Tribology

Recent studies in tribology show that deterministic surface texture enhances the tribological performance of parallel sliding lubricated contacts in terms of reduction in friction and an increase in load carrying capacity. This paper presents an experimental study to assess the effect of texture size and height on hydrodynamic performance of parallel sliding thrust bearing. Positive deterministic textures of different size and height with circular, elliptical, square and triangular cross-sections are fabricated for investigation. The experiments are performed using an in-house developed thrust bearing apparatus with constant flow lubrication system. The most important finding is that all the textured surfaces produce lower frictional torque and higher bearing clearance as compared to the untextured surface under varying load and speed. From the test results, it is found that with same texture height, specimens having small texture size perform better tribological characteristics followed by medium and large size textures. Furthermore, it is reported that with same texture size, a higher value of texture height is promising better hydrodynamic performance for all shapes.

Several studies have shown that the coefficient of friction of self-mated silicon nitride in water decreases from an initially high value to about 0.002 after a certain run-in period. Since the worn surfaces become extremely smooth, the low friction is attributed to the initiation of hydrodynamic lubrication by a thin water film at the interface. The possibility of mixed lubrication , i.e., hydrodynamic lubrication by water and boundary lubrication due to the presence of colloidal silica on the wearing surfaces, has also been proposed. The purpose of our study is to investigate the influence of load, speed, and surface roughness on the duration of the run-in period. The results confirmed that a low coefficient of friction is obtained following a run-in period when a wear scar of sufficient size is developed to reduce the contact stress. The run-in period, during which the coefficient of friction is fairly high, was shorter for smoother surfaces and at higher loads and speeds. The low friction behavior was found to be unstable and occasional high friction spikes were observed. The surfaces of the wear tracks and wear scars contained a series of striations parallel to the sliding direction and exhibiting plastic deformation, delamination and fracture. The striations that appeared to be associated with the high friction spikes, could form as a result surface film breakdown. Although these results are consistent with the proposed mechanisms of hydrodynamic lubrication or mixed lubrication, it is proposed that the low friction behavior may be also related to fundamental interactions between two hard and elastically deforming surfaces covered with hydrogen-terminated oxide films.

The dynamics of pico sliders is investigated during scratch impact using laser Doppler vibrometry. Air-bearing frequencies and damping of the pitch-2 frequency are studied as a function of disk velocity for lubricant thickness values of 1.6 nm, 1.0 nm and 2.0 nm. Time-frequency analysis is performed to study the instantaneous air-bearing frequencies.

Metal matrix composites with high interface density are produced via severe plastic co-deformation of multiphase alloys. 1–15 Corresponding compounds are first prepared by liquid or powder metallurgy3–12 or through restacking solids of different composition. 2 Subsequent extreme straining, to promote intense microstructure refinement, proceeds by wire drawing, ball milling, accumulative roll bonding, damascene forging, equal channel angular extrusion, friction, or highpressure torsion. 7

In this study, the thermal, dynamic-mechanical and tribological behavior of nanocomposites of a photocurable epoxy-acrylate resin and multiwalled carbon nanotubes (MWCNT) are investigated. A route consisting of a combination of sonication, mechanical and magnetic stirring is used to disperse 0.25-0.75 wt. (%) MWCNT into the resin. Two photocuring cycles using 12 hours and 24 hours of UV-A radiation are studied. The storage modulus, the loss modulus and the tan delta are obtained by dynamic mechanical analysis. Thermal stability is investigated by thermogravimetry, morphology by transmission electronic microscopy (TEM) and tribological performance using a pin-on-disk apparatus. The results indicate an increase in stiffness and higher ability to dissipate energy, as well as a shift in the glass transition temperature for the nanocomposites. The addition of nanofillers also decreased friction coefficient and wear rate of the nanocomposites but did not change the observed wear mechanisms.

