ARCHIVE Proceedings of the Institution of Mechanical Engineers Part J Journal of Engineering Tribology 1994-1996 (vols 208-210)

Published by SAGE Publications
Print ISSN: 1350-6501
Publications
For various reasons, manufacturers of cold-forged steel parts are becoming increasingly interested in forming at elevated temperatures below 500 °C. The objective of this study, published by the Institute for Metal Forming Technology (IFU) of the University of Stuttgart, is to evaluate the capability of various phosphate coatings in combination with MoS2 lubrication for extrusion processes of steel parts at elevated temperatures; it emphasizes the temperature range between 250 °C and 500 °C. Temperature resistance and the lubricating effect of the tested lubrication systems were examined using the double-cup-extrusion-test. Additionally, friction factors were calculated by comparing the test results with finite-element analysis.
 
The erosion wear resistance of silicon carbide (SiC) filled Zn–Al alloys is determined insolid particle erosive wear test rig under five different operation conditions such as impact velocity, SiC content, erodent temperature, impingement angle, and erodent size. This study evaluates the influence of independent parameters on erosive wear behaviour of composites. A design of experiments L16 orthogonal array design is conducted in a controlled way and a regression model is developed in order to verify the experimental results. This article tries to develop finite element simulation model (ANSYS/AUTODYN) to validate the experimental results. The results obtained in this study enable the influence and significance of various parameters to be better understood. It is observed SiC-reinforced ZA-27 alloy composites exhibit better erosion resistance as compared with ZA-27 alloy composite. In this investigation, the physical and mechanical properties of all the filled and unfilled composites are also evaluated for structural applications.
 
Surface roughness plays an important role in the performance of soft elastohydrodynamically lubricated contacts. When a soft and smooth body is in contact with a very rigid and rough one, the roughness creates pressure fluctuations, resulting in the deformation of the soft body. As the contact pressure is low, the fluid can be considered isoviscous and incompressible. An extension of the amplitude reduction theory from the piezoviscous to isoviscous elastic regime is performed under pure rolling conditions. It shows that a single master curve can be obtained by providing an analytic formula, but the power on the load parameter is different in the piezoviscous and isoviscous elastic zones.
 
In this study, plain iron powder (ASC.100.29) was mixed with 0.35–1.1 % graphite + 3 % Si + 2 % Ni and 0.35–1.1 % graphite + 3 % Si + 2 % Mn powders. While coarse pearlitic structure with homogeneous distribution of Mn was obtained in Mn-added specimens, Ni-rich austenitic areas with divorced pearlite structure were observed in Ni-added specimens. Wear tests were carried out at a load of 50 N. The experimental results showed that the highest wear resistance was obtained in the Ni-added specimen. While subsurface brittle cracking caused more wear in the Mn-added specimens, the wear occured by plastic deformation of surface Ni-added specimens.
 
The AISI 316L type of stainless steel is a popular steel material, as it has excellent corrosion resistance in aqueous solutions at ambient temperatures. However, the application of the AISI 316L stainless steel is limited by its relatively low hardness and low wear resistance. In this study, the electroless Ni–B coating was deposited on the AISI 316L stainless steel, and its structural, tribological and corrosion properties were characterised. Microstructural analysis showed that the electroless Ni–B coating deposited on the AISI 316L steel substrate exhibited a typical cauliflower-like structure exhibits an amorphous growth. From this study, it may be concluded that this process cannot only improve the hardness and wear resistance of the 316L stainless steel, but can also provide cathodic protection without losing or sacrificing the original properties of the 316L stainless steel.
 
Hard turning with minimal fluid application is an emerging machining technique in which cutting fluid is applied in the form of a minimal high velocity narrow pulsed jet so that for all practical purpose it resembles dry and wet turning but at the same time offers better cutting performance. Semi-solid assisted machining is a novel concept to control cutting force, cutting temperature, tool wear and to improve surface finish. In the present investigation, an attempt is made to improve the cutting performance during turning of hardened AISI 4340 steel with minimal fluid through the application of a semi-solid lubricant namely grease in pure form and as a mixture with 10% graphite applied at the tool–chip interface, tool–work interface and at the back side of the chip using a special semi-solid lubricant applicator developed for this purpose. The results indicated that the use of semi-solid lubricants – grease and graphite at the tool–chip interface along with minimal fluid application reduces tool vibration, cutting force, cutting temperature, tool wear and improves surface finish.
 
This article reports the surface modification of Ti-6Al-4V, which is widely used for mechanical engineering applications by laser texturing in order to enhance its tribological properties. Surface patterns with three different diametered dimples were prepared for Ti-6Al-4V. Two types of oil with different viscosities were evaluated as lubricants using a pin-disc tribometer. The results show that the textured surfaces exhibit lower friction coefficients and wear compared with the untextured surface. However, as the load increases, the effect of friction reduction for all the textured surfaces decreases when lubricated with lower viscosity oil. The beneficial effects of the dimples are more pronounced at higher speeds and loads when lubricated with higher viscosity oil. The influence of dimple sizes on lubricating-regime transitions is investigated in this study, and the mechanism for friction reduction is discussed.
 
This article reports on the influence of nitriding treatment of titanium alloy on the tribological behaviour of amorphous carbon or graphite/Ti–6Al–4V couples. This contact was investigated in pin-on-disc geometry in an ambient atmosphere. The pins were made of amorphous carbon or graphite and the discs were made of Ti–6Al–4V, nitrided or not. The treatment of nitriding for this study was an N 2 –H 2 plasma nitriding at a low temperature (700 °C) for 12 h. In these conditions, the top surface hardness was improved by a factor of 3. In this study, the mechanism of transfer and wear of carbon against Ti–6Al–4V, nitrided or not, has been studied with a scanning electron microscope, an optical microscope, etc. The analyses show that the nitriding of Ti–6Al–4V improves the tribological behaviour of the couples investigated. In fact, with the disc made of Ti–6Al–4V, the wear of carbon is very high and the disc is worn down at the end of the test. In contrast, after nitriding of the disc, the wear of carbon decreases, and there is a carbon film transfer on the disc. Moreover, with the nitriding of Ti–6Al–4V, the friction coefficient is stabilized, whereas without the nitriding of Ti–6Al–4V, the curve of the friction coefficient is marked by a very important increase during a short time. With the pin in graphite, the nitriding decreases the friction and increases the adhesion on the disc. Furthermore, the tests have shown that the contact temperature increases with the nitriding of Ti–6Al–4V.
 
