bluuebunny/crossref_metadata_2025 huggingface dataset:
Tribological Characteristics of a Dynamic O-Ring in Abrasive Environment
Authors: Sui Ping C.
Published: November 2008

A rotary seal tester simulating the abrasive down-hole environment was used to investigate the sealing, friction, and wear performance of the selected, “rubber” seal material molded into an o-ring configuration. Dynamic frictional torque and surface temperature within the sealing region were measured throughout the test duration. Test results indicate that the seal surface temperature is very sensitive to the variation of frictional torque. The average surface temperature is almost linearly proportional to the average frictional torque. Wear phenomena on the post-test sample surfaces were recorded by a surface profilometer. Observations showed that abrasive wear constantly produces a deep wear scar at the front, sealing edge of the journal surface. Furthermore, the reduction in seal cross-sectional diameter was found to be inversely proportional to the depth of the wear scar.
Numerical Analysis on the Effect of Transverse Surface Roughness in Non-Newtonian Fluid Lubrication
Authors: Chen Haosheng , Li Yongjian , Chen Darong , Wang Jiadao
Published: November 2008

To analyze non-Newtonian fluid lubrication with the effect of large surface roughness amplitude, Navier-Stokes equation is used and a finite volume method is adopted to acquire the lubrication results of an inclined slider model. The numerical results show that the pressure mutation occurs at the edges of surface roughness. When the roughness height is more than 1% lubricant thickness, the surface roughness takes an obvious effect on the lubrication results. The pressure drag increase as the roughness height increases, the friction drag decreases and the total drag force keeps constant. When the roughness height is more than 10% lubricant thickness, the friction force begins to increase and the total drag force increases rapidly. Non-Newtonian fluid affects the lubrication results more greatly than the surface roughness height does, but it does not affect the variation process caused by different surface roughness.
Flash Temperature Parameter Number Prediction Model by Design of Tribological Experiments for Basestock Mineral Oil Containing Palm Olein and Aminephosphate Additives
Authors: Masjuki H. H. , Saifullah M. G. , Husnawan M. , Faizul M. S. , Shaaban M. G.
Published: November 2008

This paper presents a study of the development of first order flash temperature models for basestock mineral oil containing palm olein and aminephosphate additives. The flash temperature parameters are developed in terms of load, rotational speed and operating time using response surface method and design experiment. Flash temperature contours have been generated from these model equations and are shown in different plots. This paper shows palm olein indeed itself is a good anti wear lubricant compared to mineral oil base stock (SN500) but the use of antiwear additives shows an increase in better lubrication as smaller wear scars are found out from using palm olein in the test runs using a fourball machine.
A Novel Method of Characterizing Slider Dynamic Motion During Intermittent Head-Disk Contact
Authors: Kiely James , Hsia Yiao-Tee
Published: November 2008

Characterization of slider motion induced by contact is becoming a critical aspect of developing advanced head-disc interfaces. While vertical motion induced by contact has been studied, very little is known about down-track motion. We have introduced a new technique where the down-track motion is captured and the dynamics in three dimensions are analyzed. We have applied this technique to measure the position of a slider as it transitions from flying to making full contact with the media surface. We find that slider motion varies considerably with varying levels of interference and that motion in all three directions is considerable. Spectral decomposition is used to identify the vibration modes that are excited in each direction, and we find that for most of the test velocities, vertical modes give rise to motion in the two orthogonal directions. In addition, we present a depiction of the vertical, down-track, and off-track position changes by plotting the position of the slider in real space coordinates to help visualize more completely the slider trajectory. Analysis of motion identifies that at some levels of interference, a majority of motion is repeatable, but that non-repeatable components increase with the amount of interference. Additionally, down-track motion is the only component whose magnitude increases monotonically with increasing interference.
A Finite Element Based Technique for Simulating Sliding Wear
Authors: Hegadekatte V. , Huber N. , Kraft O.
Published: November 2008

Micro-machines are known to fail prematurely due to excessive wear by virtue of their inherent high operating frequencies and high surface to volume ratio. In order to predict wear and eventually the life-span of such complex systems, several hundreds of thousand operating cycles have to be simulated. Due to the complexity of wear, the existing wear models are insufficient to reliably predict wear based on the material properties and the contact information. As a first step, a technique has been developed which involves post processing of the results from a finite element (FE) contact simulation with a simple wear model to compute wear. The technique can be used to simulate wear in a pin-on-disc set-up in order to improve and verify the wear models.
Unique Fatigue Failure of Spherical Roller Bearings and Life-Enhancing Measures
Authors: Ueda Tohru , Ueda Koji , Mitamura Nobuaki
Published: November 2008

In this paper, the mechanism of the unique surface originated fatigue failure of spherical roller bearings will be clarified. Also, how the tangential force generated by rolling friction between rolling elements and raceways severely affects bearing life. This paper also outlines a method of enhancing the life of spherical roller bearings based on an understanding of the mechanism of the surface originated fatigue. This method involves improving the rolling friction conditions between rolling elements and raceways.
Capillary Induced Stiction and Adhesion of MEMS Materials
Authors: Zhuang Yan Xin , Menon Aric K.
Published: November 2008

