bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Black Bearing Balls From a Space Shuttle Body Flap Actuator
Authors: Street Kenneth W. , Sovinski Marjorie F.
Published: November 2008

A significantly deteriorated ball bearing mechanism from a body flap actuator on Space Shuttle OV-103 was disassembled and the balls submitted for analysis in conjunction with Return to Flight activities. The OV-103 balls, referred to as the “black balls”, were subjected to X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared (FT-IR) and Raman micro spectroscopy, surface profilometry, and optical and electron microscopy. The spectroscopic results in combination with microscopy analysis allowed a determination of the lubricant degradation pathway. The chemical attack mechanism does not adequately explain the unique visual appearance of the black balls. Numerous efforts have unsuccessfully focused on duplication of the phenomena causing this unique surface structure and appearance of the black balls. Further detail will be presented supporting these conclusions along with plausible explanations of the unique black appearance to the balls.
Complex Micromodel Analysis of Wearing Contact Interfaces
Authors: Franek Friedrich , Pauschitz Andreas , Lazarev Vladislav E. , Vorlaufer Georg , Dick Thomas , Jisa Robin
Published: November 2008

The behavior of tribological systems with hybrid lubrication using solid lubricants on graphite basis and/or liquid lubricant can be optimized. This can be achieved by a detailed knowledge of the transfer mechanisms induced by the tribological stress and consequential material and surface design adaptations. Our first approach is a finite element model containing a representative model of the real asperity geometry and distribution. With this model we can estimate the temperature and pressure distribution in the contact zone. The model is based on an assembly of volumes which limit the surfaces taking part in heat exchange and load transfer. Each surface has a set of equations for heat exchange and mechanical loading in the contact. Similarly, transport mechanisms concerning the liquid lubricant, solid lubricant particles and the dissemination of wear particles are considered.
Multi-Scale Enveloping Spectrogram for Bearing Defect Detection
Authors: Yan Ruqiang , Gao Robert X.
Published: November 2008

This paper presents a new signal processing technique for bearing defect detection, called Multi-Scale Enveloping Spectrogram (MUSENS). The technique decomposes vibration signals measured on rolling bearings into different scales by means of a continuous wavelet transform (CWT). The envelope signal in each scale is then calculated from the modulus of the wavelet coefficients. Subsequently, Fourier transform is performed repetitively on the envelope of the signal at each scale, resulting in an “envelop spectrum” of the original signal at the various scales. The final output is a three-dimensional scale-frequency map that indicates the intensity and location of the defect-related frequency lines.
Passive Magnetic Bearings: Low Instability and Possible Stability
Authors: Bassani R. , Ciulli E.
Published: November 2008

Permanent magnet bearings and systems offer negligible friction and no wear, but static instability too. Nevertheless, spaces of low static instability exhist, and stability may be possible in non static conditions.
Effect of Non-Operational Shock on Interaction Between Suspension Lift-Tab and Load/Unload Ramp
Authors: Murthy Aravind N. , Jayson Eric M. , Talke Frank E.
Published: November 2008

Most hard disk drives manufactured in the last few years have Load/Unload (L/UL) technology. As opposed to the Contact Start/Stop (CSS) technology, L/UL technology has the advantage of improved areal density because of more disk space availability and better shock performance. The latter characteristic has significant benefits during the non-operational state of the hard disk drive since head/disk interactions are eliminated and the head is parked on a ramp adjacent to the disk. However, even if head/disk interactions are absent, other failure modes may occur such as lift-tab damage and dimple separation leading to flexure damage. A number of investigations have been made to study the response of the head disk interface with respect to shock when the head is parked on the disk ([1], [2]). In this paper, we address the effect of non-operational shock for L/UL disk drives.
Influence of Material Property on Micropitting and Pitting Behavior
Authors: Jao T. C. , Rollin A. J. , Carter R. O. , Aylott C. J. , Shaw B. A.
Published: November 2008

Recent studies have shown that micropitting initiated pitting appears to be the dominant metal fatigue mode in modern bearings and gears. If the formation of micropits can be controlled, the fatigue life of the bearings and gears can be readily lengthened, so the useful life of the engine or transmission can be radically extended. The lack of in-depth understanding of micropitting initiation mechanism hinders progress to control the micropitting-initiated pitting failure mode. In this study, we explore the initial stages of micropitting in relation to material differences that impact the crack propagation process. To investigate these mechanisms, we study micropitting and subsequent pitting using pinion and wheel pairs made from two different carburized steels, SAE 8620 and SAE 4027, in a 91.5mm helical back-to-back gear test rig using a typical transmission fluid. For comparison, a similar study is being carried out with the pinion and wheel pairs made from the same SAE 8620 steel. The preliminary results show that steel material differences may change the ultimate pitting fatigue life but may not significantly influence the micropit formation process and subsequent pitting failure mode.
Effect of Detailed Base Oil Structure on Oxidation Performance of Automatic Transmission Fluids
Authors: Devlin Mark T. , Baren Randall E. , Tersigni Samuel H. , Jao Tze-Chi
Published: November 2008

