What is Tribology? Tribology is the science of wear, friction and lubrication, and encompasses how interacting surfaces and other tribo-elements behave in relative motion in natural and artificial systems.This inclues bearing design and lubrication. Tribology is not an isolated science, but rather a complex, multidisciplinary endeavor where advances are made by collaborative efforts of researchers from fields including mechanical engineering, manufacturing, materials science and engineering, chemistry and chemical engineering, physics, mathematics, biomedical science and engineering, computer science, and more. This tribological system is composed of the collective stress/operational inputs, system structure and the functional and loss outputs. The collective stress includes the technical and physical load parameters including load, sliding speed and duration along with the movement and temerature conditions stressing the system-structure. The system-structure is determined by the property profiles of the substantial elements including the base, opposing body and ambient and the intermediate medium. 1 Horst Czichos, Karl-Heinz Habig: Tribologie Handbuch: Tribometrie, Tribomaterialien, Tribotechnik, Vieweg+Teubner Verlag, 2010 2 Theo Mang, Kirsten Bobzin, Thorsten Bartels: Industrial Tribology: Tribosystems, Friction, Wear and Surface Engineering, Lubrication, Wiley-VCH, 2011 3 Theo Mang et al.: Encyclopedia of Lubricants and Lubrication, Springer Verlag, 2014.
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What is friction? Friction is the force of resistance to motion between two bodies in contact. Friction can be described on the macroscopic level by the basic laws of friction from physicists Guillaume Amontons and Charles-Augustin de Coulomb. These physicists found a linear relationship between resulting friction force and applied normal load. Based on this, a dimensionless main parameter can be derived, called the coefficient of friction. It is defined by the ratio of the resulting friction force and applied normal force. However, the actual mechanism of sliding friction occurs at a microscopic level, which means tribological theories on friction also involve the topography of the surfaces.
Covering both the mechanical and materials aspects of tribology, this accessible text provides the scientific and practical foundations necessary for a thorough understanding of the phenomena of friction, wear and lubrication. [download] ebooks tribology friction and wear of engineering materials pdf. ACT TEST HOW TO SCORE HIGH ON YOUR FIRST TRYALSO get free act.
Friction And Wear Of Composite Materials
The tribologist differentiates between the real contact area and the nominal contact area (geometric dimensions), which accounts for any voids or non-contacting portions of a solid element. The mechanisms responsible for the energy transforming process in the near surface area include: 1.
Friction and wear mechanisms are strongly affected by the structure of the tribological system as well as on the induced collective stress: µ=f(tribo-structure(t),induced collective stress(t)) w=f(tribo-structure (t),induced collective stress(t)) Friction and wear mechanisms do not occur in an isolated fashion, but rather through a superposition of mechanisms that is challenging to quantify and control for. This superposition occurs in tribo-technical systems in non-detectable proportions and in proportions that vary across time and place, making it nearly impossible to calculate friction and wear processes in a tribo-contact. This is why tribological tests are so crucial for estimating tribological behavior. If we want to interpret and understand tribologically-measured data and mechanism-oriented research, we need complete knowledge of the acting mechanisms in a tribo-contact.
Tribologists classify friction, wear and lubrication conditions according to the following schedules:. Friction Regime 0: Solid friction: Friction is created between direct contacting solid surfaces without any lubricant.
Friction Regime I: Boundary friction: Solid friction, in which the surfaces of the friction partners are covered with a molecular lubricant film that has no load carrying capacity. The Lubricant has an influence on the friction and wear characteristics. Friction Regime II: Mixed friction: Friction regime I and III co-exist. The friction value is a combination of solid and hydrodynamic friction.
A fluid film created by the lubricant has a load carrying capacity. Friction regime III: Hydrodynamic friction: Friction value is determined by shearing in the fluid. The load carrying capacity of the fluid film prevents direct contact between the two solid surfaces. Wear regime a: High wear rates due to solid friction and direct contact of surfaces. Wear regime b: Lower wear values due to a molecular fluid film. Wear regime c: Mild wear due to a partial separation of the surfaces through a thicker fluid film. Wear regime d: “Zero wear,“ resulting from hydrodynamic or elastohydrodynamic fluid films that prevent direct contact of the two surfaces.
How can Tribology lead to measurable product improvement? Tribological testing allows us to gain information about tribo-performance of materials to drive new and better material designs. We can then target material compositions to achieve specific and better tribological properties.