The friction-reducing and antiwear effects of the 500SN base oil containing diisopropyl phosphite (T451) and ashless organic ammonium phosphate salt (KT139) on AISI 52100 steel/Al2O3 ceramic were investigated with a ball-on-disc tribometer at a light load of 200 N and a high load of 400 N. The results indicate that the 500SN base oil containing T451 and KT139 appears with a synergistic effect on AISI 52100 steel/Al2O3 ceramic. Under a single additive, increasing percentage of T451 or KT139 can decrease the friction coefficient and the wear rate of the pair monotonously. However, under the compound system, the tribological behaviour of the pair is strongly dependent of the concentrations of additives. Within the experimental data, the most effective compositions for the loads 200 and 400 N are 2 wt%T451 + 2 wt%KT139 and 1 wt%T451 + 3 wt%KT139, respectively. The scanning electron microscopic images showed that plowed grooves, spalling, and corrosion are the dominant wear modes for the pair. The energy dispersive spectroscopy analysis shows that a protective tribochemical film containing both S and P forms on the steel ball worn surface. Nevertheless, the atom concentrations of P and S are too low to be referred for further analysis of the tribochemical reaction mechanism.
 
Particle-reinforced metal–matrix composites (MMC) with prerequisites such as uniform distribution and minimum porosity have superior mechanical properties than matrix material. Nevertheless, their tribological characteristics come next to justify the practical applicability. In this study, tribological characteristics of Al 6063–SiCp MMC, under reciprocating and wet conditions, have been assessed and reported. The process parameters selected were the applied load, sliding distance, reciprocating velocity, counter-surface temperature, and SiC percentage. The responses measured were wear loss and coefficient of friction (COF). Mathematical models have been proposed for modelling and analysis of the effects of selected process parameters. The results reveal that a proper control of process parameters can result in improved tribological characteristics. The applied load, sliding distance, reciprocating velocity, counter-surface temperature, and SiC percentage significantly affect wear loss. The applied load, sliding distance, and SiC percentage significantly affect COF. The assessment can be used to predict the tribological performance of MMCs in engineering applications subjected to similar operating environmental conditions.
 
The friction and wear properties of glass fibre-reinforced polyamide 66 composite, quenched QT600-3 ductile iron were investigated against ceramic Al2O3 on the pin-on-disc testing machine under oilfield water-lubricated condition. Optical microscope, scanning electron microscopy, Fourier transform infrared spectrometer, digital temperature measurement system, and X-ray photoelectron spectroscope were used to characterize the microstructure, worn surface, and binding energy of C=O and C–C bonds for the studied materials. The GF/Nylon 66 composite had lower coefficient of friction than the quenched ductile iron, but it exhibited inferior wear resistance to the quenched QT600-3 ductile iron under oilfield water-lubricated condition, which was ascribed to combination of thermal softening, degradation of Nylon matrix, micro-ploughing, and tearing caused by hard Al2O3 disc during the wear testing.
 
Wear, which is attributed to the presence of powdered material, is one of the main factors responsible for material degradation in industry, affecting the performance of important equipments such as valves, vessels, pipeline walls, catalytic reactors, and steam generators. The appropriate selection of materials is of great economical relevance in such degradation situations. The evaluation of materials subjected to severe service conditions is fundamental for estimating their performance. Both low- and high-temperature erosive wears are main concerns due to the catastrophic consequences they may cause. An apparatus for the evaluation of the performance of materials subjected to erosive wear up to 800 °C is presented, described, and validated. During its validation, different materials under different parameter conditions were tested. Results show that the apparatus is able to quantify erosive wear and control process parameters with excellent accuracy.
 
High-velocity oxy-fuel (HVOF) spray ceramic oxide coatings have immense potential in industrial applications. However, they are not widely used yet due to the lack of an adequate scientific database created after testing these coatings for specific industrial applications. Two such ceramic coating powders, Al2O3+(40%)TiO2 and Cr2O3, were deposited on AISI 309 SS stainless steel by the HVOF spray technique, in order to enhance its wear resistance. This stainless steel is used in many components of thermal power plants in India, where it suffers one or more types of wear. The as-sprayed coatings were characterized by XRD and SEM analyses. Subsequently, the sliding wear behaviours of the uncoated, HVOF spray Al2O3+(40%)TiO2 and Cr2O3 coated AISI 309 SS were investigated according to ASTM standard G99-03 on a pin-on-disc wear test rig. Cumulative wear rate and coefficient of friction (μ) were calculated for the coated as well as the uncoated specimens for 30, 50, and 70 N normal loads at a constant sliding velocity of 1 m/s. Some of the worn-out surfaces were characterized by SEM analysis. Both the as-sprayed coatings exhibited typical splat morphology of a thermal spray process. The XRD analysis indicated the formation of Al2O3 and TiO2 phases for the Al2O3+(40%)TiO2 coating, and Cr2O3 phase for the Cr2O3 coating. It has been concluded that HVOF spray Al2O3+(40%)TiO2 and Cr2O3 coatings can be useful in minimizing the wear problem of AISI 309 SS. These coatings were found to be successful in retaining their surface contact with the substrate after the wear tests. The HVOF spray Cr2O3 coating can be recommended as a slightly better choice to reduce the wear of AISI 309 SS in comparison with the Al2O3+(40%)TiO2 coating.
 
