bluuebunny/crossref_metadata_2025 huggingface dataset:
Concurrent Design of Sheet Metal Forming Product and Process
Authors: Yang S. , Nezu K.
Published: February 2008

An inverse finite element (FE) algorithm is used to develop a sheet forming process modeling module and numeric models are extracted out of the process modeling results. Both the representation schemes for numeric models and the empirical knowledge along with their integration into the knowledge base are discussed. To facilitate the definition of knowledge and the assertion of facts and support the inference capability, a shell called “Concurrent Design Environment (CDE)” is developed. Certainty factors for quality assurance can be evaluated by using the concurrent design system which is aimed at achieving a compatible design of sheet product and forming process at the preliminary design stage. Case studies are included to demonstrate the feasibility of this proposed system.
Direct Upper Bound Solution to Rectangular-to-Polygonal Extrusion Through Square Die
Authors: Sahoo S. K. , Kar P. K. , Singh K. C.
Published: February 2008

This paper is concerned with an attempt to find an upper bound solution for the problems of steady-state extrusion of asymmetric polygonal section bars through rough square dies. A class of kinematically admissible velocity fields is examined, reformulating the SERR technique, to get the velocity field that gives the lowest upper bound. This velocity field is utilized to compute the non-dimensional average extrusion pressure at various area reductions for different billet aspect ratios.
Distortion of U-Channel Sections in Plastic Bending
Authors: Stelson K. A. , Kramer A.
Published: February 2008

When a thin-walled U-channel section is plastically bent, considerable in-plane distortion occurs. The initially flat base of the U is deformed into a circular arc. The sides remain perpendicular to the base so that an angle between the sides develops. In this paper, an analytical expression for the amount of distortion is derived based on energy minimization. The expression is purely geometrical indicating that distortion should not depend on material properties. The theory is compared with fourpoint bending experiments of thin-walled channels, with good agreement found.
Even Fitting Closed Curves: 2-D Algorithm and Assembly Applications
Authors: Fainberg Z. , Zussman E.
Published: February 2008

In certain assemblies there exists a requirement for the evenness of the gap between a “peg” and a “hole.” In these cases, when given a “peg” and a “hole” that must be fitted the task is to find the positioning of the “peg” such that the gap will be as even as possible. In this paper the even fitting requirement is formulated for two planar closed curves. The optimal fitting demand is found to be equivalent to the maximization of the minimal distance between the curves. Both convex and nonconvex curves with “tolerances” are considered and optimized. It is proven that for certain shape characteristics, fitting for evenness can be further improved by minimization of the Haussdorff distance between the curves. We demonstrate the algorithm by fitting an automobile door into a frame. The best door positioning is found in such a way that the variation gap is minimized according to the selected metrics.
Tolerance Analysis of Machining Fixture Locators
Authors: Choudhuri S. A. , De Meter E. C.
Published: February 2008

The geometric variability of locators within a machining fixture is a known source of datum establishment error and machined feature geometric error. A locator tolerance is used to specify the range of permissible locator variation. Currently there are no models that relate a locator tolerance scheme to the worst case geometric errors that may result due to datum establishment error. This paper presents a methodology for modeling and analyzing the impact of a locator tolerance scheme on the potential datum related, geometric errors of linear, machined features. This paper also provides a simulation study in which locator tolerance analysis is applied to reveal some important insights into the relationship between machined feature geometric error, locator design, and locator tolerance scheme.
Estimation of Critical System Parameters That Affect Orbit Motor Performance—Combining Simulation and Experiments
Authors: Dasgupta K. , Mukherjee A. , Maiti R.
Published: February 2008

In this paper the authors have presented an integrated study of an orbital rotor Low Speed High Torque (LSHT) hydrostatic unit in a Hydrostatic Transmission (HST) System and an attempt has been made to estimate some critical parameters of such class of geometrically complex machine. Owing to the close tolerance in between the rotor-stator interface of the motor leakage takes place from the high pressure to the low pressure chamber and is difficult to estimate during operation. Based on the simulation and experimental investigations, a semi-empirical approach is proposed here to estimate its interchamber leakage resistance and for that the machine need not be disassembled. Using the actual parametric values, the overall dynamic model of the plant has been validated experimentally.
Chatter Frequency in Turning Considering Tool Compliance and Wearland
Authors: Chiou R. Y. S. , Liang S. Y.
Published: February 2008

An analytical model for the chatter frequency of a turning cutter considering system compliance and flank wear of the tool is presented in this research. The fundamental mechanism of selfexcited vibration at the presence of tool wearland is examined, and a mathematical model is developed to describe the frequency characteristics of the vibration. In the paper a comparison of the chatter frequencies for a fresh cutting tool and a worn cutting tool is provided to demonstrate the coupling between wearland and chatter. The theoretical model of chatter frequency is validated by experimental observations over a range of turning conditions.
A Fractal Theory of the Temperature Distribution at Elastic Contacts of Fast Sliding Surfaces
Authors: Wang S. , Komvopoulos K.
Published: February 2008