The aeration of an oil film flowing between the faces of two closely spaced circular plates (one stationary, and one rotating) is examined experimentally, numerically, and with an improved lubrication model. The gap between the plates is small compared to their radii, making lubrication theory appropriate for modeling the flow. However, standard lubrication boundary conditions suggested by Reynolds (1886, "On the Theory of Lubrication and its Application to Mr. Beauchamp Tower’s Experiments, Including an Experimental Determination of the Viscosity of Olive Oil," Philos. Trans. R. Soc. London, 177, pp. 157-234) of p = 0 and pn = 0 (Dirichlet and Neumann conditions on pressure) at the gas-liquid interface do not allow for the inclusion of a contact line model, a phenomenon that is important in the inception of aeration. Hence, the standard theory does not adequately predict the experimentally observed onset of aeration. In the present work, we modify the Neumann boundary con...

Dry abrasive wear performance of five plain weave carbon fabric (CF) reinforced Polyetherimide (PEI) composites, developed with increasing CF contents (in the step of C10 vol%) is reported in this paper. It was observed that composite reinforced with 65 vol% CF (IP 65) exhibited the best tensile and shear strength and closely followed the leader (IP 75) in flexural strength. IP 65 when abraded against silicon carbide paper showed highest wear resistance (W R) and lowest friction coefficient (m) among all composites. The composites IP 85 and IP 40 containing highest and lowest amount of CF respectively showed least enhancement in strength properties and poorest wear performance. Parallel studies on the influence of fabric orientation with respect to the sliding plane and direction, on W R showed that when CF was oriented parallel to the sliding plane, it had poorest wear resistance. The performance improved for the composites when fabric was oriented normal to the plane. The parallel or anti-parallel orientation of warp or weft fibers with respect to sliding direction showed marginal changes in friction and wear performance. Wear mechanisms were suggested and strongly supported by worn surface analysis using SEM. Efforts were also done to investigate the wear-property correlation. It was observed that the W R was directly proportional to the product of interlaminar shear strength (I s) and elastic modulus (E). Fairly good linearity was shown for specific wear rate (K 0) as a function of factor (mP/I s E) where m is coefficient of friction and P is the normal pressure (N/mm 2).

Potential applications of diamond-like carbon (DLC) coatings range from precision tools and biomedical implants to micro mechanical devices and engine components. Where uniform coatings are required on substrates with complex geometries, plasma enhanced chemical vapour deposition (PECVD) is often a preferred deposition method. As a non-line of sight process, the geometry of the substrate is often considered negligible. For this reason analysis of PECVD coatings, such as amorphous carbon, has mostly been concerned with reactor deposition variables, such as bias voltage, pressure and gas ratios. Samples are therefore usually prepared and positioned to minimise the influence of other variables. By depositing nominally similar DLC films on silicon samples positioned horizontally and vertically on the reactor cathode plate it was possible to examine the variations in the coating characteristics and mechanical properties that occur due to the geometry of the substrate being coated. Topographic measurements and analysis of bonding structures revealed significant heterogeneity in the coatings. Electron microscopy showed variation in surface structure as well as thickness disparities of up to 50% in the vertical sample. Atomic force microscopy showed roughness, Ra, varied from 0.37 nm to 15.4 nm between samples. Raman spectroscopy highlighted variations in the sp2/sp3 bonding ratios whilst micro wear tests demonstrated how these variations reduce the critical load performance. These effects are explained in terms of the deposition mechanisms involved and are related to variation in deposition species and geometrical field enhancements within the deposition chamber. Improved understanding of these local variations will aid in the optimization of coatings for complex substrate geometries.

We propose a microphysical theory of the triboelectric effect by which mechanical rubbing separates charges across the interface between two surfaces. Surface electrons are treated as an open system, weakly coupled to two baths, corresponding to the bulk materials. We show that work can be extracted from the motion-induced population inversion of fermions, thus extending and generalizing Zel'dovich's theory of bosonic superradiance. We argue that this is consistent with the basic phenomenology of triboelectrification and triboluminescence as off-equilibrium processes.

