bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study on Friction Noise of Dry Rough Surfaces
Authors: Ben Abdelounis H. , Le Bot A. , Zahouani H. , Perret-Liaudet J.
Published: June 2009

This paper presents an experimental study of the friction noise, between two rough and dry surfaces. Two different geometries of contact have been studied: flat-flat contact and sphere-flat contact. The domain of interest is the dry contact under light pressure where the roughness is the dominant cause of noise. In agreement with some other studies, it has been observed that the sound pressure level Lp (dB) is a logarithmic function of the surface roughness and the sliding speed. However, the exponent of the logarithmic law between sound pressure level and surface roughness largely depends on the topography of the sliding surfaces. On the other hand, the exponent of the law between sound pressure level and sliding speed depends on the contact geometry.
High-Vacuum Tribometers: State of the Art and Current Developments
Authors: Molina G. J. , Kajdas C. , Furey M. J. , McDaniel R.
Published: June 2009

This paper reviews the application to tribology research of the techniques of high-vacuum surface science, in particular their integration into high-vacuum tribometers. The state of the art, the varied research interests, and the rationale for requiring such research instruments are discussed. The authors have developed a new type of high-vacuum tribometer that is aimed to the detection and characterization of charged-particle triboemission. This tribometer has been successfully used to count triboemitted charges as channel-electron-multiplier pulses and their energy distribution from different material pairs (i.e., ceramics and semiconductors when scratched by a diamond pin, and ceramics-on-same-ceramics). Instrument enhancement is ongoing to include simultaneous under-vacuum photon counting and surface work-function measurement by Kelvin-probe. The enhanced facility will enable one-of-a-kind experiments by characterizations and correlations of electron and photon emission, and of surface property evolution dynamics during sliding contact.
Limits to Lubrication Theory in Microsystems
Authors: Tichy John , Marrero Victor , Borca-Tasciuc Diana-Andra
Published: June 2009

Lubrication theory has been one of the most successful and widely used theories in all of engineering and applied science. Therefore, researchers from tribology’s ‘traditional’ wing would be surprised to know that lubrication theory is not at all treated as a given by large group of nontraditional users. In a wide range of conditions applicable to many researchers in microelectromechanical systems (MEMS), experimental results seem to indicate that forces separating surfaces vary according to film thickness to the power minus one, rather than minus three, as lubrication theory requires — a large fundamental discrepancy indeed. Hydrodynamic forces are not generally used to separate surfaces, but arise incidentally, and are usually the largest source of parasitic losses. Clearly, they must be accounted for in the design process.
A Performance Prediction of Microgrooved Bearings Under Mixed Lubrication
Authors: Ashihara Katsuhiro , Hashimoto Hiromu
Published: June 2009

In the designs and analysis of engine bearings for automobiles, the precise prediction of the lubrication condition in severe condition is important. In the mixed-elasto-hydrodynamic lubrication analysis, the contact between the projections of surface roughness distributed stochastically is usually considered. This paper describes a theoretical model under the mixed lubrication in the microgrooved bearing. In this modeling, it is assumed that the section shape of microgrooved bearing alloy takes the circular arc form. In the part where contact is caused, the contact pressure is calculated by the Hertzian equation. The elastic deformation of the bearing by the mixed pressure with which oil film pressure and contact pressure are mixed by each allotment ratio is considered. Moreover, the balance requirement between the sum total of mixed pressure on bearing surface and the journal load is met. Under such an assumption, the numerical calculation model is newly obtained to predict the bearing performance in the mixed lubrication of microgrooved bearing. The numeric solutions of EHL based on the mixed lubrication are compared with EHL based on the fluid lubrication. The predicted oil film thickness at the center of bearing by the mixed lubrication model is remarkably thin compared with that by the fluid lubrication model. This shows that the load ability of the oil film thickness decreases by generating contact.
A Comparison of Three Methods for the Measurement of Wheel Rail Contact
Authors: Dwyer-Joyce R. S. , Yao C. , Lewis R.
Published: June 2009

Measurement of wheel rail contact has been carried out using three techniques in a lab based experiment. The simplest is with the use of commercially available pressure sensitive film. This has been compared to two methods based on reflected ultrasound. The proportion of an ultrasonic wave reflected from a contact depends on the degree of conformity between the surfaces. Maps of reflection have been produced by scanning a transducer back and forth over the region of contact. However, this scanning process is time consuming, and so would be unsuitable for measuring real wheel rail contacts travelling atfull train speed. For this reason a third approach has been used, whereby an array transducer performs a line scan of the contact. The motion of the wheel is then simulated to record several parallel scans to create a contact map.
Wall Slip in EHD Journal Bearings
Authors: Fatu A. , Hajjam M. , Bonneau D.
Published: June 2009

In the present paper the influence of wall slip on the EHD lubrication performance is studed. Steady state and dynamically loaded bearings are investigated. The results show that well-chosen slip/no-slip regions can increase the film thickness and considerably decrease the power loss.
A Numerical Model of Twin Disc Test Arrangement for Evaluating Railway Wheel Wear Prediction Algorithms
Authors: Tassini Nicola , Quost Xavier , Lewis Roger , Dwyer-Joyce Rob , Ariaudo Caterina , Kuka Naim
Published: June 2009