The statistical temperature distribution at fast sliding interfaces is studied by characterizing the surfaces as fractals and considering elastic deformation of the asperities. The fractions of the real contact area in the slow, transitional, and fast sliding regimes are determined based on the microcontact size distribution. For a smooth surface in contact with a rough surface, the temperature rises at the real contact area are determined under the assumption that most of the frictional heat is transferred to one of the surfaces. The interfacial temperature rises are bounded by the maximum temperature rise at the largest microcontact when the fractal dimension is 1.5 or less, and are unbounded when it is greater than 1.5. Higher temperature rises occur at larger microcontacts when the fractal dimension is less than 1.5, and at smaller microcontacts when it is greater than 1.5. For a fractal dimension of 1.5, the maximum temperature rise at a microcontact is independent of its size. The maximum temperature rise at the largest microcontact is expressed as a function of the friction coefficient, sliding speed, elastic and thermal properties, real and apparent contact areas, and fractal parameters. The closed-form solutions for the distribution density function of the temperature rise can be used to calculate the fraction of the real contact area of fast sliding surfaces subjected to temperature rises in any given range. The present theory is applied to boundary-lubricated and dry sliding contacts to determine the fractions of the real contact area where lubricant degradation and thermal surface failure may occur.
A Study of the Starting Characteristics of an Unlubricated Journal Bearing
Authors: Sun D. C. , Xu Jing
Published: February 2008

The complicated motion of the journal in an unlubricated bearing in response to an applied torque is analyzed. The theory identifies the conditions for various distinct modes of motion to occur, including the “dry friction whirl” cited in the literature. The crucial dependence of the motion on the friction coefficient and the normal and tangential restitution coefficients, as revealed by the theory, suggest that perhaps these latter parameters of motion can be determined by measuring the journal’s motion in an unlubricated journal bearing.
A Direct Analysis of Three-Dimensional Elastic-Plastic Rolling Contact
Authors: Yu Maria M.-H. , Moran Brian , Keer Leon M.
Published: February 2008

A novel treatment of a direct procedure for elastic-plastic analysis and shakedown is presented and its application to problems in three-dimensional rolling contact with or without case-hardened layers is demonstrated. The direct approach consists of an operator split technique, which transforms the elastic-plastic problem into a purely elastic problem and a residual problem with prescribed eigenstrains. These eigenstrains are determined using an incremental projection method based on the purely elastic solution and a special representation of the yield condition for a linear-kinematic hardening material. The three-dimensional residual problem is then further split into a plane problem and an anti-plane problem which are readily solved using the finite element method. A significant advantage of the present analysis over the alternative approach of simulating repeated rolling until shakedown occurs is that in the present analysis, the final shakedown solution is obtained directly by solving three elasticity problems. Results are compared with full elastic-plastic finite element calculations available from the literature and good agreement is observed. The effects of surface hardened layers on the distributions of residual stress and displacement are investigated for both two- and three-dimensional contact. The direct approach is shown to be a straightforward and efficient method for obtaining the steady state solution in the analysis of three-dimensional problems in rolling and/or sliding contact.
A Study of the Durability of a Paper-Based Friction Material Influenced by Porosity
Authors: Matsumoto Takayuki
Published: February 2008

The friction performance and thermal resistance of paper-based oil immersed friction materials are influenced by the material structure formed as a result of the combination of porosity and resiliency. In this paper, the effects of porosity on the thermal durability of paper-based friction materials were studied, of which the contents are varied but the geometries are the same as used in real applications. The relationship between the degree of carbonization and the durability was discussed in several terms of mechanical property changes of the material. The friction and thermal durability tests were conducted by using an SAE No. 2 apparatus under a repeated engage-disengagement condition. To obtain the thermal durability performance the sliding surface temperature was also measured. Coefficients of friction of the low porosity material tend to decrease as the test cycle increases. And the total thickness loss of the low porosity material after durability test is bigger than that of the high porosity material. These durability performances were well correlated with the mechanical and physical property changes of the material, that is, variations of carbonization degree, permeability and hysteresis loss energy.
Theoretical and Experimental Comparisons for Rotordynamic Coefficients of a High-Speed, High-Pressure, Orifice-Compensated Hybrid Bearing
Authors: Franchek Nancy M. , Childs Dara W. , San Andres Luis
Published: February 2008