The frictional response of a multi-component phenolic-based friction material is highly complex under a set of variable loads and speeds. The present paper discusses the sensitivity of friction coefficient () of friction composites containing synthetic graphite with different particle sizes (with similar crystallinity range) to braking pressure and sliding speed. The friction studies were carried out on a sub scale brake-testrig, following 4 loads × 3 speeds experimental design. The best combination of performance properties was observed for the composite containing synthetic graphite with an average particle size of 410 m. Other particle sizes which resulted in good performance were 38 and 169 m. Very fine particle sizes were not beneficial for desired combination of performance properties. Regression analysis of following an orthogonal L 9 (3 × 3) experimental design method revealed that the first order influences of sliding speed and braking pressure were significant. When all the combinatorial influences of braking pressure and sliding speed are taken into account together their simultaneous effects would be most effective in the range of graphite particle size ∼80-250 m.

Mineral oil based lubricants are generally used in hydrodynamic journal bearing. These lubricants are toxic, non biodegradable and harmful for the environment. Vegetable oil being biodegradable and non-toxic has emerged as an alternative lubricant. This paper reviews recent researches related to biodegradable, environment friendly vegetable oil based lubricant and its application in hydrodynamic journal bearing. Important physicochemical properties of biolubricant for hydrodynamic journal bearing have also been discussed in the paper. Challenges relating to the usage of vegetable oil based biolubricant along with available mitigation strategies are also highlighted. Based on the study it can be concluded that chemically modified vegetable oil along with properly selected additives can effectively replace conventional lubricants.

Nickel-titanium (NiTi) alloys combine several remarkable characteristics, among them are shapememory, superelasticity, great strain recovery, good biocompatibility, and corrosion resistance. These render them well suited to a wide range of medical applications, such as cardiovascular stents, laparoscopy, and dental applications such as NiTi endodontic files (EFs) used for root canal treatment, which are the focus of this work. Unfortunately, fatigue-induced and incidental failure of NiTi EFs is not uncommon, which may lead to severe medical consequences. Here we examine the effects of cobalt coatings with impregnated fullerene-like WS 2 nanoparticles on file fatigue and failure. Dynamic x-ray diffraction, nanoindentation and torque measurements all indicate a significant improvement in the fatigue resistance and time to breakage of the coated files, stemming from reduced friction between the file and the surrounding tissue. These methods are possibly applicable to a variety of NiTi-based medical devices where fatigue and consequent failure are of relevance.

Lubricant accumulation on the slider's surface of a hard disk drive (HDD) has a detrimental effect on its read/write performance. Air flow through the slider-disk clearance moves some of the lubricant from the air-bearing surface (ABS) toward the slider's lateral walls where it accumulates. In this article, we show by numerical simulations that the lubricant accumulation characteristics are strongly dependent on the slider's flying height, skew angle and ABS design. The lubricant flow on the slider's surface is quantified numerically. Air shear stress, air pressure and disjoining pressure are used as driving forces in the simulations. The lubricant thickness profile and volume evolution are calculated for two states of the HDD: operating and at rest. In the first state, lubricant is driven by air shear stress toward the trailing edge of the slider where it accumulates on the deposit end. In the second state, lubricant from the deposit end flows back into the ABS driven by the action of disjoining pressure. Lubricant accumulation on the four lateral walls of the slider is taken into account. The lateral walls are unfolded to study the flow using a two-dimensional lubrication model. The effects of flying height, skew angle and slider design on the accumulation removal of lubricant from the ABS are determined for the two states of the drive. Keywords Air bearings Á Lubricant transfer Á Head–disk interface Á Hard disk drive

Machine dynamics can contribute to a difference between results in coefficient of friction, vibration level and wear rate of the same tribo-couple concerning the compliance of the support provided to a sliding counterbody. The aim of the present work is revealing the effect of loading system inertia on laboratory tests results. A developed pendulum-type tribo-tester was used for testing ceramicceramic, ceramic-metal and metal-metal sliding contact combinations. Diamond-like, AlTiN, TiCN and AlCrN/Si 3 N 4 PVD coatings and bare EN X30WCrV9-3 steel disks were tested against yttria-stabilized zirconia and EN 100Cr6 steel balls. Discussion on the mechanisms of materials degradation is based on SEM and EDS observations. It was found that inertia of loading system influences compaction of wear debris.