Adhesion and stiction are serious problems in microelectromechanical systems (MEMS) fabrication and application. The wettability, surface energies, and nano-scale adhesive forces of commonly used MEMS materials have been examined by contact angle meter and atomic force microscopy. Silicon and silicon compounds have higher surface energy than that of PMMA and SU-8 due to larger polar component of surface energy. The nano-scale adhesive forces of PMMA and SU-8 are 3–4 times smaller than that of as-received silicon with native oxide. It has been shown that the materials with higher surface energy have higher adhesive forces. One efficient way to avoid stiction in silicon microstructures is to deposit a thin fluorocarbon film coating.
Prediction of Wear Rate Dispersion in Mixed Lubrication
Authors: Robbe-Valloire F. , Progri R. , Paffoni B. , Gras R.
Published: November 2008

Mixed lubrication is usually related to the partition of contacts, and these latter may be divided into two categories. The first includes all asperities working in thin lubricated film (physico-chemical film) conditions. This situation corresponds to local boundary lubrication and is characterised by a local friction coefficient around 0.1. The second category contains all other asperity types. Due to the existence of a thick lubricant films asperities belonging to the second category exhibit a low friction coefficient. The global tribological behaviour for a given contact, however, is function of both categories, since it involves asperities from both categories.
Synthesis and Wear Performance of New Thiocarbamate Derivatives
Authors: Kim Y.-W. , Chung K. , Yang T.-K. , Hwang D.-H. , Cho W.-O.
Published: November 2008

A series of sebacic acid esters containing mercaptobenzothiazole and dialkylenedithiocarbamate, which are potential environmentally friendly lubricating grease additives, were synthesized. The tribological properties as lubricating additives in Li-soap greases were evaluated using a 4-ball tester and SRV tester. The results show that the series of sebasic acid esters with dioctyldithiocarbamate group and mercaptobenzothiazole groups possess better antiwear performance than that of ZnDTP. Whereas, SRV EP characteristics showed worse than that of ZnDTP.
Tribological Properties of Associated Structures at Solid–Liquid Interfaces
Authors: Ruths M. , Lundgren S. , Persson K. , Hillerstro¨m A. , Boschkova K.
Published: November 2008

We have studied the friction-modifying properties of associated amphiphile structures formed at solid–liquid interfaces from bulk solutions. The mechanisms of friction at the molecular level are only partially understood, but are expected to be strongly affected by the phase state of the confined thin film, i.e., by molecular structure and ordering, and also by interactions between confined molecules and the solid surfaces. In contrast to pre-applied lubricant films, self-assembling systems present the advantage of being self-healing, so that upon local fluctuations in pressure and wear, the film may spontaneously reform.
Numerical Investigations of Various Surface Roughness Parameters on the Performance of Profiled Hydrostatic Thrust Bearing
Authors: Shah Kirat , Johnson Robert E. , Cherukuri Harish P.
Published: November 2008

Measurements of surface roughness on hydrostatic bearing slipper indicate that the surfaces are not always Gaussian. Previous studies in this area were primarily concerned with Gaussian surfaces. In this research the effects of non-Gaussian surface roughness on the performance of profiled hydrostatic thrust bearings are analyzed. This study is applicable to the lubrication conditions where the surface roughness is of the same order of magnitude as the minimum film thickness. Surfaces with different skewness, kurtosis, mean, auto-correlation function and standard deviation are generated numerically using a combination of Fast Fourier Transform (FFT) and Johnson translatory system. The finite difference method is used to solve the Reynolds lubrication equation. The effect of roughness on the load carrying capacity is investigated and compared with the results for ideal smooth surfaces.
Magne´li-Type Phases for Dry High-Speed Sliding Applications Up to 800°C
Authors: Woydt M. , Ko¨hler N. , Kelling N.
Published: November 2008

The wear rates established up to 800°C and 7,5 m/s qualify the new and non-commercial available metallurgical concepts (Ti,Mo)(C,N) and Tin-2Cr2O2n-1 qualify both metallurgical concepts for radial and axial air foil bearings in small jet turbines, APUs and turbochargers, but are not limited to these, as well as the values of wear rates are comparable to those typically attributed under mixed/boundary lubrication of liquid lubricated tribosystems. The selection between (Ti,Mo)(C,N) and Tin-2Cr2O2n-1 under tribological considerations depends from the operating conditions and thermal cycles of the regarded foil bearing.
Elasto-Plastic Hemispherical Contact Models for Various Mechanical Properties
Authors: Quicksall John J. , Jackson Robert L. , Green Itzhak
Published: November 2008