Automatic transmission fluids (ATF) should be oxidatively stable so that their frictional properties are maintained as the fluids are aged. To test the oxidative stability of ATFs, automobile manufacturers have created oxidation tests in which ATFs are aged in operating transmissions. In these tests, the total acid number (TAN) of the oil is measured throughout the test, and at the end of the test the TAN of the oil must be below specified limits. In general, oxidation of oils occurs by formation of free radicals that can react with the oils to form acidic species that are detected by the TAN of the used oils [1, 2]. Peroxides also form when an oil is oxidized and the peroxides can react with the oil to form acids [1,2]. Base oil structure, presence of wear metals, and the amount of oxygen dissolved in the oil can all affect the oxidative stability of oils [1,2]. Therefore, we investigated how each of these three factors affect changes in TAN as oils are aged in the GM cycling and GM oxidation tests (GMOT). Base oil structure is the major factor affecting the oxidative stability of ATFs. In particular, we have found that the cyclo-paraffin concentration in the base oils used to formulate ATFs can be related to oxidative stability. The lower the number of cycloparaffins in the base oil, the better the oxidative stability of the ATF.
A Multi-Scale Model for Contact Between Rough Surfaces
Authors: Jackson Robert L. , Streator Jeffrey L.
Published: November 2008

This work describes a non-statistical multi-scale model of the normal contact between rough surfaces. The model produces predictions for contact area as a function of contact load, and is compared to the traditional Greenwood and Williamson (GW) and Majumdar and Bhushan (MB) rough surface contact models, which represent single-scale and fractal analyses, respectively. The current model incorporates the effect of asperity deformations at multiple scales into a simple framework for modeling the contact between nominally flat rough surfaces. Similar to the “protuberance upon protuberance” theory proposed by Archard, the model considers the effect of having smaller asperities located on top of larger asperities in repeated fashion with increasing detail down to the limits of current measurement techniques. The parameters describing the surface topography (areal asperity density and asperity radius) are calculated from an FFT performed of the surface profile. Thus, the model considers multi-scale effects, which fractal methods have addressed, while attempting to more accurately incorporate the deformation mechanics into the solution. After the FFT of a real surface is calculated, the computational resources needed for the method are very small. Perhaps surprisingly, the trends produced by this non-statistical multi-scale model are quite similar to those arising from the GW and MB models.
Atomic Layer Deposition of Solid Lubricant Thin Films
Authors: Scharf T. W. , Prasad S. V. , Dugger M. T. , Mayer T. M.
Published: November 2008

Tungsten disulphide (WS2) and molybdenum disulfide (MoS2), which belong to the family of transition metal dichalcogenides, are well known for their solid lubricating behavior. Thin films of MoS2 and WS2 exhibit extremely low coefficient of friction (COF ∼0.02 to 0.05) in dry environments, and are typically applied by sputter deposition, pulsed laser ablation, evaporation or chemical vapor deposition, which are essentially either line-of-sight or high temperature processes. With these techniques it is difficult to coat surfaces shadowed from the target, or uniformly coat sidewalls of three-dimensional or high aspect ratio structures. For applications such as micromechanical (MEMS) devices, where dimensions and separation tolerances are small, and aspect ratios are large, these traditional deposition techniques are inadequate. Atomic layer deposition (ALD) is a chemical vapor deposition technique that could overcome many of these problems by using sequential introduction of gaseous precursors and selective surface chemistry to achieve controlled growth at lower temperatures, but the chemistry needed to grow transition metal dichalcogenide films by ALD is not known.
Adaptive Nanocomposite Films Exhibiting Low Friction in a Broad Temperature Range
Authors: Muratore C. , Voevodin A. A. , Hu J. J. , Zabinski J. S.
Published: November 2008

A hybrid magnetron sputtering/pulsed laser deposition process was used to grow nanocrystalline yttria stabilized zirconia (YSZ) embedded in an amorphous YSZ/metal matrix. This nanocomposite design reduced friction and improved the toughness of YSZ. Films containing both silver and molybdenum exhibited friction coefficients between 0.2 and 0.4 in air (40% relative humidity) against silicon nitride balls at temperatures between 25° C and 700 °C. Additional solid lubricants reduced the friction coefficient to <0.2 for over 10000 cycles at all temperatures. A multilayer film architecture was developed to further enhance the lifetime of the adaptive coatings. Electron microscopy, x-ray diffraction and x-ray photoelectron spectroscopy were used to correlate adaptive behavior at different temperatures to the composition and structure of the films.
Surface Treatments for Modifying the Tribological Behavior of Microsystems (Keynote)
Authors: Dugger Michael T.
Published: November 2008

