresponding fracture surface energies and proportional to Kc3/2H.
Influence of the Grinding Wheel in the Ductile Grinding of Brittle Materials: Development and Verification of Kinematic Based Model
Authors: Miller M. H. , Dow T. A.
Published: February 2008

Empirical evidence has shown that grinding wheel characteristics significantly affect performance in the grinding of brittle materials. In this research a grit depth of cut model was developed based on a kinematic simulation of the grinding process. The model describes the relationships between grinding wheel parameters (grit size, concentration, binder modulus) and chip thickness and area. It was corroborated by the measurement of number of cutting grits in tests using a fly wheel with small abrasive area. Based on this grit depth of cut model, the “critical depth of cut” model for the grinding of brittle materials was modified to include wheel parameter effects. The new critical depth of cut model was tested using “crossfeed” experiments. Although the theoretical and experimental results show less agreement than for the grit depth of cut model, the model equations provide guidelines for choosing wheel specifications.
A Wrinkled Membrane Model for Cloth Draping with Multigrid Acceleration
Authors: Chen M. X. , Sun Q. P. , Wu Z. , Yuen M. M. F.
Published: February 2008

Fabric is modeled as a particular type of membrane formed from two orthogonal families of yarns. In contrast to usual membrane theory, the fabric is regarded to possess a certain compressive rigidity which is much weaker than its tensile rigidity. An energy density function is defined corresponding to the material model. The finite element formulation is based on the total Lagrangian approach. Four node quadrilateral elements are adopted. An accelerated multigrid technique using the conjugate gradient method as basic iterative method is employed to minimize energy to reach the final equilibrium position. Two examples of fabric draping are analyzed using the proposed model. The influence of the material parameters on the draping behavior is discussed.
A Neural Network/Expert System Approach for Design Improvement of Products Manufactured by EDM
Authors: Katz Z. , Naude J.
Published: February 2008

The stochastic nature of the electro discharge machining (EDM) process does not allow for a precise prediction of its effect on the machined features. However, there is a direct interrelation between feature design and the process results. The objective of this work is to suggest a neural network based system to facilitate and optimize the design process of products to be machined by EDM. A comprehensive analysis by a neural network and expert system is presented. Aspects of features coding and relations with the process parameters are discussed. Experimental results confirm design improvements and a practical system is described.
Physically-Accurate Synthetic Images for Machine Vision Design
Authors: Parker J. M. , Lee Kok-Meng
Published: February 2008

In machine vision applications, accuracy of the image far outweighs image appearance. This paper presents physically-accurate image synthesis as a flexible, practical tool for examining a large number of hardware/software configuration combinations for a wide range of parts. Synthetic images can efficiently be used to study the effects of vision system design parameters on image accuracy, providing insight into the accuracy and efficiency of image-processing algorithms in determining part location and orientation for specific applications, as well as reducing the number of hardware prototype configurations to be built and evaluated. We present results illustrating that physically accurate, rather than photo-realistic, synthesis methods are necessary to sufficiently simulate captured image gray-scale values. The usefulness of physically-accurate synthetic images in evaluating the effect of conditions in the manufacturing environment on captured images is also investigated. The prevalent factors investigated in this study are the effects of illumination, the sensor non-linearity and the finite-size pinhole on the captured image of retroreflective vision sensing and, therefore, on camera calibration was shown; if not fully understood, these effects can introduce apparent error in calibration results. While synthetic images cannot fully compensate for the real environment, they can be efficiently used to study the effects of ambient lighting and other important parameters, such as true part and environment reflectance, on image accuracy. We conclude with an evaluation of results and recommendations for improving the accuracy of the synthesis methodology.
Fixture Failure Diagnosis for Sheet Metal Assembly with Consideration of Measurement Noise
Authors: Ceglarek D. , Shi J.
Published: February 2008

This paper expands previously developed assembly fixture fault diagnosis methodology (Ceglarek and Shi, 1996) by considering the impact of measurement noise on the diagnostic results. The proposed solution provides a new analytical tool to address the diagnosability issue during the assembly process design stage. An evaluation of fault diagnosis index as a function of noise, fixture geometry, and sensor location is presented. The index is derived from the general class of covariance matrices describing tooling faults. Simulation based on the real fixture is presented to illustrate the proposed method.
Parts Mating Aided by Constant-Amplitude Sinusoidal Motions
Authors: Leu Ming C. , Liao Hsin-Te
Published: February 2008