This work uses the finite element technique to model the elasto-plastic deformation of a hemisphere contacting a rigid flat for various material properties typical of aluminum, bronze, copper, titanium and malleable cast iron. Additionally, this work conducted parametric FEM tests on a generic material in which the elastic modulus and Poisson’s ratio are varied independently while the yield strength is held constant. A larger spectrum of material properties are covered in this work than in most previous works. The results are compared to two previously formulated elasto-plastic models simulating the deformation of a hemisphere in contact with a rigid flat. Both of the previously formulated models use carbon steel mechanical properties to arrive at empirical formulations implied to pertain to various materials. While both models considered several carbon steels with varying yield strengths, they did not test materials with varying Poisson’s ratio or elastic modulus. The previously generated elasto-plastic models give fairly good predictions when compared to the FEM results for various material properties from the current work, except that one model produces more accurate predictions overall, especially at large deformations where other models neglect important trends due to decreases in “hardness” with increasing deformation.
Sensibility Analysis of Design Parameters for Journal Bearings Optimization of Mass Balancing Systems
Authors: Morais L. , Ferreira L. A.
Published: November 2008

This work presents a sensibility analysis for the journal bearings of combustion engines mass balancing systems. Applying it, it’s possible to improve the journal bearings and avoid possible failures. This analysis consists on studying the effects of the variation of the journal bearings main parameters (radial clearance, journal bearing diameter and journal bearing length) on the journal bearings operating conditions (minimum film thickness, maximum pressure and power loss). The analysis also includes the comparison and selection of the different metallic materials that can be used in these journal bearings, as well as the selection of the lubrication system groove suitable for the journal bearings used in this kind of application. This sensibility analysis shows that: increasing the radial clearance the minimum film thickness increases, the maximum pressure remains approximately the same and the power loss decreases; increasing the journal bearing length, the minimum film thickness and power loss increase and the maximum pressure decreases; increasing the journal bearing diameter, the minimum film thickness and power loss increase and the maximum pressure decreases. At last, it’s found that the white metals (Babbitts) are considered the most advantageous and indicated materials for these journal bearings, and that the lubrication system grooves should be circumferential.
Tribofilms Generated From ZDDP and DDP on Steel Surfaces: Part 1 — Growth, Wear and Morphology
Authors: Zhang Z. , Yamaguchi E. S. , Kasrai M. , Bancroft G. M.
Published: November 2008

The growth and morphology of tribofilms, generated from zinc dialkyldithiophosphate (ZDDP) and an ashless dialkyldithiophosphate (DDP) over a wide range of rubbing times (10 seconds to 10 hours) and concentrations (0.1 to 5 wt % ZDDP), have been examined using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption near edge structure (XANES) spectroscopy at the O, P and S K-edges, and the P, S, and Fe L-edges. The physical aspects of the growth and morphology of the tribofilms will be presented here (Part I) and the chemistry of the films will be discussed in (Part II).
Solid Lubrication by Multiwalled Carbon Nanotubes in Air and in Vacuum for Space and Aeronautics Applications
Authors: Miyoshi K. , Street K. W. , Vander Wal R. L. , Andrews R. , Jacques David , Sayir A.
Published: November 2008

To evaluate recently developed aligned multiwalled carbon nanotubes (MWNTs) and dispersed MWNTs for solid lubrication applications, unidirectional sliding friction experiments were conducted with 440C stainless steel balls and hemispherical alumina-yttria stabilized zirconia pins in sliding contact with the MWNTs deposited on quartz disks in air and in vacuum. The results indicate that MWNTs have superior solid lubrication friction properties and endurance lives in air and vacuum under dry conditions. The coefficient of friction of the dispersed MWNTs is close to 0.05 and 0.009 in air and in vacuum, respectively, showing good dry lubricating ability. The wear life of MWNTs exceeds 1 million passes in both air and vacuum showing good durability. In general, the low coefficient of friction can be attributed to the combination of the transferred, agglomerated patches of MWNTs on the counterpart ball or pin surfaces and the presence of tubular MWNTs at interfaces.
Tribofilms Generated From ZDDP and DDP on Steel Surfaces: Part 2 — Chemistry
Authors: Zhang Z. , Yamaguchi E. S. , Kasrai M. , Bancroft G. M. , Liu X. , Fleet M. E.
Published: November 2008

The chemical constitution of tribofilms, generated from zinc dialkyldithiophosphate (ZDDP) and ashless dialkyldithiophosphate (DDP), has been examined by X-ray Absorption Near Edge Structure (XANES) spectroscopy. The identification of spectral features and interpretation of the results for P, O, Fe, and S species are given, allowing an overall mechanism to be deduced. The role of Fe in these films was investigated in some detail using P L-edge, O K-edge and Fe L-edge XANES spectra.
Research on the Identification Methods of Friction in Kinematical Joints of Mechanical Systems
Authors: Wu Ziying , Liu Hongzhao , Liu Lilan , Li Pengfei , Yuan Daning
Published: November 2008

This paper describes two approaches for the simultaneous identification of the coulomb and viscous parameters in kinematical joints. One is a time-domain method (TDM) and the other is a frequency-domain method (FDM). Simulation shows that both of the two methods have good performances in identifying friction at high SNR (90dB). But at low SNR (20dB), the estimation accuracy of the frequency-domain method is higher than that of the time-domain method. A field experiment employing a linkage mechanism driven by motor is also carried out. The experimental results obtained by the two approaches are almost identical under different experiment conditions. It has been concluded that the presented identification methods of friction in kinematical joints are correct and applicable.
Ceramic Rolls for Wires, Tubes and Sheets
Authors: Kailer Andreas , Hollstein Thomas
Published: November 2008