Twin disc tests are commonly used to study wear in railway materials. In this work the implementation of a numerical model of the twin disc arrangement is given, which reproduces the distribution of tangential forces over the contact patch between the two discs. Wear is subsequently calculated by relating the forces and creepage between the two discs using three different wear functions found in the literature. The resulting wear rates are compared with experimental data found at the University of Sheffield for discs made of common railway wheel and rail steels. This allows a comparison and assessment of the validity of the different wear algorithms considered.
Improved Temperature Mapping of EHL Contacts
Authors: Reddyhoff T. , Spikes H. A. , Olver A. V.
Published: June 2009

An effective means of studying lubricant film rheology within EHL contacts is by detailed mapping of the temperature of the fluid and the bounding surfaces within the lubricated contact area. This provides a way of directly measuring the rheology of lubricant films under true EHL conditions. Furthermore, temperature measurement itself provides a very effective means of testing and validating computer simulations. In the current work, the experimental approach initially developed by Sanborn and Winer [1] and then by Spikes and co-workers [2], has been advanced to include a high specification infrared (IR) camera and microscope. This is a similar approach to that taken by Yagi and Kyogoku [3]. As well as the instantaneous capture of full field measurements, this has the advantage of increased sensitivity and higher spatial resolution than previous systems used. The increased sensitivity enables a much larger range of testable operating conditions; namely lower loads, speeds and reduced sliding. In addition, the range of test lubricants can be extended beyond high shearing traction fluids. One additional advantage of instantaneous full field measurements is that the weak infrared optical interference caused by the film can be observed and can used to exactly locate the centre of the contact in the resulting temperature maps. These new possibilities have been used to investigate and compare the rheological properties and compression cooling effects exhibited by a PAO, a group II mineral oil, and a traction fluid.
Pre-Sliding of a Spherical Elastic-Plastic Contact
Authors: Ovcharenko Andrey , Halperin Gregory , Etsion Izhak
Published: June 2009

The elastic-plastic contact between a deformable sphere and a rigid flat during pre-sliding is studied experimentally. Measurements of friction force and contact area are done in real time along with an accurate identification of the instant of sliding inception. The static friction force and relative tangential displacement are investigated over a wide range of normal preloads for several sphere materials and diameters. It is found that at low normal loads the static friction coefficient depends on the normal load in breach of the classical laws of friction. The pre-sliding displacement is found to be less than 5 percent of the contact diameter, and the interface mean shear stress at sliding inception is found to be slightly below the shear strength of the sphere material. Good correlation is found between the present experimental results and a recent theoretical model in the elastic-plastic regime of deformation.
A Microcontact Model Developed for Asperity Heights With a Variable Profile Fractal Dimension, a Surface Fractal Dimension, Topothesy, and Non-Gaussian Distribution
Authors: Liou Jen Luen , Lin Jen Fin
Published: June 2009

The cross sections formed by the contact asperities of two rough surfaces at an interference are island-shaped, rather than having the commonly assumed circular contour. These island-shaped contact surface contours show fractal behavior with a profile fractal dimension Ds. The surface fractal dimension for the asperity heights is defined as D and the topothesy is defined as G. In the study of Mandelbrot, the relationship between D and Ds was given as D = Ds+1 if these two fractal dimensions are obtained before contact deformation. In the present study, D, G, and Ds are considered to be varying with the mean separation (or the interference at the rough surface) between two contact surfaces. The D-Ds relationships for the contacts at the elastic, elastoplastic, and fully plastic deformations are derived and the inceptions of the elastoplastic deformation regime and the fully plastic deformation regime are redefined using the equality of two expressions established in two different ways for the number of contact spots (N).
An Investigation on Elastic-Plastic Rolling Contact Over Rough Surfaces Using a 3-D Dynamic Finite Element Model
Authors: Zhao Xin , Li Zili , Dollevoet Rolf
Published: June 2009

A full-scale 3-D dynamic finite element (FE) model is created to solve the elastic-plastic wheel-rail rolling contact over rough surfaces under different friction forces. Both normal and tangential loads are applied properly. A bi-linear plastic material model is introduced and the real wheel and rail head geometries are simulated. The rolling of a drive wheel with full friction exploitation over a rough contact surface is analyzed in this paper. The stress distributions at the zone with rough surface are derived. From the results at a selected instant, it is found that roughness significantly increases the stress level of the surface layer. Furthermore, plasticity can greatly reduce stress peaks and change stress distributions. The maximum shear stress distribution at the rough surface is also analyzed to assess effects of roughness on fatigue crack initiation.
Performance and Potential of Dry Running Vehicle Clutch Systems With Advanced Ceramics as Friction Materials
Authors: Albers A. , Ott S. , Mitariu M.
Published: June 2009

