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This paper deals with the application of the lattice-Boltzmann method (LBM) to fluid-film lubrication. Compared with the traditional computational approach in lubrication (based on Reynolds equation), LBM does not neglect inertia forces. The implementation of LBM is less demanding than that of the Navier--Stokes solvers for complex geometric configurations. Various wall boundary conditions, as well as the multiple relaxation time model, are discussed. Bearing cavitation is approached in a simplified manner. The LBM solutions for two classic configurations are compared with the corresponding analytic and numeric solutions of the Reynolds or Navier--Stokes equations. The LBM results were satisfactory for the investigated cases. [DOI: 10.1115/1.4000694] Keywords: bearings, fluid-film lubrication, cavitation

A compliance operator is often utilized to evaluate the elastic displacement of surfaces in the simulation of transient and steady-state elastohydrodynamic lubrication of conformal-contact systems. The values of the compliance operator represent the elastic responses of all nodes when only one node is under a unit load. The accuracy of compliance operator values, computational cost, and storage size are important issues. Our study of steady-state conformal-contact elastohydrodynamic lubrication analyses suggests a method of selective-fine-mesh with selective-storage, as well as a special technique of the combined selective-fine-mesh with selective-storage mapping. These two techniques enable an efficient elasticity procedure for the simulation of steady-state and transient conformal-contact elastohydrodynamic lubrication systems by means of the finite element method. [DOI: 10.1115/1.4001120] Keywords: conformal-contact elastohydrodynamic lubrication, finite element, transient

The objective of the present work is to study theoretically the influence of wear on the performance of four-pocket capillary-compensated hydrostatic journal bearing operating with micropolar lubricant. In the present study, the lubricant containing additives and contaminants is modeled as micropolar fluid. The modified Reynolds equation for micropolar lubricant is solved using finite element method along with capillary restrictor flow equation as a constraint together with appropriate boundary conditions. The performance characteristics of a capillary-compensated four-pocket worn hydrostatic journal bearing operating with micropolar lubricant have been presented for a wide range of values of nondimensional external load, wear depth parameter, and micropolar parameters. The simulated results have also been presented for two different loading arrangements. In arrangement I, the load line acts through centers of the pockets, whereas in arrangement II, the load line bisects the land between two pockets. The simulated results suggest that a bearing lubricated with lubricant having higher micropolar effect has better static and dynamic performance characteristics as compared with Newtonian lubricant but the bearing lubricated with lubricant having higher micropolar effect is predominantly affected by the wear visa vis static characteristics parameters as compared with Newtonian lubricant for both loading arrangements. However, in the case of stiffness and damping coefficients, loading arrangement II shows a significant higher enhancement in the value of direct stiffness and damping coefficients in z-direction due to micropolar effect as compared with load arrangement I. And also, the effect of wear on stiffness and damping coefficients in z-direction for bearing operating with micropolar lubricant is of same order as Newtonian lubricant for the loading arrangement II. A similar behavior is observed for the case of stiffness and damping coefficients in x-direction for loading arrangement I. [DOI: 10.1115/1.4000940] Keywords: wear, hydrostatic journal bearings, capillary compensation, micropolar lubricant

Inconel alloys have been used as engineering materials in high temperature and high stress applications due to their excellent mechanical properties. Tribological performances of these alloys, however, have not been conducted extensively. This is because in tribological applications, these materials have not often been utilized in friction and wear-related applications, resulting in a deficiency in the characterization of their tribomechanical properties. In the present research, we investigate the mechanisms of tribological performance of two different Inconel alloys in terms of contact pressures and sliding speeds. We studied their frictional behavior The wear data were plotted against the pressure x velocity (PV parameter) in order to investigate the changes of surface properties and wear behaviors of the same under the influence of mechanical energy input. It was interesting to find that the wear mechanisms were influenced by the process of tribotesting. There are three competing wear mechanisms found, abrasion, adhesion, and oxidation. Each of those dominates the tribological performance under different conditions. [DOI: 10.1115/1.4001170] Keywords: friction, wear, Inconels, abrasion, adhesion

A slurry whirling arm erosion test ring was constructed and a series of erosion tests and post-erosion analysis were carried out using a paint erosion indication technique. The pattern of the paint removal presented a highly visual and accelerated map for the erosion process and its behavior. Also, the erosion rate of paint removal was investigated under a number of erosion variables. It was observed that the rebounding of the erodent particles from the sample surface play an important role in developing erosion for this tester. The erosion pattern showed that the effect of the rebound particles depends on the impact velocity and impingement angle. It was also observed that the erosion behavior of paint as a function of impingement angle, impact velocity, and erosion time was similar to that reported in literature for engineering materials. The slurry whirling arm erosion tester seems to be promising for simulating the slurry process in real cases. [DOI: 10.1115/1.4001449] Keywords: slurry erosion, erodent-target dynamics, painting, erosion patterns, particles rebound effect

It has been widely accepted that the microstructure of bearing materials can significantly affect their rolling contact fatigue (RCF) lives. Hence, microlevel topological features of materials will be of significant importance to RCF investigation. In order to estimate the fatigue lives of bearing elements and account for the effects of topological randomness of the bearing materials, in this work, damage mechanics modeling approach is incorporated into a Voronoi finite element method recently developed by the authors. Contrary to most of the life models existing in the literature for estimating the RCF lives, the current model considers microcrack initiation, coalescence, and propagation stages. The proposed model relates the fatigue life to a damage parameter D, which is a measure of the gradual material degradation under cyclic loading. In this investigation, 40 semi-infinite domains with different microstructural distributions are subjected to a moving Hertzian pressure. Using the fatigue damage model developed, the initiation and total lives of the 40 domains are obtained. Also, the effects of initial material flaws and inhomogeneous material properties (in the form of normal distribution of the elastic modulus) on the fatigue lives are investigated. It is observed that the fatigue lives calculated and their Weibull slopes are in good agreement with previous experimental and analytical results. It is noted that introducing inhomogeneous material properties and initial flaws within the domains decreases the fatigue lives and increases their scatters. [DOI: 10.1115/1.4001012] Keywords: damage mechanics, Voronoi finite element method, rolling contact fatigue, numerical simulation, material microstructure