The main reason for using ceramic materials for metal working tools is the significantly higher wear resistance with respect to commonly used steel tools and therefore the possibility to improve the lifetime as well as the product quality. Ceramic rolls were developed and tested in different applications. In this paper the work on the development of the ceramic rolls and the evaluation of several roll types in field tests are summarized.
Quantification of Accelerated Wear for Road Materials by Using a New Testing Apparatus
Authors: Hammoum F. , Stefani C. , Cottineau L.-M. , Desroches J. P.
Published: November 2008

This paper focuses on problem of loss aggregates on the surface layer of pavements in particular sites such as approaches to roundabouts and pedestrian crossings. Obtaining a long life-wearing course requires more than can be achieved by improving the properties of the wearing course in it. Generally, the traffic loads, temperature variations, the intrusion of water and freeze-thaw cycles, which will reduce the life of the wearing course, regardless of how well it is designed and constructed. The wearing course is an important interdependent component of the whole pavement. A durable and faultless wearing course acts to protect the base layers against the intrusion of water from above, which is essential to maintain its strength and serviceable life. The objective of this study is to evaluate the wear of a controlled set of pavements with various aggregate mixtures. A single parameter is not enough to describe the mechanisms of surface damage but we propose relationships between the constituents used in pavements and loss of aggregates.
Friction of Different Surface Layer of Pavements in Contact With a Rubber
Authors: Hammoum F. , Hamlat S. , Hicher P. Y.
Published: November 2008

We analyse the physical mechanisms taking place in unlubricated friction between surface layer of pavements and a piece of rubber at low sliding speeds < 200 mm/s. This analysis is based on extensive experimental investigations of the load and velocity dependences of dynamic friction forces. The dynamical behaviour caused by dry friction is studied for a rubber-block system pulled with constant velocity over a surface layer of pavements. The dynamical consequences of a general type of phenomenological friction law (stick-time dependent static friction, velocity-dependent kinetic friction) are investigated. Three types of motion are possible: stick-slip motion, continuous sliding, and oscillations without sticking events. In the last case, we propose values of friction coefficient of different surface layer of pavements.
A Contact-Wear Model for the EHL Analysis of Engine Journal Bearings
Authors: Wang Ducai
Published: November 2008

Engine journal bearings are now routinely analysed using elasto-hydrodynamic lubrication (EHL) methods [1,2]. This analysis technique takes into account interaction of the hydrodynamic film with the elastic distortion produced in both the bearing and the journal. It has proved a robust analytic tool for designers in predicting the value and location of such parameters as minimum oil film thickness and maximum film pressure. However, for some very heavily loaded cases, the normal EHL analysis technique may fail to produce realistic solutions. Due to ‘cusping’ of the bearing surface under extreme pressures the edges of bearing may be predicted to penetrate the journal surface leading to a ‘negative’ film thickness. In reality, the surfaces will interact and a ‘running-in’ process will result in subtle changes to the bearing surface profile such that a hydrodynamic film can be maintained across the whole bearing surface. This study introduces a contact-wear model which attempts to model this situation.
Frequency Dependent Dynamic Properties of Tilting Pad Journal Bearings: Experimental Results and Uncertainty Analysis
Authors: Dmochowski Waldemar , Dmochowski Jacek
Published: November 2008

The paper presents experimentally obtained TPJB response to multifrequency excitation and its comparison with theoretically obtained data. Uncertainty considerations for the results obtained using the power spectral density method are also presented. It has been concluded that inertia forces and pivot flexibility effects are behind the variations of dynamic coefficients with frequency of excitation.
Commercial Spool Pump Bearing Performance Testing
Authors: Sibley Lewis , Nair Bala R.
Published: November 2008

Canned motor pumps have been used for decades in nuclear power systems to eliminate seal leakage by using water coolant lubricated hydrodynamic bearings. Other process fluids like pressurized hazardous propylene also need such pumps. Hydrodynamic propylene bearings run with high-loss turbulent flow, which requires high cooling flow that is not available. Therefore, an alternative, almost frictionless, bearing system has been tested successfully for propylene and similar process fluid canned motor Spool Pumps™. This innovative double-row hybrid-ceramic ball bearing uses patented AEROFLOAT® design cages to reduce ball/raceway lubricant film shear stresses and patented solid-lubricant supply components called RINGLUBE®, thus eliminating the need for any external lubrication. After accelerated life testing for the equivalent of almost two months of continuous pump service, there was so little wear on the ball tracks and the RINGLUBE® that the projected continuous pump service life is likely 10 to 20 years.
Determination of Young’s Modulus and Poisson’s Ratio of Coatings With Non-Destructive Indentation
Authors: Liu S. Jordan , Wang Q. Jane
Published: November 2008

