bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring the Impact of a Continuing Medical Education Program on Patient Blood Pressure
Authors: Allaire Benjamin T. , Trogdon Justin G. , Egan Brent M. , Lackland Daniel T. , Masters Dory
Published: April 2011

J Clin Hypertens (Greenwich). 2011;13:517–522. ©2011 Wiley Periodicals, Inc.

An increased focus on hypertension prevention and control, especially in high‐risk populations, may have a substantial impact on cardiovascular health outcomes. A continuing medical education (CME) program trained primary care providers in evidence‐based guidelines for hypertension prevention and control. This study evaluated its effectiveness in reducing patients’ blood pressure for the sessions occurring from 2003 to 2007. Using the Hypertension Initiative Database, 8183 patients of CME providers (CME patients) were paired with controls and changes in blood pressure, provider visits, prescription months, and the proportion of patients with blood pressure <140/90 mm Hg before and after the intervention date were estimated. In the 2‐year period before training and the 2‐year period afterwards, CME patients’ systolic blood pressure decreased by 1.99 mm Hg and diastolic blood pressure decreased by 1.49 mm Hg. The CME patients displayed an increase in provider visits but no statistically significant change in prescription months. Restricting the analysis to the subsample of patients with uncontrolled hypertension (>140/90 mm Hg), the changes in blood pressure were similar in magnitude to those in the entire population. The CME program, by promoting evidence‐based practice, improves patients’ blood pressure and could serve as a positive model for future hypertension interventions.
Transcriptional control of the main aromatic hydrocarbon efflux pump in Pseudomonas
Authors: Fillet Sandy , Daniels Craig , Pini Cecilia , Krell Tino , Duque Estrella , Bernal Patricia , Segura Ana , Lu Duo , Zhang Xiadong , Ramos Juan‐Luis
Published: April 2011

Bacteria of the species Pseudomonas putida are ubiquitous soil inhabitants, and a few strains are able to thrive in the presence of extremely high concentrations of toxic solvents such as toluene and related aromatic hydrocarbons. Toluene tolerance is multifactorial in the sense that bacteria use a wide range of physiological and genetic changes to overcome solvent damage. This includes enhanced membrane impermeabilization through cis to trans isomerization of unsaturated fatty acids, activation of a stress response programme, and induction of efflux pumps that expulse toxic hydrocarbons to the outer medium. The most relevant element in this toluene tolerance arsenal is the TtgGHI efflux pump controlled by the TtgV regulator. We discuss here how TtgV controls expression of this efflux pump in response to solvents.
When does the socio‐cultural context matter? Communal orientation and entrepreneurs’ resource accumulation efforts in Africa
Authors: Khayesi Jane N. O. , George Gerard
Published: April 2011

We examined the effect of entrepreneurs’communal orientation and social capital on entrepreneurs’ acquisition of resources, and the cost of raising those resources. Using an errors‐in‐variables estimation in a sample of 242 Ugandan entrepreneurs from Kampala, we find that shared identity is positively associated with the quantity of resources raised by entrepreneurs, whereas shared identity and communal orientation are associated with a higher cost of raising resources. Further, communal orientation positively moderates the relationship between kin composition and the quantity of resources raised; whereas communal orientation negatively moderates the relationship between trust, shared identity, and resources. In contrast, a high communal orientation is associated with increased cost of raising resources when shared identity is high. These findings reveal that entrepreneurs’ socio‐cultural contexts, particularly communal orientation, has a moderating effect on the relationship between entrepreneurs’ social capital and resource accumulation.
Modeling of Surge Characteristics in Turbo Heat Pumps
Authors: Kim Hye Rim , Song Seung Jin
Published: April 2011

This paper presents a new analytical model of surge dynamics in turbo heat pumps. Turbo heat pumps use refrigerants as the working fluid and consist of a centrifugal compressor, condenser, expansion valve, and evaporator. Compared with a gas turbine engine, the turbo heat pump system introduces additional complexities. First, the turbo heat pump forms a closed-loop system. Second, the system has two plenums, condenser and evaporator, which are coupled to each other. Third, the heat pump runs on a refrigeration cycle with two phases: vapor and liquid. Fourth, heat transfer effects of evaporation and condensation have to be considered. Fifth, unlike air, a refrigerant has strong real gas effects and thus cannot be modeled as an ideal gas. The new model addresses such additional complexities on the basis of the first principles of conservation of mass, momentum, and energy. When applied to a gas turbine system, the new model’s predictions become identical to those from the Greitzer’s model. Furthermore, comparison with the available experimental data shows that the model can also accurately predict surge behavior in actual turbo heat pumps. Finally, the effects of Greitzer’s B parameter and the ratio of evaporator and condenser volume have been examined. Parameter B influences both surge shape and frequency. Finally, surge frequency is extremely sensitive to the ratio of the two plenum volumes.
Transient Contact Between a Sphere and a Moving Flat
Authors: Ovcharenko A. , Yang M. , Chun K. , Talke F. E.
Published: April 2011