Inside the mouth, tooth wear is a very complex phenomenon that occurs due to physiological, pathological, oral hygiene and orthodontics causes. Abrasion is a type of tooth wear, which causes severe damage compared to attrition, abfraction and erosion wear modes that occur simultaneously; principally on occlusal area during close phase of mastication process when abrasive particles from different sources are located between tooth and tooth or tooth and dental composite contact, designated as three-body abrasion wear in Tribology. ‘In vitro’ wear tests were carried out for three different dental composite restorative base resins, using the Micro-scale TE 66 wear test machine that offers the possibility to reproduce micro-abrasive wear (three-body rolling wear). Two different slurries were used; distillate water and artificial saliva containing SiC abrasive particles, F 1200 4 µm. Three dental composites materials and human enamel were tested at 0.25 N load applied, 0.1 m/s speed ball, 7.98 m sliding distance and 22% of volume containing SiC, at room temperature. Lost volume and wear coefficient, k, were calculated. Scanning electron microscopic and atomic force microscopic images were obtained and wear scars were analysed in order to identify wear mechanisms, such as ploughing, cutting and microcraking. Also, brittle delamination was found only for human enamel.
 
For a very long time, debris particles have been blamed to causing serious problems in machine-element contacts such as those of bearings and gears. This involves a huge number of mechanisms and machines worldwide. The financial cost associated with machinery failure under such circumstances is enormous. Past research has identified the main mechanisms governing damage from debris particles. A few theoretical models have been built on the experience accumulated on damage mechanics. The capabilities of said models vary a lot. The model originally developed by this author in the 1990s was recently expanded. The previous version of the model, which was published in this journal in May 2012, offered a number of innovative features to calculate spherical-particle indentation and soft abrasion in lubricated rolling-sliding contacts. It was experimentally validated following a rigorous programme. However, it neglected frictional heating from particle extrusion. This study significantly expands the previous model of the author by integrating thermal effects. It includes flash temperature calculations with moving sources of heat, dynamic heat partition, three-dimensional conduction and convection, and thermally anisotropic surfaces with temperature-dependent thermal and mechanical properties, all integrated in the elastoplastic model of indentation and abrasion. These are in addition to model features such as nonlinear strain hardening, strain-gradient plasticity, particle work hardening, generalised local kinematics, pile-up/sink-in plasticity effects and many more. The same rigorous experimental verification programme as in the previous model of the author is used here, too. It is shown that in some cases, the theoretical results on dent geometry are even closer to the experimental ones than with the isothermal model of the author. Furthermore, the thermal analysis reveals that extreme frictional heating can take place, often leading to melting wear in a fraction of a millisecond. The formation of dimples inside and outside main dents, which have been shown experimentally and verified theoretically by this author’s previous model, is revisited in light of frictional heating. A parametric study shows the effects of particle size and hardness, kinetic friction coefficients, and strain hardening on dent geometry and flash temperatures, including effects on particle and surface melting. Finally, the reality of flash temperatures is explored.
 
Earth moving and processing machinery has to withstand heavy wear caused by impacts and scratching by the soil. Especially, the edges are subjected to heavy wear. To simulate these conditions, impeller–tumbler impact-abrasion wear testing equipment was used to determine the wear resistance of four steel grades at perpendicular and tilted sample angles. The angles were selected to simulate the loading conditions. Natural granite rock was used as abrasive. The amount of wear was clearly smaller in the harder materials. The significance of hardness was quite similar at both sample angles in the steady-state wear of wear-resistant steels. On the initial state wear, hardness had a slightly greater effect at the perpendicular angle due to more severe wear in sample edges already at the beginning of the test. Overall, the largest differences in wear were observed in the sample edges. At the perpendicular sample angle, the sample edges were much more rounded. Some small differences were observed in the surface formations due to dissimilar movement of the abrasive. Deformed surfaces and fractured lips indicated that wear occurred mainly by the deformation of material followed by the removal of the deformed areas through impacts. In addition, scratches and dents were observed. It was found that larger sized abrasives caused higher mass loss than abrasives of similar mass but smaller size. Moreover, same amount of abrasive particles in each test reduces the scatter of the results.
 
Indentation and abrasion of machine-element contacts by solid contamination particles is a major problem in many industries and manufacturing processes involving the automotive, aerospace, medical and electronics industries among others. Published theoretical studies on indentation and soft abrasion of surfaces by ductile debris particles other than those of the author are based on several major simplifications concerning material properties, hardness, plasticity modelling, interfacial friction, kinematic conditions, etc. None of the studies published in the literature to date (2011) have those simplifications concurrently relaxed.
 
This article presents an outline of a method of planning an experiment developed by Taguchi for the optimisation of processes and as an example of its application in the optimisation of parameters of a ball-cratering method. Abrasive wear tests were performed on chosen antiwear physical vapour deposition coatings with the optimum work parameters of friction node. (The test friction node is created by the rotating ball and the immobile sample disc that is pressed against it and an abrasive slurry is drip fed into the contact zone.) Then the factor of resistance to abrasive wear was calculated based on the evaluation of their resistance to abrasive wear. The Taguchi optimisation method was used in order to devise and verify the methodology of the abrasive wear research of physical vapour deposition coatings deposited using cathodic arc evaporation on two differently prepared substrates. A series of resistance tests to abrasive wear performed using ball-cratering method was conducted in accordance with the test plan based on the Taguchi design. The variable test parameters were load, the speed of ball rotation and sliding distance. A measuring device, an optical microscope, was used to take pictures and measure the diameters of the wear traces visible in the form of craters received after the performance of tribological tests. The purpose of this research was to devise a method for testing the resistance of antiwear physical vapour deposition coatings deposited on tools and machine parts to abrasive wear (performed using the ball-cratering method) by applying the Taguchi optimisation method. The experiments were carried out using the combination of tribological test parameters based on the nine experiments (L9) using Taguchi orthogonal design with variable three test parameters of load, the speed of ball rotation and sliding distance. The results of the abrasive wear test performed using ball-cratering method on duplex and non-duplex coatings were successfully verified using the Taguchi optimisation program. Optimisation of the tribological test parameters based on the Taguchi method has been found to be very efficient and convenient for the investigation of the abrasive wear rate of the duplex and non-duplex coatings.
 