This paper presents an analytical and experimental investigation of engagement of parts aided by two orthogonal constant-amplitude sinusoidal motions in mechanical assembly. In the analytical investigation we analyze how the amplitudes, frequencies, frequency ratio, and phase angle of the two motions affect the engagement. A numerical technique is developed for selecting these parameters, and a parts engagement strategy capable of recognizing various failure situations in peg-in-hole assembly is developed. Experiments are conducted to verify the validity of the parts engagement strategy as well as to provide useful information about the characteristics of contact force during the engagement.
Effect of Workpiece Flatness and Surface Finish on the Holding Force of a Magnetic Chuck
Authors: Felix A. , Melkote S. N.
Published: February 2008

Magnetic chucks are commonly used for workholding in precision grinding and turning of ferromagnetic materials. The workholding force produced by the chuck is strongly influenced by the texture and form of the workpiece surface in contact with the chuck surface. This paper presents the results of an experimental investigation into the effects of workpiece surface flatness, finish, and texture on the normal and frictional workholding forces produced by a radial 4-pole electromagnetic chuck. Ring shaped case-hardened steel specimens were used in the experiments. The results show that the normal holding force decreases with increasing flatness deviation. The effect of surface roughness on the normal holding force was found to be small compared to the effect of flatness but significantly impacts the tangential holding force. The workpiece surface texture was also found to have an effect on the workholding forces.
Semi-Analytical Modeling of Crack Initiation Dominant Contact Fatigue Life for Roller Bearings
Authors: Cheng Wangquan (Winston) , Cheng Herbert S.
Published: February 2008

The fatigue test of a needle roller bearing suggests that the dominant failure mechanism is subsurface crack initiation and propagation. Therefore, a new semi-analytical contact fatigue model is derived from a micromechanics based crack initiation model. The analysis indicates that in the life calculation the selection of the critical stress, such as the maximum orthogonal shear stress, maximum shear stress, octahedral shear stress, or von Mises equivalent stress, becomes arbitrary under the nonfrictional Hertzian line contact condition. The fatigue life of roller bearings under the pure rolling condition can be predicted by simply knowing the Hertzian contact pressure and the contact width, which avoids complicated calculation of the subsurface stresses. The film thickness, roughness, and the material hardness effects on contact fatigue are also included in the new model. The comparisons with different models and the experimental data indicate that the new model makes similar life predictions as the Ioannides-Harris model, but the new model is much simpler to use. The Lundberg-Palmgren model does not fit with the experiment data.
Numerical Analysis of Temperature Distribution at the Lip Seal-Shaft Interface
Authors: Kang Young Sup , Sadeghi Farshid
Published: February 2008

A numerical model has been developed to investigate thermal effects at the lip seal shaft interface. The thermal Reynolds, film thickness, and energy equations with appropriate boundary conditions were discretized according to the control volume finite difference approach and solved using the multigrid multilevel technique. The pressure distribution at the lip seal shaft interface for both isothermal and thermal cases are obtained. The temperature effects on leakage rates are obtained for various operating conditions. The results indicate that temperature effects within the film are significant and increase the side leakage rate as compared to the isothermal case.
Fluid Inertia Effects on the Performance of Short and Long Squeeze Film Dampers Executing Periodic Vibration
Authors: Zhang J. X.
Published: February 2008

A comprehensive study is made to examine effects of fluid inertia on pressure distribution, load capacity, wall shear stress differences (defined in Nomenclature), and velocity variation of flow in short and long Squeeze Film Dampers (SFDs). The SFD is assumed to execute a small excursion around an arbitrary static position. Exact solutions, in the form of a Fourier series, for fluid pressure and velocity are obtained for periodic motions of the SFD journal. An example of a horizontal motion, with various static positions in bearing clearance, is studied in detail for both short and long bearing configurations. It is found that the existence of fluid inertia generally increases the peak pressure value, and hence the load capacity. Wall shear stress differences and velocity distribution are also altered by the presence of the fluid inertia compared with inertialess flow, but the parabolic shape of the velocity may be maintained. Insight on how the fluid inertia effect is internally related to the viscous effects is also gained from this study.
Three-Dimensional Finite Element Analysis of Subsurface Stress and Strain Fields Due to Sliding Contact on an Elastic-Plastic Layered Medium
Authors: Kral E. R. , Komvopoulos K.
Published: February 2008