The surfaces of microelectromechanical systems (MEMS) that have impacting and sliding contacts are frequently modified by coatings to improve the tribological behavior of the structural material. In silicon microsystems, chemisorbed hydrocarbon or fluorocarbon monolayers are commonly used to modify the surface energy of the oxidized silicon to resist water adsorption and adhesion. Thin conformal solid films can also be employed to improve the wear resistance of the structural material. The requirements of coatings for microsystems will be discussed in terms of tribological behavior, processing, operation and aging characteristics. Although contacting surfaces of polycrystalline silicon have arithmetic roughness of less than 50 nm, contact forces below 1 mN prescribe that real contact occurs at only a few asperities. Defects in the coatings, and interfaces that are deeply buried present opportunities for adsorption of reactive species and degradation of the coating over time. An understanding of the mechanical and chemical degradation mechanisms of tribological coatings is of primary importance for the reliable operation of microsystems. At the same time, relating composition and structure of the contacting surfaces to the tribological behavior is quite challenging due to the limited size and number of real contact spots. A variety of surface treatments for silicon microsystems have been investigated, including chemisorbed monolayers, vapor phase lubricants and hard coatings. The tribological behavior of polycrystalline silicon containing chemisorbed monolayers is dramatically influenced by water vapor in the environment during fabrication processes, storage or operation. Surface analytical tools and friction measurements using micromachined tribometers to understand the impact of coating degradation on the tribological behavior of microsystems are illustrated.
On the Evolution of Friction-Induced Nanostructures in Single Crystal Nickel
Authors: Prasad S. V. , Michael J. R. , Battaile C. , Kotula P. G. , Majumdar B. S.
Published: November 2008

We have investigated the fundamental phenomena governing the friction-induced microstructures in single crystal nickel. Friction measurements were made using a unidirectional linear wear tester against a hard Si3N4 ball so that deformation is confined to the softer Ni surface. To minimize the environmental effects on friction, we conducted the experiments in dry nitrogen atmosphere. A high precision rotary stage was designed and built to enable friction measurements to be made in specific crystallographic directions. Measurements were made on (100), (110) and (111) crystal faces. Focused ion beam (FIB) microscopy was used to prepare cross-sections of wear scars suitable for electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) analyses. The EBSD data revealed the formation of low-angle grain boundaries leading to the development of fine-grained equiaxed recrystallized substructues underneath the wear scars. The extent of subsurface deformation and the steady state friction coefficients were strongly dependent on the crystal orientation. At higher contact stresses, TEM analysis confirmed the formation of fine-grained equiaxed nanocrystalline grain structures. Subsequent friction tests on these nanostructured layers performed at much reduced contact stresses showed significant reductions in the friction coefficients. The role of the friction-induced nanostructures on the mechanisms of metallic friction is discussed.
Mechanical Analysis of the Damage of a Thin Polymeric Coating During Scratching
Authors: Demirci Ibrahim , Gauthier Christian , Fond Christophe , Schirrer Robert
Published: November 2008

Coating is a common way of improving the scratch behaviour of polymeric glasses. A thin coating will prevent the micro-scratches created by the roughness of a diamond tip at the surface of the macro-groove left on the substrate and allow recovery of the groove. The ratio of the thickness of the coating to the roughness of the tip is a critical parameter, which enables one to increase the scratch resistance in the case of a thin coating. A single value of the critical load cannot describe the damage behaviour of a coating on a polymeric material. It is generally assumed that cracking appears at the rear edge of the contact area and is related to the tensile stress, whereas we observed that cracking of the coating appears within the contact area. The mechanical behaviour of a coating on a viscoelastic material should be analysed in terms of the shape of the stress field, modified by the effect of the local friction between a scratching tip and the coat, where this local friction will depend on the roughness of the tip. Some numerical simulations were performed to attempt to elucidate the cracking mechanism.
The Study on Abrasive Wear of Carbon of High Vanadium High Speed Steel Compared With That of High Chromium Cast Iron
Authors: Wei Shizhong , Zhu Jinhua , Xu Liujie , Long Rui
Published: November 2008

It is studied the carbons abrasive wear property of high vanadium high speed steel compared with that of general high chromium cast iron (Cr20) in this paper. The vanadium content is 10% in the high vanadium high speed steel, and it is a kind of new wear material that has been studied in the past ten years. In the experiment the three materials were used to resist the abrasive wear of Al2O3, the wear test was conducted on a ML-10 abrasive wear-testing machine. The abrasive surfaces, cross-section and sloping -section surfaces were scanned by means of a SEM (JSM-5160LV) device. The typical morphology photos of VC and Cr7C3 were taken in course of abrasive wear, which not only describe the different abrasive wear property of the carbons in the two materials, but also make the cause of the excellent wear property of this HSS clear. The research results have showed that the service lives (V10) are three times longer than that of high chromium cast iron (Cr20). The excellent wear resistance of high vanadium high-speed steel depends on the characters of high hardness, lumpy morphology of VC which are scattered in hard matrix of HSS.
Nano-Particle Interaction During Chemical-Mechanical Polishing
Authors: Ng Dedy , Kulkarni Milind , Liang Hong , Jeng Yeau-Ren , Huang Pai-Yau
Published: November 2008