In order to explore the possible synergetic action of a combination of low and high-temperature solid lubricant, nickel-base composites containing nano-powders of silver and hBN were prepared by powder metallurgy (P/M) method. The silver content was varied from 8 to 20 wt.% while keeping the hBN content at a fixed level of 8 wt.%. The friction and wear properties of composites were investigated in the range from room temperature to 600 • C by carrying out dry sliding wear tests against a ring made of AISI52100 steel using a flat-on-flat configuration under a constant load of 20 N and fixed sliding speed of 1 m/s. The hardness of the composites was found to decrease with addition of solid lubricants and it has been attributed to the poor sintering characteristics of hBN. The friction coefficients were observed to decrease with increasing temperature. However, friction coefficients of silver and hBN containing composites were observed to be lower than the base alloy having no lubricant at all the temperatures which has been attributed to the presence of solid lubricants and their synergy. The presence of Ag and BN at the worn surface was confirmed by XRD analysis.

The development of aerodynamic foil bearings in the past decade is due, for a major part to environmental reasons because: first, air is a clean lubricant and second foil bearings can be used in very critical thermal environment: air has a poor sensitivity to high temperature changes. Foil bearings are often used for very high velocity turbines. Experimental studies have shown the capability of foil bearing to work under rather high load capacity with good dynamic behavior. Numerical simulations are now able to predict with a good accuracy foil bearing load capacity. They take into account foil deformation and dry friction between foils. For dynamic simulation, dry friction has been taken into account only through damping coefficient. As damping is not completely similar to dry friction, this paper is a first attempt in taking account its effect in the foil bearing dynamic behavior. A non-linear model, coupling a simplified equation for the rotor motion to both Reynolds equation and foil assembly model is described. Then the dynamic behavior, for a given unbalance is studied. For different values of friction coefficient, the rotor trajectory is studied when velocity increased. For low and high friction coefficient, the dynamic behavior shows critical speeds. For medium values (between 0.2 and 0.4), these critical speeds disappear. This work outlines that it is possible to optimize the friction between the foils in order to greatly improve the dynamic behavior of foil bearings. With a detailed analysis of these first results we propose primary physical explanation of this phenomena. r

Raman spectroscopy of solid lubricant coatings during high temperature (300-700 • C) wear testing was employed for real-time correlation of sliding contact surface chemistry to the measured friction coefficient. Two coatings were investigated in this work -MoS 2 and VN-Ag. Immediately prior to failure of the MoS 2 coating at 350 • C, molybdenum trioxide was detected in the wear track, and an increase in friction coefficient and ultimate failure of the coating was associated with buildup of the abrasive oxide compound. For the VN-Ag nanocomposite coating, in situ Raman analysis of the contact surface during heating revealed the appearance of silver vanadate compounds at a temperature of 375 • C. At higher temperatures, competitive evolution of different silver vanadate phases (i.e., Ag 3 VO 4 , AgVO 3 ) was observed. For the conditions examined in this work, the wear process at 700 • C inhibited formation of AgVO 3 in the sliding contact, as determined by comparison of the composition of the wear track to that of the adjacent, unworn coating surface. Additionally, the composition of the wear track was significantly different after the sample had cooled sufficiently to allow handling for post-test surface characterization with conventional Raman, XRD, and SEM techniques, further illustrating the utility of in situ diagnostics for identification of active lubricant phases during wear tests. This ability to characterize surfaces during wear tests at elevated temperatures fills an important gap left by current in situ tribology techniques that are currently used to provide insight on mechanisms governing the performance of solid lubricant film materials.