This paper presents a study of the spinning influence on film thickness and friction in EHL circular contacts under isothermal and fully flooded conditions. Pressure and film thickness profiles are computed with an original full-system finite element approach. Friction was thereafter investigated with the help of a classical Ree--Eyring model to calculate the longitudinal and transverse shear stresses. An analysis of both the velocity and shear stress distributions at every point of the contact surfaces has allowed explaining the fall of the longitudinal friction coefficient due to the occurrence of opposite shear stresses over the contact area. Moreover in the transverse direction spinning favors large shear stresses of opposite signs, decreasing the fluid viscosity by non-Newtonian effects. These effects have direct and coupled consequences on the friction reduction that is observed in the presence of spinning. They are expected to further decrease friction in real situations due to shear heating. [DOI: 10.1115/1.4001104] Keywords: elastohydrodynamic lubrication, point contact, spinning, film thickness, traction, non-Newtonian behavior, complex kinematics, shear stress distribution

In tribological applications, calculating the contact temperature between contacting surfaces makes it possible to estimate lubricant failure and effectiveness, material failure, and other phenomena. The contact temperature can be divided into two scales: the macroscopic and the microscopic scales. In this article, a semi-analytical transient temperature model is presented, which can be used at both scales. The general theory, is presented here and used to calculate the contact temperatures of single micro- and macrocontacts. For the steady state situation, the results obtained are in good agreement with those found in literature. Further, it is shown that the simplification of modeling a microcontact as an equivalent square uniform heat source to simplify the calculation of the maximum temperature is justified in the fully plastic regime. The partition is calculated by setting a continuity condition on the temperature field over the contact. From the results, it can be concluded that at low sliding velocities the steady state assumption, which is often used for microcontacts, is correct. However, at higher sliding velocities, the microcontact is not in the steady state and transient calculation methods are advised. [DOI: 10.1115/1.4000693] Keywords: transient temperature, semi-analytical, flash temperature

The Cattaneo--Mindlin concept of interfacial slip in tangentially loaded compliant bodies is revisited and its basic simplifying assumptions are critically examined. It is shown that these assumptions, which, in the absence of modern numerical techniques, were essential in 1949 to enable an elegant quantitative solution of the basic problem of presliding between contacting bodies, may be nonphysical. An alternative approach to the same problem that is based on treating sliding inception as a failure mode involving material plastic yield is discussed. This alternative approach was suggested even before 1949 but for the same lack of modern numerical techniques could only be promoted qualitatively. Some recent theoretical models, which are based on this earlier alternative approach, and in which the simplifying assumptions of the Cattaneo--Mindlin concept were completely relaxed, are described along with their experimental verification. It is shown that the presliding problem between contacting bodies can be accurately solved by these models using realistic physical assumptions and failure criterion. [DOI: 10.1115/1.4001238] Keywords: spherical contact, presliding, static friction, junction growth, contact condition

An elastic contact model for three-dimensional layered or coated materials under coupled normal and tangential loads, with consideration of partial slip effects, has been developed in this paper. The response functions for calculating the displacements and stresses were determined in the frequency domain by using the Papkovich--Neuber potentials. The partial slip contact problem was solved by a numerical procedure based on the conjugate Gradient method and fast Fourier transform technique. The contact pressure, surface shear tractions, stick ratios, rigid body displacements, and subsurface stresses are analyzed under different conditions with variations in the material properties and coating thickness. Results show that stiffer coatings tend to decrease the stick ratios and the rigid ball tangential displacements in comparison to those with compliant coatings under the same contact conditions. For stiffer coatings, the values of the yon Mises stress and compressive surface stress increase and the positions of maximum von Mises stress move up to the surface; meanwhile, the distributions of the compressive stress become asymmetric due to the action of the tangential load. [DOI: 10.1115/1.4001011] Keywords: partial slip, coating, dry. contact, CGM

This paper presents an efficient numerical method based on quadratic programming, which may be used to analyze fretting contacts in the presence of wear The approach provides an alternative to a full finite element analysis, and is much less computationally expensive. Results are presented for wear of a Hertzian contact under full sliding and under partial slip. These are compared with previously published finite element analyses of the same problem. Results are also obtained for the fully worn problem by allowing a large number of wear cycles to accumulate. The predicted traction distributions for this case compare well with the fully worn analytical solution presented in part one of this paper. [DOI: 10.1115/1.4000733] Keywords: fretting wear, fretting fatigue, contact mechanics, quadratic programming

Modifying the surface topography of tribological interfaces has the potential to improve the friction performance of certain mechanical components that experience sliding contact. Vibromechanical texturing (VMT), an improved texturing method based on the convenient turning process, is introduced. This process is performed on a standard computer numeric controlled (CNC) lathe, which is retrofitted with a piezoelectric-actuated tool positioning stage. Controlled vibratory, motion of the tool is used to cut microsized dimples into the surface of the workpiece. Two types of workpiece materials are used: aluminum and hardened steel with three forms of workpiece geometries: outer cylinder, inner cylinder; and flat/end face. The accuracy of the texturing method is compared with a basic surface topography model, which predicts texture dimensions within an 11% error for aluminum and up to 90% error for hardened steel using the current open-loop control system. Further analysis of the textured samples shows no significant signs of process-induced damage. It is demonstrated that this VMT method is a versatile, accurate technique that has potential to be a cost-effective means for surface texturing of tribological components. [DOI: 10.1115/1.4000418]

Recently, much attention has been paid to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles in urban environments. In this study airborne particles generated from a sliding steel-on-steel combination are studied using a pin-on-disk tribometer equipped with airborne-particle counting instrumentation. The instrumentation measured particles in size intervals from 0.01 [micro]m to 32 [micro]m. The result shows three particle size regimes with distinct number peaks: ultrafine particles with a size distribution peak around 0.08 [micro]m, fine particles with a peak around 0.35 [micro]m, and coarse particles with a peak around 2 or 4 [micro]m. Both the particle generation rate and the wear rate increase with increasing sliding velocity and contact pressure. [DOI: 10.1115/1.3176990] Keywords: wear, airborne particles, sliding

