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.

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

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...

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.

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.

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

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 ...

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

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.

6 th International Conference on Advances in Mechanical Engineering (AME 2020) will provide an excellent international forum for sharing knowledge and results in theory, methodology and applications impacts and challenges of Mechanical Engineering. The conference documents practical and theoretical results which make a fundamental contribution for the development of Mechanical Engineering. The aim of the conference is to provide a platform to the researchers and practitioners from both academia as well as industry to meet and share cutting-edge development in the field. Authors are solicited to contribute to the conference by submitting articles that illustrate research results, projects, surveying works and industrial experiences that describe significant advances in the following areas, but are not limited to Topics of interest include, but are not limited to, the following • Advances of Aero space Technology • Artificial Intelligence and Expert Systems

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.

http://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.

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.

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.