Comparisons are presented between measurements and predictions for a 76.2 mm diameter, high-speed (24,600 rpm), high-pressure (7.0 MPa), hybrid bearings using warm (54°C) water as a test fluid. “Hybrid” refers to combined hydrostatic and hydrodynamic action. Test results are presented for an orifice-fed, square-recess configuration with five recesses. Data are provided for rotordynamic coefficients including direct and cross-coupled stiffness, direct damping, direct added-mass coefficients, and the whirl-frequency ratio. Experimental results are compared to predictions from an analysis by San Andres (1990a), which accounts for both temporal and convective acceleration terms in the fluid film. San Andres’ development uses an orifice discharge coefficient to model the pressure drop from supply pressure to recess pressure. With experimentally determined discharge-coefficient values as input, good agreement is obtained between theory and experiment. However, predictions are sensitive to changes in the orifice discharge coefficients.
On the Motion of an Elastic Body Rolling/Sliding on an Elastic Substrate
Authors: Spector A. , Batra R. C.
Published: February 2008

The three-dimensional evolutionary problem of rolling/sliding of a linear elastic body on a linear elastic substrate is studied. The inertial properties of the body regarded as rigid are accounted for. By employing an asymptotic analysis, it is shown that the process can be divided into two phases: transient and quasistationary. An expression for the frictional force as a function of the externally applied forces and moments, and inertial properties of the body is derived. For an ellipsoid rolling/sliding on a linear elastic substrate, numerical results for the frictional force distribution, slip/adhesion subareas, and the evolution of the slip velocity are given.
Investigation of the Deformation and Damage Sustained by a Wearing Surface in Sliding Metallic Friction
Authors: Kopalinsky E. M. , Oxley P. L. B.
Published: February 2008

It is shown how the characteristic deformation observed in wearing surfaces can be explained in terms of the wave model of asperity deformation. Possible explanations of the damage sustained by the surface with repeated wave passes, which eventually results in wear particles being formed, are given by considering the strain cycle undergone by material as it flows through the wave.
Friction and Wear of Aluminum Alloys Containing Hard Phases
Authors: Fujii Kenji , Sugishita Junji , Egami Noboru , Tabata Minoru
Published: February 2008

Adhesion energy between two surfaces containing intermetallic compounds is low, and adhesive wear is expected to be inhibited in such materials. Accordingly, the effects of intermetallic compounds have to be taken into account in the material design stage as a measure for improving wear resistance. Wear tests for specimens containing intermetallic compound phases, such as FeAl, TiAl and NiAl, were carried out under dry and lubricated conditions. The composite specimens used for the tests were fabricated by using a centrifugal casting method. In dry sliding of iron-aluminide composite materials, adhesion was mitigated and specific wear rate decreased with increases in the area fraction up to 60 percent. The titanium aluminide composite material showed the same trend of wear as that of the iron-aluminide composite materials. Under lubrication, specific wear rates increased due to the surface containing brittle intermetallic compounds. For the nickel aluminide composite material, the adhesion-inhibiting effect was remarkable. For particle reinforced metal matrix composites, friction coefficients depend on the protrusion height of alumina particles from the surface. The coefficient of friction for the surface with particles protruding was higher than that for the surface with embedded particles.
Dependence of Nano-Friction and Nano-Wear on Loading Force for Sharp Diamond Tips Sliding on Si, Mn-Zn Ferrite, and Au
Authors: Jiang Zhaoguo , Lu C.-J. , Bogy D. B. , Miyamoto T.
Published: February 2008

Microscopic friction and wear were measured on both the original top surfaces and freshly worn surfaces of three solid materials including a silicon wafer, a Mn-Zn ferrite block and an Au film, using a recently developed scanning probe microscope with sharp diamond tips. A critical point was observed on the friction versus normal loading force curve. The critical point divides the friction curve into two distinct regimes: a low friction regime in which the friction coefficients are from 0.03–0.06, and a high friction regime where the friction coefficients are between 0.12 and 0.38 depending on the materials tested and the tips. The critical loads at the critical points are different for different materials and different tips. But the average pressures corresponding to the critical points calculated by the Hertz elastic contact theory for different tips are close to each other for the same material. The freshly worn surfaces have tribological behaviors similar to those of the corresponding original top surfaces. Below the critical load no wear is detectable, whereas above the critical load wear is obtained with the wear depth proportional to the load. The implications are that a no-wear sliding condition is possible, for example in contact recording systems, if the asperity contact loads all remain less than the critical value for the particular sliding system.
Galling Resistant Surfaces on Stainless Steel Through Electrospark Alloying
Authors: Sheldon G. L.
Published: February 2008

Galling is a severe type of wear usually occurring at high normal stress and small relative movement between contacting surfaces. Surface protrusions, plastic deformation, magnified increases in roughness, and final seizure of the coupled pair characterize galling. Austenitic stainless steels are particularly prone to this surface disruption and a number of processes have been used to reduce or eliminate this extreme form of adhesion. In this study 316 stainless steel surfaces are treated by means of the microwelding process electrospark alloying (ESA). A variety of electrode compositions ranging from very hard (WC) to very soft (Ag) were used in both self mated and single surfaced tests. A standard gall test supplemented by a recording torque wrench was used for evaluation of surfaces. Tests were run at normal stresses of 35.1, 123, and 211 MPa. While all the compositions evaluated eliminated galling some showed abrasive cutting and the rotational torque requirements were high. Cobalt used in a self mated couple and silver used in a single surfaced couple were found to be the superior electrode materials for eliminating galling tendencies of 316 stainless steel.
The Dependency of Takeoff Velocity and Friction on Head Geometry and Drive Configuration
Authors: Lee Jerry J. K. , Enguero J. , Smallen M. , Chao A. , Cha E.
Published: February 2008