Coatings are now extensively used in engineering practice to modify the surfaces of mechanical components for enhanced load-bearing ability, lubricity, and service endurance. Designing thin-film coatings to meet particular engineering needs requires the knowledge of accurate mechanical properties of the coatings. Young’s modulus and Poisson’s ratio are two basic mechanical properties of materials, which should be conveniently measured. However, the measurement of Young’s modulus of a thin film is hindered by the inevitable substrate effect when the conventional methods for a bulk material are used to obtain so called “reduced modulus”. This paper presents a direct and non-destructive method for the measurement of Young’s modulus and Poisson’s ratio of a thin-film coating and its substrate, based on the extended-Hertz theory developed for coated bodies in contact. The theory is used to analyze load-displacement data from a spherical indentation in the elastic range, where the substrate effect is intrinsically modeled. Two sets of validation experiments are shown for coatings of a few microns thick. This new method does not need any assumption on pressure distribution and Poisson’s ratio and can be easily incorporated into current indentation analysis systems.
Evaluation of Ultra High Speed Micro Traction Drive
Authors: Tozaki Yasuyoshi , Umeda Akihiko , Yoshimi Takeshi , Shiotsu Isamu , Sonobe Hiroyuki , Matsumoto Susumu
Published: November 2008

Micro traction drive is a device to transmit driving force modified from angular ball bearing. The micro traction drive consists of an input/inner ring, an outer ring, a rolling element, a retainer/output shaft, and a casing. In addition, the micro traction drive of the tandem type that combined two bearings was developed to obtain a big reduction ratio. As a result, we are able to attain the reduction ratio 7.3. Traction oil on the market was sealed in the test piece for oil bath lubrication. Input shaft could be driven with a motor in ultra high speed. Power absorbing type test equipment was made the efficiency and temperature of micro traction drive operated at high speed were successfully measured. In the result of measurement, temperature rise are a few and it turns out a micro traction drive can be used by ultra high-speed.
Development of an Experimental Device for Studying Real Connecting-Rod Bearings Functioning in Severe Conditions
Authors: Michaud Philippe , Fatu Aurelian , Villechaise Bernard
Published: November 2008

Nowdays, automotive designers attempt to limit the pollution and the fuel consumption, in order to answer customer’s environmental demands. To assist designers in this effort, it is important to analyze and to understand engines bearing mechanical behavior. Therefore, many experimental studies have been undertaken in the last 20 years [1–3]. Because of the great complexity of the con-rod bearing real environment, no experimental tests have been realized in realistic and severe conditions. This paper presents an experimental device “MEGAPASCALE” made to analyze the thermoelastohydrodynamic (TEHD) behavior of connecting rod bearings functioning in severe conditions.
Influence of Particle Content and Porosity on the Dry Sliding Wear Behaviour of Cast In-Situ Al(Ti)-Al2O3(TiO2) Composites
Authors: Hamid Abdulhaqq A. , Ray Subrata , Jain Satish C. , Ghosh Prakriti K.
Published: November 2008

Cast in-situ Al(Ti)-Al2O3(TiO2) composites, synthesized by dispersing titanium dioxide (TiO2) particles in molten aluminium, which reduces these particles, partially or fully, forming alumina (Al2O3) and releasing titanium to the matrix alloy, may provide materials for lightweight components in automobiles and aircrafts. Wear tests, conducted at different normal loads and at constant sliding velocity of 1.05 m/s using a pin-on-disc wear testing m/c, under dry sliding conditions, indicate that the cumulative volume loss and wear rate of in-situ composites are significantly lower than those observed in either the commercial aluminium or Al-Ti base alloys, under similar load and sliding conditions. At a given particle content, the wear rate increases with increasing porosity content presumably due to its combined effect on real area of contact as well as subsurface cracking. The wear rate of in-situ composites having relatively lower porosity decreases with increasing particle content, but, at relatively higher porosity, decreases a little or remains unchanged with increasing particle content.
An Approach to Predicting Evolution of Material Properties Near Surfaces With High Friction in Metal Forming
Authors: Alexandrov S.
Published: November 2008

In the case of rigid/perfectly plastic material, the velocity fields in the vicinity of maximum friction surfaces must be describable by nondifferentiable functions. In particular, the equivalent strain rate follows an inverse square root rule near such surfaces and, therefore, approaches infinity at the surface. Because the equivalent strain rate is involved in many evolution equations for material properties, its behavior near the maximum friction surfaces should lead to high gradients in the material properties near the surface, which is confirmed by experiment. To quantitatively describe the evolution of material properties in the vicinity of surfaces with high friction, the concept of strain rate intensity factor can be adopted.
Finite Element Simulation of Wheel-Rail Contact Dynamic Instabilities Under Sliding Conditions
Authors: Saulot A. , Baillet L.
Published: November 2008