Tribological test results and surface analytical methods help us estimate the tribo-performance including friction and wear, failure mechanisms, kinetics of transfer films of existing materials and new prototypes based on various factors and influences. This information helps us see and understand variables like the effects of various material compositions including filler, filler concentration, synergetic effects of fillers, material structure as well as the impact of other elements of they system structure. How does Tribology improve efficiency and extend service life of bearing materials? Tribologically optimised contacting surfaces. Identifying critical factors influencing the tribo-system. Identifying solutions to improve efficiency and reducing wear, including:.
Use of friction and wear optimized materials. Optimizing material pairings, which leads to low friction and wear levels. Selecting and using the correct lubricants. Arriving at design changes that have a beneficial impact on overall tribo-system performance. What are some examples of bearing technology advancements tribological research has delivered? For an overview of the historical advancements in bearing technology driven by tribo-research, read. It covers rudimentary roller bearings used by the ancient Egyptians, ball bearings used by the Romans 40BC, the roles of heat treatment of hardened steel and oxide-based ceramics.
It also covers he development of the first self-lubricating plain metal-polymer bearing by GGB. In what industries and applications is tribology useful? Tribology plays a central role in applications in which two contacting surfaces move in relation to each other. Some industries place higher demands on tribological systems due to their mission criticality, continuous operation requirements or extreme conditions. This depends strongly on the application.
Some applications require low friction (e.g. Bearing materials) while others require high friction (e.g. Brake systems). For most of the applications, minimum wear of the materials is a primary goal.
For many applications, a defined sweet spot between low friction levels and good wear performance is often targeted. When designing experiments describing friction and wear, tribological testing can be placed into one of six main categories, from field tests in Category I to simplest laboratory model tests Category VI. Category I: A field trial is conducted under normal operating conditions, which may include extended operating conditions. This results in poor repeatability but is close to real world requirements the tribological system will face. Category II: Experiments are undertaken with a complete piece of equipment in a plant environment.
These experiments may achieve results close to normal operating conditions and can be conducted over a period of time to replicate extended operating conditions while limiting environmental impact. Category III: Components, subsystems or assemblies are tested in a laboratory approximating normal extended operating conditions, yielding medium repeatability Category IV: Laboratory testing is conducted on serial standard components using scaled down testing plant apparatus.
Category V: Experiments are conducted on a specimen with test equipment to deliver close to normal operating conditions with excellent repeatability. Category VI: A bench test is conducted with simple laboratory test equipment.
It is important to remember that in categories I through III, the system structure of the original tribo- aggregate remains consistent, and only the collective stress is simplified. Categories II and III offer more reproducible collective stresses than category I. In contrast, in categories IV through VI, the system structure is simplified with the disadvantage of decreasing predictability in the transferability of test results to comparable practical tribo-technical systems. Categories IV through VI offer better metrology of the sub tribo-contact, lower cost and a tighter testing timeframe. 1 So with an ascending order of the test categories the test time as well as the test cost increases significantly, but transferability of the test result increases as well. How can we apply the test categories to the sub tribo-system bearing? Tribological testing of bearing materials can be divided into four main categories:.
Product performance descriptions, which would include categories IV and III to ensure the transferability of results. Production/Manufacturing monitoring, including categories VI through IV, with category III also being a possibility. Customer-related testing of bearings may include categories III through V, keeping in mind that category V is relevant only if the test can be adapted as close as possible to the application. All categories may be used to support material designers, with lower categories in the early stages of development for pre-selection and higher-numbered categories coming into play as the subcomponents and the final product are available. 1 Horst Czichos, Karl-Heinz Habig: Tribologie Handbuch: Tribometrie, Tribomaterialien, Tribotechnik, Vieweg+Teubner Verlag, 2010. In 2015, launched the and the.
Launched a series of self-lubricating sintered bronze and sintered iron bearings in 2014, including the, and. The serve as the primary suspension components for the rover’s drill spindle. Dynamic trader 7 crackle. In 2010, launched materials for superior performance under marginally-lubricated or dry conditions, including the lead-free metal-polymer materials and.
Launched a filament-wound product range for the European and Asian markets in 2009, including a strong, stable structure for high-load, low-wear requirements. New are recognized by winning the 2008 North American Frost & Sullivan Award for Product Innovation of the Year award in the Class 7-8 truck bearings category, awarded for excellence in new products and technologies in the industry. In 2003, introduced thewith improved performance under lubricated conditions and lower friction, better wear resistance and improved fatigue strength.
Launched, a new range of injection-molded thermoplastic solid polymer bearings. In 1995, introduced the to satisfy the needs of automotive shock absorbers and other hydraulic applications.
Took on high-temperature applications with the 1986 launch of bearing material. Launched the first filament wound product range in the U.S. Including, supporting high static and dynamic loads. In 1965, launched the for grease or oil-lubricated applications. In 1956, GGB introduced the for excellent low friction and wear resistance.