Transient contact between a sphere and a moving flat is investigated using finite element analysis. The sphere is assumed to be rigid while the flat is treated as an elastic-plastic body with isotropic hardening. Temperature and strain distributions of the sphere and the flat are obtained as a function of the vertical initial velocity of the sphere, the coefficient of friction between the sphere and the flat, and the tangential velocity of the flat. In addition, dimensionless solutions are presented for the maximum temperature rise and the maximum residual penetration as a function of the dimensionless vertical initial velocity of the sphere. The numerical solutions are independent of material properties and sphere radius, and can be applied to minimize data loss of the slider disk interface during slider-disk contacts.
Slider Dynamics Over a Discrete Track Medium With Servo Patterns
Authors: Li Jianhua , Xu Junguo , Kobayashi Masahito
Published: April 2011

The dynamic characteristics of a slider flying over various servo patterns on a disk surface were investigated. The investigation shows that the air-flow field is disturbed and causes flying modulation during the transition from grooved longitudinal discrete tracks to a transversal and near-random pattern in the servo field. The effects of the parameters that define the servo pattern — including land area ratio of burst patterns, groove depth, servo-pattern frequency, and the lengths of synchronization (sync), servo address mark (SAM), postamble (PAD) blocks, and burst pattern type — on the flying height responses were evaluated. The evaluation results indicate that the flying-height modulation depends on servo-pattern frequency, burst land-area ratio, groove depth, and the lengths of the sync, SAM, and PAD block and burst pattern type. Modulation of a slider flying over a servo pattern therefore can be reduced by optimizing the servo-pattern design from the viewpoint of these parameters.
The Sealing Function of Grease: Contamination Migration in Grease Lubricated Radial Lip Seals
Authors: Baart Pieter , Lugt Piet , Prakash Braham
Published: April 2011

Lubricating grease is commonly used for lubricating ‘sealed and greased for life’ bearings. This grease lubricates the rolling contacts. It also provides an additional sealing function to protect the bearing against ingress of contamination. The sealing function of lubricating grease in the vicinity of the seal lip contact has been studied experimentally. The effects of the lubricant rheology on the migration of ingress particles has been examined. In grease, experimental results reveal that contaminant particles consistently migrate towards the sealing contact where the shear rate reaches its highest value. In contrast, for a Newtonian base oil and a non shear thinning elastic fluid, it has been observed that the migration effect takes place in the opposite direction, and brings particles away from the sealing contact. It is concluded that the sealing function of grease in the vicinity of the sealing contact is due to the fluid rheology and more specifically to the shear thinning behaviour of the lubricant.
Physico-Chemical Modeling of Third Body Rheology
Authors: Renouf Mathieu
Published: April 2011

The well-known concept of third body was introduced by Godet in the seventies to characterise the discontinuous and heterogeneous interface that separates two bodies in contact. This thin layer (from some nanometers to some micrometers high) appears to possess its own rheology depending of contact conditions, material properties and often, extra unknown parameters. If its main common role concerns essentially mechanical aspects such as velocity accommodation, load carrying capacity and solid lubricant, it plays an important role in other physical aspects. For example, it ensures the thermal continuity between two bodies in contact and explains the jump of temperature observed experimentally. Moreover, it is able to capture the maximal temperature through its thickness. Due to the difficulty to instrument a real contact without disturbing the local rheology, observations of the third body rheology occur only on simplified experimental set-up. To reproduce and try to understand “real contact in presence of third body”, numerical tools have been developed and adapt to face new challenge raised by the third-body concept. The discontinuity and heterogeneity of such interface led researchers to use discrete element methods (DEM) to describe its evolution. Several improvments of the method allow to deal with the mechanical and the thermal behaviour of such media but without interactions. The integration of physicochemical aspects is presented in the paper to link thermal and mechanical behaviour and proposed a model able to represent the multi-physical feature of a contact interface.
Axiomatic Design of a Multi-Directional Motion Pin on Disk Apparatus for Biotribology Study
Authors: Hua Zikai , Zhang Jianhua
Published: April 2011

A new multidirectional motion pin-on-disk (MPOD) apparatus was designed, built and validated. Multidirectional motion was proven to have influence on the wear behaviour due to the difference in shear stress, especially in biotribology experiments for prosthetic joint materials. This MPOD was designed to realize the ‘adhesive polishing’ effect observed in multidirectional sliding wear test. Following axiomatic design principle, several modules, such as loading unit, motion generation and pin guiding modules were developed according to the uncoupled design matrix. Force transducers were assembled separately in X and Y direction for precisely measuring, and a frequency control system was assembled to provide a wide range of rotation speed. Preliminary tests were performed by using ultra high molecular weight polyethylene pins against zirconium oxide disks, and the experimental results were analyzed and compared with those observed in unidirectional wear tester.
Molecular Dynamics and Multiscale Simulations of Nanoindentation and Nanoscratch
Authors: Zhu Peng-zhe , Wang Hui , Hu Yuan-zhong
Published: April 2011