Approximate closed-form equations are derived for normal contact force between nominally flat rough surfaces in dry contact. The formulation is based on the asperity-level interaction in which adhesive forces between two asperities and elastic and rate-dependent forces are included. The elastic and time rate-dependent portion of force is derived using a viscoelastic interaction of the two asperities. Statistical consideration of rough surfaces then furnishes the mathematical formulation of total normal force due to adhesion, elastic, and rate-dependent properties of the solids in contact. The probabilistic formulation of contact force leads to integral equations. From these are derived approximate closed-form expressions that relate the microscale properties of the surfaces to the macroscale behavior in the form of the total normal contact force between the surfaces. The approximate equations for visco-elasto-adhesive contact of rough surfaces illustrate the dependence of the contact force on the time rate of approach based on a combination of 1/6, 1/3, and 1 power laws. [DOI: 10.1115/1.4000015] Keywords: rough surface, asperity, viscoelastic, adhesion

Previously it was shown that including smaller inset regions of less stiff material in the larger O-ring section at locations of high stress results in lower strain energy density in the section. This lower energy content is expected to lead to improved long-term seal performance due to less permanent material deformation and so less loss of seal-housing contact pressure. The shape of the inset region, the time-dependent change in material properties, and hence change in seal behavior over time in use were not considered. In this research experimental and numerical simulation studies were conducted to characterize the time-dependent performance of O-ring section designs with small inset regions of different mechanical behaviors than the larger surrounding section. Seal performance in terms of the rate of loss of contact pressure of modified designs and a baseline elastic, one-material design was calculated in finite element models using experimentally measured time-dependent material behavior. The elastic strain energy fields in O-ring sections were calculated under applied pressure and applied displacement loadings. The highest stress, strain, and strain energy regions in O-rings are near seal-gland surface contacts with significantly lower stress in regions of applied pressure. If the size of the modified region of the seal is comparable to the size of the highest energy density region, the shape of the inset is not a major factor in determining overall seal section behavior The rate of loss of seal-housing contact pressure over time was less for the modified design O-ring sections compared with the baseline seal design. The time-dependent performance of elastomeric seals can be improved by designing seals based on variation of mechanical behavior of the seal over the seal section. Improvement in retention of sealing contact pressure is expected for seal designs with less stiff material in regions of high strain energy density. [DOI: 10.1115/1.3203148] Keywords: contact pressure retention, seals, seal design, viscoelastic material

This paper discussed the computational accuracy of roughsurface point-contact isothermal elastohydrodynamic lubrication (EHL) analysis by investigating the effects of differential scheme, viscosity-pressure, and shear-thinning models. An EHL experiment with multitransverse ridges was employed as simulated target. Four differential schemes, including the combined and the separate first-order and second-order backward schemes, were investigated. It is found that the separate second-order backward scheme offers the best results based on the comparison with the experimental data, with which two roughness derivatives may be fully or partially canceled each other; thus, the discretization error induced by roughness can be reduced. The consistency of differential schemes is an important issue for the separate schemes. The Yasutomi free-volume viscosity-pressure model and the Eyring rheological model are found to yield the numerical simulations the closest to experimental results. [DOI: 10.1115/1.2842245] Keywords: EHL, differential schemes, viscosity-pressure models, rheological models

Contours of surface texture of contact faces are not always parallel to the directions of the axis in solving Reynolds equations with finite difference method, and this often induces significant pressure saw-tooth effect, which results in an unignored analysis error. In this paper, pseudo-nine-point finite difference, as a new finite difference method, is introduced to solve the lubrication numerical problem of pressure saw-tooth. Also, application is carried out in gas lubrication of hard disk systems to verify the validity of the new method. In analysis, pressure distributions and gas floating forces are calculated for two different types of sliders, and the astringency and efficiency of the new method is discussed. Numerical results show that the pseudo-nine-point finite difference method can restrain pressure saw-tooth evidently, and presents better astringency and efficiency than the traditional five-point finite difference method. With the increase in mesh density, pressure distribution and gas floating force trend to steady. Also, numerical values of the floating force agree well with the experimental ones. [DOI: 10.1115/1.3195039] Keywords: pseudo-nine-point finite difference, pressure saw-tooth, gas lubrication

When machining miniaturized components, the contact conditions between the tool and the workpiece exhibit very small contact areas that are on the order of [10.sup.-5] [mm.sup.2]. Under these conditions, extremely high contact stresses are generated, and it is not clear whether macroscopic theories for the chip formation, cutting forces, and friction mechanisms are applicable. For this reason, the present investigation has focused on creating a basic understanding of the frictional behavior in very small scale machining processes so that evaluations of standard macroscale models could be performed. Specialized machining experiments were conducted on 70/30 brass materials using high-speed steel tools over a range of speeds, feeds, depths of cut, and tool rake angles. At each operating condition studied, the friction coefficient and the shear factor [[tau].sub.k] were obtained. Based on the experimental results, it was determined that the standard macroscopic theory for analyzing detailed friction mechanisms was insufficient in very small scale machining processes. An approach that utilized the shear factor, in contrast, was found to be better for decoupling the physical phenomena involved. Utilizing the shear factor as an analysis parameter, the parameters that significantly influence the friction in microscale machining processes were ascertained and discussed. [DOI: 10.1115/1.3195038] Keywords: machining, shear factor, strain hardening

The performance of elastomeric seals degrades over time in use due to the development of permanent material deformation. The existence of localized high stress regions below seal-housing contact areas led to consideration of improving O-ring design by modifying material behavior to decrease strain energy, and so permanent deformation, in these regions. Photoelastic stress analysis was used to experimentally characterize the stress and strain fields in O-ring sections and to validate finite element models used in design studies. O-ring section designs that included small inset regions of different material behavior than the larger surrounding section were investigated with the intent of manipulating and reducing the strain energy content. Finite element models of O-rings were used to characterize the strain energy content and distribution for inset materials with various stress-strain behaviors. Measurements of permanent deformation and load-deflection behavior of specimens held under applied compression over time showed dependence of the amount of permanent deformation on strain energy. Design rules were extracted from results of studies in which inset region material stiffness, stress-strain behavior, size, and location in the larger section were varied. O-ring sections with regions of less stiff material result in lower strain energy and more uniform strain energy density distribution than the typical one-material seal. Inclusion of less stiff softening stress-strain behavior material insets in the larger O-ring section produced reduction in strain energy level and favorable redistribution of the high strain energy density regions compared with the conventional one-material one-material-behavior design. Similar concepts will apply to the design of other elastomeric structures in which permanent material deformation affects structure performance. [DOI: 10.1115/1.3203147] Keywords: compression set, design, elastomer, material behavior, seals