More than ever, the development process in the field of automotive engineering requires shorter development cycles for a higher range of vehicles. In order to meet the ambitious goals of the automotive industry regarding CO2 reduction and at the same time increasing the vehicle requirements in view of comfort and dynamics, it is necessary to decrease the drivetrain weight. Parallel, research and development in the field of automotive engineering is e.g. characterized by power upgraded combustion engines and by higher transmission ratios in the drive train. As a result, the rising of the weight specific power should not involve a reduction of the drivetrain reliability and the related increase of the failure probability. These demands lead to the conclusion that lightweight and robust designs have to be applied for all drivetrain components. All these factors affect the dimensioning of today’s clutch systems and step up the demands for future clutch systems. Thus, organic friction facings are getting closer to their limits due to temperature resistance. Within the frame work of the Centre of Excellence in Research CER 483 “High performance sliding and friction systems based on advanced ceramics” one approach is to apply advanced ceramics as friction material for e.g. a dry running motor vehicle clutch using the ceramic specific benefits as wear and temperature resistance combined with lightweight design to fulfill today’s demands.
Mixed Lubrication Modelling in Mechanical Face Seals
Authors: Minet C. , Brunetie`re N. , Tournerie B.
Published: June 2009

This paper presents a numerical model of mechanical seal operating in mixed lubrication. It is based on a deterministic approach using realistic roughness description. This model is able to simulate the transition from mixed to hydrodynamic lubrication regimes corresponding to a minimum of the friction coefficient. Moreover it is able to work with non Gaussian surfaces and oriented surfaces.
Modelling of Micro Textured Bearings With Mass-Conserving Cavitation: A Two Dimensional Problem
Authors: Fowell Mark T. , Olver Andrew V. , Spikes Hugh A. , Pegg Ian G.
Published: June 2009

There has recently been much interest in the micro-texturing of slider bearings, where many tiny micro-pockets are incorporated into one of the bearing surfaces. Proponents of this technology have reported that the application of micro-texture to sliding bearing surfaces can result in up to 40% reduction in friction, when the two bearing surfaces have low or zero convergence ratio, i.e. are near parallel [1]. The authors have shown previously, through a series of one dimensional analyses, that the ability of such bearings to generate load support can be explained by a lubrication mechanism termed “Inlet Suction” [2, 3]. In the current paper, these one dimensional analyses are extended to two dimensions with the inclusion of a mass-conserving cavitation algorithm based on Elrod [4]. This allows for a more complete understanding of “Inlet Suction” in real bearing geometries.
Scale Effects in Generalized Newtonian Elastohydrodynamic Films
Authors: Kudish I. I. , Kumar P. , Khonsary M. M. , Bair S.
Published: June 2009

The prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the properties have been obtained from a measurement of the central film thickness in an optical EHL point contact simulator and the assumption of a classical Newtonian film thickness formula. This technique has the practical advantage of using an effective pressure-viscosity coefficient which compensates for shear-thinning. We have shown by a perturbation analysis and by a full EHL numerical solution that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact within a real machine may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning in the inlet zone.
Simulation of Flow in Thin Fluid Films Using the Lattice Boltzmann Method
Authors: Kucinschi Bogdan R. , Afjeh Abdollah A.
Published: June 2009

The present work deals with the application of the Lattice Boltzmann Method (LBM), which is a relatively new Computational Fluid Dynamics approach, to fluid film lubrication. LBM accounts for the inertia forces, while being easier to implement than Navier-Stokes solvers for complex geometric configurations. The LBM solution for a classic case is presented in comparison with the analytic Reynolds solution and the numeric solution obtained with Navier-Stokes solvers.
Contact Mechanics of a High Load Capacity Piston Pin
Authors: Cao Don , Doll Gary L.
Published: June 2009

A novel piston pin design is proposed for diesel engines having higher load capacity than current pin designs. This shaped piston pin incorporates a stress-reducing profile with lubricant film thickness enhancing features on the surface. Three dimensional FEA models were built and are used to model the dynamic contact between the piston and connecting rod interfaces with a standard piston pin and the new piston pin design.
On the Effects of Surface Forces on the Contact of a Wafer and Abrasive Particles in CMP
Authors: Bozkaya Dinc¸er , Mu¨ftu¨ Sinan
Published: June 2009

Chemical mechanical polishing (CMP) of ultra-low-k (ULK) dielectic materials is challenging, as they are susceptible to fracture under typical CMP pressures [1]. Low-pressure (lp) CMP is one of the solutions for polishing ULK dielectrics [1]. In order to implement lp-CMP the process should be optimized to maximize the material removal rate (MRR).
Applications of Crystal Plasticity in Contact Mechanics
Authors: Neu R. W. , Dawkins J. J. , Zhang M.
Published: June 2009

The microstructures of structural metals and alloys are highly heterogeneous due to their crystalline structure often coupled with multiple phases and inclusions, yet most contact mechanics models assume the material is homogeneous and usually isotropic. This is a severe limitation if one desires to quantify the influence of different microstructure attributes on the mechanical behavior. This limitation is overcome through the finite element method using crystal plasticity models. Examples of normal, sliding, and fretting contacts are presented.
Effect of Material Characteristics on Viscoelastic Frictionless Contact Configuration
Authors: Mahmoud Fatin F. , El-Shafei Ahmed G. , Attia Mohamed A.
Published: June 2009