Wear at the head-disk interface of magnetic recording devices is dependent on the contact sliding distance between the head and disk. The sliding distance is dependent on the head takeoff velocity and frictional drag. In this study, the dependence of takeoff velocity and friction on selected head parameters was measured with an air bearing spindle equipped with a strain gauge. For the thin film head, crown had the greatest influence on takeoff velocity, followed by bolt pattern runout, suspension preload, camber, skew angle, and rail width in decreasing order. For the metal-ingap head, ski jump had the greatest influence. The rest of the parameters followed in the same order as they did for the thin film head. Twist and edge blend did not affect takeoff velocity, but larger edge blends did improve contact start-stop performance. Lower mass disk stacks did better in contact start-stop tests because of their shorter sliding distance before reaching the takeoff velocity or after achieving the landing velocity. Finally, both crown and skew angle affected the coefficient of friction between the head and disk. Heads with a more positive crown or zero skew angle had the lowest coefficient of friction.
Experiment on Mixed Lubrication of Hydrostatic Thrust Bearings for Hydraulic Equipment
Authors: Kazama Toshiharu , Yamaguchi Atsushi
Published: February 2008

Mixed lubrication characteristics of hydrostatic thrust bearings are examined experimentally. The effects of the surface roughness, supply pressure, loads, speed of rotation and size of restrictors on the frictional force, leakage-flow rate and power losses are clarified. Introducing the concept of mean pressure based on load-carrying capacity due to asperities, and the ratios of hydrostatic balance and leakage-flow rate, the experimental data can be normalized. Also good agreement is found between theoretical results based on a mixed lubrication model presented in a previous paper and the experiment.
Transient Response Solution Applying ADI Scheme to Boltzmann Flow-Modified Reynolds Equation Averaged With Respect to Surface Roughness
Authors: Mitsuya Yasunaga , Koumura Tetsushi
Published: February 2008

A numerical calculation methodology applying the alternating direction implicit (ADI) scheme is derived for the solution to the averaged Reynolds equation in volving flow factors resulting from Boltzmann molecular free flow. This methodology features the transformation of the dependent variable in the Reynolds equation from the pressure to the product of the averaged pressure times the averaged spacing, in combination with the determination of the flow factor using averaged spacing. This technique can be used to obtain the dynamic characteristics of compressible lubricating films incurring surface roughness effects under rarefaction conditions. In applying this method to a head slider in practical use, transient responses resulting from the slider flying over a bump and incurring surface roughness effects are compared for three roughness pattern cases. Longitudinal roughness effects are found to appear in the transient response with regard to a simultaneous decrease in the natural frequency and in the damping speed. Conversely, moving transverse roughness affects the response inversely, and stationary transverse roughness influences it only slightly.
An Analysis of Gas-Lubricated, Multileaf Foil Journal Bearings With Backing Springs
Authors: Heshmat C. A. , Heshmat H.
Published: February 2008

This paper describes the development of a new analysis technique that was used to evaluate the performance of a class of gas-lubricated journal bearings. The surface of these bearings is made up of preformed, leaf-type, compliant foils that are anchored to the bearing housing by spacer keys. Each leaf overlaps an adjacent leaf. Beneath each foil and attached to the inside of the bearing housing is a strip of backing spring. The stiffnesses of various foil bearing structures are modeled and presented as influence coefficients. Unlike conventional approaches, the solution of the governing hydrodynamic equations dealing with compressible fluid is coupled with the structural resiliency of the bearing surfaces. The distribution of the fluid film thickness and pressures, as well as the shear stresses in a finite-width journal bearing, are computed. The solutions include values of bearing stiffness coefficients due to both structural and hydrodynamic stiffnesses. The analysis, which is conducted for multileaf configurations by varying the number of leaves, uncovers the effects that the various structural, geometric, and operational variables have on bearing behavior. Also discussed are design guidelines with regard to the number of leaves, the degree of compliance, and bearing operational parameters.
Inertia Effects in a Hybrid Bearing With a 45 Degree Entrance Region
Authors: Hill D. L. , Baskharone E. A. , San Andres Luis
Published: February 2008

