Tribological Design Research Articles

Critical analysis of a coaxial configuration for the characterization of adhesive wear and its application to Al and Al–Sn alloys

One of the main challenges of a tribological design is to find suitable pairs of materials to minimize friction and wear under specific operating conditions. To reproduce conditions of sliding and adhesive wear, a coaxial tribometer was developed. The equipment uses real-time data acquisition and feedback, allowing continuous control over a wide range of loads and rotational speed. Finite element analysis and experiments on selected materials are used to present a critical assessment of the advantages and drawbacks of the proposed configuration. Specifically, the tribological behaviour of cold-rolled and recrystallized AA1100 Al alloy and Al–Sn alloys is revisited. Worn surfaces are characterized by optical roughness measurement and SEM observation. Optical profilometry shows higher values of roughness in cold-rolled materials and confirms the essential contribution of Sn to the reduction of adhesive wear in Al-based alloys. At the surface of the SAE 783 alloy, severe mechanical mixing of the Al and Sn phases was observed in the worn zones as the result of severe plastic deformation during the formation of the tribologically modified surface layer.

マイクロスケールにおけるトライボロジー設計

マイクロスケールにおけるトライボロジー設計

A Wear Model of Plane Sliding Pairs Based on Fatigue Contact Analysis of Asperities

Wear modeling is essential to predict and improve wear resistance of machine parts. This article presents a fatigue wear model of plane sliding pairs under dry friction. The wear model is constructed through developing a dynamic contact model of surfaces and proposing a mean fatigue damage constant of asperities. It is simpler and more practical than existing fatigue wear models because it describes the quantitative relationship between the wear behaviors of the plane sliding pairs and the main factors including the load and sliding speed, material property, friction property, and surface topography of the pairs. Furthermore, the wear model can predict the wear of each component of the sliding pairs. Reasonability and applicability of the wear model are validated via pin-on-disc wear tests. The wear model is applicable to predict the wear of the plane sliding pairs, which is characterized by friction fatigue of contact surfaces. The wear model can also be used to guide the tribological design of sliding pairs in machinery.

The Tribology Design in Transport Machinery Design

A common problem in transport machinery equipment is friction and wear. This problem largely affects the service life in a transport machinery equipment. It should be given enough attention to the tribology design in transport machinery design. This article mainly describe the tribology design content from the material choice, surface design, structural design to lubrication technology, etc.

Selected papers from those presented at the 3rd International Tribology Symposium of IFToMM

The International Federation for the Promotion of Mechanism and Machine Science (IFToMM) is an organisation aimed at promoting research and development in the field of machines and mechanisms by theoretical and experimental methods, along with their practical application. IFToMM has several technical committees in different fields, and one is dedicated to Tribology. The technical committee for tribology requests prominent research groups in tribology to host and organise an international symposium on tribology. The 1st International Conference on Tribology of IFToMM was held in Bejing, China, in 2008, and the 2nd symposium was organised in Rio de Janeiro, Brazil, in 2010. The 3rd International Tribology Symposium of IFToMM was organised by the Division of Machine Elements of Luleå University of Technology in Sweden from March 19–21, 2013. The symposium was held in the Luleå University of Technology campus during three fantastic winter days, providing a perfect forum for the tribologists for presenting their latest research and exchange of ideas. The participants were also given the opportunity to experience the snowy landscape during a memorable outdoor dinner. The symposium attracted 146 participants from 26 countries. In all, 92 papers spread over 32 sessions (including six plenary sessions) were presented. These papers covered both the fundamental and applied aspects of wide ranging topics such as friction, wear, lubrication, lubricants, tribology in hostile environment, tribomaterials, solid lubricants, surface engineering, tribotesting, tribological design and optimisation of machine components, modelling in tribology, biotribology, micro/nanotribology, tribotronics, tribology in power generating systems, metal working tribology and tribology in rail and road transport. Two additional events were also organised in conjunction with the conference, a young researcher forum and the second international high temperature tribology workshop. This special issue of Lubrication Science contains papers1-8 from those presented at the 3rd International Tribology Symposium of IFToMM (ITS 2013) that were recommended by the organising committee of ITS 2013. Zhmud et al.1 introduced the triboconditioning process, which is a mechanochemical surface finishing technique developed for improving the tribological properties of mechanical components made of steel or cast iron. The process combines elements of extreme pressure mechanical burnishing of the component surface with a tribochemical deposition of a low-friction anti-wear film of tungsten disulphide (WS2). In the paper of Kaneta et al.,2 the effects of microgrooves in elliptical EHL contacts is studied by means of numerical analysis. The results show that the formation of microgrooves induced by local high pressures may influence the surface failure of machine elements. Lijesh and Hirani3 studied the stiffness and damping characteristics of a special type of rubber-mounted hybrid bearing. For example, by softening the rubber through immersing it in an aromatic liquid, the effect of rubber Young's modulus on the damping was studied. Courbon et al.4 focused their study on the influence of cryogenic lubrication on friction within the context of machining TiAl6V4 and Inconel 718 alloys with carbide cutting tools. For this purpose, they used a specially designed open tribometer in order to characterise macroscopic friction coefficient, heat transfer and adhesion in the contact for a large range of sliding velocities. In the paper5 by Tuszynski et al., they performed model and component scuffing test with gear oils formulated with biodegradable and non-toxic base oils. They draw the conclusion that rapeseed-based gear oils can be used only for the lubrication of gears working under moderate load conditions Rajput and Sharma6 investigated the influence of micropolar lubrication on the stability of a constant flow valve compensated multi-recess conical hybrid journal bearing system. They performed numerical simulations of the micropolar lubricated bearing system by means of a finite element discretisation of a Reynolds equation modified according to Eringen theory. Lichun et al.7 studied the effect of surface texturing on friction, and wear properties of a line contact between cylindrical and plane surfaces in sliding were investigated experimentally in mixed lubrication conditions. In their tests, lower dimple area density and larger dimple size showed a better lubrication performance. Minami et al.8 investigated new tribosystems composed of green chemicals. For example, they assessed the compatibility of a Zn-free lubricant with hydrogen-free amorphous DLC by means of an SRV test machine and a friction coefficient of 0.02 with steel as counter surface. The organising committee would like to thank all the authors and delegates who made ITS 2013 a very successful and much memorable event. Finally, the guest editors of this special issue of Lubrication Science would also like to sincerely thank all the reviewers for devoting their time and providing their valuable inputs during the reviewing process of these papers.