The tribological status of contact systems is affected by the contact configuration; contact stress distribution throughout the contact interface. Viscoelastic materials have the capability of storing and dissipating energy. When the contacting bodies are made of viscoelastic material, viscous and elastic properties of the material have a vital effect upon the contact pressure distribution and the extent of the contact interface. This paper illustrates the effect of viscoelastic material parameters on the contact configuration. Two material parameters are considered; the ratio of the delayed elasticity to the instantaneous elasticity and the material relaxation time. The results are obtained by using a time-dependent nonlinear computational model capable of analyzing quasistatic viscoelastic frictionless contact problems. This computational model adopts the Wiechert model to simulate the linear behavior of viscoelastic materials and the modified incremental convex programming method to accommodate the contact problem of viscoelastic bodies.
Study on the Atomic-Scale Mechanism of Static Friction
Authors: Ding Lingyun , Gong Zhongliang , Huang Ping
Published: June 2009

A new model named as the coupled-oscillator model, is proposed to study the atomic-scale static friction. The Maugis-Dugdal model is used to approximately substitute the Lennard-Jones potential of the interfacial friction in new model. Then, the formulas for static friction force and coefficient calculation are deduced. A comparison between the theoretical result and the experimental value obtained by an atomic force microscope is presented to show the model and the formulas practically feasible.
Identification of the Multiple Flying Heights in a Loading Process
Authors: Zhang Shuyu , Suk Mike , Tyndall George
Published: June 2009

The slider of a Load/unload (LUL) drive can be loaded to a high flying stable state under certain conditions, which positions the read/write transducers much higher from the disk surface than the normal flying height (FH) and resulting in the issues in read or write. To avoid the issues caused by the high flying loading, it is necessary to find ways to recognize the existence of the high FH and eliminate it in the design stages. In this paper, we introduce a method that can identify the existences of the multiple FHs in loading process conveniently. The basic idea is to plot surfaces of air bearing forces in a domain of flying attitude, and then check if multiple FHs exist to generate the same air bearing forces that match the suspension forces. The analysis results indicate that the method is easy and efficient in identifying multiple FHs in loading process.
Wear of Silicon and Carbon-Based Nanoscale Asperities
Authors: Liu Jingjing , O’Connor Sean D. , Gotsmann Bernd , Lantz Mark A. , Cannara Rachel J. , Notbohm Jacob , Moldovan Nicolaie , Carlisle John A. , Sridharan Kumar , Turner Kevin T. , Carpick Robert W.
Published: June 2009

Wear at the nanoscale is a key limitation of conventional silicon and silicon nitride atomic force microscope (AFM) probe tips. Tip degradation and contamination induced by tip-sample interactions can result in decreased resolution and uncertainty in AFM measurements. Prediction and control of the wear behavior is challenging since there is no rigorous theory for the wear of a <100 nm asperity. However, ultrananocrystalline diamond (UNCD) and diamond-like carbon (DLC) are potentially ideal materials for AFM probe applications because of their high stiffness and hardness, low surface roughness, low macroscale friction coefficient and wear, and chemical inertness. The nanoscale adhesion and wear behavior of UNCD, DLC, silicon, and silicon nitride AFM probes have been characterized through systematic AFM wear tests and characterization of the corresponding nanoscale modification of the tips through transmission electron microscopy (TEM) imaging, AFM-based adhesion measurements, and AFM-based blind reconstruction of the tip shape. Our results demonstrate that significant reductions in the nanoscale wear can be achieved through the use of these carbon-based materials. We will discuss how the nanoscale wear behavior of the tips can be linked to their intrinsic materials properties through consideration of the mechanics and physics of nanoscale contacts.
Mechanical Properties of ZDTP Tribofilms Measured by Nanoindentation: Strain Rate and Temperature Effects
Authors: Bec S. , Demmou K. , Loubet J.-L.
Published: June 2009

This study aims to contribute to better understand the antiwear action of zinc dialkyldithiophosphate (ZDTP) additives used in car engine lubrication. The antiwear action of ZDTP is associated to the formation of a protective tribofilm onto the rubbing surface. On a mechanical point of view, the efficiency of ZDTP tribofilms results from equilibrium between film formation and wear rates, associated with appropriate rheological properties. In this work, the mechanical properties of a ZDTP tribofilm have been measured by nanoindentation in different test conditions in order to investigate the effect of temperature and strain rate. A Nanoindenter XP® entirely set into a climatic chamber was used to perform the nanoindentation tests. For all tests, an increase of the elastic modulus was observed from a threshold contact pressure value. This effect is similar to the anvil effect observed on polymers: in confined geometry, the elastic modulus increases versus hydrostatic pressure. For the tribofilm, in the studied range, this effect is enhanced at high temperature and low strain rate. Furthermore, when the temperature increases, a change in the rheological behavior of the tribofilm is observed. Up to about 50°C, the tribofilm exhibits viscoplastic behavior — the hardness increases versus strain rate — and above 50°C, the hardness decreases versus strain rate (“shear thinning-like” behavior).
Blade Bearing Friction and Fatigue Mathematical Mode
Authors: Gonza´lez Jon Plaza , Echarte Casquero Francisco Javier , Va´zquez Mato Javier , Gonza´lez-Posada Miguel A´ngel
Published: June 2009