Grooved thrust air bearings are widely used to support high-speed, low-loaded shafts in many rotating systems because of their low friction, noiseless operation, and simple structure. Several types of groove geometries, such as straight line, spiral, and herringbone, are commonly used in actual applications. Among these, the spiral groove is mainly used. However, as far as the authors know, there is no theoretical evidence that the spiral groove is the most optimized groove geometry in all possible groove geometries. This paper describes the optimum design for the groove geometry of thrust air bearings according to various objective functions such as air film thickness, bearing torque, dynamic stiffness of air film, and other similar combinations. In an optimum design, groove geometries are expressed by the third degree of spline function, and sequential quadratic programming is used as the optimization method. It is understood that the groove geometry for optimizing air film thickness or friction torque takes the basic form of spiral groove geometry. The geometry design for optimizing the dynamic stiffness is the modified spiral groove. Numerical results are compared with the measured data, and good agreements can be seen between them. [DOI: 10.1115/1.3201860] Keywords: bearing, geometrical optimum design, thrust gas bearings, objective function, groove geometry, measurement

This paper deals with a noncontact moving table using squeeze-film gas bearings for a linear motion guide, and investigates the dynamic behavior of the moving table under impulse load, experimentally and numerically, to clarify the dynamic characteristics of a squeeze-film gas bearing. This squeeze bearing for a noncontact moving table uses piezoelectric actuators as an ultrasonic vibrator to make the bearing surface vibrate at the ultrasonic resonant frequency of the bearing plate. The squeeze-film pressure is generated in the gap beneath the vibrating bearing surface and can support the moving table without any contact. It was consequently found that the numerical calculation method presented in this paper could predict well the dynamic behavior of the moving table using the squeeze-film gas bearing under impulse load. [DOI: 10.1115/1.3201894] Keywords: aerodynamic bearing, squeeze-film gas bearing, linear motion guide, moving table, impulse response, dynamic behavior

According to the first order slip velocity boundary, a modified Reynolds equation for micro gas journal bearings is presented with consideration of effective viscosity under a rarefied flow condition. A modified Reynolds equation is attained and solved using the finite difference method. The nondimensional pressure, load capacity, and attitude angle for micro gas journal bearings under different reference Knudsen numbers (the ratio of ambient molecular mean free path to the average radial clearance), bearing numbers, and eccentricity ratios are obtained. The numerical analysis demonstrates that the slip model with effective viscosity is in a better agreement with the FK model derived by Fukui and Kaneko than that without effective viscosity. When the bearing number is constant, the pressure and load capacity decrease, and the attitude angle changes inversely with the increasing reference Knudsen number. The larger the eccentricity ratio, the larger change in attitude angle from effective viscosity. When eccentricity ratio is less than 0.6, the attitude angle changes softly, and the effect of effective viscosity is unobvious. When the eccentricity ratio is constant, the influence of effective viscosity on nondimensional load capacity and attitude angle becomes larger with the increasing bearing number, and the influence is more prominent with a larger reference Knudsen number. [DOI: 10.1115/1.3209145] Keywords: slip velocity boundary, micro gas journal bearings, effective viscosity, reference Knudsen number

The dynamic performance of the herringbone groove journal bearings (HGJBs) with the effects of gas rarefaction taken into account is considered for applications in microsystems. Two important parameters (the Knudsen number Kn and the tangential momentum accommodation coefficients, TMACs or the accommodation coefficients, A Cs) that affect gas rarefaction significantly are considered. Small variations in film thickness and pressure from the equilibrium state are substituted into the transient modified molecular gas lubrication (MMGL) equation, which considers effects of gas rarefactions with the Poiseuille and Couette flow rate correctors. The gas film in the rotor-bearing system is modeled as stiffness and damping elements with coefficients dependent on the exciting frequency. The dynamic coefficients are then obtained by solving the linearized MMGL equations. The equations of motion of the rotor as well as the dynamic coefficients are performed for the present linear stability analysis. Due to the exciting frequencydependent nature of the dynamic coefficients, an iterative method with the golden section technique is introduced in the linear stability analysis of rotor-bearing systems. The critical mass parameters and the related threshold speed are computed and discussed. The results of this study prove that HGJBs in microsystems can operate at concentric conditions at very high speeds. [DOI: 10.1115/1.3201872] Keywords: linear stability analysis, MMGL, Knudsen number, tangential momentum accommodation coefficient

This paper presents a theoretical study and experimental method to recognize the dynamic performance (stiffness and damping coefficients) of an externally pressurized deep/ shallow pockets hybrid conical bearing compensated by flat capillary restrictors. The equations governing the flow of fluid film in the conical bearing together with the pressure boundary condition and the restrictor flow equation are solved by using the finite element method. A delicate test rig is constructed and bearings having a big end diameter of 97 mm, a length of 90 mm, and a radial clearance of 0.02-0.025 mm are analyzed. It is assumed that the fluid film force of the hydrostatic/hydrodynamic conical bearing is characterized by a set of linear stiffness and damping coefficients. The experiment used the impulse excitation method to recognize these coefficients and established their characteristics under different operating conditions. Numerical results are compared with the experimental results. The stability parameters of hybrid conical, hydrodynamic, and hydrostatic bearings are compared. The results show that the hybrid conical bearing has the advantages of high load carrying capability and high stability under small eccentricity. [DOI: 10.1115/1.3176991] Keywords: conical hybrid bearing, linear dynamic coefficients, impulse excitation