The Development of Tribology

In the past 20 years, with the rapid development of nanotechnology and increasing people's social needs, tribology gained the rapid development. Meanwhile, many new areas produced. This article describes a simple spherical roller bearing down tribology design. Thus the development of tribology and trends are explained.

Lubricating a bright future: Lubrication contribution to energy saving and low carbon emission

Both the academic society and the industry are hunting for new energy forms for the future. However, the world should not forget the conventional technologies that contribute to the sustainable society by technical innovations. Among them, lubrication plays a significant role in energy saving and in low CO2 emission by increasing the fuel efficiency and by prolonging the service life of machines. With the advance of novel synthetic approaches, and nanoscience and technologies, novel lubrication oils and additives and their formulations are being developed to reduce friction and wear, and novel surface treatment routes and surface coatings are invented and provide more efficient lubrication. These technologies create tremendous chances for machines to work more efficiently with low energy consumption. Here we review the recent progresses and challenges associated with some novel lubrication techniques that include novel surface treatment (such as texturing, high-performance nanocomposite coatings, adapting coating), tribology design (solid and liquid lubrication), energy-conserving engine oil and novel lubricants and formula (such as ionic liquids, low S, P content additives) which are to be adopted to enhance the fuel efficiency to achieve energy saving and low carbon emission. There is increased demand to replace fossil lubricants by degradable green lubricants. Specially designed coatings can reduce drag significantly during navigation of both airplanes and ships. All these aspects will be also reviewed in the paper.

A Dynamic Contact Model of Rough Surfaces Based on the Microscopic Contact Analysis of Asperities

Dynamic contact model of rough surfaces can provide the theoretical basis for analyzing the microscopic damage of surfaces in wear process and constructing the analytical wear model to predict wear. A dynamic contact model of sliding rough surfaces is innovatively constructed based on the characterization of the contact asperities on rough surfaces in this paper. Firstly, an asperity model of rough surface is set up according to the surface topography parameters and the static contact parameters is evaluated in the light of statistics contact theory; Then the contact characteristic of surface topography in sliding is analyzed and a series of equivalent contact models are proposed; Finally, the dynamic contact model of rough surfaces is established and from which the dynamic contact parameter of rough surfaces is formulated. The dynamic contact model can be further improved to analyze the friction fatigue wear of sliding pairs and provide reference for tribology design of mechanical surfaces.