Modern Wind Turbines adjust their blades orientation at different wind speeds for power control and optimum energy production. A big slewing ring about 2 metres diameter placed at each blade root, allows the blade orientation withstanding highly variable heavy loads, vibrations, continuous rotating oscillations and severe ambient conditions. The blade pitch system design and control strategy in a WTG is strongly conditioned by the load dependant friction of the bearing that shall be accurately defined for cost-effective designs. The pitch system is also the main brake of the rotor requiring high reliability for their components under fatigue loads, and in particular for the slewing rings due to its inherent difficulties for maintenance or replacement. The present methodology allows the fatigue and friction estimation of slewing rings, based on rolling bearing models and classical theories like Hertz, Lundberg-Palmgren, and Miner fatigue cumulative damage. This approach simulates the stress supported by each ball in the contact with the raceways, estimates the bearing friction due to these contact stresses, and the fatigue life of the overall bearing.
Planar Flat Product Transport Using Viscous Traction
Authors: van Rij Jeroen , Wesselingh Jasper , van Ostayen Ron A. J. , Spronck Jo W. , Munnig Schmidt Robert H. , van Eijk Jan
Published: June 2009

In this paper a new contactless transport system for thin, flat products, such as glass substrates and silicon wafers, is introduced. The transport function is realized using viscous traction on the product surface. After an explanation of the operating principles, a mathematical model is presented. Preliminary computations indicate that the generated acceleration is approximately 2.5 m/s2 for a glass substrate with a surface area of 2 m2 and a thickness of 0.7 mm. Furthermore, the vertical bearing stiffness for the considered actuator geometry of the system is 4.2·106 N/m, depending on the properties of the inflow and outflow points of the actuator cells.
Fast Computation of Frictional Energy Dissipation in Rough Contacts Under Partial Slip
Authors: Medina Simon , Dini Daniele , Olver Andrew V. , Hills David A.
Published: June 2009

The multilevel multi-integration technique has been used here to numerically solve the normal and tangential loading of rough surfaces, employing the theory of Ciavarella [1] & Ja¨ger [2] to determinine the tangential shear tractions. Regular asperity surfaces, for which analytical solutions have previously been reported, have been analysed and results showed good agreement with the analytical solution. Random Gaussian surfaces have also been investigated to assess the effect of roughness on contact compliance and frictional energy dissipation.
A Bio-Tribological Analysis of Paratenonitis
Authors: Landham Priyan R. , Nokes Len D. M. , Byrne Carl , Dowson Duncan , Dent Colin M. , Theobald Peter
Published: June 2009

The paratenon is a soft tissue structure that surrounds some tendons, acting to reduce friction during sliding on muscular contraction. Such sliding can, however, cause inflammation of the tissue, leading to paratenonitis. It has previously been reported that paratenonitis incidence was greater in colder temperatures, possibly due to an increase in synovial fluid viscosity and thus friction. This study examined the friction and lubrication between two surfaces approximating the in vivo conjunction, at two different temperatures. The results suggest that an increase in temperature serves to increase friction, in contrast to the previous hypothesis. These results imply that physical activities encourage paratenonitis.
Lubricating Performance of Mixtures of Bio-Diesel and Mineral Diesel Investigated in a Model Tribometer With Radioactive Isotopes
Authors: Jech M. , Wopelka Th. , Franek F.
Published: June 2009

For the investigation of piston ring and cylinder liner systems, screening tests are usually run with pure engine oil as the only lubricant. Due to the fact that the combustion chamber of a cylinder is filled with a high-pressure gas-fuel-mixture, we assume that the piston ring and cylinder liner contact is lubricated by a mixture of oil and fuel rather than by pure oil. As numerous investigations already deal with the effect of oil on the piston ring and cylinder liner system, we will concentrate in this paper on the effect of diesel, especially the effect of the admixture of bio-diesel, on the wear behavior of such a system.
Tribological Properties of Physisorbed, Unsaturated Fatty Acids
Authors: Ruths M. , Lundgren S. , Danerlo¨v K. , Persson K.
Published: June 2009

We have measured normal and lateral (friction) forces across films of saturated and unsaturated fatty acids with the Surface Forces Apparatus (SFA). When adsorbed onto mica from n-hexadecane, linoleic acid forms a dimer layer between monolayer-covered surfaces. This dimer layer, which is not observed in stearic or oleic acid, is removed at low loads. The remaining linoleic acid monolayers are thinner than the ones formed by stearic and oleic acid, and show a more complex friction response with two regimes of linear friction, higher stability at very high loads, and a dependence of the friction on sliding speed and adsorption time.
A Mode-Based Elastohydrodynamic Formulation Employing Low Modulus Hyperelastic Material Models
Authors: Richie A. , Boedo S. , Metcalfe R. W.
Published: June 2009

This paper presents a mode-based elastohydrodynamic formulation employing low-modulus hyperelastic material models which exhibit strongly non-linear load-deflection characteristics. The mode-based method is applied to a reciprocating liquid O-ring seal, where it is found under steady axial motion that a relatively small set of modes captures the essential features of seal deformation when compared with that obtained with standard node-based methods.
Temperature Dependence of Viscoelasticity of PFPE Lubricant Confined in Nanometer-Sized Gaps
Authors: Itoh Shintaro , Fukuzawa Kenji , Hamamoto Yuya , Zhang Hedong
Published: June 2009