A three-dimensional finite element analysis of a rigid sphere sliding on an elastic-plastic layered medium is presented. Results for the subsurface stress and strain fields are given for a perfectly adhering layer with an elastic modulus and yield stress both two and four times that of the substrate, and contact loads 100 and 200 times the initial yield load of the substrate material. Sliding is simulated to distances of approximately two to three times the initial contact radius. The sphere is modeled by contact elements, and the interface friction coefficient is assumed equal to 0.1 and 0.25. The effects of layer material properties, contact friction, and normal load on the sliding and residual stresses in the layer and the substrate are examined. The distributions of tensile stresses in the layered medium and shear stresses at the layer/substrate interface are presented and their significance for crack initiation and layer decohesion is discussed. Reyielding during unloading is also analyzed for different material properties and contact loads.
Hydrodynamic Segregation, Entrainment and Rejection of Oil in Emulsion Lubrication Problems
Authors: Schmid S. R.
Published: February 2008

Emulsions are widely used as metal rolling and ironing lubricants, but their application is still an art in that no widely accepted and robust models of emulsion lubrication exist. Of particular confusion to date is the mechanism through which oil particles penetrate an inlet zone and serve as a lubricant. This paper addresses hydrodynamic behavior of emulsions and addresses topics such as droplet segregation in the inlet zone and the forces acting upon individual droplets in a worst case analysis of entrainment. In segregation, a phenomenon first noted in Poiseuille tube flows, neutrally buoyant particles will cross flow streamlines to an equilibrium position a finite distance from the edge of the flow. This paper includes an analysis of segregation using the empirical results obtained elsewhere, and describes the relevance of segregation to metal forming inlet zones. If a droplet does penetrate the inlet zone to a point near the edge of contact, and it has not adhered to a roll or strip surface, hydrodynamic forces will determine whether or not the particle will become entrained. This paper analyzes the forces involved using a foil bearing analogy. The situations under which a droplet is entrained or rejected are described, and the important parameters to achieve entrainment are discussed.
A Fractal Analysis of Stiction in Microelectromechanical Systems
Authors: Komvopoulos K. , Yan W.
Published: February 2008

The strong adherence (stiction) of adjacent surfaces is a major design concern in microelectromechanical systems (MEMS). Advances in micromachine technology greatly depend on basic understanding of microscale stiction phenomena. An analysis of the different stiction micromechanisms and the elastic deformation of asperities at MEMS interfaces is developed using a two-dimensional fractal description of the surface topography. The fractal contact model is scale independent since it is based on parameters invariant of the sample area size and resolution of measuring instrument. The influence of surface roughness, relative humidity, applied voltage, and material properties on the contributions of the van der Waals, electrostatic, and capillary forces to the total stiction force is analyzed in light of simulation results. It is shown that the effects of surface roughness and applied voltage on the maximum stiction force are significantly more pronounced than that of material properties. Results for the critical pull-off stiffness versus surface roughness are presented for different material properties and microstructure stand-free surface spacings. The present analysis can be used to determine the minimum stiffness of microdevices required to prevent stiction in terms of surface roughness, apparent contact area, relative humidity, applied voltage, and material properties.
Analysis of a Test Case for Annular Seal Flows
Authors: Arghir Mihai , Freˆne Jean
Published: February 2008

The paper presents a theoretical investigation of the flow field inside a 50 percent eccentricity, synchronously whirling, annular seal. The numerical results are obtained using a specific rotordynamic method based on the perturbed form of the averaged full Navier-Stokes equations. Experimental data for this seal are provided by Morrison et al. (1994, 1995) and Morrison and Winslow (1995). The calculated flow field (stator pressures and shear stresses, distributed forces, velocity and turbulent kinetic energy distributions) is in good qualitative agreement with the measured one. It is evidenced that the particular form of the pressure field is due to a great pressure recovery effect in the exit section. This problem could be used as a test case for annular seal flows, but the high eccentricity is at the limit of a perturbation-based method.
Parameter Identification of Hysteresis Friction for Coated Ball Bearings Based on Three-Dimensional FEM Analysis
Authors: Lovell M. R. , Khonsari M. M. , Marangoni R. D.
Published: February 2008

Using a three-dimensional finite element model, the hysteresis friction behavior of coated ball bearings is investigated. Ninety-six distinct operating conditions were examined by the finite element model that include normal loads of 81.6, 133.5, and 185.4 N per ball, ball diameters of .0127 m and .0191 m, ball materials of Si3N4 and steel, substrate materials of Si3N4 and steel, and coating materials of MoS2, NbSe2, Si3N4, and steel. From the finite element results, general trends for the two parameters of Dahl’s friction model, the rest slope, σ, and the steady friction torque, Ts, are established for coated surfaces. By performing a regression analysis of the data points, empirical expressions for σ and Ts are derived for coated bearing surfaces. These expressions are authenticated by comparisons to laboratory experimental results.
Friction and Wear Studies of Carbon Overcoated Thin Films Magnetic Sliders: Application of Raman Microspectroscopy
Authors: Varanasi S. S. , Lauer J. L. , Talke F. E. , Wang Geng , Judy J. H.
Published: February 2008