Study on Influence of Cylinder Liner Surface Texture on Lubrication Performance for Cylinder Liner–Piston Ring Components

A marine diesel engine, where the cylinder liner–piston ring (CLPR) pair is one of the most important rubbing pairs, is the heart of a marine system. Studying the lubrication characteristics of the CLPR will provide a guide for rational design of the CLPR to reduce wear and prolong its service life. The surface texture features have a significant impact on the lubricating performance of the CLPR. In this study, the tribological system of the CLPR was investigated. Different surface textures (such as different sizes of surface concaves and grooves, etc.) were designed and produced on the cylinder liners using surface treatment. A series of experimental tests were then carried out in a specially designed diesel engine tester to investigate the tribological characteristics of the treated CLPR pairs. The comparison analyses of the worn surface texture features, element content of the lubrication oil, and abrasive particle characteristics were conducted under different wear surface texture features and cylinder liner speeds. The analysis results showed that there were significant differences in the tribological and lubrication properties of the rubbing pairs in different wear surface texture features. The wear performance of the CLPR pair with a regular concave texture was superior to that of the concave and groove, and regular groove textures. In addition, the regular concave with a depth-diameter ratio of 0.1 was the most effective surface texture to improve the lubrication and wear properties of the CLPR pairs. It is believed that the knowledge obtained in this study provides the real practical basis for tribological design and manufacturing of CLPR pair in marine diesel engines.

Reprint of Nanowear behaviour of monocrystalline silicon against SiO2 tip in water

By using an atomic force microscopy, the wear tests of Si(100) surface against SiO2 microsphere were performed both in water and in air. During the tests, the contact pressure was varied between 0.78GPa and 1.1GPa, the displacement amplitude was set as 250nm and the number of wear cycles was 200. As a comparison, the wear tests of Si(100) surface against diamond tip were also performed in water and air. The experimental results indicated that water environment played an important role in the wear behaviour of Si/SiO2 pair. Under a contact pressure of 1.1GPa, the wear depth of silicon in water was about 0.25nm, which was less than 10% of that in air. Since the wear depths of silicon in water were similar at various velocities (0.04–5μm/s), the hydrodynamic lubrication was not the main reason causing the slight wear of silicon in water. Further analysis indicated that the distinct wear behaviour of Si/SiO2 pair in air and in water could be mainly explained as the different intensity of chemical reactions in two environments for the pair of Si/SiO2. In air, the SiOSi bridges could easily form between SiO2 microsphere and silicon substrate and induced serious tribochemical wear of silicon. When the Si/SiO2 pair was immersed in water, the tribochemical reaction was largely resisted by the electrical double layer and the wear of silicon was slight. Even though, since the contact pressure was too low to induce the mechanical wear of silicon, the limited wear of silicon in water was still attributed to the tribochemical reaction. The results may help us understand the nanowear mechanism of silicon and optimize the tribological design of dynamic MEMS working in water environment.

Nanowear behaviour of monocrystalline silicon against SiO2 tip in water

By using an atomic force microscopy, the wear tests of Si(100) surface against SiO2 microsphere were performed both in water and in air. During the tests, the contact pressure was varied between 0.78GPa and 1.1GPa, the displacement amplitude was set as 250nm and the number of wear cycles was 200. As a comparison, the wear tests of Si(100) surface against diamond tip were also performed in water and air. The experimental results indicated that water environment played an important role in the wear behaviour of Si/SiO2 pair. Under a contact pressure of 1.1GPa, the wear depth of silicon in water was about 0.25nm, which was less than 10% of that in air. Since the wear depths of silicon in water were similar at various sliding velocities (0.04–5μm/s), the hydrodynamic lubrication was not the main reason causing the slight wear of silicon in water. Further analysis indicated that the distinct wear behaviour of Si/SiO2 pair in air and in water could be mainly explained as the different intensity of chemical reactions in two environments for the pair of Si/SiO2. In air, the SiOSi bridges could easily form between SiO2 microsphere and silicon substrate and induced serious tribochemical wear of silicon. When the Si/SiO2 pair was immersed in water, because of the different structure of the adsorbed water layer on silicon surface and the effect of the electrical double layer, the tribochemical reaction was largely resisted and the wear of silicon was slight. Even though, since the contact pressure was too low to induce the mechanical wear of silicon, the limited wear of silicon in water was still attributed to the tribochemical reaction. The results may help us understand the nanowear mechanism of silicon and optimize the tribological design of dynamic MEMS working in water environment.