We investigate the particle adhering and removal processes during CMP and post-CMP cleaning. The mechanical interaction between abrasive particles and wafer surface was studied using a microcontact wear model. This model considers the particle effects between the polishing interfaces during load balancing. Experimental results on polishing and cleaning are compared with numerical analysis. This study suggests that during post-CMP cleaning, a combined effort in chemical and mechanical interaction (tribochemical interactions) would be effective in removal small particles during cleaning. For large particles, more mechanical forces would be more effective.
Effects of Tube Diameter on Frictional Characteristics of Carbon Nanotubes
Authors: Kawakubo Y. , Gotou M. , Toumatsu M. , Miyazaki K.
Published: November 2008

Frictional characteristics of carbon nano-tube powders were measured and compared with those of conventional solid lubricants, MoS2 and graphite. In linear one way sliding tests, a multi-wall CNT showed similar coefficient of friction with graphite. It was also showed that the larger the particle sizes, the smaller the COF for those powders. A sliding model considering CNT geometry was proposed.
Variable Valve Actuation Mechanism Using Magnetorheological Fluid
Authors: Hirani H. , Dani S.
Published: November 2008

A magnetorheological (MR) fluid based variable valve lift mechanism is presented. A test setup is designed to measure the frictional-torque and valve-displacement of a direct acting valve mechanism under various speed conditions. Results of valve lifts at different speeds and control currents are presented.
The Effect of Interaction Between Neighboring Asperity Contacts on Wear Mode Transition in Sliding Contact of Rough Surfaces
Authors: Tanaka Tomohisa , Yamanaka Chikara , Kyogoku Keiji , Nakahara Tsunamitsu
Published: November 2008

Concerning the final aim, that is to make clear the mechanism of the wear mode transition from mild to severe belong to the increase of contact pressure in adhesive wear, estimation of the yielding condition in subsurface under contact boundary between rough surfaces was attempted in this study. Especially the effects of interaction between neighboring contacts as well as relative sliding on the yielding area were focused. The contacts between asperities were modeled by the contact between two neighboring hard wedges with the parallel axes and soft plane to be simplified. These models were calculated by commercial FEM solver in 2-dimension. Additionally, the effect of the difference between the heights of two wedges on the yielding region was evaluated by comparing the result with that obtained from the simple model of two wedges with the same height in non-sliding contact. The results showed that the effect of the interaction between adjacent contacts and existence of relative slip motion give significant factors to the yielding state, on the other hand, the height difference between neighboring asperities affects little the determination of the yielding region.
Frictional Properties of Alkyl-Substituted Phthalocyanines Physisorbed on Graphite
Authors: Miyake K. , Hori Y. , Ikeda T. , Asakawa M. , Shimizu T. , Sasaki S.
Published: November 2008

The frictional properties of alkyl-substituted phthalocyanines physisorbed on the graphite substrate are investigated by atomic force microscopy in liquid condition. the frictional process of alkyl-substituted phthalocyanines physisorbed on the graphite substrate consists of two regions of “shear” and “wear”. In the “shear” process, friction force varies approximately as power law with exponent of 0.6–0.7 (Region I). On the other hand, friction force is maintained substantially constant in the “wear” process (Region II). The experimental data are qualitatively explained by the simplified model, which assumes that the alkyl-substrate and alkyl-alkyl interactions are approximated by Lennard-Jones interactions.
Deformation and Stability Analysis of Ultra-Thin Lubricant Films by the Long Wave Equation: Analysis Considering the van der Waals Force and Gas Pressure at the Liquid Surface
Authors: Fukui Shigehisa , Yorino Kazuya , Yamane Kiyomi , Matsuoka Hiroshige
Published: November 2008

To examine deformations of ultra-thin but continuum liquid film, the long wave theory was employed, which is the time-evolution equation for the shape and deformation of the thin liquid film and includes the surface tension and surface forces such as the van der Waals (vdW) force. By solving the linearized long wave equation considering the vdW pressure and gas pressures at the lubricant surface, deformations of the ultra-thin lubricant film caused by air pressure were obtained. Stability/instability of the liquid surface was analyzed as the growth and decay problem of the infinitesimal deformation of the liquid surface.
General Problems of Tribology of Thermal Sprayed Composite Coatings
Authors: Kharlamov Y. A. , Rahman Fazli , Chattha J. A. , Shevchenko A. V. , Kharlamov M. Y.
Published: November 2008

Many different methods of thermal spraying are used for deposition of coatings. The use of thermal spray technology in tribological applications is growing and will continue to grow. There is a need for a strategy or methodology for selecting a surface layer composition and structure and methods of their obtaining for a given tribological application. In this paper such a strategy is proposed and its elements are discussed.
Modeling Airflow and Particle Trajectories Near the Head/Disk Interface Region of a Small Form Factor Hard Disk Drive Enclosure
Authors: Goh H. J. , Damodaran M. , Ng Q. Y.
Published: November 2008