The friction and wear behavior of diamond-like carbon (DLC) overcoated sliders is investigated as a function of DLC overcoat thickness using contact-start-stop and constant speed drag tests. The dependence of the Raman signal on DLC film thickness is studied. Raman spectra obtained from different locations on the air bearing surface are analyzed before and after wear testing to study wear of the DLC overcoat. The dependence of D and G band areas on DLC film thickness is investigated and the use of Raman spectroscopy for auxiliary measurement of carbon overcoat thickness is discussed.
Effect of Sliding Friction on Contact Stresses for Multi-Layered Elastic Bodies With Rough Surfaces
Authors: Mao K. , Bell T. , Sun Y.
Published: February 2008

The stress distributions associated with frictionless and smooth surfaces in contact are rarely experienced in practice. Factors such as layers, friction, surface roughness, lubricant films, and third body particulate are known to influence the state of stress and the resulting rolling contact fatigue life. A numerical technique for evaluating the subsurface stresses arising from the two-dimensional sliding contact of two elastic bodies with real rough surfaces has been developed, where an elastic body contacts with a multi-layer surface under both normal and tangential forces. The presence of friction and asperities within the contact region causes a large, highly stress region exposed to the surface. The significance of these near-surface stresses is related to modes of surface distress leading to surface eventual failure (Mao et al., 1997).
An FFT-Based Method for Rough Surface Contact
Authors: Stanley H. M. , Kato T.
Published: February 2008

Elastic contact between a rigid plane and a halfspace whose surface height is described by a bandwidth-limited Fourier series is considered. The surface normal displacements and contact pressures are found by a numerical technique that exploits the structure of the Fast Fourier Transform (FFT) and an exact result in linear elasticity. The multiscale nature of rough surface contact is implicit to the method, and features such as contact agglomeration and asperity interaction—a source of difficulty for asperity-based models—evolve naturally. Both two-dimensional (2-D) and three-dimensional (3-D) contact are handled with equal ease. Finally, the implementation is simple, compact, and fast.
Theoretical and Experimental Investigation of an Externally Pressurized Porous Annular Thrust Gas Bearing and Its Optimal Design
Authors: Cui Changzhi , Ono Kyosuke
Published: February 2008

Static and dynamic characteristics of an externally pressurized porous annular thrust gas bearing (PATGB), which has a thin restricted surface layer, are investigated by numerical analysis and experiment. In the analysis, it is assumed that the fluid flow obeys Darcy’s law in the porous material, restricted with Darcy’s restrictor (Darcy-Darcy model) or orifice restrictor (Darcy-Orifice model) in the surface layer. From experimental investigation, it is found that the theoretical results calculated by the Darcy-Darcy model agree with the experimental data better than those of the Darcy-Orifice model. Based on the Darcy-Darcy model, the unique relationships among the design parameters, which can provide the maximum damping ratio, were derived as functions of feeding parameter under the conditions of allowable static stiffness and the local minimum dynamic stiffness. Considering the dimensionless mass of the body supported by the bearing, an optimal design method is proposed to maximize the damping ratio at the natural frequency, while maintaining the required stiffness in the low frequency region.
Influence of a Hard Surface Layer on the Limit of Elastic Contact—Part I: Analysis Using a Real Surface Model
Authors: Nogi Takashi , Kato Takahisa
Published: February 2008

A numerical simulation technique for calculating the pressure distribution and the deformed geometry of an elastic half-space which has a hard surface layer in contact with a rigid indenter with a rough surface is presented. In order to reduce the computing time, the Conjugate Gradient Method (CGM) is applied to solve a set of linear equations for unknown pressures. In each iteration of the CGM, the Fast Fourier Transform (FFT) is used for the task of multiplying a direction vector by an influence coefficient matrix. An FFT-based scheme for evaluating subsurface stresses in the layer and the substrate is also presented. As an example, the pressure distribution and the deformed geometry of a steel surface coated with a TiN layer in contact with a rigid rough indenter are calculated. The subsurface stresses are also compared with von Mises yield criterion to investigate the deformation mode at the asperity contacts. The results show that the limit of elastic contact is highly dependent on the layer thickness and the surface roughness.
A Numerical Study of the Stable Dynamic Behavior of Radial Face Seals With Grooved Faces
Authors: Person V. , Tournerie B. , Freˆne J.
Published: February 2008