An investigation is presented that illustrates the effects of inertia on the flow and pressure field throughout a hybrid hearing with a 45 degree entrance region. This type of bearing has been previously shown to offer better performance over the hybrid bearing with a normal entry region. A two-dimensional planar approach is adopted and the resulting flow governing equations are solved using the Galerkin Weighted Residual finite element method. This algorithm incorporates an advanced streamline upwinding method to evaluate the nonlinear effects of the convection terms. The results demonstrate the complex nature of the velocity field and its subsequent impact on the pressure field. This comprehensive parametric study also shows why traditional lubrication approaches that typically exclude convection effects will become unreliable at high operating speeds of turbomachinery. A set of loss coefficients modeling the pressure ‘ram’ effects are provided to illustrate the inertia effects in the entrance region of the film lands. In a hybrid bearing, these effects have to be characterized according to the operating parameters of the bearing and the journal direction of rotation.
Performance of Powder-Lubricated Journal Bearings With MoS2 Powder: Experimental Study of Thermal Phenomena
Authors: Heshmat H. , Brewe D.
Published: February 2008

Powder-lubricated, quasi-hydrodynamic journal bearings assist in controlling wear and hold promise for integration in outer space systems/mechanisms and in other hostile-environment applications where the use of conventional lubricants is impractical. Described herein are the thermal phenomena and an assessment of the thermal stability, heat generation and dissipation characteristics of slider-type, powder-lubricated bearings. Powder lubricant films provide lift and separate bearing surfaces and cause side leakage. The reduction in friction coefficient and, consequently, in the heat generated in the bearings, drastically reduces wear of the tribomaterials. Further, bearing side leakage carries away most of the heat generated by shear, reducing the heat to the critical bearing surfaces. Also presented are the thermohydrodynamic effects of powder lubrication (MoS2) on bearing performance criteria, e.g., temperature and friction coefficient as a function of speed and load, including the effect of powder flow rate on bearing performance and wear.
Squeeze Film Characteristics Between Parallel Circular Plates Containing a Single Central Air Bubble in the Inertial Flow Regime
Authors: Hashimoto H.
Published: February 2008

In this paper, the effects of an air bubble on the Newtonian squeeze film characteristics between two circular parallel plates with sinusoidal relative motion are theoretically investigated by considering the fluid film inertia effects. In the derivation of the lubrication equation, a single central air bubble of a cylindrical shape is considered. Approximating the momentum equation governing the squeeze film flow by the mean value averaged across the film thickness and assuming an ideal gas under isothermal condition for an air bubble, a nonlinear differential equation for the bubble radius is obtained. The nonlinear differential equation is solved by the Runge-Kutta-Gill method, and then the squeeze film force is determined. Moreover, the analytical solutions for the air bubble radius and pressure distribution are derived based on the perturbation method for a small amplitude of sinusoidal motion, and the analytical results are compared with the numerical results. From the calculated results, the combined effects of air bubble and fluid film inertia on the squeeze film force are clarified.
Determination of Ball and Roller Compliances Using a Vibration Measuring Technique
Authors: Sherif A.
Published: February 2008

A new experimental method to estimate the compliances induced by the compression of smooth steel balls and rollers of different sizes, between two rigid flat smooth surfaces, is presented. When a single-degree-of-freedom system is brought into contact with an elastic body whose mass can be neglected, the system’s natural frequency will increase by virtue of the additional stiffness produced due to contact with the elastic body. If the system’s natural frequency is measured with and without contact with such elastic body, at different applied normal loads, it is possible to calculate the corresponding body stiffness and compliance is then obtained. A simple test rig has been built to investigate the feasibility of this approach. A comparison of the theoretically calculated values of compliances, using Hertz theory and the formula quoted by Palmgren with those determined experimentally, demonstrates the applicability of this new technique and shows good accuracy.
Dynamically Loaded Journal Bearings: Position of Maximum Pressure Ratio
Authors: Martin F. A.
Published: February 2008

The position of the maximum “pressure ratio” in dynamically loaded bearings, using short bearing theory, has previously been published only in graphical (map) form. Simple equations are derived here so that this position (relative to the load line) can be obtained directly in numerical form.
Piston-Ring Lubrication Problems for Refrigeration Compressors Considering Combined Effects of Supply Oil Quantity and Surface Roughness
Authors: Nakai H. , Ino N. , Hashimoto H.
Published: February 2008

Reciprocating-type compressors are widely used for refrigeration systems, and an understanding of piston-ring lubrication in the compressor is vital for designers in reducing the energy losses due to friction because a substantial portion of friction in the compressors is attributable to the piston-ring assembly. This study aimed at developing a one-dimensional analysis for lubrication between the piston-ring and cylinder of refrigeration compressors considering the combined effects of supply oil quantity and surface roughness on piston-ring face and cylinder wall. In the theoretical model, the piston-ring is treated as a one-dimensional dynamically loaded bearing with combined sliding and squeezing motion. The one-dimensional modified Reynolds equation based on the average flow model by Patir and Cheng is used as a governing equation. In the analysis of the modified Reynolds equation, two-types of inlet boundary conditions, flooded condition and starvation condition, are applied at the leading edge according to the supply oil quantity, and the Reynolds boundary condition is applied at the trailing edge. A numerical procedure is then developed to estimate the cyclic variation of minimum film thickness, inlet and outlet positions of lubrication film and friction force, and the combined effects of supply oil quantity and surface roughness height are examined for a typical refrigeration compressor. It is clarified from the numerical results that the supply oil quantity and surface roughness affect significantly the friction force of the piston-ring for refrigeration compressors.
Non-Newtonian Lubrication With the Convected Maxwell Model
Authors: Tichy J. A.
Published: February 2008