Mechanical Hybrid KERS Based on Toroidal Traction Drives: An Example of Smart Tribological Design to Improve Terrestrial Vehicle Performance

We analyse in terms of efficiency and traction capabilities a recently patented traction drive, referred to as the double roller full-toroidal variator (DFTV). We compare its performance with the single roller full-toroidal variator (SFTV) and the single roller half-toroidal variator (SHTV). Modeling of these variators involves challenging tribological issues; the traction and efficiency performances depend on tribological phenomena occurring at the interface between rollers and disks, where the lubricant undergoes very severe elastohydrodynamic lubrication regimes. Interestingly, the DFTV shows an improvement of the mechanical efficiency over a wide range of transmission ratios and in particular at the unit speed ratio as in such conditions in which the DFTV allows for zero-spin, thus strongly enhancing its traction capabilities. The very high mechanical efficiency and traction performances of the DFTV are exploited to investigate the performance of a flywheel-based Kinetic Energy Recovery System (KERS), where the efficiency of the variator plays an important role in determining the overall energy recovery performance. The energy boost capabilities and the round-trip efficiency are calculated for the three different variators considered in this study. The results suggest that the energy recovery potential of the mechanical KERS can be improved with a proper choice of the variator.

Predicting Film Parameter and Friction Coefficient for Helical Gears Considering Surface Roughness and Load Variation

Lubricant film parameters and the friction coefficient play an important role in improving the reliability and efficiency of helical gear sets. This article proposes a methodology to predict the film parameter and friction coefficient of involute helical gears considering surface roughness and load variation. Geometric and kinematic parameters at each contact point in the plane of action were calculated. A load distribution model without finite element analysis, which saves computing time and makes load variation along the contact line considered possible, was employed. The load-sharing concept was firstly employed in helical gears to obtain the film parameters and friction coefficient. Then distributions of the film parameters and friction coefficient through the plane of action of helical gears were presented. Comparisons were carried out to verify the validation of proposed model. Furthermore, the effects of surface roughness, rotation speed, and transmitted load on the friction coefficient were investigated and discussed. The results show that the pinion addendum will firstly enter a mixed lubrication regime and the friction coefficient in the plane of action will increase with rougher surfaces or less transmitted load, whereas the increase in pinion rotating speed will speed up the transition from a boundary lubrication regime to a mixed lubrication regime. The proposed model provides a useful tool for tribology design and further dynamic analysis of helical gear sets under real conditions.

Evaluation on tribological design coatings of Al2O3, Ni–P–PTFE and MoS2 on aluminium alloy 7075 under oil lubrication

The current work evaluated the friction and wear properties of tribological design surface coatings on aluminium alloy 7075 under various speed and nominal contact pressure. Hard-anodized Aluminium Oxide (Al2O3), burnished Refractory Metal Sulfide (MoS2) and composite electroless nickel coatings with polytetrafluoroethylene (Ni–P–PTFE) particles were subjected to pin-on-disc sliding test against grey cast iron (GCI) under Mach 5 SL SAE 10W-30 lubrication. The results indicated that Ni–P–PTFE composite coating possessed excellent friction–reduction capability but limited wear resistance due to low mechanical strength. Al2O3 coated sample showed outstanding wear resistance with high friction characteristic leading to high surface contact temperature. Furthermore, MoS2 coating improved the wear resistance of the aluminium alloy.

Modeling of Magnetorheological Fluids by the Discrete Element Method

Magnetorheological (MR) fluids are fluids whose properties vary in response to an applied magnetic field. Such fluids are typically composed of microscopic iron particles (~1-20μm diameter, 20-40% by volume) suspended in a carrier fluid such as mineral oil or water. MR fluids are increasingly proposed for use in various mechanical system applications, many of which fall in the domain of tribology, such as smart dampers and clutches, prosthetic articulations, and controllable polishing fluids. The goal of this study is to present an overview of the topic to the tribology audience, and to develop an MR fluid model from the microscopic point of view using the discrete element method (DEM), with a long range objective to better optimize and understand MR fluid behavior in such tribological applications. As in most DEM studies, inter-particle forces are determined by a force-displacement law and trajectories are calculated using Newton’s second law. In this study, particle magnetization and magnetic interactions between particles have been added to the discrete element code. The global behavior of the MR fluid can be analyzed by examining the time evolution of the ensemble of particles. Microscopically, the known behavior is observed: particles align themselves with the external magnetic field. Macroscopically, averaging over a number of particles and a significant time interval, effective viscosity increases significantly when an external magnetic field is applied. These preliminary results would appear to establish that the DEM is a promising method to study MR fluids at the microscopic and macroscopic scales as an aid to tribological design.