This paper presents a simple numerical method for modeling the dynamic tracking modes of a grooved face seal. The stability is verified using a method derived from that developed for smooth face seals. The method, enabling the calculation of the kinematic parameters which describe the steady-state response of the grooved seal, is of interest in designing this type of seal. A parametric study is presented for the case of a rotor face with eight semicircular grooves. The principal effect of the grooves is to increase the hydrostatic component of the load. In turn, this makes the seal less sensitive to fluctuations of the hydrodynamic phenomena. Sinusoidal waviness is used to simulate the periodic distortions induced by the grooves and affects the dynamic behavior only in the presence of cavitation. This occurs for very small values of the film thickness and, consequently, for very small leakage flow. In this case, the dynamic response of the seal is then strongly dependent upon the hydrodynamic effects.
Lubrication of Slow Rolling Contacts—The NASA Ball on Plate Tribometer
Authors: Kingsbury E. , Pepper S. V. , Ebihara B.
Published: February 2008

The NASA Ball on Plate Tribometer was built for the investigation of boundary lubricated rolling. Its contact conditions are easily calculated, and can be adjusted to match a range of real hearing applications for stress, surface velocity, pivot, and contact severity. The rig operates under high vacuum at room temperature. Lubricant charge and specimen preparation are well-controlled and well-characterized. Mass spectroscopy instrumentation allows an indication of lubricant degradation during rolling. Other tribological quantities immediately available are contact resistance, friction coefficient, transverse creep, and orbit velocity deficit. Simple specimens allow post-test surface analysis such as FTIR, XPS, microscopy, and profilometry. Here we describe the Tribometer and discuss representative results obtained with liquid, solid, and no lubricant.
Floating Characteristics of Squeeze-Film Gas Bearings With Vibration Absorber for Linear Motion Guide
Authors: Yoshimoto S.
Published: February 2008

This paper describes the floating characteristics of squeeze-film gas bearings with a vibration absorber. This bearing uses a piezoelectric actuator directly attached to a counterweight to impart oscillations to a bearing surface and, therefore, can generate a squeeze-film between the bearing and the guideway surfaces. Furthermore, in this squeeze bearing, a vibration absorber is inserted between a counterweight and a carried object to reduce the vibrational amplitude of the carried object and improve the motion accuracy. The effects of the vibration absorber on the floating characteristics are discussed theoretically and experimentally. It was found that the material of the vibration absorber greatly affected the floating characteristics, and the absorber made of silicone rubber was very effective to reduce the vibrational amplitude of the carried object.
Slider Designs for Controlling Contamination
Authors: Zhang Shuyu , Bogy David B.
Published: February 2008

This paper presents a method for reducing particle contamination on sliders. A model for simulating particle movement in an air bearing is developed and solved numerically. Through the simulation, the paths of particles moving in the air bearing are studied for various designs of sliders. It is found that some slider designs have good characteristics that make most of the particles entering the air bearing leave the slider from the sides instead of from the trailing edge, which is regarded as beneficial to reduce the particle contamination on the sliders.
Pressure and Shear Flow in a Rough Hydrodynamic Bearing, Flow Factor Calculation
Authors: Lunde L. , To̸nder K.
Published: February 2008

The lubrication of isotropic rough surfaces has been studied numerically, and the flow factors given in the so-called Average Flow Model have been calculated. Both pressure flow and shear flow are considered. The flow factors are calculated from a small hearing part, and it is shown that the flow in the interior of this subarea is nearly unaffected by the bearing part’s boundary conditions. The surface roughness is generated numerically, and the Reynolds equation is solved by the finite element method. The method used for calculating the flow factors can be used for different roughness patterns.
Determination of Accommodation Coefficients for N2 at Disk-Drive Air-Bearing Surfaces
Authors: Rettner C. T.
Published: February 2008

Thermal and tangential momentum accommodation coefficients have been obtained for N2 colliding with various surfaces of relevance to the disk-drive air bearing using molecular beam scattering techniques. Analysis of the velocity and angular distributions of scattered species indicates that N2 is essentially fully accommodated at the relevant surfaces for energies characteristic of room temperature gas.
Effects of the Non-Newtonian Behavior of Lubricants on the Temperature, Traction, and Film Thickness in an Elliptical EHD Contact Under Heavy Loads
Authors: Ma Ming-Tang
Published: February 2008