Three-dimensional molecular dynamics (MD) simulations have been performed to investigate behaviors of nanoindentation and nano-scratch. The first case concerns the effects of material defect on the nanoindentation of nickel thin film. The defect is modeled by a spherical void embedded in the substrate and located under the surface of indentation. The simulation results reveal that compared to the case without defect, the presence of the void softens the material and allows for larger indentation depth at a given load. MD simulations are then performed for nano-scratch of single crystal copper, with emphasis on the effect of indenter shape (sharp and blunt) on the substrate deformation. The results show that the blunt indenter causes larger deformation region and much more dislocations at both the indentation and scratch stages. It is also found that during the scratching stage the blunt indenter results in larger chip volume in front of the indenter and gives rise to more friction than the sharp indenter. The scope of the simulations has been extended by introducing a multiscale model which couples MD simulations with Finite Element Method (FEM), and multiscale simulations are performed for two-dimensional nanoindentation of copper. The model has been validated by well-consistent load-depth curves obtained from both multiscale and full MD simulations, and by good continuity of deformation observed in the handshake region. The simulations also reveal that indenter radius and indentation velocity significantly affect the nanoindentation behavior. By use of multiscale method, the system size to be explored can be greatly expanded without increasing much computational cost.
The Flow Field Simulation of a Novel Water-Lubricated Hybrid Bearing for High-Speed Spindle
Authors: Chen Wei , Wang Fangfang , Zhang Youfeng
Published: April 2011

A shaft of spindle with high speed and high stiffness could be stuck due to overheat generated by bearing and poor lubrication, and then the failure of spindle may occur. It should be seriously considered as a key factor for the bearing design of high-speed and high-stiffness spindle in order to increase the flow rate within the bearing with small clearance. A water lubricated hybrid bearing with multi-holes and deep/shallow recesses is proposed in the paper, which can be used in high-speed machine tool spindle. The FLUENT software is used to simulate flow field inside of bearing. For a compute time efficiency, a one-eighth bearing model is built for CFD analysis according to the bearing symmetry. The results show that, inlet and outlet oil ports could be placed in the same deep recess. Lubricant flowing into deep recess through the orifice restrictor could work appropriately for lubrication purpose of high-speed bearing, but not directly flowing out of outlet in the same groove as many people assumed. The remarkable turbulence flow occurs for lubricant in deep recess and gradually weakens in the shallow recesses.
A Reduced Full-System Finite Element Approach to the Solution of EHL Problems: Line Contacts
Authors: Habchi W. , Issa J.
Published: April 2011

This paper presents a reduced full-system finite element solution of isothermal elastohydrodynamic (EHD) line contact problems. The proposed model is based on a full-system finite element resolution of the EHL equations: Reynolds, linear elasticity and load balance. A reduced model is proposed for the linear elasticity problem. For this, three different techniques are tested: the classical “Modal reduction” and “Ritz-vector” methods and a novel “EHL-basis” method. The reduction order in the first two appears to be insufficient and a large number of degrees of freedom is required in order to attain an acceptable solution. On the other hand, the “EHL-basis” method shows up to be much more efficient, requiring only a few degrees of freedom to compose the elastic deformation of the solid components. In addition, a comparison with the full model shows an order of magnitude cpu time gain with errors of the order of only 1‰ for the central and minimum film thicknesses.
Coupling System Dynamics and Contact Behaviour by Numerical Modelling at Different Scales
Authors: Massi Francesco , Berthier Yves
Published: April 2011

When dealing with mechanical systems including contact interfaces, two different mechanics at two different time and length scales have to be accounted for: the contact mechanics and the structural mechanics. The mechanics of the contact and the mechanics of structure are coupled by friction (forces and moments), local body deformations and wear (geometrical coupling). In the past, dynamic and tribological problems were treated separately and the analysis was focused either on the mechanism scales or on the contact scales, as a function of the problem. The analysis of the dynamic response of the mechanical system accounted for the contact interfaces thought global coefficients (global contact stiffness, damping, energy loss factor, etc.); vice versa, the analysis of the local behaviour at the contact interface accounted for the system dynamics imposing global boundary conditions on the contact model (pressure distribution, relative velocities, etc.). During last decades mechanical system design led to a power increase and to a drastic optimization, increasing as well the number of contact interfaces between deformable bodies. Thus, the need for coupling dynamic and tribological analyses arises for solving and understanding either wear phenomena or dynamic response of a mechanical system. On this sense, experimental tools showed their limits on the estimation and prediction of friction and wear phenomena. This paper proposes a first step toward a more general approach aimed to couple the dynamic analysis of the mechanism with the local tribological analysis at the contact, by the coupling of two different numerical models dealing with the two different scales. Two applications are then mentioned: the analysis of “false Brinelling” wear and the understanding of brake squeal instability.
Mass Conserving Cavitation Effects in Squeeze-Film Journal Bearings Subjected to Fully Reversing Loads
Authors: Boedo S.
Published: April 2011

This paper presents a study of cavitation effects associated with the performance of fluid-film journal bearings subjected to fully-reversing sinusoidal loading. Employing an established mass-conserving cavitation algorithm, it is observed that periodic time histories of journal eccentricity and maximum film pressure are strongly influenced by the process of cavitation formation and collapse. Good agreement of predicted and experimental results is obtained over a large range of loads for cavitation threshold pressure values typically associated with vapor cavitation.
Ultrasonic Measurement for Film Thickness and Solid Contact in Elastohydrodynamic Lubrication
Authors: Dwyer-Joyce R. S. , Zhu J. , Reddyhoff T.
Published: April 2011