In certain applications where the lubricant is subjected to rapidly changing conditions along its flowing path (such as an elastohydrodynamic contact), the time dependent nature of the lubricant may be significant. One of the simplest types of models to account for such fluid time dependence is the Maxwell model. The time derivative used in such a model must be written with respect to coordinates which translate and rotate with the fluid, or coordinates which deform with the fluid. Unfortunately, such derivatives greatly complicate problems and are rarely used, due to nonlinear coupling of stresses. An admissible formulation of the Maxwell viscoelastic fluid model using the convected derivative has been applied to lubrication flow. Using a regular perturbation in the Deborah number, with the conventional lubrication solution as the leading term, a solution can be obtained. Viscoelasticity may raise or lower pressure depending on combinations of surface slope and curvature.
Transient EHD Connecting Rod Analysis: Full Dynamic Versus Quasi-Static Deformation
Authors: Knoll G. , Lang J. , Riena¨cker A.
Published: February 2008

A system of computer simulation programs was developed for the calculation of transient EHD analyses of connecting rods. Two different models for the calculation of the elastic deformations are compared: full dynamic deformations and quasi static deformations. For the quasi static analyses fixed displacement boundary conditions have to be applied, whereas for the full dynamic simulation no displacement boundary conditions are necessary. The presented results show, that the choice of boundary conditions and distributed mass effects strongly influence global and local deformations and lead to the conclusion, that the full dynamic solution should be used for connecting rod analyses.
Study of Slider Dynamics Over Very Smooth Magnetic Disks
Authors: Suzuki Shoji , Nishihira Henry
Published: February 2008

Flying characteristics of 50 percent negative pressure sliders on aluminum, glass, and silicon disks with different surface characteristics are described. By using an AE (acoustic emission) and LDV (Laser Doppler Vibrometer) we were able to study the effect of surface roughness and disk materials on the dynamics of the slider. In the regime where the slider flies below the glide height (30 nm) and contact with the disk surface can occur, the AE signal consisted of low frequencies related to air bearing resonance (around 100 kHz), and high frequency related to slider body vibrations (735 kHz). Interestingly, in the high speed regime the AE signal contained low frequency signals. The signal increased as the fly height of the slider increased when flying on the smooth surfaces except on the silicon disk. LDV measurements revealed that the excitation from the silicon disk surface was smaller than on the aluminum disk or the glass disk by 10 dB, which contributed to suppress the vibration of the slider. For a given excitation from the disk, the surface roughness played a key role in determining the slider vibration. We also determined that a fly height fluctuation occurred due to the surface roughness, but the effect was found to be very small. The difference between the textured and smooth surface was from the damping effect on the slider vibration. The slider was made to collide with a protrusion fabricated on a disk surface to study the damping characteristics of the slider. The textured disk surface gave more damping than on the smooth disk surface by up to 20 percent.
Redesigning Mechanical Systems for Low Wear Using System Dynamics Modeling
Authors: Dinc O. S. , Cromer R. , Calabrese S. J.
Published: February 2008

This work describes a method of minimizing wear and extending the life of machinery components and large, complex machine structures by controlling the overall system dynamics. The method consists of the following steps: first, developing a system dynamics model for the entire machine structure using available rigid multi-body dynamic analysis computer codes; second, obtaining dynamic performance data from the system dynamics model for each sliding contact in the actual machine, and feeding this information into a suitable wear model which is either being used or developed for the particular material combination; third, matching the results of the wear prediction with actual machine wear inspection data; and last and most important, returning to the dynamic analysis model and modifying or redesigning the machine to minimize the intensity of the system dynamics, thus extending the wear life of the components. The method is being developed for application to large, complex machines which have numerous sliding contacts. Many of these contacts are at junctions between subcomponents assembled together. These junctions are often designed to accommodate relative motion due to vibration or thermal mismatches. After the initial analyses have been done, both minor and major mechanical design and material changes must be investigated to determine how effectively these could reduce wear. Each successive configuration can be evaluated using the dynamic analysis model. Application of this approach to the mechanical design of a gas turbine combustor reduced the noise level of the entire system and tripled the average machine life.
Effect of Thermal Distortion on Wear of Composites
Authors: Obara Shingo , Kato Takahisa
Published: February 2008