An approximate but economical approach to the non-Newtonian thermal elastohydrodynamic (EHD) lubrication in heavily loaded elliptical contacts (p0 ≥ 1 GPa) has been developed by the author. From an empirically corrected Hertzian pressure distribution, the rheology, generalized momentum, and energy equations were solved to obtain the shear stress, velocity, and temperature distributions in the film. The computerized model, incorporating a number of fluid rheological laws, has been used to examine the influences of the non-Newtonian behavior of lubricants on the temperature, film thickness, and traction in the EHD contact. In this paper, the numerical formulation and computation scheme are briefly described. Then a comparison between the results obtained with some well known rheological laws is presented. The results show that the non-Newtonian characteristic of lubricants has a significant effect on the temperature and traction for lower sliding speeds, but it has a modest influence on the film thickness. By comparison with experiment, Bair and Winer’s fluid model appears to be quite realistic.
FEM Simulation of a Friction Testing Metliod Based on Combined Forward Conical Can-Backward Straight Can Extrusion
Authors: Nakamura Tamotsu , Bay Niels , Zhang Zhi-Liang
Published: February 2008

A new friction testing method based on combined forward conical can-backward straight can extrusion is proposed in order to evaluate friction characteristics in severe metal forming operations. By this method the friction coefficient along the conical punch surface is determined knowing the friction coefficient along the die wall. The latter is determined by a combined forward and backward can extrusion of straight cans. Calibration curves determining the relationship between punch travel, can heights, and friction coefficient for the two tests are calculated based on a rigid-plastic FEM analysis. Experimental friction tests are carried out in a mechanical press with aluminium alloy A6061 as the workpiece material and different kinds of lubricants. They confirm that the theoretical analysis results in reasonable values for the friction coefficient.
Theoretical Analysis of Heat Partition and Temperatures in Grinding
Authors: Ju Y. , Farris T. N. , Chandrasekar S.
Published: February 2008

A theoretical analysis is presented of heat partition and surface temperatures for the grinding of hardened steel with both aluminum oxide and CBN wheels. The numerical predictions of the model are shown to agree with experimental results available in the literature. It is found that heat partition varies over a wide range depending on grinding conditions. Also, heat partition is a strong function of position inside the grinding zone. The presence of the fluid inside the grinding zone can reduce the heat flux into the workpiece and the workpiece temperature significantly. For typical grinding of steel with CBN wheels, or creep feed grinding of steel with aluminum oxide or CBN wheels, it is possible to keep the fluid active and therefore to reduce thermal damage. However, the analysis suggests that the fluid may not be effective inside the grinding zone, in the conventional grinding of steel with aluminum oxide, due to boiling.
Ultra-Thin Overcoats for the Head/Disk Interface Tribology
Authors: Bhatia C. Singh , Anders S. , Brown I. G. , Bobb K. , Hsiao R. , Bogy D. B.
Published: February 2008

Cathodic arc deposition forms ultra-thin amorphous hard carbon films of high sp3 content, high hardness, and low coefficient of friction. These properties make it of great interest for head/disk interface application, in particular for contact recording. In many cases, the tribological properties of the head disk interface could be improved by factors up to ten by applying cathodic arc overcoats to the slider or disk surface. This paper reviews the results of cathodic arc ultra-thin (2–10 nm) carbon overcoats for head/disk interface tribological applications.
Elastic Contact and Friction Between Sliders and Circumferentially Textured Disks—Part III: Experiments
Authors: Tanaka K. , Ishikawa J. , Shimamoto A.
Published: February 2008

This three part paper presents the experiment and numerical analysis of the friction of a thin-film rigid disk with circumferential surface texture. In Part III, we examine the friction of a disk on the unworn virgin and worn tracks at various relative humidities. The real contact areas and pressures on both tracks are estimated using the Hertz contact model of two-dimensional asperities in Part I and related to the frictional coefficients on the basis of the meniscus model in Part II. The analysis yields that the effect of meniscus is predominant in the flat contact situation, particularly on the worn track at high humidity, while the effect is negligible in the taper/flat edge contact situation on both the tracks even at high humidity.
Three-Dimensional Elastic-Plastic Fractal Analysis of Surface Adhesion in Microelectromechanical Systems
Authors: Komvopoulos K. , Yan W.
Published: February 2008