In this study, we measured temperature dependence of viscoelastic properties of PFPE lubricant that was confined in nanometer-sized gap widths. In the viscoelastic measurement, we used the fiber wobbling method, which is the highly sensitive shear force measuring method that we have originally developed. Our experimental results showed that the temperature dependence of the lubricant’s viscosity was declined at the gap width of less than 5 nm. Since the elasticity also appeared at the gap width of 5 nm, the reduced temperature dependence is considered to be caused by the repression of molecular mobility due to the solidification of the confined lubricant.
Complete Modeling of Squeeze Film Dampers Using the Bulk Flow Model
Authors: Gehannin Je´roˆme , Arghir Mihai , Bonneau Olivier
Published: June 2009

The present work presents a bulk flow based numerical analysis of squeeze film dampers (SFD) provided with circumferential grooves, feeding orifices and piston ring sealing devices. This means that the bulk flow model for inertia dominated flow regimes (high Re) was adapted for taking into account thin film discontinuities, mass sources located in the thin film zone (for modelling feeding orifices) or on the boundaries (piston ring seals with open slots). In the present work the rotor is whirling on a centered whirl and the bulk flow equation are solved by following a time step integration.
A Viscosity-Based Study of the Tribo-Physical Effects in Boundary-Lubricated DLC Contacts
Authors: Kalin M. , Velkavrh I. , Vizˇintin J.
Published: June 2009

In about a decade, since interest about boundary lubrication properties of diamond-like carbon (DLC) coatings exists, mainly chemical aspects of the DLC lubrication were investigated, i.e. focusing on interactions between various additives and coatings, while physical aspects of coating-oil interactions were not discussed in a greater extent. To elucidate some of these effects, we have analyzed the friction behaviour of DLC coatings and steel under different boundary lubrication conditions by using polyalphaolefin (PAO) base oils having different viscosity grades. Based on this, we have identified several tribo-physical effects in these contacts and for the purposes of this paper we briefly discuss the physical adsorption between the oils and the DLC surfaces, clearly indicating existence of rather strong physically adsorbed layers, which were able to resist high shear stresses under severe boundary lubrication.
An Asymptotic Expansion Approach to Modeling the Heat Transfer in a Reservoir-Extended Porous Slider Bearing
Authors: Johnston Joshua D. , Braun Minel J. , Young Gerald W.
Published: June 2009

This work is a thermal simulation extension to the modeling of the fluid flow inside a reservoir-extended porous slider bearing [1]. The bearing system consists of a lubricating film, porous medium, and a reservoir. The velocity flow field generated by the modeling of the fluid flow is used as an input to solve the heat transfer problem. The small parameter used in the asymptotic expansion is the ratio of the reservoir depth to the length of the slider. The thermal effects upon the operation of this system are discussed.
The Pressure to Cause Complete Contact Between Elastic-Plastic Sinusoidal Surfaces
Authors: Jackson Robert L. , Krithivasan Vijaykumar , Wilson W. Everett
Published: June 2009

This work examines the average pressure required to cause complete contact between sinusoidal shaped surfaces deforming elastically and plastically. Complete contact is defined as when there are no gaps remaining between the surfaces. The material of the surface is modeled as being elastic-perfectly plastic. This work confirms the results of a recent finite element analysis using a semi-analytical model. The results suggest that the pressure required to cause complete contact between surfaces can be much higher than the yield strength or hardness of the surface (in some cases 9 times the yield strength or more). This is because it appears that as the surfaces near complete contact, they begin to act again like an elastic contact. The critical amplitude of a sinusoidal surface below which it will deform entirely in the elastic regime from initial to complete contact is also derived.
Friction Characteristics of the Curved Sidewall Surfaces of a Rotary MEMS Device in Oscillating Motion
Authors: Wu Jie , Wang Shao , Miao Jianmin
Published: June 2009

A MEMS device with a configuration similar to that of a micro-bearing was developed to study the friction behavior of the curved sidewall surfaces. This friction testing device consists of two sets of actuators for normal motion and rotation, respectively. Friction measurements were performed at the curved sidewall surfaces of single-crystal silicon. A general model was developed for the equivalent tangential stiffness of the bush-flexure assembly at the contact point by reducing a matrix equation to a one-dimensional formulation for the purpose of using a recently developed quasi-static stick-slip model. The measurement results show that the coefficient of static friction exhibits a nonlinear dependence on the normal load. The true coefficient of static friction was determined by fitting the experimental friction curve.
Optimum Roughness for Minimum Adhesion
Authors: Liu D.-L. , Martin J. , Burnham N. A.
Published: June 2009