Approximate closed-form equations governing the shoulder-shoulder contact of asperities are derived based on a generalization by Chang, Etsion, and Bogy. The work entails the consideration of asperity shoulder-shoulder contact in which the 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 plastic terms, which upon statistical summation yields the force component for the elastic and plastic forces 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 equations are found. In the first set of equations the functional forms are simpler and provide approximation of contact force to within 9%. The second set is enhanced equations derived from the first set of approximate equations that achieve an accuracy of within 0.2%. [DOI: 10.1115/1.3204775] Keywords: rough surface, asperity, elastic-plastic, approximate equations, constitutive equations

Mechanical properties of materials in small-scale applications, such as thin coatings, are often different from those of bulk materials due to the difference in the manufacturing process. Indentation has been a convenient tool to study the mechanical properties in such applications. In this paper, a numerical technique is proposed that can identify the mechanical properties using optimization and evaluate the robustness of identified material properties using sensitivity analysis. First, two response surfaces are constructed for loading and unloading curves from the indentation experiment of a gold film on the silicon substrate. Unessential coefficients of the response surface are then removed based on the test statistics. Unlike the traditional methods of identification, the tip geometry, of the indenter is included because its uncertainty significantly affects the results. In order to validate the accuracy, and stability of the method, the sensitivity of the identified material properties with respect to each coefficient is analyzed. It turns out that the plastic hardening parameter is the most sensitive to the experimental data. In addition, all material parameters are sensitive to the coefficients of higher-order bases. However, their effects are diminished because the magnitudes of these coefficients are small. [DOI: 10.1115/1.3142902] Keywords: indentation, material property identification, regression, sensitivity analysis, elastoplasticity, contact, tip geometry

Reynolds equation in polar cylindrical (polar) coordinates is used for numerous tribological applications that feature thin fluid films in sliding contacts, such as chemical mechanical polishing and pin-on-disk testing. Although unstated, tribology textbooks and literal' resources that present Reynolds equation in polar coordinates often make assumptions that the radial and tangential entrainment velocities are independent of the radial and tangential directions, respectively. The form of polar Reynolds equation is thus typically presented, while neglecting additional terms crucial to obtaining accurate solutions when these assumptions are not met. In the present investigation, the polar Reynolds equation is derived from the cylindrical Navier-Stokes equations without the aforementioned assumptions, and the resulting form is compared with results obtained from more traditionally used forms of the polar Reynolds equation. The polar form of Reynolds equation derived in this manuscript yields results that agree with the commonly used Cartesian form of Reynolds equation but are drastically different from the typically published form of the polar Reynolds equation. It is therefore suggested that the polar form of Reynolds equation proposed in this technical note be utilized when entrainment velocities are known to vary with either radial or angular position. [DOI: 10.1115/l.3118783] Keywords: Reynolds equation, polar coordinates, pin-on-disk, chemical mechanical polishing

Pulverulent and granular materials processed in any suction-type dilute-phase pneumatic transport system tribocharge the pipes they move through. The aim of this study is to refine the understanding of the triboelectrostatic phenomena involved. A laboratory installation was employed for the investigation of the charging and discharging of various zones of an insulating pipe during and after the suction of a well-defined quantity of fine, dust-like, particles. The amount and the sign of the charge that was measured using several custom-designed electrostatic induction probes depended on the nature of the processed powders and varied from one zone of the pipe to another. Surface potential decay measurements confirmed that the insulating pipe retains high levels of charge for several hours after the cease of the suction. These observations point out he need of thorough laboratory modelling of any new pneumatic transport system, in order to avoid the electrostatic hazards related to electric charge build-up in various parts of the installation during operation. Index Terms --electrostatic measurements, oneumatic svstems, triboelectricitv.

The major focus of this study was to examine the feasibility of applying diamond-like nanocomposite (DLN) coatings on the sidewalls of Ni alloy parts fabricated using lithographie, galvanoformung and abformung (LIGA: a German acronym that means lithography, electroforming, and molding) for friction and wear control. Planar test coupons were employed to understand the friction mechanisms in regimes relevant to LIGA microsytems. Friction tests were conducted on planar test coupons as well as between LIGA-fabricated test structures in planar-sidewall and sidewall-sidewall configurations. Measurements were made in dry nitrogen and air with 50% relative humidity by enclosing the friction tester in an environmental chamber. In contrast to bare metal-metal contacts, minimal wear was exhibited for the DLN-coated LIGA NiMn alloy parts and test coupons. The low friction behavior of DLN was attributed to its ability to transfer to the rubbing counterface providing low interfacial shear at the sliding contact. The coating coverage and chemistry on the sidewalls and the substrate-coating interface integrity were examined by transmission electron microscopy, Automated eXpert Spectral Image Analysis, and electron backscatter diffraction on cross sections prepared by focused ion beam microscopy. The role of novel characterization techniques to evaluate the surface coatings for LIGA microsystems technology is highlighted. [2008-0007] Index Terms--Coatings, electron microscopy, friction.

Multiwalled carbon nanotubes have been synthesized by catalytic chemical vapor deposition of ethylene, using two different catalysts in order to obtain nanotubes with average diameters of 24 and 58 nm, and different lengths. Polyamide 6 (PA6) was reinforced by melt-mixing in an extruder with 2 wt% functionalized and unfunctionalized carbon nanotubes (CNTs). The nanocomposites were characterized by thermogravimetric analysis, differential scanning calorimetry, and sliding wear determination (SWD). SWD results show a reduction of the residual depth in a scratch test. The reduction is larger in the presences of unfunctionalized CNTs. A further reduction is obtained when decreasing the nanotubes dismeter, an effect which is related to larger interfaces between the nantube and polymeric matrix. CNTs enhance the crystallinity of the polymer and act as nucleation sites, thus increasing the crystallization temperature in respect to neat PA6. The addition of carbon nanotubes helps the formation of PA6 in α- crystalline form, which is thermodynamically more stable that the γ-form. CNTs also can act as heterogeneous nucleation sites, hampering the movement of the polymer chains and increasing the crystallization temperature. POLYM. ENG. SCI., 49:896-902, 2009. [C]2009 Society of Plastics Engineers, INTRODUCTION Polymer tribology seems to be an underappreciated area; however, Rabinowicz has demonstrated the importance of tribology, including from the point of view of financial welling of the industry (1). [...]