High-speed abrasive water jetting is an alternative tool for machining engineering materials. The energy dissipation processes involved in this erosion process have not been investigated systematically. In this paper, a model is developed to calculate the energy dissipation in workpieces eroded by abrasive water jets. By introducing an energy dissipation function χ(Φ). the model enables the estimation of the energy absorption as a function of the erosion depth. The energy dissipation function can be expressed by a second-order polynomial approximation. Measurements of the reaction forces on the exiting slurry after the erosion process, material removal experiments and fracture tests are conducted to separate the components of the energy dissipation parameter, such as damping, friction and erosion debris generation.
 
In this study, the Taguchi–grey relational analysis was used for the optimization of hybrid aluminium composites considering multiple quality characteristics of the material and process parameters relevant to two-body abrasive wear behaviour. Hybrid aluminium composites containing alumina and molybdenum disulphide particulates were produced by stir casting method. Volume loss and frictional force were measured using a pin-on-disc apparatus. In this study, applied load, sliding speed and abrasive size were taken as process parameters and percentage of molybdenum disulphide considered as material parameter. An L9 orthogonal array was used for the Taguchi experimental design. Optimum process parameters were determined using the grey relational analysis for multiple performance characteristics such as wear rate and coefficient of friction. Analysis of variance was used to study the impact of individual factors on the wear rate and coefficient of friction. Experimental results showed that two-body abrasive wear performance of the hybrid composites improved under optimal test conditions. Scanning electron microscopy investigations of the worn out specimens were carried out to explain the wear mechanism of the hybrid composites during two-body abrasive wear.
 
Investigations were carried out on three-body abrasive wear behaviour on six aluminium alloys (AA1050, AA2014-T6, AA3003, AA5052, AA6061-T6 and AA6351-T6). Evaluation and comparison of the abrasion resistance of the aluminium alloys were carried out using silica sand of size 150-250 µm by dry sand rubber wheel (DSRW) test rig at room temperature. The tests were performed at constant rubber wheel sliding velocity (V = 2.4 m/s) at different loads (5-20 N). Abrasion studies reveal that abrasive wear increases with increase in load. The wear volume was found to be in linear relationship with sliding distance and the steady state behaviour of the materials was attained around a sliding distance of 5760 m. Correlation of abrasive wear rate with hardness, ultimate strength and percentage elongation at break are reported. Wear mechanisms involved in material removal process were studied with the aid of optical microscope and scanning electron microscope (SEM).
 
In this study, the effects of the reinforcement volume fraction on the abrasive wear behaviour of reinforced MgO composites produced by the vacuum infiltration method with 5, 10, and 15 vol% of the volume fraction of Al matrix were investigated. The abrasive wear tests were carried out by 80, 100, and 180 mesh Al2O3 abrasive paper and the pin-on-disc wear device under 10, 20, and 30 N loads at 0.2 m/s sliding speed for 3 s. At the end of the wear tests, scanning electron microscope photographs of worn surfaces were taken and the microstructures were analysed by energy dispersive spectrometer (EDS). By checking the images of the worn surfaces, it was observed that the abrasive wear effect increased by increasing the reinforcement ratio. The maximum wear loss was reported under 30 N loads and by 80 mesh abrasive paper. It was found that according to the increment of reinforced MgO in the composite, the amount of wear also increased. On the other hand, the amount of porosity and the reinforcement volume fraction are crucial parameters in the abrasive wear effect.
 
In order to minimize the investment costs, the use of ferritic stainless steels is being explored for various processing industries. International Stainless Steel Forum suggested the use of ferritic steels AISI 439 and 444 in cane sugar industry instead of austenitic steels and low-carbon steels. The objective of this investigation is to evaluate the abrasion resistance of these ferritic grades and to compare and rank them against austenitic steel AISI 304 and low-carbon steel SAE 1010 for use as construction material in sugar mills. Optical microscope, microhardness tester, and scanning electron microscope have been used to characterize the abraded specimens.The abrasion resistances AISI 439 and 444 grade steels are found to be moderately better than those of the other two materials in the abrasion test.
 
Material constants for Ti-6Al-4V
Material constants for steel ball
In this study, an attempt has been made to study the basic aspects of abrasive waterjet (AWJ) controlled-depth process using the finite element (FE) method to predict the profile of the crater produced by single particle impact rather than to perform first the simulation of full jet plume impingement. It is believed that the first should be a sine-qua-non-condition for developing the multiparticle impingement simulation to address the real-life AWJ milling process. The main objective of this article is to simulate and experimentally validate the profile of the craters at different impact angles of particles accelerated with waterjet. The workpiece material modelled is a Ti-based superalloy (Ti–6Al–4V) extensively used in the aerospace industry. The current model takes into account the effects of high-strain rate plastic deformation and adiabatic heating. The FE-simulated profiles of the craters are found to be in good agreement with experimentally generated data. The presented work provides a good (experimentally validated) basis for further FE modelling of the AWJ milling process, where influences such as particles’ shape, rotation, and multiple overlapping impacts can be further investigated.
 
Most people clean their teeth using toothpaste, consisting of abrasive particles in a carrier fluid, and a filament based toothbrush to remove plaque and stain. In order to optimise cleaning efficiency it is important to understand how toothbrush filaments, abrasive particles and fluid interact in a tooth cleaning contact. Work has been carried out to visualise, simulate, and model the processes in teeth cleaning. Laboratory cleaning contacts were created between a toothbrush and a transparent surface. Video and short duration flash photography were used to study the processes by which a toothbrush traps abrasive particles, loads them against the counterface, and removes material. Small abrasive particles tend to be trapped at the contact between the filament tip and the counterface, whilst larger particles are trapped by clumps of filaments or at the contact with the side of a bent filament. Measurements of brush friction force were recorded during cleaning for a range of operating conditions. The presence of abrasive particles in the cleaning mixture increased the coefficient of friction, but the absolute particle concentration showed a lesser effect. It is surmised that only a few particles carry any load and cause any abrasion; increasing the particle concentration does not directly increase the number of load bearing particles. Abrasive scratch tests were also carried out, using PMMA as a wearing substrate. The scratches produced during these tests were studied. The microscopy images were used to deduce how the filaments deflect and drag, and how particles are trapped by filaments and scratch the surface. Again, it was observed that few of the brush filaments loaded particles to produce scratches, and that when a filament changes direction of travel the trapped particle is lost. Results of these studies were used to develop both qualitative and quantitative models of the process by which material is removed in teeth cleaning. The quantitative model contains, by necessity, several empirical factors, but nonetheless predictions compare well with in vitro wear results from the literature. The results were also used to draw some broad conclusions on appropriate brushing techniques for optimum tooth cleaning.
 