The reflection of ultrasound can be used to determine oil film thickness from the stiffness of the separating film. However, boundary or mixed film lubrication is a common occurrence in elastohydrodynamic lubricated (EHL) contacts, as the nominal thickness of the separating film approaches the surface asperity height. In this paper an ultrasonic investigation was carried out on the interface between a steel ball sliding on a flat disc as the speed was reduced into the boundary regime. The ultrasonic reflection then depends on the stiffness of the interface that now consists of an oil layer and asperity contacts. To distinguish the stiffness contribution from asperity contact and oil layer, a mixed lubrication model for circular contacts was established. This predicted the lubricant film thickness and proportions of solid and liquid mediated contact. The total stiffness predicted by theoretical models showed a good agreement with experimental measurement for kinematic cases. The model can then be used to extract the proportion of real area of contact, and the oil film thickness, from ultrasonic results.
Simultaneous Film Thickness and Friction Measurement for a Piston Ring-Cylinder Contact
Authors: Avan Emin Y. , Mills Robin S. , Dwyer-Joyce Rob S.
Published: April 2011

A significant part of the total parasitic loss in an internal combustion (IC) engine is due to the piston ring and cylinder liner friction. In this work, a piston ring-liner reciprocating test rig combined with non-invasive ultrasonic film thickness measurement system was used to understand frictional characteristic of the lubricant and the lubrication regime in the contact. Two test procedures were performed for three lubricants with different viscosities. These procedures were a step load increment at a constant speed and a step speed increment at a constant load. The results showed that minimum oil film thickness under the ring increased with speed and decreased with load but friction coefficient followed various trends depending on the viscosity of the lubricant.
Contact Model of Two Rough Surfaces Based on a Visco-Elasto-Adhesive Interaction
Authors: Sepehri Ali , Farhang Kambiz
Published: April 2011

Mathematical formulae are derived for normal contact force component between two nominally flat rough surfaces. The development of the contact model is based on the asperity level interaction in which adhesive forces between two asperities as well as elastic and rate-dependent forces are included. Statistical consideration of rough surfaces yields the mathematical formulation of total normal force due to adhesion, elastic and rate-dependent properties of the surfaces in contact.
Effect of Loading and Shear Rate on Tribological Behaviour of Dodecanethiol Self Assembled Monolayer on Au(111): A Molecular Dynamic Simulation Study
Authors: Ramin Leyla , Jabbarzadeh Ahmad
Published: April 2011

Molecular dynamic simulation of nanoscale self assembled monolayers (SAMs) is used to predict the tribological properties of thiol based monolayers attached on Au(111) surfaces. Different loading conditions between 10MPa to 7GPa have been applied to dodecanethiol SHCH2(CH2)10CH3 monolayers to study the molecular structure and physical properties at rest, under loading and under shear. At loads lower than 700MPa, we observe smaller fluctuations in tilt and orientation angles due to a lower level of film compression. Above this critical load, the monolayers backbone starts to compress and a dramatic increase of energy is observed. Film thickness also reduces by 87% as the loading is increased. At loads higher than 5GPa, the SAM monolayer undergoes progressive disorganization resulting in a crushed and disordered system. We have investigated the tribology of the SAM films under various loads and shear rates in the range of 108-1011(s−1). We have found that the friction coefficient increases by increasing the shear rate and decrease by increasing the loading.
Piston Ring Cavitation and Starvation During Entrainment Motion Reversal
Authors: Chong W. W. F. , Teodorescu M. , Vaughan N. D.
Published: April 2011

The current paper investigates the correlation between oil film formation, cavitation and starvation during inlet reversal of an Internal Combustion (IC) engine piston-ring conjunction. Piston ring lubrication is critical in the vicinity of Top Dead Center (TDC) and Bottom Dead Center (BDC) where low entrainment velocity leads to very thin films. The current study predicts that cavities formed at the trailing edge of the contact before the entrainment reversal briefly survive at the leading edge after the reversal. This contributes to contact starvation and thinner films than previously thought.
Thermal-Mechanical Contact of a Sphere on a Layered Surface
Authors: Song Wenping , Ovcharenko Andrey , Zhang Guangyu , Talke Frank E.
Published: April 2011

The effect of coating thickness is investigated during transient thermal-mechanical contact between a sphere and a layered surface. The range of coating thicknesses studied was from 0.001≤t/R≤0.1, where t is the coating thickness and R is the radius of the contacting sphere. It was found that for the range of coating thickness and material properties investigated, the coating thickness has only a small effect on the mechanical deformation of the interface. On the other hand, the layer thickness has a large effect on the temperature rise of the interface.
Pumping Effect of Slider Air Bearing Surface for Non-Langmuir Adsorption
Authors: Zhang Bo , Nakajima Akira
Published: April 2011