Airflow characteristics and particle trajectories inside a small form factor hard disk drive (HDD) enclosure is modeled by creating a complex unstructured mesh around the various geometrical artifacts in the HDD enclosure using a commercial flow-solver which solves the incompressible Navier-Stokes Equations. From this model insight on the airflow characteristics in the vicinity of the slider could be obtained. The effect of the read/write head on the global flow field is also addressed for typical disk operation conditions. The computed airflow patterns are then used to predict particle trajectories in the vicinity of head/disk interface (HDI), the knowledge of which has relevance for tribological aspects connected with the HDI region. The effects of gravity and thermal gradients on the airflow characteristics within the HDD enclosure are also considered. Knowledge of particle trajectories and interaction provide useful guidelines for HDD design and filter locations. Depending on the types of particles, these are likely to be subjected to gravitational and thermophoretic forces, or inter particle interactions. Particles of different materials and sizes are used to evaluate the effects of these forces, which influence the particle trajectories.
Rolling Noise and Wear Mode of Wheel on Railway
Authors: Obara T. , Ohyama T. , Kato K.
Published: November 2008

Rolling-noise between wheel and rail is a serious problem on the Japanese railway. The authors have reported that rolling-noise is affected by the roughness with about 10–50mm wavelength on a wheel surface. And they thought that two tribological factors increase the wheel roughness. The one is that a wheel surface wears out irregularly when the slipping between wheel and rail generates. The other is that the chemical elements of brake shoes transfer to the wheel surface. The authors investigate the characteristics of roughness produced by these two factors using a testing machine.
The Pressure and Film Thickness Distributions in Point Elastohydrodynamic Contact Under Dynamic Load
Authors: Panovko M. Ya.
Published: November 2008

Isothermal elastohydrodynamic (EHD) problem for dynamically loaded lubricated point contact is formulated and studied numerically. Mathematical formulation is based on the time depending nonlinear system of integrodifferential equations. In order to determine the location of the exit (free) boundary the problem is formulated as a problem of complementarity. The dimensionless system of equations and inequalities is solved using Newton method. Peculiarities of the influence of non-steady state (sinusoidal) loading on pressure and film thickness in the point EHD contact are shown.
The Characteristic Fractal Parameter for the Characterization of Rough Surfaces
Authors: Ge Shirong , Zhu Hua , Li Gang
Published: November 2008

The issues about the characterization of rough surfaces are always of concern to tribologist. Because the statistical parameters used conventionally are not ideal to characterize rough surfaces, it is very necessary to investigate the new characterization methods and characterization parameters. In this paper, the fractal geometry is applied, and a roughness parameter called the characteristic fractal parameter τ* is put forth by combining fractal dimension D and scale coefficient C. Its definition, geometric meaning and mathematical express are given. Four surfaces with different roughness formed by turning, milling, grinding and sandpaper polishing machining are characterized with the characteristic fractal parameter τ*. And the results of characterizing these surfaces are compared with that of Ra. It is proved that the characteristic fractal parameter is not only more objective but also more sensitive to characterize rough surfaces than the conventional characterization parameter Ra.
Flat Central Pressure in Circular Elastic Contacts Between High Order Surfaces
Authors: Diaconescu Emanuel , Glovnea Marilena
Published: November 2008

High order revolution surfaces are often used in electrical contacts/micro-contacts or in miniature thrust bearings. This paper advances general contact formulae for these bounding surfaces. In a particular case, these relations yield known Hertz pressure distribution and contact elements. Then, the contacts between fourth and sixth order surfaces are analyzed.
Elastic Contact Pressure Under Flat Punches Having Smooth Cross-Sections
Authors: Glovnea Marilena , Diaconescu Emanuel
Published: November 2008

Surface contacts modeled by a flat ended rigid punch pressed on an elastic half-space possess analytical solution only for circular and elliptical cross-sections. This paper extends analytical solutions to the class of punch cross-sections bounded by mathematically smooth curves and applies the theory to Cassini’s ovals contours.
Comparison of Aluminum Cold Strip Rolling Lubricant Additives
Authors: Riss Arnaud , Combarieu Robert , Montmitonnet Pierre , Deneuville Patrick
Published: November 2008

Strip rolling processes are conducted in the mixed lubrication regime, so that boundary additives are an essential feature of the rolling oil. Fatty alcohols are by far the preferred additives: why are they dominant, and what makes them so good for this particular application? A series of model lubricants have been formulated and tested first with the Plane-Strain Compression Test (PSCT) from RT to 200°C. Then some of the formulations have been studied on a high-speed experimental rolling mill. Conclusions from PSCT and rolling tests converge on several points. Fatty alcohols indeed outperform all other formulations; combining them with other molecules may degrade their action.
Numerical Simulation of Material Sub-Surface Defects in Rolling Contact Fatigue
Authors: Taraf M. , Ghanameh M. F. , Touati M. Mliha , Oussouaddi O. , Zeghloul A.
Published: November 2008

To ensure the safety and of reducing the costs of maintenances in railways systems, it is necessary to evaluate the life prediction of fatigue crack initiation in rolling contact fatigue starting from the defects. The influence of defects on the rolling contact fatigue was studied, we simulated two types of geometry of defect (circular and elliptic) and also we studied the influence of defects clusters. The stresses and deformations were analyzed in the vicinity of the defect. Calculations were carried out with four levels of loading with the code of finite elements ABAQUS-standard (version 6.3). The fatigue impact was evaluated by using the multiaxial fatigue parameter to estimate the rolling contact fatigue life.
Finite Element Analysis on Vibration Characteristics of a Reciprocating Sliding System
Authors: Chen G. X. , Zhou Z. R.
Published: November 2008