A four-ball tester was used to evaluate the anti-wear and friction-reducing performance of a blend of 2,5-bis((9,9-dimethyldecyl)disulfanyl)-1,3,4-thiadiazole (referred to as T561) and molybdenum naphthenate (referred to as MoNAP) in hydrogenated oils. The results indicate that the blend of T561 and MoNAP (referred to as TMoNAP) has excellent anti-wear and friction-reducing properties, as well as good load-carrying capacity. Then, X-ray absorption near edge structure (XANES) spectroscopy was employed to provide further insight into the chemical composition of films generated from thermal oxidation and friction process. According to the results, thermal films are composed mainly of ferrous sulphate, whereas anti-wear films are composed mainly of ferrous sulphide, ferrous disulphide, sulphite, ferrous sulphate, molybdenum disulphide, and molybdenum oxide. The mechanisms of friction reducing and anti-wear are discussed.
 
This article describes fretting wear damage of Ni-MoS2 coatings in terms of the friction coefficient (COF) and accumulated dissipated energy. Multi-layer dry lubricant coatings containing the elements Mo and S are known to maintain low friction under reciprocal relative displacement, and are considered for this purpose in fan blade attachments within aero-engines. The durability of these coatings for a dovetail connection needs to be investigated in order to help design calculations and overhaul scheduling. Experimental characterization of durability can be achieved by measuring COF as a function of the number of fretting cycles, or, alternatively, the accumulated sliding distance. Dissipated energy is also considered as an alternative indicator for characterizing fretting wear damage. In this article, fretting wear tests with Ni-MoS2 coatings and various surface treatments were performed using idealized contact geometries and loading conditions similar to those found in aero-engine components. Additionally, COF evolutions of Ni-MoS2 coatings were numerically determined as a function of accumulated dissipated energy. A direct comparison between a numerical evolution and a measured one was performed, and excellent agreement between the two evolutions was obtained.
 
The development of a large lubricant film thickness generally depends upon the large elastic deformations of the bearing surfaces from the elastohydrodynamic lubrication (EHL) point of view. The deformation of the bearing surfaces of total hip joint replacements can be influenced by the material properties as well as the structural supports. A conceptual sandwich cup, which consists of a hemispherical metallic bearing shell bonded to a polyethylene backing, together with a solid metallic femoral head was considered in an EHL analysis for quasi-static conditions of load and speed to investigate the effect of the sandwich cup upon lubricant film thickness in total hip replacements. It was found that a reduction in the cup wall thickness of the metallic shell and an increase in the polyethylene thickness resulted in an increase in the predicted lubricant film thickness and a decrease in the hydrodynamic pressure. A general relationship was found between the film thickness and the metallic inlay thickness.
 
The moisture uptake of the three unsaturated fatty acids, oleic acid, linoleic acid, and linolenic acid has been investigated. The amount of water absorbed by the fatty acids increased with increasing degree of unsaturation. The influence of the water on the adsorption onto steel and lubricating properties of the fatty acid in hexadecane was investigated. The adsorption, as determined with quartz crystal microbalance of 0.1 and 1 wt% of oleic acid onto steel was not affected by the presence of water (1.5 mole% water in fatty acid) while 5.6 mole% water enhanced the adsorbed amount of linolenic acid. Even though this amount of water had a large influence on the adsorption of linolenic acid, it did not affect the friction and wear measured with high frequency reciprocating rig using oleic acid or linolenic acid in hexadecane.
 
Results of a study to examine a unique idea of self-levitating journal bearing are presented in this article. The idea represents a radical departure from the current bearing technology. It utilizes acoustic levitation, which relies on the sound energy radiated by an object supporting a load. Acoustic levitation has been demonstrated to support loads of up to 10 kg. In order to support a load the acoustic wave emitted by the radiating surface must be reflected back towards the radiating surface by the levitating object. The radiation pressure increases as the gap between the source of sound and levitating object narrows. Computer simulation and experimental testing of a prototype device were carried out and provided a conclusive proof of the idea.
 
In this article, the acoustic emission technique has been used to study a well-known surface damage mechanism, known as galling, during experimental simulation of sheet metal forming process. Results illustrated that the galling starts with relatively low-amplitude acoustic emission waves, corresponding to the elastic–plastic deformation of surface asperities (stage I), followed by a continually graduate rise in the acoustic emission activities related to the sheet material transfer to the slider tool along with lump growth (stage II), and ended to some waves with the highest amplitude and energy corresponding to the severe plowing and rupture of the friction junctions (stage III).
 
Acrylonitrile-butadiene rubber elastomers are widely used in seal and tire industries. Physiochemical, surface and tribological properties of acrylonitrile-butadiene rubber exposed to a lubricant in a sealed mechanical contact may gradually change, in particular, at elevated temperatures. In this study, industrial-grade acrylonitrile-butadiene rubber elastomers were aged in two model non-additivated base oils, namely non-polar hexadecane and polar diethylene glycol dibutyl ether at both ambient (298 K) and elevated (398 K) temperatures from 1 to 168 h. Mass changes of acrylonitrile-butadiene rubber before and after ageing indicated that acrylonitrile-butadiene rubber had distinct ageing dynamics in different model base oils and at different temperatures. For acrylonitrile-butadiene rubber aged in nonpolar hexadecane, the rate of weight loss of the rubber was larger at 398 K compared to that at 298 K. On the contrary, distinct weight-gaining (swelling) dynamics were observed for acrylonitrile-butadiene rubber aged in polar diethylene glycol dibutyl ether at 298 and 398 K. Based on Fourier transform infrared spectroscopy, liquid and solid-state nuclear magnetic resonance spectroscopy and energy dispersive spectroscopy analyses, it was found that aldehydes and sulfur- and zinc-containing compounds were leached out from acrylonitrile-butadiene rubber aged in both hexadecane and diethylene glycol dibutyl ether. The results of tribological studies showed that the non-aged acrylonitrile-butadiene rubber has a good wear-resistance. Acrylonitrile-butadiene rubber samples had a very similar surface topography before and after tribo-tests. However, the worn surfaces of acrylonitrile-butadiene rubber samples were characterized by fine scoring (abrasion) marks after ageing in both model base oils. This has been attributed to changes in the steel–rubber contact environment during the sliding process and degradation of mechanical properties of acrylonitrile-butadiene rubber after ageing. For one acrylonitrile-butadiene rubber sample (after ageing in hexadecane at 398 K), very stable friction in the steel–rubber contact was observed.
 