In this study, compression tests were conducted to determine the flow behavior of various types of Plasticine. True stress-true strain relations are presented in the form of a well-known power law equation. It is shown that the strength coefficient and the strain hardening exponent vary significantly among the Plasticine with different colors commercially available. Furthermore, since three dimensional simulations require arranging slabs of alternating colors to form a grid pattern, two different colors, exhibiting similar flow characteristics, are identified. The flow behavior of the composite model is usually not the same as that of the individual colors. The results presented in this paper allow selection of the type of Plasticine which most closely resembles the strain hardening characteristic of the actual metal, thereby satisfying the "similarity condition" of the Physical Modeling Technique.

The rolling process had been used in every aspect of our life. Various types of sections like tee, angle, channel, railway track, sheets, foils of different mate-rial are made by rolling process. The quality of the product depends upon the various characteristics of rolling parameters. At the junction, the key role played by lubricants for saving energy and properties of the material in contact. Re-searchers are putting continuous efforts into the tribological analysis and developing new lubricants for the rolling process according to the material. The authors had reviewed the lubricants used in different rolling processes and found out a diverse range of lubricants. Various ecologically safe and effective lubricants had been reviewed. Lubrication performance testing tribometer for testing of tribological properties of lubricants had been reviewed. Hydrodynamic, mixed and boundary lubrication mechanisms had been found in different rolling conditions. The use of lubricants was found ...

The development of railway wheel steel grades has gone towards higher strength to enhance rolling contact fatigue resistance and ability to withstand thermally induced damage throughout the service lifetime. In this study a recently developed wheel steel material for passenger trains containing high levels of manganese and silicon, approximately 1 wt% of each, was tested in low cycle fatigue at different total strain amplitudes. In addition, monotonic tensile and Charpy V-notch impact testings in the temperature range −60 • C to 180 • C were performed. The results were compared to another steel grade commonly used in Europe for railway wheels. The low cycle fatigue results show similar cyclic lifetime N f , and fatigue stress amplitude development for both materials, but the highly alloyed steel exhibits reduced cyclic softening and hardening during the fatigue life and is in this respect more stable in its behaviour. As is typical for pearlitic-ferritic steels both materials show a pronounced monotonic strain hardening. It was concluded that the increased levels of manganese and silicon have minor effects on monotonic behaviour but substantial influence on cyclic behaviour at ambient temperatures. At increased temperatures, though, there are indications of additional effects on monotonic behaviour. However, the high temperature properties have to be investigated further to gain full understanding of mechanisms and effects.

We examine the combined effect of variable viscosity, velocity slip, and the couple stress lubricant on a finite journal bearing. In our model, we utilize the Stokes micro-continuum theorem, the Barus formula, and an artificial (homogeneous) slip surface to improve the lubrication performance. Three cases of slip have also been considered: on the journal, the bearing, and both journal and bearing. The finite difference method is used to solve the equations numerically. The results indicate that the highest pressure occurs with slip on the bearing, and the lowest pressure occurs with slip on the journal. A high piezo-viscosity enhances the pressure and load-carrying capacity. Also, the slip parameter improves the load-carrying capacity. With slip on the bearing only, the frictional parameter decreases significantly.

The contact problem is considered for a system of bodies subject to wear on a common base. The deformation properties of the bodies and the base are described by the Winkler model. The problem is reduced to a system of ordinary differential equations and an integral equation of hereditary type with difference kernel. The solution of the problem is constructed with the use of the Laplace transform. The asymptotics of the solution at large times is studied. The continuity conditions for the contact of each of the bodies with the base are derived.