In this paper, a finite element method is applied to study the friction-induced vibration characteristics of a reciprocating sliding system. Finite element results are compared with vibration frequencies from an experimental test and are found to have a good agreement. Numerical results show that vibration modes corresponding to test squeals have the feature characteristic of vibration coupling in the normal and friction directions.
A New Implementation of Reynolds Equation for Analyzing Mixed EHL
Authors: Ichimaru K.
Published: November 2008

A new expression of Reynolds equation with no apparent oil-wedge term and the CIP scheme are utilized for analyzing mixed or micro EHL. A quite stable convergence has been realized in developed numerical procedure, as the fault of conventional Reynolds equation that it includes redundant terms which should be cancelled out regarding an effect of moving asperity slope on film establishment was eliminated.
The Role of Synovial Fluid Properties in a Dynamic Hip Joint Simulation
Authors: Pieterse N. , de Vaal P. L. , Sandrock C.
Published: November 2008

Accurate mathematical modelling of joints is directly related to the need to obtain a better fundamental understanding of the role that elements of the system have on the dynamic tribological behaviour of the component it represents. Simulation models also make a contribution towards reduction of the cost of in-situ experimentation in biotribological systems, as well as overcoming difficulties with ethical and practical problems related to in-situ testing. The aim of the current work is to report on the results obtained from a dynamic model of a human hip joint. The model is used to investigate the tribological performance of the synovial fluid over a varying range of operating conditions — specifically pressure, temperature and varying load conditions. The model is based on a minimum of empirical relationships, preferring relationships grounded in solid fundamental theory. This reduces the number of parameters that can be modified in the model and ensures that predictions made are not based on external manipulations.
Huber-Mises-Hencky Equivalent Stress: A Surface Failure Indicator
Authors: Irimescu Luminita , Diaconescu Emanuel , Berthier Yves
Published: November 2008

The microslip phenomenon takes place in both rolling and sliding contacts. In the latter case it occurs in fretting, when the main cause of failure is surface degradation. Both cases are experimentally investigated in order to visualise microslip initiation. The position of the first obtained microslip marks is in good agreement with positions of maximum Huber-Mises-Hencky stress. These results associate the micro-slip initiation with contact stress field and proves the ability of Huber-Mises-Hencky stress to assess the occurrence of failure at the interface of an elastic contact in sliding or rolling motion.
Model Based Method for a Sophisticated Dimensioning of Clutch Systems in View of the Occurrence of Frictional Vibration
Authors: Albers A. , Karrar C.
Published: November 2008

Occuring frictional induced vibration of dry clutches and brakes can lead to NVH (Noise Vibration Harshness) and functional disorder of clutches in machines and automobiles. This behaviour is not accepted by the costomer. In consequence the system components are often overdimensioned, which is not acceptable in reasons of economy and a decreasing mounting space. To solve these problems a model based method has been developed, which allows a sophisticated dimensioning of clutch systems in view of the occurrence of frictional vibration and transmittable torque.
A Unified Approach to Contact and Structural Fatigue
Authors: Kudish Ilya I.
Published: November 2008

A unified model of fatigue that is applicable to a variety of mechanical in nature fatigue phenomena including contact and structural fatigue is introduced. The model considers two- and three-dimensional stress states. The model is based on crack mechanics, kinetics of crack propagation, and statistical treatment of material defects. The foundation of the model follows from the analysis [1, 2], a model of contact fatigue [3], and the asymptotic formulas for the stress intensity coefficients (see [4]) developed earlier. The model takes into account the local stress distribution, initial statistical distribution of defects versus their size, defect location and crack propagation directions related to the specific stress state of the material, material fatigue resistance parameters, etc. The main assumptions used for the model derivation and their validity are discussed.
Modification of Microscopic Zirconia Surface Structure for Improvement in Tribological Characteristics of UHMWPE-on-Zirconia Sliding Pair for Joint Prostheses
Authors: Sawae Y. , Murakami T. , Qiwei H. , Sawano T.
Published: November 2008

In this study, authors attempted to improve tribological characteristics of ultra-high molecular weight polyethylene (UHMWPE)-on-zirconia sliding pair for joint prostheses by modifying a microscopic structure of ceramics articulating surface. Experimental results indicated that the friction coefficient of UHMWPE-on-zirconia sliding pair could be lowered by inhibiting a formation of crystal grain structure on an articulating surface during a heat treatment.
A Study of the Tribological Properties of Bound Plus Mobile Phase Lubricants With QCM and MEMS Sidewall Tribometers
Authors: Hook Adam , Neeyakorn W. , Krim Jacqueline , Dugger Michael T.
Published: November 2008