The nanoscale contacts, which play a key role in nanotechnology and micro-/ nanoelectromechanical systems, are fundamentally important for a wide range of problems including adhesion, contact formation, friction and wear, etc. Because continuum contact mechanics has limitations when it is applied at length of nanoscale, molecular dynamics (MD) simulations, which can investigate internal physical mechanisms of nanostructures by atomic motions in detail, become one of the most promising approaches for investigating mechanical behaviors of contacts in nanoscale. First, contacts between rigid cylindrical probes with different radii and an elastic half-space substrate are studied by using MD simulations with the assistance of the classical Lennard-Jones potential. For contacts without adhesion, the relationship between the applied force and the contact half width is analyzed. The von Mises stress distributions are then discussed. For contacts with adhesion, the phenomena of the jump-to-contact, the break-off contact, and the hysteresis are observed. The pressure distributions and the von Mises stress contours in the contact region agree with the existing solutions. Second, the effects of the surface topography on adhesive contacts are studied by using MD simulations with the embedded atom method potential. The adhesive contact mechanical characteristic of a series of asperities with different shapes, different sizes, and different numbers on contacting surfaces are discovered and compared. The results show that the surface topography is one of the major factors, which may influence the contact behaviors between the interfaces of nanoscale components. [DOI: 10.1115/1.3063812] Keywords: nanoscale surface topography, contact, adhesion, molecular dynamics simulations

With the increased use of hard disk drives (HDDs) in mobile and consumer applications combined with the requirement of higher areal density, there is enhanced focus on reducing head disk spacing, and consequently there is higher susceptibility of slider/disk impact damage during HDD operation. To investigate this impact process, a dynamic elastic-plastic finite element model of a sphere (representing a slider corner) obliquely impacting a thin-film disk was created to study the effect of the slider comer radius and the impact velocity on critical contact parameters. To characterize the energy losses due to the operational shock impact damage, the coefficient of restitution for oblique elastic-plastic impact was studied using the finite element model. A modification to an existing physics-based elastic-plastic oblique impact coefficient of restitution model was proposed to accurately predict the energy losses for a rigid sphere impacting a half-space. The analytical model results compared favorably to the finite element results for the range from low impact angles (primarily normal impacts) to high impact angles (primarily tangential impacts). [DOI: 10.1115/1.3078770] Keywords: magnetic storage tribology, oblique impact, shock, elastic-plastic impact, coefficient of restitution

A physics-based fluid mechanics model is proposed to predict spin power losses of gear pairs due to oil churning and windage. While the model is intended to simulate oil churning losses in dip-lubricated conditions, certain components of it apply to air windage losses as well. The total spin power loss is defined as the sum of (i) power losses associated with the interactions of individual gears with the fluid, and (ii) power losses due to pumping of the oil at the gear mesh. The power losses in the first group are modeled through individual formulations for drag forces induced by the fluid on a rotating gear body along its periphery and faces, as well as for eddies formed in the cavities between adjacent teeth. Gear mesh pumping losses will be predicted analytically as the power loss due to squeezing of the lubricant, as a consequence of volume contraction of the mesh space between mating gears as they rotate. The model is applied to a unity-ratio spur gear pair to quantify the individual contributions of each power loss component to the total spin power loss. The influence of operating conditions, gear geometry parameters, and lubricant properties on spin power loss are also quantified at the end. A companion paper (Seetharaman et al., 2009, 'Oil Churning Power Losses of a Gear Pair: Experiments and Model Validation,' ASME J. Tribol., 131, p. 022202) provides comparisons to experiments for validation of the proposed model. [DOI: 10.1115/1.3085943] Keywords: gears, spin power losses, oil churning, oil pocketing

A five-degree-of-freedom model was developed for the analysis of the off-track motion of the magnetic head slider in a hard disk drive. The air bearing was integrated into the dynamic system by combining its stiffness and damping matrices with those of the suspension. Simulation was conducted for the slider in intermittent contact with circumferentially located bumps on a rotating magnetic disk. For a single bump, the excitation to the transverse displacement of the slider is close to that of an impulse. However, for multiple bumps in a sequence, the excitation gives an effect similar to that of a step force function. The maximum transverse displacement increases almost linearly with both the coefficient of friction and the skew angle. The average contact force is determined by the maximum contact force, the contact time ratio, and the shape factor of the contact force, which change with the bump spacing and the rotational speed of the disk. The steady-state transverse displacement is related to the average contact force. As the bump spacing decreases, the average contact force increases, resulting in a greater transverse displacement. Based on the system dynamic characteristics alone, changing the rotational speed of the disk has only a small impact on the average contact force and, thus, on the transverse displacement. At zero skew angle with the bump path close to a rear pad edge, significant transverse motion occurs because of the excited roll mode and the coupling between the roll angle and the transverse displacement. The off-track motion of the slider is dominated by the rotational mode of the actuator arm and the sway mode of the suspension, as verified by comparing the results of the transverse displacement from the 5DOF model to that from a 2DOF model of the transverse motions of the actuator arm and suspension. The effects of the roll angle on the transverse displacement through coupling were found to be responsible for the difference in the transverse displacements obtained from the two models. [DOI: 10.1115/1.3063808] Keywords: hard disk drive, head-disk interface, head-arm assembly, actuator arm, suspension, transverse displacement, bump, contact force

In progress of anti-shock characteristics of small size precision equipment, a miniaturized damper is required to have better damping characteristics. However, damping efficiency becomes less as damper size decreases, and so for compensation of its defect, a porous elastic sheet damper with a magnetic fluid is proposed. An analytical estimation of this sheet damper is presented to investigate variation of damping characteristics with intensity and direction of a magnetic field and to give effects of porosity of porous sheets on damping characteristics. [DOI: 10.1115/1.3075870] Keywords: damping characteristics, magnetic fluid damper, porous sheet damper, porosity of porous media