A planetary trains for multi-speed is mainly used for automation in industries of automobile. A planetary
gear train is represented by a graph. It is identified by (i) number of vertices and their connectivity (ii) number of edges and their types and values (iii) fundamental circuits, their size and adjancy. Connectivity of individual link is a property characteristic of kinematic chain. It is possible to identify a planetary gear,therefore of using sets of labele (decimal numbers representing connectivity ) of individual link. The
connectivity of vertices , edges values and circuit values, related to design invariants which in turn indicates the possible behavior of the gear train ( for example capacity of power transmission, speed ratio and power carculation). For a specified degree – of – freedom a number of planetary gear kinematic chain (PGKCs) are selected and hence planetary gear trains (PGTs) can be formed with a given number of links
and joints so that designer must be able to select to select the best train from the view point of say velocity ratio and capacity of power transmission, space requirements etc. Synthesis of planetary gear kinematic chain and planetary gear trains has been studied(1-9). Almost all reported work deals with only
identification of distinct chains. Besides providing an atlus of chains, this in itself does not provide any help to designer in the selection of best possible gear train. In the present paper a simple method based of circuit property ( based on link-link shortest path distance and degree of links) is presented to determine the topology values of power transmission efficiency and topology power transmission capacity of five-links PGKCs and their distinct inversions

An iron oxide layer (mixture of Fe 3 O 4 and FeO) was formed by water-vapor treatment on tool steel plates. Bearing steel cylinders were slid against the plates in PAO with and without 1% zinc dialkyldithiophosphate (ZDDP) at 80 1C. The friction coefficient was below 0.06-0.08 with ZDDP, which is more than 20% lower than that without ZDDP and about a half of a steel/steel contact under the same condition. The formation of multi-layered tribofilm of 30-130 nm on the iron oxide was identified by TEM. The bottom part of the tribofilm is a layer of 10-30 nm that contains Zn, Fe, S, P, and O with a gradient composition, where distribution peaks of Zn and S were found by EDX.

The mechanism that is discussed in this study is cardan shaft. The main objective of the proposed and completed research within the presented work was diagnostic of bearing assembly at joints of cardan shafts, which was performed in order to define the overall reliability of shafts. Presented reliability model of cardan shafts is based on an examination of diagnostic size of the bearing assembly on cardan joints. This document presents a difference between reliability of cardan shafts investigated in pure laboratory conditions and those cardan shafts investigated in clean exploitation conditions.

Imaging  technologies  are  transforming  the  study  and  presentation  of  artefacts.  The  contributors  to  this  volume  are  at  the  vanguard  of  applying  developing  technologies  to  cultural  heritage,  and  their  chapters  discuss  ways  in  which  various  techniques  are  being  used  for  research,  digital  cataloguing,  and  public  engagement.  Eight  chapters  highlight  diverse  methods  in  imaging  and  presentation  (e.g.  photogrammetry,  multispectral  and  hyperspectral  imaging,  structure-from-light,  digital  microscopy,  3D  printing,  and  virtual  and  augmented  reality)  applied  to  objects  of  differing  forms,  size,  media  and  cultural  origin,  including  standing  stones  in  pre-Columbian  Nicaragua,  Egyptian  and  Roman  sculpture,  Mesopotamian  cylinder  seals,  and  rock  crystal  vessels  made  in  the  early  medieval  Islamic  world.  Aimed  at  contributing  to  knowledge-transfer  between  sciences,  humanities,  and  cultural  heritage  professionals,  this  volume  offers  updated,  accessible  accounts  of  digital  imaging  of  objects  for  general  and  specialist  audiences.

The objective of this paper is to present an integrated procedure which will analyse the dynamics of a foil bearing on elastic supports. A complete time-dependent Navier-Stokes formulation is used to solve for the interaction between the hydrodynamic effects of the ...

This paper presents the experimental results of normal lubricant, additives added lubricants and waste vegetable oil (WVO) contaminated bio-lubricants to evaluate the tribological properties such that friction and wear characteristics. The test was conducted using a four-ball tribotester with standard test method IP- 239. The balls used in four-ball tribotester were based on carbon-chromium steel ball bearings. To evaluate friction and wear characteristics, coefficient of friction (μ), wear scar diameter (WSD), flash temperature parameter (FTP), viscosity index (VI) and total acid number (TAN) were investigated. Each test was conducted for five different loads from 50 kg to 90 kg at an interval of 10 kg. The lubricant was contaminated with WVO from 1% to 5%. The normal lubricant (as sample A) was used for comparison purposes. The test results showed that WVO contaminated lubricants with suitable anti-wear additive (amine phosphate) can reduce friction and wear coefficient substantially. The objective of this investigation is to develop a new lubricant based on waste palm oil (such as WVO). © Sila Science.