Numerical analysis of the adsorbed film thickness at the air bearing surface is conducted using the non-Langmuir adsorption model. It is found that the adsorbed film at the air bearing surface becomes significant when the viscosity of adsorbed film is higher than about 1 Pa s. The adsorbed contaminant will accumulate at the rear end of the slider, and it is possible that the accumulated liquid-like contaminant may form a liquid tail which will directly contact with the disk surface, resulting in a crush of the head/disk interface.
Tribological Properties of Thin Functionalized Polyethylene Film on Si With Chemical Modifications
Authors: Minn Myo , Gunawan Soetanto Yanadi S. , Sinha Sujeet K.
Published: April 2011

A very thin functionalized polyethylene (fPE) film is successfully attached to Si substrate via a reactive benzophenone (Ben) layer. The presence of fPE promotes the wear durability of Si/Ben/fPE to 1000 cycles compares with 100 cycles of Si/Ben under 40 mN applied load and 500 rpm sliding speed. As an enhancement, perfluoropolyether (PFPE) is applied as a top mobile lubricant layer coated onto Si/Ben and Si/Ben/fPE and their tribological properties are evaluated under the same experimental conditions. A significant improvement in the wear durability is observed as Si/Ben/PFPE fails at 250,000 cycles and Si/Ben/fPE/PFPE does not fail till one million cycles. Si/Ben/fPE/PFPE can withstand the maximum applied load of 150 mN that provides the PV limit of 106.6 MPa ms−1.
Transient Thermal Lubrication Analysis of Involute Gear
Authors: Wang Wen-zhong , Hu Jibin , Cao Hong , Hu Yuan-zhong
Published: April 2011

With the development of modern machine, the gear sets have to operate under high power high revolution; lubrication performance plays a vital role to the gear sets. In this study, lubrication analysis of spur gears under high speed is conducted based on the elliptical contact and unified Reynolds equation system model. The transient effect and thermal effect are taken into considered. The results show that the transient effect strongly influences the lubrication characteristics during the mesh cycle, while thermal effect enhances the transient effect.
Cage Instabilities in High-Speed Cylindrical Roller Bearings
Authors: Ye Zhenhuan , Wang Liqin , Gu Le , Zheng Dezhi
Published: April 2011

A dynamic model of the cage in an oil-lubricated cylindrical roller bearing was developed and the cage whirl has been researched by this model. In model, the forces between elements, especially the effect of EHL (Elastic Hydrodynamic Lubrication) between cage pockets and rollers were fully considered according to the geometry relationship between elements. The effects of variation in clearance ratio, load and bearing operating velocity on cage whirl have been investigated. The results of the effect of cage clearance on cage instability basically accord with the Gupta’s results, but the starting time of the direct contact between cage and guiding race is delayed while the EHL was considered. The effect of normal load is more important than bearing angular velocity on cage whirl.
The Fretting Wear Characteristics of CrN and TiN Coating on Steam Generator Tube
Authors: Kim Jin-Seon , Choi Joo Hoon , Lee Young-Ze
Published: April 2011

A steam generator tube of a nuclear power plant is damaged by a fretting phenomenon caused by flow induced vibrations (FIV). In this work, the surface of the tube was coated with CrN or TiN as a measure to improve performance of the fretting wear resistance. Fretting wear regime was classified by determining a phase difference between friction and relative displacement signals and contact characteristics were analyzed. As a result, coating increased the friction coefficient. At a lower load, contact condition shifted from gross slip to stick slip.
Antifriction Bearing Sleeves for Diagnostics and Energy Harvesting
Authors: Singh Kamaljit , Sharma Sudhanshu , Sharma J. P.
Published: April 2011

Roller ball bearings are the most common and one of the most important components in rotating machinery. Bearings, in general produce vibrations which can be harvested to produce energy and analysis of these vibrations can also be used to determine the condition of ball bearing. In this paper we discuss how to use the bearings for energy harvesting and conditioning monitoring in machines. A sleeve, padded with piezoelectric material, is designed to solve the dual purpose. Piezo electric materials have the ability to generate an electric field or electric potential in response to applied mechanical strain. Tests are conducted on the good and defective bearings to study the effectiveness of the sleeve. Phase fluctuation based processors are found to be effective in ball bearing condition monitoring. For condition monitoring the signature responses for a given time period are studied. At a constant speed of increase in load leads to an increase in voltage generated. For a single non-coated piezo film, voltage varies from 383 mV at 80 lbf to 683 mV at 320 lbf at 40Hz. With the increased stacking of non-coated piezo films at 320 lbf, voltage generated shows an increase of 23 %. Nano-coating mixture (Ferrofluid and Zinc oxide nanoparticles) causes an additional piezoelectric effect on the surface of piezo film as ZnO acts as an additional source of electrons, due to its ability to emit charges at room temperature. The single piezo film configuration at 320 lbf generates a voltage of 663 mV while the voltage increases 2.1 times for a single nano-coated piezo film. Introduction of defects causes increases in the contact stress at the asperities leading to an increase in the vibrations and forces. Also, an increase in vibration and force, leads to an increase in the voltage generated. For a single piezo film configuration, in a normal bearing, the voltage generated is 663 mV while a defective bearing gives a voltage of 698 mV.
Dynamic Finite Element Analysis of an Elastic-Plastic Half-Space Indented by a Rigid Sphere
Authors: Lee A. , Komvopoulos K.
Published: April 2011