Surface roughness has a significant affect on adhesion. We used a single-asperity model to describe a smooth tip in contact with a rough surface and predicted that an optimal size of asperity will yield a minimum of adhesion. Experimentally, adhesive forces on silicon wafers with varying roughness were measured using AFM cantilevers with varying tip radii. It was found that minima do exist, and for all tip radii, the adhesion falls significantly for roughness greater than 1–2 nm and drops at higher roughness for larger tips. In addition to RMS roughness, the roughness exponent is another important parameter for the characterization of rough surfaces and its affect on adhesion was also investigated. We developed computer programs to simulate a set of fractal rough surfaces with differing roughness exponents. The adhesive forces between an AFM tip and the fractal surfaces were calculated and the adhesion was seen to decrease as the roughness exponent increases. This work should help minimize MEMS stiction and progress the understanding of nanoscale contact mechanics.
A Performance Surface Method for Characterizing the Nonlinear Air Bearing Forces and Moments With Application to the Unloading Process
Authors: Liu Yan , Wang Shao
Published: June 2009

An efficient scheme was developed to analyze the dynamics of a magnetic head slider during the unloading process. The nonlinearity of the air bearing forces and moments was described by analytical expressions obtained from a surface fitting procedure. Combined with a dual-scale suspension model, the force and moment functions determined can be used to obtain the instantaneous flying attitude of the slider and the unloading time with a very short computation time, thus providing a way of exploring a large number of parameter values of the suspension stiffness matrix.
A Combined Scanning Tunneling Microscope-Quartz Crystal Microbalance Study of Heating and Wear at a Sliding Interface
Authors: Dawson Benjamin D. , Krim Jacqueline
Published: June 2009

The unique capabilities resulting from combining a scanning tunneling microscope (STM) and a quartz crystal microbalance (QCM) have been used to characterize the heating and wear at the interface of a tungsten tip and Indium substrate with a change in the contact characteristics of the interface occurring for sufficient sliding speeds. The advantage of this system is the ability to probe heat rise from an asperity contact which will aide in developing a more complete understanding of the complex issue of heat generated via friction.
Effect of Mechanical Preloads on the Dynamic Performance of Gas Foil Bearings
Authors: Kim Tae Ho , San Andre´s Luis
Published: June 2009

Gas foil bearings (GFBs) enable efficient, reliable and maintenance free operation of high-power-density microturbomachinery (< 200 kW). High speed rotors supported on bump-type GFBs, however, are prone to show large-amplitude subsynchronous motions albeit reaching limit cycle performance. Presently, commercial GFBs are simply modified to introduce a mechanical preload that induces a hydrodynamic wedge to generate more load support and direct stiffnesses. Three metal shims inserted under the bump strip layers and in contact with the bearing housing create a multiple lobe clearance profile at a very low cost. Shaft speed coastdown measurements reveal the rotordynamic performance of a rotor supported on original GBFs and (modified) shimmed GFBs. The later GFBs determine a raise in the rotor-bearing system natural frequency, as expected, and also act to delay the onset speed of large-amplitude subsynchronous motions. Predictions of imbalance response implementing linearized bearing force coefficients are in good agreement with measured amplitudes of synchronous response for both GFB configurations, original and modified.
Nanoscale Design of Adaptive Tribological Coatings
Authors: Pan Liming , Dawson Ben , Krim Jacqueline , Baker Colin , Pearson James , Zikry Mohammed , Vovoedin Andrey
Published: June 2009

We report a joint theoretical and experimental study of the tribological properties of gold-yttrium stabilized zirconia (YSZ) based nanocomposite coatings, with a focus on the role of nanocrystalline grain size. Nanocomposites hold great promise for space and ambient applications, on account of their ability to adapt to and exhibit low friction and wear rates in constantly varying environmental conditions. Their internal structure has been the topic of prior literature, but the impact of grain size on tribological performance has heretofore not been considered, and the surface topology has not been reported. As such, we have performed both experimental and theoretical studies, to model the impact of grain size on film stress and wear attributes, and to document surface region grain size distributions through scanning tunneling microscopy (STM) measurements of self-affine fractal scaling properties. Nanocrystalline gold crystal sizes, as determined from STM and x-ray diffraction (XRD) data are consistent with those inferred from high resolution transmission electron microscopy (HRTEM) measurements. Our modeling results associate smaller grain sizes with lower wear rates, consistent with experiments. The findings show promise for nanoscale customization of coatings so as to tailor them at the nanoscale in an application specific manner.
Transient Thermo-Elasto-Plastic Spherical Contact Analyses Considering Effects of Thermal Softening and Heat Partition
Authors: Chen W. Wayne , Wang Q. Jane
Published: June 2009

Frictional heating leads to the temperature rise, thermal expansion, and the thermo-elasto-plastic deformation, which may be responsible for the failure of components under contact and relative motion. This paper reports the development of a three-dimensional thermo-elasto-plastic contact model of counterformal bodies, which account for the transient heat transfer, temperature-dependent strain hardening behavior of materials, and realistic heat partition between surfaces. An extensive study on the contact of a sliding half-space over a stationary ball is conducted using this model.
A Study on Surface Friction on Gold Substrate With 2D Molecular Dynamics Simulation
Authors: Yu Hualong , Wang Q. Jane
Published: June 2009