Using dynamic finite element methods, a temporal study of the dynamic response of a 2D mechanical model composed of a deformable rotating disc (wheel) in contact with a deformable translating body (rail) with constant Coulomb friction is presented. Under global sliding conditions, instabilities at specific frequencies appear in the contact patch even in the case of a constant friction coefficient. The influence of parameters such as global sliding ratio, friction coefficient and transient value of applied sliding on local contact conditions is evaluated. A parallel is then drawn between the frequencies of these instabilities and the modal analysis of the entire mechanical model. Finally, consequences of these instabilities on local rail plastification are presented and correlated with rail corrugation appearing on straight tracks under acceleration or deceleration conditions.
Elastic-Plastic Contact Between Rough Surfaces: Proposal for a Wear Model
Authors: Ne´lias D. , Boucly V. , Brunet M.
Published: November 2008

A semi-analytical thermo-elastic-plastic contact model has been recently developed, and presented in a companion paper. The main advantage of this approach over the classical Finite Element Method (FEM) is the treatment of transient problems with the use of fine meshing, and the possibility of studying the effect of a surface defect on the surface deflection as well as on subsurface stress state. A return-mapping algorithm with an elastic predictor / plastic corrector scheme and a Von Mises criterion is now used, which improves the plasticity loop. This improvement in the numerical algorithm increases the computing speed significantly, and shows a much better convergence and accuracy. The contact model is validated through a comparison with the FEM results of Kogut and Etsion (2002), which correspond to the axisymmetric contact between an elastic-perfectly plastic sphere and a rigid flat. A model for wear prediction based on the material removal during cyclic loading is then proposed. Results are presented for rough surfaces.
A Critical Assessment of Tribopolymerization as an Antiwear Mechanism
Authors: Furey Michael J. , Kajdas Czeslaw , Molina Gustavo J. , Vick Brian
Published: November 2008

By tribopolymerization, we mean the planned, intentional, and continuous formation of protective polymeric films on tribological surfaces by the use of minor concentrations of selected monomers capable of forming polymer films “in situ” by polycondensation or addition polymerization. The approach involves the design of molecules which will form polymeric surface films in critical regions of boundary lubrication. The concept has been shown to be effective in reducing wear with ceramics as well as metals in both liquid and vapor phase applications. The purpose of this paper is threefold, namely: 1. To review our key fundamental research on the topic of tribopolymerization, including more recent views based on measurements of triboelectron emission. 2. To summarize the applications of this concept to a variety of industrial problems, including the use of the compounds in fuels as well as in areas in which environmental issues are important. 3. To briefly outline future plans for fundamental research on tribopolymerization, including theoretical and experimental studies to examine the roles of surface temperature, triboelectron emission, and catalysis on surface polymerization.
Examination of Roughness Effects on Bio-Adhesion of SAM Through Numerical Simulation
Authors: Cheng W. , Farhang K.
Published: November 2008

Self-assembled monolayers (SAM) formed on gold or hydroxylated surfaces are well ordered organic surfaces that enable the control of interface property at the molecular scale. Microcontact printing is a simple technique that can pattern the formation of SAM in the plane with dimensions on the micron scale. The combination of SAM and microcontact printing makes a technique useful for studying a variety of fundamental phenomena in bio-interfacial science such as cell adhesion. However, the existence of surface roughness tends to impede the effectiveness of the method in generating the desirable interface properties. Studies have shown that surface roughness significantly changes adhesion of SAM coated material. The current study tries to understand the roughness effects on bio-adhesion of cell-SAM substratum. A current model of cell adhesion considers the effects of nonspecific and specific interactions between adhesion molecules and the substrate assuming an isotropic Gaussian distributed roughness. Simulation results show the change of pull-off force and contact area due to different scales of roughness. The reduction rate of cell adhesion due to roughness and chemical-mechanical factors are then compared to show the significance of roughness effects on SAM adhesion. Results suggest that caution must be taken in quantitative interpretation of protein and cell adsorption strength by using SAM device as a biosensor.
Role of Misorientation in Assessing Fretting Damage
Authors: Swalla Dana R. , Neu Richard W.
Published: November 2008

The primary focus of the current work is to develop quantifying measures that can describe the evolution of fretting damage at the microstructural scale in a dual phase Ti-6Al-4V as well as two single phase materials: commercially pure titanium (CP-Ti), which consists of pure alpha-phase titanium, and a near alpha Ti-5Al-2.5Sn. It is important to understand deformation behavior at the microstructural scale in heterogeneous materials because features at this scale, such as grain size, crystallographic orientation, and phase distribution, strongly influence crack development and are dimensionally of the same magnitude as the fretting damage volume. In Ti-6Al-4V, the size, distribution, and crystallographic orientation of the alpha-phase, which has an HCP crystalline structure, is particularly significant in fretting crack formation. Recent studies have linked an increase in average intra-grain misorientation (AMIS) measured using electron backscatter diffraction (EBSD) to increasing strain in medium to high stacking fault metals such as titanium, nickel, copper, and aluminum. A high AMIS value in the near surface layers of specimens subjected to procedures that may induce surface damage has been shown to correlate with a reduction in low-cycle fatigue life. Furthermore, AMIS may be used to estimate plastic strain accumulation when calibrated to specimens tested at a known plastic strain. In the current study, the effect of slip displacement amplitude and number of fretting cycles on the evolution of fretting damage is quantified using AMIS. Additional supporting evidence of significant plastic strain accumulation in the near surface layers of the fretted specimens obtained using nanoindentation and energy dispersive X-ray analysis (EDX) will also be presented. An opportunity exists to directly link microstructural damage measures such as AMIS with life prediction procedures, and therefore, remaining challenges in developing such methods will be discussed.
Nano-Mechanical Property and Nano-Tribological Behaviors of Nitrogen-Doped Diamond-Like (DLC) Coatings
Authors: Zhang Ruijun , Ma Hongtao
Published: November 2008