Long chain alkylsilane monolayers used in the release process to protect MEMS devices from adhesion due to water adsorption also provide a very low coefficient of friction. One such monolayer, perfluorodecyltrichlorosilane (PFTS) has been shown to have very good thermal stability, keeping a water contact angle above 100° in air up to 400°C. [1] The monolayer will however wear under mechanical rubbing, causing the MEMS device to irreversibly adhere rendering it useless. Vapor phase lubricants (VPL) used in conjunction with self-assembled monolayers. may be the key to extending the life of rubbing contacts in MEMS. It is believed that the temperature characteristics of the VPL and its ability to replenish itself will provide a sufficient protective layer for the PFTS and extend the life of MEMS devices well into the range where their use in military and industrial applications can be fully realized. Here we have studied two vapor phase lubricants, tricresyl phosphate (TCP) and t-butyl phenyl phosphate (TBPP) on a PFTS monolayer. Previous work done with a quartz crystal microbalance has suggested that TBPP would be a better lubricant than TCP. [2] We have evaluated the effectiveness of these lubricant systems using a MEMS sidewall tribometer in a vacuum environment. Relationships between lubricant composition, behavior in an isolated asperity contact in the quartz crystal microbalance studies, and performance in a MEMS friction device will be discussed.
The Cooperative Effects of Protein and Lipid on Wear Behavior of Ultra-High Molecular Weight Polyethylene
Authors: Sawae Y. , Murakami T.
Published: November 2008

The cooperative effects of protein and lipid on the wear behavior of ultra-high molecular weight polyethylene (UHMWPE) was examined in laboratory wear tests with a multidirectional sliding pin-on-plate wear tester. Results indicated that the protein and lipid composition of lubricant used in the wear test had substantial effects on the wear behavior of UHMWPE sliding against a metal counter face. Not only the amount of protein and lipid content but also a preparation procedure of the lubricant might affect the UHMWPE wear.
A Scanning Method to Study the Influence of Roughness, Microwaviness, and Lubricant Thickness Variation on Slider Dynamics
Authors: Duwensee Maik , Knigge Bernhard E. , Baumgart Peter , Talke Frank E.
Published: November 2008

Flying height modulation maps and microwaviness maps are obtained by using laser Doppler vibrometry (LDV) and acoustic emission (AE) transducers which are moved radially over the complete disk surface. The sensitivity of the acoustic emission measurement is improved by applying a current to the write element, thereby increasing pole tip protrusion. Disk and slider displacement maps are obtained using a radially scratched disk. Acoustic emission maps are presented for a scratched disk and for a non-scratched disk. For the non-scratched disk, AE maps are obtained with an inactive and active write element.
Geometry and Speed Effects on the Performance of the Herringbone Grooved Gas Lubricated Journal Bearing
Authors: Foster D. J.
Published: November 2008

The plain gas lubricated journal bearing is dynamically unstable. The addition of grooving on the bearing surface has been found to overcome this instability. In particular, the herringbone groove pattern has been found to provide damping with increase of static stiffness. The effect of the available geometry characteristics on performance is computed from solution of the compressible Reynolds equation. The geometry features examined are groove angle, and the ratios:- groove depth to clearance, groove-to-land width, axial groove length to bearing length and bearing eccentricity. The performance is determined over a range of compressibility numbers.
High-Temperature High-Speed Tribometer With Complex Motion
Authors: Heshmat Hooshang , Tomaszewski Michael J. , Heshmat Crystal , Walton James F. , Jahanmir Said
Published: November 2008

Complex motions and wide variations in relative surface velocities are likely to be experienced in mechanical systems such as an engine (e.g., piston rings, wrist pins and crankshaft main bearings in a piston type engine). Currently available tribometers use simple motions and often a constant speed. A new tribometer is designed with the capability of three types of motions: (1) unidirectional rotary motion (similar to a conventional pin-on-disk tribometer), (2) reciprocating sliding motion, and (3) complex multi-directional motion that can be achieved when the disk rotates and the pin reciprocates along a linear path. Depending on the pin location with respect to the center of the disk, the reciprocation frequency, and the rotational speed of the disk, a wide range of complex motions are possible. Tribological testing can be performed at contact loads up to 400 N, at speeds up to 80m/s, and temperatures of 600 °C in superheated steam. Due to complex motions, the measurement of friction force becomes challenging. To properly monitor the normal force and the friction force along two orthogonal axes, three force transducers are used. This unique design allows for the determination of tribological performance of advanced materials and coatings under conditions that simulate those encountered in small steam engines currently under development.
A Simple Investigation Method of Rheological Properties of Molecular Substances
Authors: Diaconescu Emanuel , Miron Onciul Oana , Balan Mircea
Published: November 2008

This paper shows that rheological properties of molecular liquids, relevant for EHD contacts, can be determined experimentally on molecular solids. A shear head is developed to measure the viscosity and limiting shear stress of solid paraffin. Preliminary results show that this idea is feasible.
Lubricity Synergism in Boundary Lubrication
Authors: Sivebaek Ion M. , Hansen Nadja L. , Johansen Kenneth H.
Published: November 2008