A prototype X–Y stage for ultraprecise positioning composed of six pneumatic servo bearing actuators was proposed and developed. First, the basic performance of the pneumatic servo bearing actuator with a spherical aerostatic bearing was investigated before assembling it to the X–Y stage. In the actuator, pressurized air controlled by a servo valve moves an actuated spool ultraprecisely. Even under open-loop control, the actuator provided accurate replication and positioning resolution on a nanometer order. Second, the specifications of the constructed X–Y stage were evaluated, especially focusing on its minimum resolution. The minimum positioning resolution of the X–Y stage was 3 nm under the best conditions, and the positioning resolution as a practical specification was approximately 10 nm for all conditions, even without feedback controls.
 
Shapes of structural elements: (a) flat, (b) line, (c) triangular, and (d) semicircular
Photographic view of experimental set-up and locating of test bearing on shaft: (a) complete experimental set-up, (b) constraining the test bearing, and (c) accommodation of test bearing with lock nut in housing
Noise reduction in bearing signal with defective inner race using ANC: (a) LMS with signum function (sample size 2048 samples), (b) enlarged view of encircled zone, (c) LMS with signum function (sample size 4096 samples), and (d) LMS without signum function (sample size 2048 samples)
Identifying the signals of defective rolling element bearings of industrial machines in the presence of external vibrations is a difficult task. Therefore, in this article, attempt has been done to improve the defect detection of rolling element bearings in the presence of external vibrations using adaptive noise cancellation (ANC), self-adaptive noise cancellation (SANC), and mathematical multiscale morphology (MMM). Circular defects (diameter = 400 µm), on either of the races of the test bearings, have been artificially created and external random vibrations have been imparted to the defective test bearings using an electromechanical shaker in the experimentation reported herein. The defective bearing signal-to-external noise (vibration) ratio has been significantly enhanced after the application of ANC, SANC, and MMM. This resulted in the clear identification of defect frequencies in the vibration spectrum. It is essential to mention here that in ANC technique the least mean square (LMS) algorithm with and without signum function has been used. However, in MMM technique, triangular structural elements are utilized during the closing operation and bottom-hat transform (BHat). In comparison to the LMS algorithm without signum function, the LMS algorithm with signum function has been proved more effective and efficient in minimizing the error. Authors noticed that the MMM filter is much effective for noise removal.
 
Accurate prediction of tool life is essential to guarantee surface quality and economics of cutting operations in face milling. This article presents a procedure for tool life prediction through in-process adaptation of tool wear rate based on indirect measures. The procedure effectively accounts for the uncertainty of tool wear progress owing to the complexity of the machining process. First, sensor fusion of spindle motor current AC and DC portions is taken to estimate the actual tool wear through relevance vector machine. Then, a tool life prediction model relating flank wear with cutting time is proposed for tracking the progress of tool wear under certain cutting settings. Further, a recursive least square algorithm is developed to update the parameters of the tool life prediction model by considering the error between the predicted tool wear and the estimated tool wear. Finally, the updated model capturing the uncertainty of tool wear progress is used to predict tool life in face milling. Tool life experiments validate that the adaptive procedure can quickly track the progress of tool wear, and make more accurate prediction of tool life compared with the procedure with constant model parameters.
 
This article presents a new numerical method to solve transient line contact elastohydrodynamic lubrication (EHL) problems. A high-order discontinuous Galerkin (DG) finite element method is used for the spatial discretization, and the standard Crank-Nicolson method is employed to approximate the time derivative. An h-adaptivity method is used for grid adaptation with the time-stepping, and the penalty method is employed to handle the cavitation condition. The roughness model employed here is a simple indentation, which is located on the upper surface. Numerical results are presented comparing the DG method to standard finite difference (FD) techniques. It is shown that micro-EHL features are captured with far fewer degrees of freedom than when using low-order FD methods.
 
With various daily activities, the effectiveness of adsorbed film formed on a gel-like layer at the uppermost superficial articular cartilage in natural synovial joints becomes important to control the friction and wear of articular cartilage in mixed or boundary lubrication regime as an adaptive multimode lubrication mechanism. Furthermore, in the case where the adsorbed film has been removed, the proteoglycan gel layer is expected to preserve low friction and protect against the wear of bulk cartilage tissue with an effective hydration lubrication mechanism. Besides, it is indicated that the biphasic lubrication plays an important role in lowering of friction in articular cartilage containing a large amount of water. At the present stage, however, the detailed relationship between adsorbed films and hydrated gel layers has not yet been elucidated. In this article, the frictional behaviours of articular cartilage on a glass plate were observed in the reciprocating tests with the restarting process after interruption and unloading. The lubricating effectiveness of adsorbed films in hyaluronate (HA) solutions was examined using intact and partially damaged cartilage specimens. The role of albumin and γ-globulin in relation to the surface conditions of gel layer is discussed. The restarting friction immediately after reloading became lower as a result of recovery of the effective interstitial fluid pressurization and hydration and adsorbed films have a significant effect on the frictional behaviour at local contacts. To clarify the molecular phenomena taking place under rubbing condition, in situ observations of the forming adsorbed film were conducted. The measurements were performed using the fluorescent staining method for protein and HA molecules at low contact pressures.
 