High adhesion is often encountered at contact interfaces of miniaturized devices, known as microelectromechanical systems, due to the development of capillary, electrostatic, and van der Waals attractive forces. In addition, deformation of contacting asperities on opposing surfaces produces a repulsive interfacial force. Permanent surface adhesion (referred to as stiction) occurs when the total interfacial force is attractive and exceeds the micromachine restoring force. In the present study, a three-dimensional fractal topography description is incorporated into an elastic-plastic contact mechanics analysis of asperity deformation. Simulation results revealing the contribution of capillary, electrostatic, van der Waals, and asperity deformation forces to the total interfacial force are presented for silicon/silicon and aluminum/aluminum material systems and different mean surface separation distances. Results demonstrate a pronounced effect of surface roughness on the micromachine critical stiffness required to overcome interfacial adhesion.
Friction Force Microscopy Measurements: Normal and Torsional Spring Constants for V-Shaped Cantilevers
Authors: Hazel J. L , Tsukruk V. V.
Published: February 2008

A combination of finite element analysis (FEA) calculations and resonant frequency measurements are applied for determining normal and lateral spring constants of microfabricated ceramic/gold cantilevers for friction force microscopes. The cantilever Si3N4 and Au layers are combined analytically into an equivalent single composite layer. Bending and torsion behavior of the cantilever under typical operating forces are determined through FEA. Effective Young’s modulus for the composite Si3N4-Au beam from 172 to 185 GPa is determined through assimilation of FEA and fundamental resonant frequency measurements. Several current analytical solutions are compared to the full FEA evaluation. A new analytical expression is derived for obtaining the ratio of lateral to normal spring constants and thereby evaluation of absolute values of friction coefficients. Calibration plots are presented for assessment of both vertical and torsion spring constants of bicomponent cantilevers by measuring their resonant frequencies and thickness of gold overlay.
True Friction Power Intensity and Scuffing in Sliding Contacts
Authors: Horng Jeng Haur
Published: February 2008

Scuffing failure phenomenon in sliding lubricated contacts is studied experimentally in this work. Factors influencing the scuffing resistance of rough surfaces, including contact temperature, surface pitting, specific film thickness, and frictional heating, are investigated. A new criterion (the TFPI criterion) that takes into account the effect of oil in surface roughness valleys, microcontact characteristics, and the protective film formation mechanism is proposed to predict onset of scuffing failure. Good agreement is found between experimental scuffing data and predicted failure criterion. The results show that the modified TFPI value can be considered as a performance parameter that represents the scuffing failure resistance capacity and the effectiveness of the running-in process. A low modified TFPI value has a high scuffing resistance in lubricated systems.
A Comparison Study on the Performance of Four Types of Oil Lubricated Hydrodynamic Thrust Bearings for Hard Disk Spindles
Authors: Zhu Jiasheng , Ono Kyosuke
Published: February 2008

In this paper, the static and dynamic performance of herringbone, step-pocket, taper-pocket, and taper-flat thrust bearings were numerically analyzed. Optimal values for the design parameters of each type of bearing were analyzed in terms of both maximum axial stiffness (kzz) and maximum ratio of axial stiffness to friction torque (kzz/T) and bearing performance for both cases was calculated. The optimal performance characteristics of these bearings were compared in terms of application to hard disk spindles. Step-pocket and taper-pocket thrust bearings are superior to herringbone and taper-flat thrust bearings with respect to both the maximum kkk and the maximum kzz/T conditions. It was found that the dams of thrust bearings with pockets play an important part in improving the hearing performance. It was made clear that the taper-pocket and the taper-flat thrust bearings have a much larger load capacity than the other two types of thrust bearings in the proximity of zero clearance.
Improved Method for the Measurement of Asperity Compliance of Magnetic Tapes
Authors: Tan Sanwu , Baugh Eric , Talke Frank E.
Published: February 2008

Asperity compliance of typical magnetic tapes is investigated as a function of contact pressure using intensity-based three-wavelength interferometry. Each spacing data is the average of 300 × 700 physical points. Asperity compliance curves for BaFe tape, MP tape, ME tape, and CrO2 tape were obtained. The experimental data was curve-fit using a parabolic contact model and the Greenwood-Williamson contact model. In addition, a comparison of the present results with previous measurements is presented.
Adhesive Contact of Flat-Ended Wedges: Theory and Computer Experiments
Authors: Yongsheng Leng , Yuanzhong Hu , Linqing Zheng
Published: February 2008

We give the closed-form solutions for the two-dimensional adhesive contact of a flat-ended wedge with an elastic half-space, including contact pressure distribution and load-contact width relationship. The approach is derived from contact mechanics in plane-strain elasticity and fracture mechanics concepts. The contact pressure has stress singularities both at the edges of contact due to molecular attractive forces and at the wedge corners, and is compared with those without adhesion. Under zero load, we find the contact strip has a finite width which is greater than that of the wedge end, and the central region of contact is under compression, similar to that of a flat punch problem, while the regions near the contact edges are under tension. Unlike the usual experiments with smooth and low modulus materials, we conduct molecular dynamics (MD) experiments via embedded-atom method (EAM), brownian dynamics algorithm and dynamical theory of crystal lattices. The results, including the “pull-off” force for contacting surfaces to peel apart, conform reasonably well with those derived from a continuum model.
Rotordynamic Evaluation of a Roughened-Land Hybrid Bearing
Authors: Fayolle Patrice , Childs Dara W.
Published: February 2008