This paper reports a study on the contact and friction between a gold surface and a rigid tip with a two-dimensional (2D) classical Molecular Dynamics (MD) simulation method. A multiscale method is used in the MD simulation. The MD simulation results are compared with the Hertzian cylindrical contact results. A criterion for the transition from surface sliding to surface scratching is also discussed with the assistance of stress analyses.
Sliding Properties of Pure Metals in Hydrogen Environment
Authors: Fukuda K. , Sugimura J.
Published: June 2009

As the first step to understand how hydrogen influences the sliding properties of metallic materials, nine self-mated pairs of metallic elements were tested using a pin-on-disk apparatus. The results of friction force, wear amount, and observations of wear debris showed that the elements could be roughly categorized into two groups; transition and non-transition elements. Chemisorption of hydrogen on the sliding surfaces was thought to be predominant of the tribological properties in the first group of elements, while chemisorption did not take place on the sliding surfaces of the latter group. The effect of hydrogen on sliding appeared similar to that of oxygen in terms of chemisorption.
Boundary Lubrication and Its Stability
Authors: Singh Kamaljit , Baghmar Saurabh , Sharma Jagdish , Khemchandani M. V. , Wang Q. J.
Published: June 2009

The interaction between lubricant molecules and the solid surface to be lubricated depends upon the surface forces which can be attractive, and repulsive. It thus forms an interactive zone above the solid surface having a band width and height of surface potential and is considered as ‘Zone of Influence’-(ZOI). Its value will vary with the nature of surface finish, distribution of alloying constituents on surface matrix and its size which play very important role in prediction of stability and failure of boundary lubrication friction including absorption and desorption of lubricant molecules. A theoretical model for the formation of boundary lubrication is proposed by combining Lennard Jones (6–12) potential to incorporate for estimating the critical temperature of boundary lubricant, friction coefficient and variation of ZOI for a given condition. Experimental values using EN 31 Ball sliding against the aluminum surface with 0.4% stearic acid as lubricant data agrees well with theoretical values.
Tribo-Oxidation of Tantalum During ECMP
Authors: Gao Feng , Kar Presenjit , Wang Ke , Liang Hong
Published: June 2009

Tribo-oxidation of metals plays important roles in electro-chemical-mechanical planarization (ECMP). Using an electrochemical-tribological technique, we conducted investigation of tantalum tribo-oxidation during ECMP. Adding an electrochemical system to a tribometer, we were able to monitor surface changes through friction. We were able to generate tantalum oxides with assistance of friction. It was found that meta-stable suboxides of tantalum formed. The mechanisms of tribo-oxidation are experimentally studied and discussed here.
Note on the FFT Based Computational Code and Its Application
Authors: Jin Xiaoqing , Keer Leon M. , Wang Qian
Published: June 2009

The discrete convolution based Fast Fourier Transform algorithm (DC-FFT) has been successfully applied in numerical simulation of contact problems. The algorithm is revisited from a mathematical point of view, equivalent to a Toeplitz matrix multiplied by a vector. The nature of the convolution property permits one to implement the algorithm with fewer constraints in choosing the computational domains. This advantageous feature is explored in the present work, and is expected to be beneficial to many tribological studies.
Nano-Scale Contact Model for Microfiber Tip Attachment, Detachment and Friction
Authors: Teodorescu Mircea , Rahnejat Homer
Published: June 2009

The paper investigates the forces that can contribute to the attachment and detachment of the tip of a synthetic fiber to a substrate in normal atmosphere. The contact is subjected to a number of competing forces, which together with the localized contact deflection can promote equilibrium. The pull-off force is predicted as a function of the angle of approach of the fiber toward a substrate and an initial fiber preload.
Nanomechanical Properties of Fluorocarbon Films Grafted Onto Plasma-Treated Low-Density Polyethylene Surfaces
Authors: Cheng Q. , Komvopoulos K.
Published: June 2009

Fluorocarbon (FC) films were grafted on low-density polyethylene (LDPE) by a plasma polymerization and deposition process. Nanoscale indentation and friction tests performed with a surface force microscope provided insight into the nanomechanical properties of the grafted FC films. The time-dependent deformation behavior of the FC films is examined in the context of nanoindentation responses. It is shown that plasma treatment modified the surface properties of LDPE significantly.
Wear Behavior of Polymeric Sealing Material in Gaseous Hydrogen
Authors: Sawae Y. , Yamaguchi A. , Nakashima K. , Murakami T. , Sugimura J.
Published: June 2009

Wear behavior of polymeric sealing material sliding against austenitic stainless steel was evaluated within gaseous hydrogen atmosphere to ensure the durability and longevity of polymeric seals used in fuel cell vehicles and related hydrogen infrastructures. In this study, unfilled polytetrafluoroethylene (PTFE) was considered as a representative polymeric material for seals and its wear behavior was evaluated by using 3pin-on-disk wear tester coupled with the environmental test chamber. Results indicated that the specific wear rate of unfilled PTFE became significantly smaller in gaseous hydrogen compared with that in air. However, the specific wear rate further decreased in argon gas. Optical microscopy and XPS analysis of the disk specimen surface indicated that the wear behavior of PTFE highly depended on the transfer film formation on the sliding counterface. Notable influences of gaseous hydrogen on the formation process of PTFE transfer film and subsequent wear behavior could be postulated from XPS spectra.