The healthy natural synovial joints maintain excellent load-carrying capacity and lubricating properties with extremely low friction and minimum wear even under heavily loaded conditions. The superior lubricating performance appears to be actualized by not single lubrication mode but the synergistic combination of various modes depending on the severity of operating conditions. This mechanism is called adaptive multimode lubrication and the application of this good working lubrication mechanism to artificial joints with soft layer is expected to contribute to remarkable improvement in longevity of joint prostheses. However, some of detailed mechanisms in natural synovial joints have not yet been clarified. In this article, the effectiveness of biphasic lubrication in natural synovial joints was examined by biphasic finite element analysis under both the on–off loading (migrating contact) and the continuous loading (continuous contact) to cartilage. Then, the method to suppress the gradual rising in friction for articular cartilage under the continuous loading is discussed. Finally, the effectiveness of fibre reinforcement in hydrogel artificial cartilage was examined in walking simulator test.
 
Base oil properties
Functional additives, particularly extreme-pressure and antiwear additives, in formulated oil will compete to adsorb and form a protective layer in tribological contacts. The thickness of the layer is determined by the equilibrium between the formation and removal processes. In this article, the interactions between additives and base oil molecules and operating conditions influence friction and wear are studied. One polar (ester oil) and one non-polar (poly-α-olefin) commercial base oil blended with zinc dialkyl dithiophosphates were studied. The tribological performance was evaluated using a ball-on-disc test rig under mixed rolling–sliding conditions in the boundary lubrication regime. An adapted in situ interferometry technique was used to monitor the additive-derived reaction layer formation. The properties of the additive-derived reaction layers were studied using surface analysis techniques, X-ray photoelectron spectroscopy and atomic force microscopy. A thicker layer was formed when the additive is blended in the non-polar oil. This observation suggests that base oil polarity determines the transport of additives to the surface, thereby controlling the maximum reaction layer thickness, friction and wear, as well as the morphology of the additive-derived reaction layer. However, the reaction layer chemical composition is not strongly influenced by the base oil polarity. Among the operating conditions, shear was identified as a fundamental parameter for the activation of additives on rubbing steel surfaces and the properties of the derived reaction layer.
 
The aim of this study is to find a connection between mechanical engineering and biotechnology by utilizing biomimetics in lubrication. The objective is to improve boundary lubrication by biomolecules in water-based systems. Proteins were used because they can form films and multilayers on the surfaces and thus prevent direct contact between them. In this study, hydrophobin and albumin proteins are studied as additives to enable water lubrication. © VTT Technical Research Centre of Finland, Espoo, Finland, 2011.
 
In this work, we report on the BuMepyr-MeSO4 and Et3MeN-MeSO4 ionic liquids that were synthesized and used as additives in a glycerol model lubricant for steel/steel contacts. Tests were performed with three different ionic liquid concentrations, i.e. 0.625 wt%, 2.5 wt% and 8 wt%, as well as in glycerol without any ionic liquid (neat glycerol) and in neat ionic liquids (100%) at 100 °C. The wear and friction were measured and the worn surfaces were examined with scanning electron microscopy and atomic force microscopy. The results show a reduction of the wear and friction with the use of ionic liquids as additives, when compared to the neat glycerol. With an increasing ionic-liquid concentration in the glycerol, the friction was observed to decrease and the wear to increase. In this work, however, the results obtained for neat ionic liquids represent the lowest values in terms of both friction and wear.
 
In this article, a systematic study is carried out to assess the influence of lubricant additives on the durability of a hydrogenated diamond-like carbon (DLC) coating under mixed rolling/sliding contact is provided. Experiments were performed in a mini traction machine using a DLC (15 at.% hydrogen) coated disc on an uncoated steel ball at 50 per cent sliding/rolling ratio and in a motorized cylinder head (Ford Zetec) cam/follower test rig. Five different lubricants containing zinc dialkyldithiophosphate (ZDDP) and/or friction modifiers (Moly Dimer (MD)/Moly Trimer (MT)) were used. This study reveals that the lubricant additives have a strong influence on the coating durability while ZDDP additive effectively reduces wear to extremely low levels. The addition of the MT additives only has a marginal effect on wear, whereas the MD additive substantially reduces the performance. The mechanisms by which the additives affect the wear in this ultralow-wear regime are discussed.
 
This article describes the tribological characterization of dispersions consisting of irradiated poly(tetrafluoroethylene) (PTFE) micropowder (Zonyl® MP1100) and an ester oil (Synative ES TMP 05). A series of PTFE/oil dispersions were prepared with different amounts of PTFE micropowder (10–25 wt%) to study the influence of the PTFE in these dispersions on their tribological properties. The PTFE/oil dispersion with 10 wt% PTFE micropowder was additionally synthesized in the presence of two additives which are derived from phosphoric acid to study the influence on the tribological properties. In addition, a physical mixture of the ester oil and the PTFE micropowder was prepared to illustrate the impact of the chemical coupling reaction with regard to the tribological properties. A higher concentration of PTFE micropowder more clearly reduces the coefficient of friction in the ester oil. Low coefficient of friction and transition values from static to dynamic friction were observed. The resistance to wear was increased with the amount of PTFE micropowder in the dispersions and clearly reflects the difference between chemical coupling and physical mixture of the components.
 
Three novel imidazoline-type thiadiazole derivatives are prepared and used as antiwear and extreme-pressure additives in biodegradable lithium grease, and their tribological performances are evaluated using a four-ball tester. Tribological tests show that all derivatives are effective in reducing wear, especially at lower additive concentrations. Oleic acid-imidazoline-type thiadiazole derivative is a preferred additive to reduce wear. For the friction-reducing property of base grease, improvements after using these derivatives are not remarkable. On the other hand, these derivatives are also effective extreme-pressure additives. In order to understand the friction process further, chemical composition of tribofilms under antiwear/extreme-pressure regime is analyzed by X-ray absorption near edge structure spectroscopy, and thermal films are also considered for comparison. Thermal films formed by these imidazoline-type thiadiazole derivatives consist of adsorbed organic sulfide and ferrous sulfide. Sulfur presents several chemical valences in the antiwear regime, and tribofilms generated by stearic acid and lauric acid-imidazoline-type thiadiazole derivatives at 1.0 wt% are composed of ferrous disulfide, ferrous sulfide and ferrous sulfate. The appearance of disulfide suggests that the interfacial temperature between the upper ball and three lower balls under antiwear conditions is considerably low. Composition of extreme-pressure films generated by oleic acid and lauric acid-imidazoline-type thiadiazole derivatives is only ferrous sulfide, and the extreme-pressure film for stearic acid imidazoline-type thiadiazole derivative is a mixture of ferrous sulfide, ferrous sulfate, and adsorbed organic sulfide.
 