The worn surface profile of a composite structure was experimentally and numerically investigated focusing on the effects of sliding conditions. Wear tests on composites made of an oxide ceramic and an amorphous metal against a tetragonal zirconia polycrystals-alumina were carried out under various mean contact pressures, P, and sliding velocities, V. The test results showed that the worn surface profiles of the composites changed with the PV value. A new numerical method for simulating the worn surface profile of a composite structure has been developed. The present method is based upon the assumption that the profile of a worn surface is changed by thermal distortion of the sliding bodies due to frictional heating and by elastic deformation due to normal pressure and friction traction. The calculated results were compared with the test results, and the comparison showed that the elastic deformation plays an important role in forming the worn surface profile and that the effect of thermal distortion becomes remarkable with an increase in PV values. The numerical results clarified the contribution of the thermal distortion to the change in the worn surface profile of the composite.
Rating Thread Compounds for Galling Resistance
Authors: Carper H. J. , Ertas A. , Cuvalci O.
Published: February 2008

Results are presented from an experimental study which demonstrates the feasibility of using an existing galling tester and test method as a screening device for evaluating thread compound additives for galling protection. The galling tester employs tubular pin and box specimen pairs fabricated from steel tubing used in the oil field. For the test thread compounds, four different additive packages were used, all with the same grease base of lithium stearate. For reference purposes, the lithium stearate grease base without any additives was tested as one of the thread compounds. The data obtained on contact stress at galling failure show that of the five thread compounds tested, the best galling protection is afforded by the API Modified thread compound, the industry standard for casing and tubing used by the oil industry. The other four compounds show lower galling failure contact stresses of varying degrees. Friction coefficient data obtained during the tests are also presented and discussed.
Contribution of Surface Irregularities to Rolling Contact Plasticity in Bearing Steels
Authors: Gupta V. , Hahn G. T. , Bastias P. C. , Rubin C. A.
Published: February 2008

A “two-body” elasto-plastic finite element model of two-dimensional rolling and rolling-plus-sliding has been developed to treat the effect of surface irregularities. The model consists of a smooth cylinder in contact with a semi-infinite half-space that is either smooth or fitted with one of two irregularities: a 0.4 μm deep groove, or a 7 μm deep groove. The model incorporates elastic-linear-kinematic-hardening-plastic (ELKP) and nonlinear-kinematic-hardening-plastic (NLKP) material constitutive relations appropriate for hardened bearing steel and the 440C grade. The calculated contact pressure distribution is Hertzian for smooth body contact, and it displays intense, stationary, pressure spikes superposed on the Hertzian pressure for contact with the grooved and ridged surface. The results obtained for the 0.4 μm deep groove are consistent with those reported by Elsharkawy and Hamrock (1991) for an EHD lubricated contact. The effect of translating the counterface on the half space, as opposed to indenting the counterface on the half-space with no translation, is studied. The stress and strain values near the surface are found to be similar for the two cases, whereas they are significantly different in the subsurface. Efforts have been made to identify the material constitutive relations which best describe the deformation characteristics of the bearing steels in the initial few cycles. ELKP material constitutive relations produce less net plastic deformation in the initial stages, for a given stress, than seen in experiments. NLKP model produces more plasticity than the ELKP model and shows promise for treating the net distortions in the early stages. Artificial indents were inserted on the running track of the cylindrical rolling elements and profilometer measurements of these indents were made, before and after rolling. These preliminary measurements show that substantial plastic deformation takes place in the process of rolling. The deformations of the groove calculated with the finite element model are compared to those measured experimentally.
Magnetohydrodynamic Braking
Authors: Gorla Rama Subba Reddy , Ramalingam K. , Adluri I.
Published: February 2008

A viscous and electrically conductive fluid separates two parallel plates. A magnetic field of intensity B0 is applied perpendicular to the plates. The top plate squeezes downward whereas the bottom plate moves laterally in its own plane. The nonsimilar problem is solved for the conditions of the top plate moving with constant velocity or constant force, while the bottom plate moves with a constant velocity. The effect of magnetic field on the braking action is discussed.
Thermal EHL Analysis of Circular Contacts With Measured Surface
Roughness
Authors: Xu Gang , Sadeghi Farshid
Published: February 2008

Time dependent thermal EHL circular contact results with measured surface roughness were obtained to analyze the effects of roughness on pressure, film thickness, temperature, and coefficient of friction. Both contact surfaces are considered to be rough. Multilevel multigrid techniques (with multigrid integration) were used to solve the system of two dimensional Reynolds, elasticity and three dimensional energy equations simultaneously. The effects of surface roughness under various loads, speeds, and slip conditions have been studied. Surface roughness causes pressure and temperature spikes and increases the coefficient of friction, and surface roughness flattens due to the high pressure in EHL contact. The higher the load, speed and slide to roll ratio, the more significant the effect of the surface roughness. A comparison between rough EHL and smooth EHL results indicates that surface roughness cannot be ignored in EHL analysis.
Effects of Wall Flexibility on the Rotordynamic Coefficients of
Turbulent Cryogenic Annular Seals
Authors: Venkataraman B. , Palazzolo A. B.
Published: February 2008