This paper presents the results of an experimental study on load-independent (spin) power losses of spur gear pairs operating under dip-lubricated conditions. The experiments were performed over a wide range of operating speed, temperature, oil levels, and key gear design parameters to quantify their influence on spin power losses. The measurements indicate that the static oil level, rotational speed, and face width of gears have a significant impact on spin power losses compared with other parameters such as oil temperature, gear module, and the direction of gear rotation. A physics-based gear pair spin power loss formulation that was proposed in a companion paper (Seetharaman and Kahraman, 2009, 'Load-Independent Spin Power Losses of a Spur Gear Pair: Model Formulation,' ASME J. Tribol., 131, p. 022201) was used to simulate these experiments. Direct comparisons between the model predictions and measurements are provided at the end to demonstrate that the model is capable of predicting the measured spin power loss values as well as the measured parameter sensitivities reasonably well. [DOI: 10.1115/1.3085942] Keywords: gears, spin power losses, oil churning, oil pocketing

This work is intended to evaluate a cavitation model based on the complete Rayleigh-Plesset (RP) equation for use in squeeze film damper calculations. The RP equation governs the variation in the radius of the cavitation bubbles at rest, surrounded by an infinite incompressible fluid and subjected to an external pressure. This equation is obtained from the momentum equation and it takes into account the ensemble of the phenomena related to the dynamics of the bubbles (surface tension, damping, and inertia). All the terms in the RP equation will be taken into account in the present work plus a dilatation viscosity introduced by Someya in 2003. Numerical results will be compared with experimental data obtained by Adiletta and Pietra in 2006. The results underline the influence of the effects contained in the RP equation on the pressure field. [DOI: 10.1115/1.3063819] Keywords: cavitation, squeeze film damper

Over the years, the deterministic elastohydrodynamic lubrication (EHL) approach has been widely used. This technique is very powerful in capturing details of asperity deformation and interaction. The probabilistic EHL methodology is still used when the main interest of the engineer is directed toward computations of bulk properties. During recent years, the results of many deterministic analyses have been published. The reduction of the waviness amplitude in EHL contacts under rolling-sliding was systematically studied and it was shown that the amplitude reduction is completely described by a single parameter that includes relative wavelength and the operating conditions. This approach, usually referred to as the amplitude reduction technique, has opened the way for developing improved probabilistic EHL models by incorporating the effects of fluid-induced roughness deformation, which is calculated using the fast fourier transform. In this paper we provide a review of the latest developments in the amplitude reduction technique and we present a probabilistic EHL algorithm for the computation of the load supported by the fluid, the elastically deformed asperities and the plastically deformed asperities, in a mixed EHL contact with either isotropic on nonisotropic roughness. The fluid-induced roughness deformation is incorporated into the probabilistic model via the use of the amplitude reduction technique. [DOI: 10.1115/1.2961919] Keywords: mixed elastohydrodynamic lubrication (EHL), amplitude reduction technique

To quantitatively predict the static and dynamic characteristics of a flying head slider on a patterned disk surface, the 'mixed averaging method' has been successfully applied to the molecular gas lubrication problem incurred by groove-shaped textures formed over the lubricating surface. First, formulation of the alternative direction implicit method using a 'mixed averaged' film thickness was derived and implemented as a numerical simulation system. To analyze several types of surface patterns including their mixture patterns, the mixing ratio for the pressure flow and the shear flow were tabulated and interpolated at every mesh point, and then the spacing variations of typical sliders on a discrete track recording medium were demonstrated. [DOI: 10.1115/1.3063696] Keywords: magnetic disk storage, flying head slider, patterned disk, mixed averaging method

This paper presents a nonlinear theoretical model to study the effect of laser surface texturing on the tribological performance in soft elastohydrodynamic lubrication. Both geometrical and physical nonlinearities of the elastomer are considered by using a logarithmic strain and the Mooney-Rivlin constitutive law, respectively. The results of the present nonlinear model are compared with a previous linear one over a wide range of operating conditions. It is found that the simpler linear elasticity model predicts results that are only slightly different from these predicted by the more accurate nonlinear one. Hence, the linear elasticity model can be practically considered valid over the entire range of operating conditions. [DOI: 10.1115/1.3071973] Keywords: elastohydrodynamic lubrication, nonlinear elasticity, surface texturing

The applications of foil air bearings have been extended for use in a wide range of turbomachineries with high speed and high temperature. Lubricant temperature becomes an important factor in the performance of foil air bearings, especially at high rotational speeds and high loads or at high ambient temperature. This study presents a thermohydrodynamic (THD) analysis of multiwound foil bearing, in which the Reynolds' equation is solved with gas viscosity as a function of temperature that is obtained from the energy equation. Lobatto point quadrature is utilized to accelerate the iteration process with a sparse mesh across film thickness. A finite element model of the foil is used to describe the foil elasticity. An iterative procedure is performed between the Reynolds equation, the foil elastic deflection equation, and the energy equation until convergence is achieved. A three-dimensional temperature prediction of air film is presented, and a comparison of THD to isothermal results is made to emphasize the importance of thermal effects. Finally, published experimental data are used to validate this numerical solution. [DOI: 10.1115/1.3070579] Keywords: gas foil bearing, thermohydrodynamics, Lobatto point quadrature

The interfacial contact pressure and shear traction distributions are found for a sphere pressed onto an elastically similar half-space whose surface is populated by a uniform array of spherical asperities, when the normal load is constant and an oscillatory shear, less than that needed to cause sliding, is imposed. Details of the load history suffered by asperities in an outer sliding annulus and an inner disk, where they experience partial slip, are found, together with the effects of the roughness on the overall tangential compliance and the frictional energy losses. It is shown that for the example combination of parameters chosen, under light shear loads, the rough contact absorbs less energy than a smooth one subject to the same loading history, but that for larger shearing forces the reverse is true. [DOI: 10.1115/1.3063697] Keywords: Hertzian contact, rough surface, pressure distribution, tangential compliance, partial slip

This paper presents numerical quasistatic simulation results of the air entrainment phenomenon between a web and a spirally grooved roller. The numerical results show that during one complete rotation of the spirally grooved roller, the traction coefficient between the web and the roller changes with time due to the changing shape of the groove in the contact region, and the average traction coefficient of the circumferentially grooved roller is higher than that of the spirally grooved roller. Using a laser sensor, web deflection is measured and compared with the numerical results at the inlet. Furthermore, a smoke wire experiment shows a clear view of the air entrainment phenomenon at the entrance, between the web and the roller. [DOI: 10.1115/1.3070582] Keywords: air entrainment, spirally grooved roller, traction coefficient, web deflection, numerical simulation