Dynamic indentation of an elastic-plastic half-space by a rigid sphere was studied with the finite element method. A parametric analysis was performed to examine the effects of indentation velocity and yield strength of the half-space material on dynamic contact deformation. Velocity effects are discussed in the context of simulation results of global and local contact parameters, such as mean contact pressure, contact area, and equivalent plastic strain. The evolution of deformation as the material response transitions from elastic to fully-plastic deformation during dynamic contact is interpreted in light of numerical results. This study elucidates the effect of dynamic contact loading on the deformation behavior of elastic-plastic materials for a wide range of length scales where a continuum mechanics description holds.
Effects of the Presence of Multiple Spherical Inclusions Within an Elastic Half-Space in a Circular Point Contact
Authors: Ne´lias D. , Leroux J. , Fulleringer B.
Published: April 2011

A fast method to solve contact problems when one of the mating bodies contains multiple heterogeneous inclusions is proposed, and numerical results are presented for soft or stiff inhomogeneities. The emphasis is put on the effects of spherical inclusions on the contact pressure distribution. The computing time and allocated memory are kept small, compared to the finite element method, by the use of analytical solution to account for the presence of inhomogeneities. The Eshelby’s equivalent inclusion method is considered in the contact solver. An iterative process is implemented to determine the displacements and stress fields caused by the eigenstrains of all spherical inclusions. The proposed method can be seen as an enrichment technique for which the effect of heterogeneous inclusions is superimposed to the homogeneous solution in the contact algorithm. 3D and 2D FFT are utilized to improve the computation efficiency. Configurations such as stringer and cluster of spherical inclusions are analyzed. The effects of the Young modulus, Poisson ratio, size and location of the inhomogeneities are also investigated.
Controllable Radial Oil Injection Applied to Main Engine Bearings: Hybrid Bearing Configurations and Control Pressure Rules
Authors: Estupinan Edgar A. , Santos Ilmar F.
Published: April 2011

In order to reduce friction losses and vibrations in main engine bearings, fluid film lubrication is combined to controllable radial oil injection. This work evaluates different geometric hybrid bearing configurations and control pressure rules for applying radial oil injection in main engine bearings of internal combustion engines. The conventional hydrodynamic lubrication (CHL) is combined with hydrostatic lubrication which is actively modified by radially injecting oil at controllable pressures, through orifices circumferentially located around the bearing surface. The behaviour of a main bearing of a medium size combustion engine, operating with radial oil injection and with four different control strategies is analyzed, giving some insights into the minimum fluid film thickness (OFT) and reduction of viscous friction losses. The behaviour of such parameters is compared to the case when the bearing operates with conventional hydrodynamic lubrication.
An Analysis of a Journal Bearing Sleeve Motion With a Transient Approach
Authors: Ene Nicoleta M. , Dimofte Florin , Clark David A.
Published: April 2011

The purpose of this paper is to study the dynamic behavior of a journal bearing sleeve center by using a transient approach. Unlike other papers presenting the motion of the shaft inside the bearing sleeve, in this paper the rotor is considered rigid having only a small unbalance and the motion of the sleeve center is analyzed. The sleeve is supported by elastic elements. In addition, the axial ends of the bearing are exposed at two different pressures. To the authors’ knowledge, this paper is the first study of such a bearing configuration. Moreover, the influence of the stiffness and damping properties of the elastic element on the sleeve dynamic behavior (trajectories, motion frequencies, etc.) is also analyzed. Relative and absolute trajectories of the sleeve center and FFT analysis of the motion are presented.
Clearance Effects on the Impact Behavior of Large Aspect Ratio Silicon Journal Microbearings
Authors: Demiri S. , Boedo S.
Published: April 2011

This paper investigates the effect of bearing clearance on the impact behavior of microfabricated silicon journal bearings. The design of a novel test apparatus to assess microbearing wear behavior is presented. Microbearing designs, microfabrication processes, and metrology characterization techniques are discussed. A dynamic impact model of the bearing system based on classical impulse-momentum relations is formulated in order to assess the effect of clearance on rotor speed. Coefficient of restitution values obtained over the range of kinematically allowable radial clearance specifications are found to agree well with previously published results for polysilicon microstructures.
Transient Friction Effects Due to Variable Normal Load in a Multi-Scale Asperity-Creep Friction Model
Authors: Goedecke Andreas , Mock Randolf
Published: April 2011