https://umexpert.um.edu.my/file/publication/00003184_87834.pdf

Titanium alloys have been of great interest in recent years because of their very attractive combination of high strength, low density and corrosion resistance. Application of these alloys in areas where wear resistance is also of importance calls for thorough investigations of their tribological properties. In this work, Ti–6Al–4V and Ti–24Al–11Nb alloys were subjected to dry sliding wear against hardened-steel counter bodies and their tribological response was investigated. A pin-on-disc type apparatus was used with a normal load of 15–45N and sliding speed of 1.88 ms−1. In the steady state, it was demonstrated that Ti–24Al–11Nb had a substantially higher wear resistance (about 48 times) than that of the Ti–6Al–4V alloy tested under a normal load of 45 N. Severe delamination is found to be responsible for the low wear resistance of Ti-6Al-4V. In the case of Ti–24Al–11Nb, two wear mechanisms have been suggested: delamination with a lower degree of severity and oxidative wear. It is thought that the ability of Ti–24Al–11Nb to form a protective oxide layer during wear results in a much lower wear rate in this alloy.

Ultra-high molecular weight polyethylene (UHMWPE) thin film was coated onto Ti6Al4V alloy specimens using dip coating method. Tribological performance of this coating (thickness of 19.6 ± 2.0 µm) was evaluated using 4 mm diameter Si 3 N 4 ball counterface in a ball-on-disk tribometer. Tests were carried out for different normal loads (0.5, 1.0, 2.0 and 4.0 N) and rotational speeds of the disk (200 and 400 rpm). UHMWPE coating formed in this study exhibits high hydrophobicity with water contact angle of 135.5 ± 3.3 • and meets the requirements of cytotoxicity test using the ISO 10993-5 elution method. This coating shows low coefficient of friction (0.15) and high wear durability (>96,000 cycles) for the tested conditions. PFPE overcoat on UHMWPE has further increased the wear durability of UHMWPE coating as evaluated at even higher rotational speed of 1000 rpm. c

The abrasive wear rates of materials may be very simply related to their mechanical properties, provided wear takes place under very simple conditions. However, wear rates in many practical situations can be controlled by effects which either relate to mechanical properties in more subtle ways, or which are controlled by quite different parameters. Mechanics models of the abrasive process provide a means of linking these different effects together to understand better the effects, which may determine wear under particular conditions. They can also help to design tests to measure the properties of a material under conditions similar to those pertaining in abrasion. Some progress has been made in producing integrated models of real abrasive processes, but much more could be done to improve existing models and develop new ones.

Previously, thin plate assumptions have been used to obtain a one-dimensional eddy current model for predicting the stationary, transformer-type losses in magnetic bearings built out of laminated material. Using similar assumptions as in the 1-D eddy current model, rotating losses can be predicted for a laminated heteropolar radial magnetic bearing. The thin plate model of rotating losses yields a hybrid analytical-boundary element model that is computationally inexpensive to implement. Predictions from this model compare favorably to losses experimentally measured in rotor run-down tests.

Sliding wear at elevated temperature is an important material removal mechanism in large number of engineering applications such as metal forming operation, gas turbine engines, etc. The material loss during sliding at elevated temperature is governed by the antagonistic effect of wear process and oxidation. The objective of the present work is to give an outline of the current status and future trends of wear at elevated temperature of selected metallic materials. Starting with a brief overview of present level of understanding of the elevated temperature wear of various metals and alloys, the initial parts of the paper describes various important development in recent years on elevated temperature sliding wear. The salient features which have helped us to gain in depth scientific knowledge of elevated temperature wear are discussed in the light of recent developments. The overview is further substantiated by detailed study and observation in recent times in particular, the work done at the Vienna University of Technology (Institute of Microtechnique and Precision Engineering) and at the Austrian Center of Competence for Tribology. Specific examples from the recent literatures are described to exemplify the mechanisms of formation of various types of layers during high-temperature wear. Some thoughts on the future directions for research are also outlined. r