That same year, the company introduced the DU-B, with bronze backing for improved corrosion resistance. In 1887, Olin J. Garlock patented his first industrial sealing system to seal piston rods in industrial steam engines. The scope of the tribological system is of essential importance in bearing selection. A high level overview of considerations would include the following 1.
The induced collective stress including:. Nature of the load. Nature of the motion. Temperatures.
Time factor 2. The mating partner:. Materials, including physical and chemical properties.
Geometrical features including the contact ratio and topography (roughness, isotropy and anisotropy) 3. The interfacial medium and its property profile 4. The ambient medium and its properties 5. Thermal conductivity of the construction.
Tribology is the science and engineering of interacting surfaces in relative. It includes the study and application of the principles of, and. Tribology is highly interdisciplinary in nature and draws upon several academic areas including:, and.
The word tribology derives from the root τριβ- of the verb, 'I rub' in classic Greek and the suffix from, 'study of', 'knowledge of'. It was coined by in 1966, who produced an eponymous report which highlighted the cost of, and to the UK economy. Tribological experiments suggested by Leonardo da Vinci Early History Despite the relatively recent naming of the field of tribology, quantitative studies of can be traced as far back as 1493, when first noted the two fundamental ‘laws’ of. According to da Vinci, the frictional resistance was the same for two different objects of the same weight but making contacts over different widths and lengths. He also observed that the force needed to overcome friction doubles when the weight doubles. However, da Vinci's findings remained unpublished in his notebooks. The two fundamental ‘laws’ of were first published (in 1699) by, with whose name they are now usually associated, they state that:.
the force of friction acting between two sliding surfaces is proportional to the load pressing the surfaces together. the force of friction is independent of the apparent area of contact between the two surfaces. Although not universally applicable, these simple statements hold for a surprisingly wide range of systems.
These laws were further developed by (in 1785), who noticed that sliding (kinetic) is independent of the sliding velocity. In 1798, and carried out the first reliable test on frictional. In a study commissioned by the, they used a simple reciprocating machine to evaluate the rate of. They found that coins with grit between them wore at a faster rate compared to self-mated coins. In 1953, John. F Archard developed the which describes sliding wear and is based on the theory of contact.
Other early pioneers of tribology research included Australian physicist and British physicist, both of. Together they authored the seminal textbook 'The Friction and Lubrication of Solids' (Part I originally published in 1950 and Part II in 1964). Neale was another leader the field of tribology during the mid-to-late 1900's. He specialized in solving problems in machinery design by applying his knowledge of tribology.
Neale was respected as an educator with a gift for integrating theoretical work with his own practical experience to produce easy-to-understand design guides. The Tribology Handbook, which he first edited in 1973 and updated in 1995, is still used around the world and forms the basis of numerous training courses for engineering designers.
Surveyed the history of tribology in his 1997 book History of Tribology (2nd edition). This covers developments from prehistory, through early civilizations (, ) and highlights the key developments up to the end of the twentieth century.
Stribeck Curve The 'Stribeck curve'is named after, and who developed it during the first half of the 20th century. It describes the variation in friction between two liquid-lubricated surfaces as a function of a dimensionless parameter (the Hersey number). The Hersey number can be defined as: ηN/P, where η is the dynamic, N is the sliding speed, and P is the load. Schematic Stribeck curve ( Hersey number on horizontal axis, Friction on vertical) 1. Boundary lubrication 2. Mixed lubrication 3. Hydrodynamic lubrication Stribeck curves describe the transition between different lubrication regimes with increasing speed for liquid-lubricated sliding surfaces, these can be broadly categorized as: 1.
Boundary lubrication Solid surfaces come into direct contact, load supported mainly by surface, high 2. Mixed lubrication Some asperity contact, load supported by both asperities and the liquid.
Hydrodynamic lubrication Negligible asperity contact, load supported mainly by liquid lubricant. 's research was performed in at the Royal Prussian Technical Testing Institute (MPA, now BAM). Similar work was previously performed around 1885 by at the same institute, and also in the mid-1870s by at the in the U.S. The reason why the form of the friction curve for liquid lubricated surfaces was later attributed to Stribeck, although both Thurston and Martens achieved their results considerably earlier may be because Stribeck published in the most important technical journal in Germany at that time, Zeitschrift des Vereins Deutscher Ingenieure (VDI, Journal of German Mechanical Engineers). Martens published his results in the official journal of the Royal Prussian Technical Testing Institute, which has now become BAM. The VDI journal was one of the most important journals for engineers and provided wide access to these data and later colleagues rationalized the results into the three classical friction regimes.