The study of multi-scale and fractal contact geometries holds many insights into the nature of surface contact. As a common feature of most fractal contact models, the presence of small-scale, plastically loaded asperities has emerged. The latter are, due to their loading close to the yield strength of the material, subject to creep deformation which is often held responsible for transient friction effect like dwell time- or velocity-dependent friction. In this paper, the transient behavior of friction under varying normal force will be studied in the framework of a multi-scale contact model with fractal input parameters. An advanced asperity creep model from previous research is used, yielding the time-dependent creep enlargement of the asperity contact area in response to arbitrary load transients.
Roller-Raceway Slip Simulations of Wind Turbine Gearbox Bearings Using Dynamic Bearing Model
Authors: Kang Young Sup , Evans Ryan D. , Doll Gary L.
Published: April 2011

A six degree of freedom dynamic bearing model (DBM) has been used to simulate roller-raceway slip for a cylindrical roller bearing used in an intermediate shaft location of a wind turbine gearbox. The DBM simulates the motion of bearing components such as an inner raceway, a cage, and cylindrical rollers. Radial internal clearance and operating conditions such as load and speed were varied in order to identify the most critical parameters governing roller-raceway slip. The results indicate that significant slip occurs during rapid transient accelerations and decelerations, but these high slip conditions decay to a much lower level of slip at steady state. The results also demonstrate that extreme slip occurs for low load and high speed conditions because of concomitant contact area reduction and traction loss at the roller-raceway interfaces.
Grease Degradation in Critical Helicopter Drivetrain Bearings
Authors: Dykas Brian , Krantz Timothy , Berger Gordon , Street Kenneth W. , Morales Wilfredo
Published: April 2011

An investigation of critical aviation bearings lubricated with MIL-PRF-81322 grease was conducted to derive an understanding of the mechanisms of grease degradation and the loss of lubrication over time. Chemical analysis was performed on grease samples from fielded bearings and compared to fresh grease and samples taken from bearings run for extended times in a laboratory environment. Size exclusion chromatography and Fourier transform infrared spectroscopy were used to investigate the condition of the grease, and evidence of additive depletion, oil evaporation, and thickener degradation were seen, consistent with results reported by other authors. Given the relatively light loading conditions experienced by the test bearings, they were able to continue operating at high temperature despite having most of the original oil depleted from the grease.
Contact and Adhesion of Elastic-Plastic Layered Microsphere
Authors: Eid H. , Chen L. , Joshi N. , McGruer N. E. , Adams G. G.
Published: April 2011

A finite element contact model of a layered hemisphere with a rigid flat, which includes the effect of adhesion, is developed. This configuration has been suggested as a design for a microswitch contact because it has the potential to achieve low adhesion, low contact resistance, and high durability. Elastic-plastic material properties were used for each of the materials comprising the layered hemisphere. Adhesion was modeled based on the Lennard-Jones potential. The effect of the layer thickness on the adhesive contact was investigated. In particular the influence of layer thickness on the pull-off force and maximum contact radius was studied. The results are presented as load vs. interference and contact radius vs. interference for loading and unloading from different values of the maximum interference.
Experimental Verification of a New Model for Transition Flow of Thin Films in Long Journal Bearings
Authors: Deng Dingfeng , Braun Minel J.
Published: April 2011

A new model for predicting the flow behavior in long journal bearing films in the transition regime (Taylor and wavy vortex regimes) was previously proposed by the authors. This paper presents the experimental verification. A comparison between the experimental and numerical results of the Torque–Speed graphs is presented with good agreement between the numerical and experimental data for the Couette, Taylor and pre-wavy regimes. In the wavy and turbulent regime, the magnitude of the numerically obtained data is larger than the corresponding measured torques, but the difference is confined to below 14%. A comparison between experimental and numerical flow patterns is also presented. The results match well in general, except that experimentally, a pre-wavy regime was identified. The latter is characterized by the disappearance of the Taylor vortices, while numerically the Taylor vortices are only distorted and the wavy vortices are formed in this regime.
Dynamic Elastic Contact Model for Sliding Realistic Rough Surfaces
Authors: Raeymaekers Bart , Etsion Izhak
Published: April 2011

We have investigated the sliding contact between nominally flat realistic rough surfaces. Using a technique based on filtering we have created well defined non-isotropic rough surfaces with a Gaussian distribution of asperity heights. We have studied the effect of inertia on the separation between sliding rough surfaces and found that inertia due to contacting asperities may substantially affect the separation between two sliding surfaces.
Contact Mechanics in Low Plasticity Burnishing of Biomedical Magnesium-Calcium Alloy
Authors: Salahshoor M. , Guo Y. B.
Published: April 2011

Magnesium-Calcium (Mg-Ca) alloys are promising biomedical materials in manufacturing biodegradable orthopedic fixation implants. Low plastic burnishing (LPB) has emerged as an enabling manufacturing technique to produce superior surface integrity of orthopedic implants to increase corrosion resistance of Mg-Ca implants. The basic understanding on contact mechanics between burnishing ball and the workpiece is essential to understand process mechanics. The contact mechanics is further complicated by normal force reduction due to hydraulic pressure loss, the penetration depth, and elastic recovery. In this study, the measured rolling force shows maximum 23% reduction compared with the theoretical value. A 2D axisymmetric, semi-infinite FEM model has been developed to predict the amount of elastic recovery after burnishing. The dynamic mechanical behavior of the material is modeled using a user material subroutine of the internal state variable plasticity model. The simulated dent geometry agrees with the measured data in terms of dent profile and depth. Acoustic emission (AE) process monitoring signals are recorded and the likely correlation with predicted residual stress, plastic strain, and temperature distributions are studied to obtain an in-process monitoring tool.
Surface Integrity of Biodegradable Magnesium-Calcium (Mg-Ca) Alloy by Low Plasticity Burnishing
Authors: Salahshoor M. , Guo Y. B.
Published: April 2011