A method for treating the thermomechanical interaction of bodies that undergo relative oscillatory motion is developed. The approach utilizes a combination of the transfer matrix and the finite element methods. The thermomechanical coupling process between the contacting bodies involves a transient solution scheme where the frictional heat is automatically partitioned between the contacting surfaces. The coupling between thermal and mechanical interactions is treated iteratively. An application of the proposed model in the study of thermomechanical behavior of journal bearings with oscillatory motion undergoing thermally induced seizure is presented. The results of a wide range of operating parameters ate presented. The significance of applied load, contact clearance, friction coefficient, oscillation parameters, convective heat transfer, and variable load direction condition in the thermally induced seizure is discussed in light of the numerical results. [DOI: 10.l115/1.3071976] Keywords: thermomechanical coupling (TMC), thermally induced seizure (TIS), journal bearings, oscillatory contact

The contact problem for an elastic body indenting a similar half-space resulting in multiple contacts is important for various applications. In this paper an exact fast numerical method based on singular integral equations is developed to solve the normal contact (including applied moments), partial slip, and shear-reversal problems for such contacts. The contact patches are considered to be fully interacting, with no simplifying assumptions. A contact algorithm to automatically generate trial values based on an analysis of the profile and to subsequently guide the solver toward convergence is detailed. Some applications are discussed, including regular rough cylinders and a regularly rough flat punch with rounded edges. The examples involve between 3 and 29 contacts. The partial slip problems include demonstration of cases with multiple stick zones in some contact patches and complete sliding in others. [DOI: 10.1115/1.3078772] Keywords: contact mechanics, half-space, singular integral equations, multiple contacts, rough cylinder, regular rough contacts, partial slip

In an externally adjustable fluid film bearing, the hydrodynamic conditions can be changed as required in a controlled manner. The principal feature of the bearing is the facility to adjust its radial clearance and circumferential film thickness gradient. Unlike a tilting pad bearing, this bearing can have radial adjustments. The tilt adjustments are obtained by providing flexibility to the pad at one comer. This paper deals with the effect of turbulence on the steady state performance characteristics of a centrally loaded 120 deg single pad externally adjustable fluid film bearing. The bearing has an aspect ratio of I and operates over a wide range of eccentricity ratios with different radial and tilt adjustments. The Reynolds equation is solved numerically using the finite difference method. The linearized turbulence model of Ng and Pan (1965, 'A Linearized Turbulent Lubrication Theory,' ASME J. Basic Eng., 87, pp. 675-688) as well as the simplified adiabatic model of Pinkus and Bupara (1979, 'Adiabatic Solutions for Finite Journal Bearings,' ASME J. Lubr. Technol., 101, pp. 492-496) ate incorporated in the solution scheme. The static performance characteristics calculated are presented in terms of load carrying capacity, attitude angle, friction variable, and Sommerfeld number. A comparative study with the combination of adjustments predicts that the static performance of the bearing is superior with negative radial and tilt adjustments. [DOI: 10.1115/1.3070580] Keywords: static characteristics, externally adjustable, tilt and radial adjustments, single pad, turbulence, simplified adiabatic solution

Line contact problems, such as those seen in spur gears and cam-roller follower systems, are often simplified with the plane-strain assumption and thus modeled by two-dimensional equations. However, in order to address the effects of roughness and textured surfaces, three-dimensional modeling is necessary. The challenge arises when the contact domain is several orders of magnitude greater than the grid size needed to properly describe the surface roughness or texture. Considering the surface geometry of a so-called 'line contact,' the contact domain is nonperiodic in contact width direction, but it can be treated as periodic in the contact length direction-semiperiodic line contact problem. Thus, only a section of the entire contact domain is used as the computational domain with a much-reduced size. Based on an in-depth investigation of available algorithms, DC-[FFT.sup.S] and DC-CC-FFT algorithms are proposed. The DC-[FFT.sup.S] algorithm is a modified discrete convolution and fast Fourier transform algorithm with superposition of influence coefficients. The DC-CC-FFT algorithm is a hybrid fast Fourier transform based algorithm, which combines the discrete convolution--FFT and the continuous convolution--FFT methods. The proposed algorithms are used to solve three-dimensional displacement, contact pressure, and stresses for line contact problems. The results are compared with the other available algorithms from literature. The accuracy and efficiency of different algorithms are discussed. [DOI: 10.1115/1.3084237] Keywords: elastic contact, FFT based algorithms, textured surface

A model for elastic-plastic spherical contact of rough surfaces under combined normal and tangential loadings, with full stick contact condition, is presented. The model allows evaluation of the effect of surface roughness on the real contact area, static friction and junction growth under small normal loads. It is shown that as the normal load approaches a certain threshold value, which depends on the plasticity index, the results of the present rough surface model approach these of previous corresponding models for smooth sphere and a rigid flat. At normal load values below the threshold load, the correlation of the present results and published experimental results is much better in comparison with the results of the smooth surface models. [DOI: 10.1115/1.3075866] Keywords: spherical contact, elastic-plastic contact, normal and tangential loading, static friction, junction growth, rough surfaces

The asperity contact regions in static contact are subjected to very high stress. Deformation is plastic and the material can suffer localized creep that is not usually observed at conventional stress levels. Creep of the asperity contacts causes an increase in contact area and hence an increase in the adhesive component of friction. The strains are so small compared with the bulk deflections that they are hard to measure by displacement of strain transducers. However, one measurement approach is to use the reflection of an ultrasonic pulse since this depends only on the interface behavior, specifically its stiffness. In this study, ultrasound was used to investigate the increase in interfacial stiffness with time. A power law relationship between stiffness and hold time was observed for both steel and aluminum surfaces pressed together. An analytical model that assumes a simple geometry for the contact has been developed. A single asperity was considered to determine the geometry of the whole interface by superposition. The stiffness predicted by the model was compared with experimental data and was used to determine the creep rate exponent for the material. [DOI: 10.1115/1.3089217] Keywords: asperity creep, ultrasound, rough contact