Diamond-like carbon (DLC) films doped with different nitrogen contents were prepared by an ECWR-CVD deposition technique, and their composition, structure, nano-mechanical property and nano-tribological behaviors were characterized using PHI680 type Auger Electron Spectrometer (AES), Renishaw Raman system 1000 type Laser Raman Spectroscopic technique and Hysitron Nano-indentor, respectively. It has been found that, with the increasing of nitrogen content in the films, the resultant N-doped DLC films show a monotonous drop in the sp3 ratio and a significant increase in the sp2 ratio, and, accordingly, their nano-mechanical property, including nano-hardness and reduced modulus, decreases evidently. In addition, the depths for the scratched tracks produced during the nano-scratch testing depend heavily on the nitrogen content in the N-doped DLC films, and, in the case of the same applied loads, the higher the doped nitrogen content, the deeper the resulting scratched tracks. However, at the same applied loads, the DLC fims doped with different nitrogen contents exihibit similar nominal coefficients of friction (LF/NF), indicating that the amount of doped nitrogen has little effect on the nano-frictional behavior for the N-doped DLC films.
Experimental Investigation of Drillpipe Loaded in Slips
Authors: Payne M. L. , Pattillo P. D. , Driscoll P. M. , Sathuvalli U. B.
Published: November 2008

Oilwell drillstrings are suspended in the rotary table using axisymmetric wedges in a restraining bowl structure. These wedges, are known as “slips”. Hardened dies on the inside surface of the slips grip the drillpipe. The string capacity to sustain axial loads is influenced by the slip-drillpipe interaction. When the design for a recent Gulf of Mexico (GOM) offshore well required the drillstring to support ∼4.5 kN, a test program to investigate slip-drillpipe interaction was initiated. The analysis of strain gage data revealed that drillpipe peak stresses are not confined to a single cross sectional plane on the drillpipe ID. Yielding is initiated on the ID along a line parallel to the drillpipe axis, and corresponds to the gap between slip segments. This paper presents test details and results of data analyses that are a prelude to an ongoing effort to determine a revised design basis for drillpipe loaded in slips.
Computation of Thermal Deformation of Thrust Bearing Pad Concerning the Convection by Non-Uniform Oil Flow
Authors: Hemmi Makoto , Hagiya Koushu , Ichisawa Katsuhisa , Fujita Sukeyuki
Published: November 2008

Tilting-pad thrust bearings are used to support the loads of large rotating machinery, such as water turbine generators. When such machines are in operation, thermal deformation is so extensive that it is comparable to deformation caused by the pressure of the oil film, and it influences the bearing’s performance. So, the temperature distribution in the pad, which determines the thermal deformation, should be calculated correctly. This requires precise estimation of the convection by the ambient oil at the pad’s surfaces, but the complexity of the pad’s shape and ambient oil flow of oil around it makes this estimation difficult. Using CFD (Computational Fluid Dynamics) software, we computed the temperature distribution in the pad by solving the heat transfer in the pad, in the oil and interfaces of them simultaneously. The thermal and stress deformation were then calculated by the FEM code and is used in oil film analysis to determine the characteristics of the bearing. Comparing its results with the experimental ones validated the computational process.
High Pressure Lubricant Property Measurements
Authors: Jacobson Bo O.
Published: November 2008

Using a high pressure chamber, different types of lubricants have been studied at pressures representative of elastohydrodynamically lubricated contacts. The three types of lubricants (solid, liquid and gaseous) have been compressed and sheared to measure the compression, the shear stress as a function of pressure and shear velocity, and the solidification pressure. In the high pressure chamber refrigeration gases have been compressed into solid state, lubrication oils have been compressed 35% by volume, and solid waxes have been compressed 44% by volume.
A Mixed Mode Fatigue Crack Growth Model Applied to Rolling Contact Fatigue
Authors: Ribeaucourt R. , Baietto Dubourg M. C. , Gravouil Anthony
Published: November 2008

Extended finite element method simulation were conducted in order to evaluate mode I and II stress intensity factors (SIFs) for cracks under cyclic contact rolling and rolling-sliding conditions. The crack propagation mode and direction were investigated using criteria.
Prediction of the Thermo-Mechanical Contact Behaviour of a Graded Coating/Substrate System Using Advanced Numerical Techniques
Authors: Watremetz B. , Baietto-Dubourg M. C. , Lubrecht A. A.
Published: November 2008