When a device is implanted into the body, into either hard or soft tissue, the body will respond. While the bulk material of the device is often important for integrity and mechanical success, the device surface is at the interface with biology. Major effort has been spent modifying a biomaterial surface in order to elicit or inhibit a biological response. Metallic biodegradable Magnesium-Calcium (Mg-Ca) alloys have attracted an increased attention for orthopedic fixation applications. This research focuses on low plasticity burnishing (LPB) as a novel surface modification technique that is added to the surface to control biodegradation as a biological response. The effects of burnishing pressure as an important process parameter on surface integrity characteristics such as surface roughness, surface topography, and residual stresses are investigated. Burnished surface roughness is smaller than the machined ones. However, some amount of waviness is observed which might be due to large diameter of the burnishing ball and sever plastic deformation. High compressive residual stresses are measured on the burnished surface.
The Effects of PVD Coated Tool Flank Wear and Process Parameters on Surface Integrity in Hard Milling AISI H13 Steel
Authors: Li W. , Guo Y. B.
Published: April 2011

Interfacial friction between cutting tool and work material leads to tool wear during machining, which adversely affects surface integrity of machined components. In addition, more energy is expected to be consumed to accommodate higher loading during machining. Dimensional accuracy and repeatability of the workpiece is also hard to guarantee when machining with worn tools. In this paper, surface integrity of AISI H13 samples milled using the PVD coated inserts is studied. Three levels of tool flank wear (VB = 0, 0.1mm, 0.2mm) were used to cut H13 tool steel in the experiment. At each level of flank wear, the effects of cutting speed, feed, and radial depth-of-cut on surface integrity were investigated respectively. Under a diverse combination of milling parameters, the evolution of surface integrity with tool flank wear was analyzed. A novel on-line optical tool inspection system integrated with CNC machining center was used to inspect the evolution of flank wear with milling time in order to monitor tool wear conditions.
Damage of Micropatterned Surfaces Due to Bubble Cavitation-Erosion
Authors: Jee T. , Komvopoulos K.
Published: April 2011

The capability to reliably reproduce submicrometer-scale patterns is of fundamental importance in semiconductor industry. Higher transistor speeds have been achieved through advances in device miniaturization, resulting in reduced power consumption and manufacturing cost. However, miniaturization below a critical dimension (on the order of ∼100 nm) has been linked with micropattern damage during megasonic cleaning, which decreases the device yield and increases the production cost. Micropattern surface damage due to cavitation-erosion encountered during megasonic cleaning is examined in the context of single- and multi-bubble cavitation models. The critical pressure for micropattern damage predicted by these models is interpreted in terms of important process parameters. Analytical predictions are supported by experimental results of cavitation-erosion damage of gold micropatterns induced by collapsing hydrogen bubbles generated by electrolysis. The results of this study provide insight into surface damage due to bubble cavitation-erosion, which is of great significance in megasonic cleaning of semiconductor devices, such as alternating phase-shift optical masks.
Characterization of the Mechanical Behavior of Cell Components With an Atomic Force Microscope
Authors: Tartibi M. , Komvopoulos K.
Published: April 2011

The mechanical behavior of eukaryotic cell components is critical to cell mobility, division, signaling, and proliferation. Cell components are in such harmony with each other that often mechanical testing of individual components produces less meaningful results than testing performed within living cells. Moreover, cell components are constantly undergoing growth and remodeling, normally through polymerization and depolymerization. An appropriate experimental and modeling framework is therefore essential for cell mechanics. In this study, a special atomic force microscope (AFM) with controlled adhesion area of the cell to a substrate was used to probe the mechanical response of cells to an external force. This experimental set up enables direct control of the applied force and precise measurement of the cell penetration by the AFM tip. A modeling framework that combines the displacement field with the applied force/stress obtained with the AFM is developed to estimate the mechanical properties of each cell component. The tribological relevance of this research is the viscoelastic deformation of cell components under different contact loads.
Tribological Properties of Austenitic Stainless Steel in Pressurized Hydrogen Up to 40 MPa
Authors: Fukuda Kanao , Sawae Yoshinori , Miyakoshi Eiichi , Hashimoto Masaaki , Tanaka Hiroyoshi , Watanabe Hideki , Doi Shunichiro , Sugimura Joichi
Published: April 2011

The tribological properties of austenitic stainless steel (JIS SUS316L) were studied in pressurized hydrogen, i.e. 0.3, 10 and 40 MPa. The coefficient of friction was small under all the conditions tested in this study by comparison with data obtained previously at the standard hydrogen pressure (0.1MPa). The specific wear rates decreased with an increase in the atmospheric hydrogen pressure.