The friction and wear behaviour of the laser-textured surfaces sliding against a pin under the lubrication of the polyurea grease containing various additives were investigated using an UMT-2MT reciprocating friction tester. Results show that the dimple patterns have lower friction coefficients than that of the un-textured at lower sliding speed (0.015 m/s); however, the groove patterns have higher friction coefficients than that of the un-textured at all sliding speeds investigated in this article. Also, the anti-wear properties of the base polyurea grease and the base grease containing several additives on the textured and un-textured surfaces are discussed. Scanning electron microscopy and X-ray photoelectron spectroscopy were adopted to reveal the lubricating mechanism of different additives on the laser-textured surfaces.
 
Two novel phosphorous–nitrogen type phosphoramidate derivatives, dibutyl octadecylphosphoramidate and dimethyl 4-dodecylphenylphosphoramidate, were synthesized and applied as lubricant additives in rapeseed oil. Using a four-ball machine and standard method, the tribological behaviors of these additives in rapeseed oil were compared with commercial lubricant additives dodecan-1-aminium butyl 7-methyloctyl phosphate (coded T308B) and dibutyl phosphonate (coded T304). The results show that the phosphoramidate derivatives possess excellent antiwear, friction-reducing properties and good extreme pressure capacities. The tribological mechanism was investigated by X-ray absorption near edge structure spectroscopy. It is proposed that the prepared compounds as additives in rapeseed oil form a protective film on the rubbed surface, and the film contains phosphate and/or polyphosphate which can affect the tribological behavior.
 
This article describes the synthesis of dispersions consisting of irradiated poly(tetrafluoroethylene) (PTFE) micropowder in an ester oil (Synative ES TMP 05) and presents their results of the characterization in terms of stability and rheology. The degree of PTFE micropowder in the dispersion was gradually increased from 10 wt% to 25 wt%. In addition, two additives based on phosphoric acid were used to study whether they are able to affect the properties of the dispersion with the lowest concentration of PTFE micropowder. The amount of irradiated PTFE micropowder affects the stability against separation. The dispersion with the lowest concentration of PTFE micropowder (10 wt%) showed the highest stability due to the pronounced high fine fraction of PTFE particles (Ø: 0.2–0.5 µm). On the other hand, the PTFE/oil dispersions with higher concentrations own a distinctive amount of greater particles (Ø: 0.3–3.0 µm), suggesting a negative influence on the stability of the dispersions. Nevertheless, these dispersions can stabilize themselves by these structures.
 
Two novel disulfide-type triazine derivatives, 6,6'-disulfanediylbis(4-(dibutylamino)-1,3,5-triazine-2-thiol) (coded DTBT) and 6,6'-disulfanediylbis(4-(bis(2-ethylhexyl)amino)-1,3,5-triazine-2-thiol) (coded DTOT), were prepared. A four-ball tester was used to evaluate their tribological performances as anti-wear and extreme-pressure additives in biodegradable lithium grease. The results show that the disulfide-type triazine derivatives possess good friction-reducing properties and excellent anti-wear, extreme-pressure capacities. For further understanding of their tribological behaviors, X-ray photoelectron spectroscopy and scanning electron microscopy are adopted to analyze the tribofilms generated from these additives in biodegradable lithium grease. The results of X-ray photoelectron spectroscopy analysis illustrate that the prepared compounds as additives in biodegradable lithium grease forms a protective film containing FeS, FeS2 (or S-containing organic compounds), Fe2(SO4)3, FeSO4, FeO (or Fe3O4), and N-containing organic compounds on the metal surface during the sliding process.
 
The paper describes a theoretical study of adhesion at the contact between rough surfaces with small-scale surface asperities using an elastic-plastic model of contact deformation that is based on accurate finite element analysis (FEA) of an elastic-plastic single asperity contact. The model considers a large range of interference values from fully elastic through elastic-plastic to fully plastic regimes of contacting asperities. The well-established elastic and plastic adhesion indices are used to consider the different conditions that arise as a result of varying load and material parameters. The loading and unloading behaviour for different combinations of these adhesion indices are obtained as functions of mean separation between the surfaces. Comparison with a previous elastic-plastic model that was based on some arbitrary assumptions is made, showing significant differences.
 
The adhesion force between rail and wheel is one of the important factors for proceeding towards the realization of high-speed railway. On the other hand, it is supposed that the water film formed between the rail and wheel has a remarkable influence on the adhesion force under rainy condition at higher speeds. In this paper, taking Bett and Cappi's viscosity values of water, which show quite a different behaviour from the viscosity of oil, the influence has been investigated of important factors such as rolling speed, contact pressure and temperature on water film thickness for a smooth surface by applying elastohydrodynamic lubrication theory. Based on the numerical solutions, an empirical equation has been developed for water film thickness relating to rolling speed, load and material parameter by using a linear regression method and comparing it with other authors' works on a lower material parameter or elastic-isoviscous contact. Furthermore, in order to understand the influence of the above factors and the surface roughness on the adhesion force, adhesion coefficients have been calculated on a trial basis in the case of rough surface contact under limited conditions, and the theoretical results have been compared with the measured values of the tests on Japanese Shinkansen vehicles in the field.
 
Top-cited authors
Michel Fillon
  • Institut Pprime
Roland Larsson
  • Luleå University of Technology
Duncan Dowson
  • University of Leeds
Zhongmin Jin
  • University of Leeds
Rob Dwyer-Joyce
  • The University of Sheffield