Two aluminum metal matrix composites (MMC) reinforced with 13 vol.% of SiC or B4C particles were made by stir casting followed by hot extrusion. Effects of sliding velocity on the wear, friction and tribochemistry of the worn surfaces of both composites sliding against a commercial phenolic brake pad have been investigated under dry condition. The wear tests were carried out using a pin-on-disc type apparatus at two linear sliding speeds: 1.62 and 4.17 m s-1 under a constant contact pressure of 0.75 MPa for a sliding distance of 5832 m. The coefficient of friction was recorded and wear rate of the MMC pins calculated from mass loss measurement. Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) was used to investigated the worn surface. It is observed that higher sliding velocity leads to lower wear rate and lower friction coefficient for both MMCs. Formation of a compact transfer layer has been identified in the matrix region of the worn surface of the MMCs. The transfer layer mostly consists of constituents of the phenolic pad material which acted as counterbody. The amount of the constituents of the counterbody in the transfer layer is seen to increase as sliding velocity increases. It is suggested that the transfer layer on MMC acts as a protective cover and helps reduce both wear rate and friction coefficient.

A finite-element approach to thermoelastohydrodynamic lubrication analysis is developed by extending a previous mass-and energy-conserving algorithm to include wall-convection boundary conditions, groove-mixing theory, and thermo-mechanical deformations. To this end, the cross-film-averaged energy equation is coupled with the heat conduction equations relevant to the bearing sleeve and the journal by fitting the temperature profile across the film thickness with a fourth-order polynomial. A finite-element condensation technique is used to reduce the unknowns in heat conduction equations in the bush and in the journal to the temperatures of the sleeve surface and journal axis, respectively. Applied to the analysis of steadily loaded journal bearings, the proposed method shows good agreement with published experimental results and incurs low computational cost.

With continued development and improvement of tissue engineering therapies for small articular lesions, increased attention is being focused on the challenge of engineering partial or whole synovial joints. Joint-scale constructs could have applications in the treatment of large areas of articular damage or in biological arthroplasty of severely degenerate joints. This review considers the roles of shape, loading and motion in synovial joint mechanobiology and their incorporation into the design, fabrication, and testing of engineered partial or whole joints. Incidence of degeneration, degree of impairment, and efficacy of current treatments are critical factors in choosing a target for joint bioengineering. The form and function of native joints may guide the design of engineered jointscale constructs with respect to size, shape, and maturity. Fabrication challenges for joint-scale engineering include controlling chemo-mechano-biological microenvironments to promote the development and growth of multiple tissues with integrated interfaces or lubricated surfaces into anatomical shapes, and joint-scale bioreactors which nurture and stimulate the tissue with loading and motion. Finally, evaluation of load-bearing and tribological properties can range from tissue to joint scale and can focus on biological structure at present or after adaptation.

In tribological analysis of machine elements (such as gears, ball/roller bearings etc.), surface roughness plays very important role, ultimately it affects the friction coefficient, wear, rolling contact fatigue (micro pitting) and other failure mechanisms. Surface geometry and topography changed with time (number of cycles) during rolling/sliding motion of contacting surfaces. So, it is significant to show the variation of surface topography parameter during wear process. This work presents the evolution of roughness parameters, wear and friction coefficient during pin-on-disc tribotesting under dry condition. The test is performed using pin on disc apparatus under room temperature condition. Pin (25mm long, 6mm diameter) is made of medium carbon steel (AISI 1038) whereas disc (165mm diameter, 8mm thickness) is made of high carbon steel (SAE 52100). This works demonstrates the potential of Artificial Neural Network (ANN) for prediction of roughness parameters, friction coefficient and wear coefficient. Experimental results obtained from wear testing are compared with those obtained using artificial neural network (ANN) analysis. A very good agreement in results is suggested that, a well trained neural network is capable to predict the parameters in wear process.