Coatings or coating combinations are widely used to increase operating life and running performance of engineering materials. Nevertheless, the development and choice of coatings is a very complex and costly task. This selection and optimization is thus based on a recursive procedure combining experimental tests and modeling. Numerical simulation is used to analyze coating behavior, tune the geometrical configuration and define optimal thermo-mechanical properties in relation with the applied stress. The objective of the current work is to develop a 3D thermo-elastic model for coatings with graded properties. Former models dealt with isotropic layers with constant properties adhering perfectly. These last assumptions result in discontinuities in stress and temperature fields at the interface between successive layers. The increasing use of interface layers between coatings and substrates requires theoretical models to predict the thermomechanical behavior of such graded coatings. The gradation in properties of the material reduces induced thermomechanical stress discontinuities. Multigrid techniques are used to improve solver efficiency, reduce CPU time and thus permit the use of fine grids to accurately describe the variations in elastic properties.
A New Approach to Optimization of the Metal-Polymer Tribological Characteristics
Authors: Szczerek Marian , Przepio´rka Jacek
Published: November 2008

The paper presents a new approach to optimization of the metal-polymer tribological characteristics based on correlation between the total sum of polar component values of surface free energy tribological characteristics (wear and friction) of rubbing materials. The authors predict that research of friction and wear mechanism of modified friction joints should make possible to generalize the principles of rational selection of manufacturing technology of polymer-metal friction joints.
The Role of Adhesion and Sub-Newton Pull-Off Forces on the Test Mass Release for the LISA Experiment
Authors: Benedetti M. , Bortoluzzi D. , Bosetti P. , Da Lio M. , Fontanari V.
Published: November 2008

The present paper illustrates the problematic of precise release of objects in weightless conditions. Under these circumstances, the role of weak bonds (electrostatic and van der Waals attractive forces) is not obscured by the gravity force. A finite-element analysis approach has been presented with the aim to quantify the adhesion forces between smooth surfaces in vacuum. On the basis of the obtained results, some solutions aimed at reducing adhesion pull-off forces have been discussed. Special emphasis has been placed on the role of surface roughness in reducing adhesion. To this purpose, a fractal surface theory has been used to estimate interaction forces. The obtained results have been used to discuss the role of adhesion on the release of a gold test mass under zero gravity conditions for the scientific space mission LISA.
An In-Vitro Investigation of Sliding Friction Between Biomaterials for Cartilage Substitution and Articular Cartilage
Authors: Northwood E. , Kowalski R. , Fisher J.
Published: November 2008

Understanding friction and wear of biomaterials when in contact with articular cartilage is vital within the development of future hemi-arthroplasty and cartilage substitution. This study aimed to compare the frictional properties of single phase and biphasic polymeric materials against articular cartilage. Continuous sliding friction was applied by means of a simple geometry wear simulator. The single-phase polymers produced peak frictional values of 0.37(±0.02). The biphasic hydrogel produced a peak frictional coefficient of 0.17(±0.05). It is postulated that this reduction in friction can be attributed to its biphasic properties, which instigates the fluid phase load carriage within the articular cartilage/hydrogel interface to be maintained for longer, reducing the frictional coefficient. This study illustrates the importance of biphasic properties within the tribology of future cartilage substitution materials.
Effect of Acetabular Cup Design on the Tribology of Metal-on-Metal Hip Resurfacing Replacements: A Contact Mechanics and Elastohydrodynamic Lubrication Study
Authors: Udofia I. , Liu F. , Jin Z. , Roberts P. , Grigoris P.
Published: November 2008

The tribology of metal-on-metal (MOM) hip resurfacing prostheses has been investigated in this study, with particular consideration of the effect of prosthesis design (cup wall thickness and clearance) on the contact mechanics and elastohydrodynamic lubrication (EHL) of these man-made bearings. Two commercially available MOM hip resurfacings, which differ mainly in cup-wall thickness and diametral clearance, were investigated. Finite element contact mechanics and lubrication analyses were carried out on the two MOM hip resurfacing designs. It was found that the thinner acetabular cup with a the relatively smaller clearance resulted in lower contact and hydrodynamic pressure predictions, and a significant increase in the predicted lubricant film thickness at the bearing surfaces. This was attributed to the increase in contact area, conformity between the cup and ball and to the increased influence of the underlying non-metallic structures such as bone and cement, which enhanced the elasticity of the thin acetabular cup. It was shown that full fluid-film lubrication was possible in MOM hip resurfacings during the walking cycle with the small clearance and thin cup-wall thickness model. The importance of the design and manufacturing parameters on the tribological performance of MOM hip resurfacings is highlighted in this study, particularly in promoting fluid film lubrication as a means to further reduce wear at the bearing surfaces.
Tribological Behaviour of GFR Polymer Composites
Authors: Quintelier J. , Samyn P. , De Baets P. , Degrieck J.
Published: November 2008

On a Pin-on-Disc test rig with composite disc and steel pin tribological experiments were done on pultruded glass fiber reinforced polymer matrix composites plates. The wear and frictional behavior strongly depends on the structure. Also the normal load plays an important role in the frictional behavior, which is of greater importance than the speed. The formation of a thin polymer film onto the wear track results in a lowering of the coefficient of friction with 20%.