Electrothermomechanical Finite-Element Modeling of Metal Microcontacts in MEMS

Three-dimensional fractal representations of surface roughness are incorporated into a finite-element framework to obtain the electrothermomechanical behavior of ohmic contacts in radio frequency (RF) microelectromechanical systems (MEMS) switches. Fractal surfaces are generated from the Weierstrass-Mandelbrot function and are representatives of atomic force microscope surface roughness measurements of contact surfaces in fabricated RF MEMS switches with metal contacts. A specialized finite-element scheme is developed, which couples the thermomechanical asperity creep deformations with the electromechanical contact characteristics to obtain predictions of contact parameters and their evolution as a function of time and loading. A dislocation-density-based crystal plasticity framework is also used to investigate microstructure evolution at microcontacts and its effects on contact parameters. Using this approach, simulations are made to investigate how surface roughness, initial residual strains, and operating temperature can affect asperity contact behavior. Based on these predictions, tribological design guidelines can be obtained to increase the lifetime of low-contact-resistance RF MEMS switches by limiting stiction and electrical resistance increase.

Tribological design constraints of marine renewable energy systems

Against the backdrop of increasing energy demands, the threat of climate change and dwindling fuel reserves, finding reliable, diverse, sustainable/renewable, affordable energy resources has become a priority for many countries. Marine energy conversion systems are at the forefront of providing such a resource. Most marine renewable energy conversion systems require tribological components to convert wind or tidal streams to rotational motion for generating electricity while wave machines typically use oscillating hinge or piston within cylinder geometries to promote reciprocating linear motion. This paper looks at the tribology of three green marine energy systems, offshore wind, tidal and wave machines. Areas covered include lubrication and contamination, bearing and gearbox issues, biofouling, cavitation erosion, tribocorrosion, condition monitoring as well as design trends and loading conditions associated with tribological components. Current research thrusts are highlighted along with areas needing research as well as addressing present-day issues related to the tribology of offshore energy conversion technologies.

Development of a tribological failure knowledge model

Many of the component failures occurring in service can be delayed by better incorporation of tribological principles into engineering design and maintenance. However, the concept of tribology has not yet penetrated successfully into the industry in general and there is an urgent need for the practical tribology design criteria and transference of tribological knowledge to the engineering designer and maintenance engineer. Knowledge based system offers great potential for effecting tribological knowledge transfer and promoting improved design practice and maintenance strategy. In this present work, the development and implementation of a tribological failure knowledge model (KM) for steam power plant equipment is reported. This failure KM assists the maintenance engineer and design engineer for evolution of an effective maintenance strategy and better, reliable, safe and productive design. The KM has been implemented using Protege 3.0 Beta, JDK 1.4 and Java Swing Package. The model is applied to steam turbine failure in a power plant application.

2009 Knee Society Presidential Guest Lecture: Polyethylene Wear in Total Knees

Knee arthroplasties in young and active patients place a substantial increase in the lifetime tribological demand and potential for wear-induced osteolysis. Polyethylene materials have advanced in recent years, reducing the potential for oxidative degradation and delamination failure. It is timely to consider tribological design variables and their potential to reduce surface wear and the long-term risk of osteolysis. The influence of reduced cross shear in rotating platform mobile-bearing knee designs and reduced surface wear area in low conforming fixed-bearing knees has been investigated. A reduction in cross shear substantially reduced wear in both multidirectional pin-on-plate studies and in rotating platform mobile-bearing designs in knee simulator studies. A reduction in bearing surface contact area substantially reduced surface wear in multidirectional pin-on-plate simulations and in low conforming fixed-bearing knee designs in knee simulator studies. This offers potential for a paradigm shift in knee design predicated by enhanced mechanical properties of new polymer materials. We describe two distinct low-wearing tribological design solutions: (1) a rotating platform design solution with reduced cross shear provides reduced wear with conformity and intrinsic stability; and (2) a low conformity fixed bearing with reduced surface area, provides reduced wear, but has less intrinsic stability and requires good soft tissue function.

Tribology research in China: A personal view

With the development of the economy and manufacturing industry, tribology research in China has experienced a fast growth over recent decades. This review gives an outline for the research progresses achieved by Chinese scientists and engineers in various subjects, including elastohydrodynamic lubrication (EHL) and mixed lubrication, nano-tribology, lubricants and additives, tribo-materials and coatings, tribology issues in biology and bionics, wear of materials, and tribological design that transfers research achievements to the design process of machine components. In comparison with the vastness of research activities and Chinese economy, this article is written by the present author, based on limited information and knowledge, but it may help tribologists around the world to get a better idea about what has been done by their counterparts in China, which would encourage communication and cooperation in tribology research.