A theory for analyzing the effects of elastic deformations of the seal wall on the dynamic characteristics of high pressure cryogenic annular seals under concentric operation is presented. The bulk flow continuity, axial and circumferential momentum, and the energy transport equations are utilized to determine the pressure distribution in the seal. Thermophysical properties of the cryogenic fluid are assumed to be functions of the local pressure and temperature. The wall deformations are obtained using an iso-parametric, axi-symmetric Finite Element formulation of the seal wall. A perturbation analysis is employed to arrive at the first order solution which yields the rotordynamic coefficients. Results obtained for the case of Space Shuttle Main Engine Oxygen Turbopump (SSME-HPOTP) Preburner Seal show a significant impact of seal flexibility on the dynamic coefficients.
Theory of Frictional Vibration in Wet Clutches Considering
Poroelastic Properties of Paper-Based Facing
Authors: Hattori Y. , Kato T.
Published: February 2008

This paper presents a new theory on frictional vibrations of paper-based friction material considering the interaction between its deformation and the consequent lubricant flow inside it. A frictional vibration model is proposed, in which a poroelastic body saturated by a viscous liquid is introduced, and then a stability criterion is derived on the assumption that vibrations in two directions, tangential and normal, are coupled. Compared with the experiment, it is confirmed that the proposed criterion can predict the stability limit more accurately than the conventional one, which does not take the deformation of the friction material into account and depends only on the slope of friction coefficient versus sliding velocity. Based on the present criterion, influences of material properties on the stability to frictional vibrations are discussed.
Head/Disk Interface Contact Detection Using a Refined Acoustic
Emission Technique
Authors: O'Brien K. , Harris D.
Published: February 2008

A refined technique using Acoustic Emission has been developed for use in head/disk interface contact detection. These refinements are focused on the design parameters of the Acoustic Emission electronics, amplification and filter settings, which permit accurate and repeatable contact detection measurements. A technique for determining the slider body natural frequencies is described in order that the proper filter design parameters can be determined. Experiments confirm the existence of these frequencies for a Al2O3TiC 50 percent slider are in excess of 600 KHz.
Characteristics of Air Bearing Suction Force in Magnetic Recording
Disks
Authors: Peng Jih-Ping , Hardie Cal E.
Published: February 2008

Some fundamental characteristics of the subambient pressure air bearing suction force were investigated analytically and numerically. The performance of air bearing suction force is strongly determined by the cavity bearing number, in which the cavity region recess depth is used as the characteristic film thickness. Although the optimal recess depth for maximum, suction force varies for different operation conditions, the optimal cavity bearing number can be found in a wide range of applications. The analytical model was confirmed by a finite element analysis. Examples of different disc velocities, slider dimensions, and ambient pressure effect were presented.
An Efficient Numerical Procedure for Thermohydrodynamic Analysis of
Cavitating Bearings
Authors: Vijayaraghavan D.
Published: February 2008

In this paper, an efficient and accurate numerical procedure to determine the thermo-hydrodynamic performance of cavitating bearings is described. This procedure is based on the earlier development of Elrod for lubricating films, in which the properties across the film thickness are determined at Lobatto points and their distributions are expressed by collocated polynomials. The cavitated regions and their boundaries are rigorously treated. Thermal boundary conditions at the surfaces, including heat dissipation through the metal to the ambient, are incorporated. Numerical examples are presented comparing the predictions using this procedure with earlier theoretical predictions and experimental data. With a few points across the film thickness and across the journal and the bearing in the radial direction, the temperature profile is very well predicted.
Hydrodynamic Lubrication of Face Seal in a Turbulent Flow
Regime
Authors: Lin Jen Fin , Yao Chih Chung
Published: February 2008

Models for thermohydrodynamic lubrication in the turbulent regime are developed for a mechanical end face seal with various combinations of asperity height and roughness pattern. A surface wear model, based on deformation, is established for mixed lubrication such that the displacement is at most equal to the mean asperity height. Only normal load is involved in the solution of asperity deformation, and the mean film thickness is determined based on a total volume conservation hypothesis, in conjunction with an elastic-exponential hardening model. The singularity problem, present in the expected form of the Reynolds equation for a seal surface with circumferentially-oriented roughness grain sphere grooves, is avoided by viewing the seal roughness as porous material, thereby introducing roughness permeability. Flow permeability is thus obtained by combining Darcy’s law for porous material with the average flow model developed by Patir and Cheng for mixed lubrication. The hydrodynamic pressure and thereby the hydrodynamic load support are relatively higher from a seal with radially-oriented roughness. Both the mean film thickness and the hydrodynamic load support are substantially elevated by increasing the composite rms roughness, raising the inlet-flow pressure, and decreasing the rotational speed. Good agreement has been obtained from the comparison between the results herein and Lebeck’s experimental results.