Dimethyl Ether (DME) has been known as a ultra clean smokeless fuel for diesel engines for over a decade now. A significant challenge is to ensure full lifetime for the diesel engine injection equipment when handling the low boiling point DME as this fuel has very low viscosity and lubricity. Pressurised lubricity evaluators show that boundary lubrication additives increase DME lubricity significantly but recent work indicate that adequate performance in quasi-boundary lubrication is necessary for reducing the wear effectively in real pumps. In this regime where the pump surfaces are only separated by a few molecular layers fuel molecular structure and viscosity seem to be important properties. Earlier work showed that addition of low lubricity alkanes raised the high lubricity of a boundary lubricant to an even higher level. In the present work the long linear alkane n-hexadecane was added to DME in different proportions. The lubricities of the blends do not show any minimum but reflect the lubricity of pure n-hexadecane. It is not conclusive whether DME is a boundary or a quasi-boundary lubricant but clarifying tests are currently in progress.
Influence of Die Surface Texture on Tribological Performace for Tube Hydroforming
Authors: Ngaile Gracious , Alvarado Angel
Published: November 2008

Tube hydroforming (THF) is an innovative method with a potential to form parts of various geometric complexities from tubular materials using pressurized fluid as a soft die. The process has numerous advantages over stamping: a) high strength to weight ratio, b) part consolidation, c) accuracy, d) improved stiffness, e) reduced scrap rate, and f) design flexibility. Optimal utilization of this method, particularly for hydoforming of complex parts, could be realized if better lubrication systems are devised. In an attempt to develop robust lubrication system for THF, the influence of textured die surfaces on tribological performance were studied through numerical modeling and experimentation. The pear shaped tooling developed by the author was used for evaluating the performance of hydroforming lubricants at the expansion zone. The effects of textured surfaces imprinted on the pear shaped dies were studied.
Characterization of Oil Film Control Forces Under Active Lubrication Regime
Authors: Santos Ilmar F. , Christensen Bo F.
Published: November 2008

Journal bearings under active lubrication regime are controlled by servo valves and well-tuned feedback control laws. The servo valves dynamically modify the journal pressure distribution generating active oil film forces. Such forces are dependent on the following parameters: Sommerfeld number, bearing pre-load factor, orifice diameter, excitation frequency, feedback control gain and dynamic parameters of the servo valves, i.e. their natural frequencies, damping factors and pressure-flow coefficients. The theoretical and experimental characterization of such active forces is the main focus and the main contribution of this work. The theoretical analyzes are based on the Modified Reynolds’ equation for active lubrication. The experimental analyzes are carried out by using a special test rig, designed to investigate the behavior of tilting-pad bearings (TPJB) under active lubrication. Relative good agreement between theoretical and experimental behavior of the active oil film forces as a function of the excitation frequency and control gain is achieved. Limitations of the characterization procedure is critically discussed in order to explain some discrepancies between theoretical and experimental results.
Biotribological Behavior of Boronized Tungsten
Authors: Ingole S. , Ribeiro R. , Juan O. , Liang H. , Usta M. , Bindal C. , Ucisik A. H.
Published: November 2008

Boronized tungsten is one of the potential biomaterials due to its high corrosion resistance, and high strength. Present investigation encompasses the wear behavior of this material in dry condition as well as in simulated body fluid (SBF). The pin-on-disc reciprocating tribometer was utilized to conduct the wear tests. The worn surfaces were analyzed using an atomic force microscope (AFM). Results showed that not only the SBF reduces the friction, but also shortens the initial break-in period. This presentation discusses the wear mechanisms of boronized tungsten affected by SBF.
Tribological Performance of Cell-Treated Nickel Matrix
Authors: Shi Bing , Kuhn Thomas , Duffy Lawrence , Liang Hong
Published: November 2008

In this study, effects of cell culture on surface properties, and tribological performance were investigated. The wettability of Ni under dry and lubricated conditions, as well as cell-cultured specimens was evaluated. The tribological performance of these samples was compared using a pin-on-disk tribometer. Dry friction tests were conducted and compared with the bovine serum albumin (BSA) solution lubricated Ni and the cell culture media lubricated Ni. The lubrication behavior was discussed and new biofluid mechanisms were proposed.
Effect of Colloidal Probe Random Surface Features on Adhesion
Authors: Yang Seung Ho , Hsu Stephen M.
Published: November 2008

We have uncovered the fact that colloidal probes often have random surface features which when not properly accounted for, can significantly affect the magnitudes of the measured adhesive forces using atomic force microscopes (AFM). Colloidal probes have been used to measure the pull-off forces between the probe and surfaces. We prepared a series of colloidal probes by attaching glass spheres (radii of 3.3 μm to 17.4 μm) to the end of AFM cantilevers. Adhesive force between the probes and a silicon wafer surface was measured using an AFM under various loads from 6 nN to 100 nN in dry air. Results showed that the values of the pull-off forces did not correlate with the radii of the probes. Direct imaging of the glass sphere surface using a sharp tip revealed substantial random surface features which altered the size of real contact areas. We extracted the load-bearing areas from the topography data and used them to normalize the adhesion data. The measured adhesive force, after being normalized, was found to be independent of the load and the sphere radii, in agreement with prevailing contact mechanics theory.