Hybrid bearings represent an attractive alternative to ball bearings for use in highspeed cryogenic turbopumps. However, the internally-developed cross-coupled forces can generate instabilities responsible for a speed limitation of the machine. To reduce these forces and raise the onset speed of instability, the use of deliberately-roughened stators, already successfully tested for liquid “damper” seals, is investigated. Rotor-dynamic results are presented for a five-pocket orifice-compensated hole-pattern-land hybrid bearing tested with water at high speed and high pressure. Experimental data show a good prediction of leakage flow rate and direct damping but a significant improvement in stability compared to a conventional smooth-land hybrid bearing, resulting in an elevation of the onset speed of instability. Comparisons between measurements and predictions from a code developed by San Andres (1994) shows good predictions for flowrate and direct damping but an over prediction for the direct and cross-coupled stiffness coefficients by about 30 and 50 percent, respectively. The use of the Moody friction-factor model is thought to be mainly responsible for the poorer predictions of stiffness coefficients.
Surface Roughness Effects in Infinitely Long Porous Journal Bearings
Authors: Gururajan K. , Prakash J.
Published: February 2008

Christensen’s stochastic theory of hydrodynamic lubrication of rough surfaces is used to study the effect of surface roughness in an infinitely long porous journal bearing operating under steady conditions. It is shown that the surface roughness considerably influences the bearing performance; the direction of the influence depends on the roughness type.
Comparison Between Linear and Nonlinear Transient Analysis Techniques to Find the Stability of a Rigid Rotor
Authors: Turaga Ram , Sekhar A. S. , Majumdar B. C.
Published: February 2008

The subsynchronous whirl stability limit of a rigid rotor supported on two symmetrical finite journal bearings has been studied using the linearised perturbation method and the nonlinear transient analysis technique. A quantitative comparison for journal bearings with different l/d ratios has been provided.
Test Results for Liquid “Damper” Seals Using a Round-Hole Roughness Pattern for the Stators
Authors: Childs Dara W. , Fayolle Patrice
Published: February 2008

Test results are reviewed for two annular liquid seals (L = 34.9 mm; D = 76.5 mm) at two clearances (.1 and .12 mm). The seal stators use hole-pattern-roughened stators that are identical except for hole depths of .28 and 2.0 mm. Tests are conducted at three speeds out to 24,600 rpm and three pressures out to 68 bars. Test data consist of leakage rates and rotordynamic coefficients at centered and eccentric positions with static eccentricity ratios out to 0.5. Test results are consistent with expectations in regard to the reduction of cross-coupled stiffness coefficients due to stator roughness. However, the measured direct stiffness coefficients were unexpectedly low. A partial explanation for these results is provided by measured friction factor data which show an increase in the friction factors for pressure-driven flow with an increase in clearance. A prediction model for rotordynamic coefficients, incorporating the friction-factor data, predicted a substantial loss in direct stiffness but could not explain the very low (or negative) values that were measured. The model did explain the measured drop in cross coupled stiffness (k) and provides an alternative explanation to observed reductions in k values; specifically, an increase in the friction factor with increasing clearance causes a reduction in k irrespective of any parallel reduction in the average circumferential velocity.
Effects of Groove Orientation on Hydrodynamic Behavior of Wet Clutch Coolant Films
Authors: Razzaque M. Mahbubur , Kato Takahisa
Published: February 2008

A steady-state Reynolds type equation with inertia consideration is solved numerically for a coolant film entrapped between a grooved separator-friction plate pair of a multidisk wet clutch arrangement at a particular instant of the disengaged state. Straight grooves with rounded, trapezoidal, and V-section at different angular orientations are considered and the effects of their geometry and orientation on viscous torque, flow rate, and axial force are presented. Among the profiles studied, the rounded one is found to be better. Grooves inclined with the flow direction cause less viscous torque and, hence, less power loss. The choice of orientation angle, β, to give a maximum outflow or inflow may be helpful for cooling by better convection. For wider radial span and large number of grooves, the minimum operating gap ratio is suggested to be around 2.0. Inertia effects may shift the optimum orientation angle by as much as 10 deg, even at a moderate value of gap Reynolds number.