Thurston did not have the experimental means to record a continuous graph of the coefficient of friction but only measured it at discrete points. This may be the reason why the minimum in the coefficient of friction for a liquid-lubricated was not discovered by him, but was demonstrated by the graphs of Martens and Stribeck. A typical Stribeck curve obtained by Martens The graphs of friction force reported by Stribeck stem from a carefully conducted, wide-ranging series of experiments on. Stribeck systematically studied the variation of friction between two liquid lubricated surfaces. His results were presented on 5 December 1901 during a public session of the railway society and published on 6 September 1902, They clearly showed the minimum value of friction as the demarcation between full fluid-film lubrication and some solid asperity interactions. Stribeck studied different bearing materials and aspect ratios D/L from 1:1 to 1:2.
The maximum sliding speed was 4 m/s and the contact pressure was limited to 5 MPa, conditions relevant to railway wagon journal bearings. The Jost Report The term tribology became widely used following 'The Report', published in 1966. The report highlighted the huge cost of friction, wear and corrosion to the UK economy (1.1-1.4% of ).
As a result, the government established several national centres for tribology to address tribological problems. Since then the term has diffused into the international community, with many specialists now identifying as 'tribologists'. There are now numerous national and international societies, including: the Society for Tribologists and Lubrication Engineers in the USA, the ' and (, ) in the UK, the German Society for Tribology , the Malaysian Tribology Society , the Japanese Society of Tribologists , and the Chinese Mechanical Engineering Society. Technical universities all over the world have researchers working on tribology problems, often as part of departments. However, tribology groups now generally include at least as many materials scientists, physicists and chemists as they do mechanical engineers. Worldwide Importance Despite considerable research since The Report, the global impact of and on, economic expenditure, and are still considerable. In 2017, Kenneth Holmberg and attempted to quantify their impact worldwide.
They considered the four main energy consuming sectors:, and. The following were concluded:. In total, 23% of the world’s total energy consumption originates from tribological contacts.
Of that 20% is used to overcome friction and 3% is used to remanufacture worn parts and spare equipment due to wear and wear-related failures. By taking advantage of the new surface, materials, and lubrication technologies for friction reduction and wear protection in vehicles, machinery and other equipment worldwide, energy losses due to friction and wear could potentially be reduced by 40% in the long term (15 years) and by 18% in the short term (8 years). On a global scale, these savings would amount to 1.4% of annually and 8.7% of the total energy consumption in the long term. The largest short term energy savings are envisioned in (25%) and in the (20%) while the potential savings in the and sectors are estimated to be 10%. In the longer term, the savings would be 55%, 40%, 25%, and 20%, respectively. Implementing advanced tribological technologies can also reduce global by as much as 1,460 metric tons of carbon dioxide equivalent (MtCO 2) and result in 450,000 million cost savings in the short term.
In the long term, the reduction could be as large as 3,140 MtCO 2 and the cost savings 970,000 million. Applications Tribology problems range from to scales, in areas as diverse as the movement of continental plates and glaciers to the locomotion of animals and insects.
Until recently, most tribology research was concentrated on and sectors, but this has considerably diversified in recent times. Traditional Research Areas Historically, most tribology research concentrated on the design and effective lubrication of machine components, particularly for. However, the study of tribology extends into almost all other aspects of modern technology and any system where one material slides over another can be affected by complex tribological interactions. Tribology has played an important the industry, with effective of moving parts being critical to progress. In the past, tribology research in the industry focused on reliability, ensuring the safe, continuous operation of machine components.
Friction And Wear Of Grease Block-on-ring
Over the last few decades, due to an increased focus on, has become increasingly important and thus have become progressively more complex and sophisticated in order to improve this. Tribology also plays an important role in. For example, in metal-forming operations, friction increases tool wear and the power required to work a piece. This results in increased costs due to more frequent tool replacement, loss of tolerance as tool dimensions shift, and greater forces required to shape a piece.
The use of lubricants which minimize direct surface contact reduces tool and power requirements. New Research Areas Since the 1990s, new areas of tribology have emerged, including the, and. Nanotribology and biotribology study, and in nanoscale and biological systems respectively, whilst green tribology focuses on ecological considerations, such as sourcing of lubricant. Nanotribology is becoming increasingly important as devices become smaller (e.g. Micro/nanoelectromechanical systems, /) and research has been aided by the invention of.
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Recently, intensive studies of (phenomenon of vanishing friction) have sparked due to increasing demand for energy savings. Development of new materials, such as, have initiated the development of fundamentally new approaches to tribology problems. See also.