1 Introduction Question: What is tribology? Tribology: Originated from the Greek word, tribos, meaning to rub The science of surfaces in contact under relative motion Generally involves the studies of friction, wear and lubrication Highly multi-disciplinary field (materials science, lubrication, chemistry, etc.) Historical perspectives 1. 1880 B.C.: ancient Egyptian lubricant animal fats, vegetable oils, water? Figure 1. Transporting an Egyptian colossus from the tomb of Tehuti-Hetep, El Bersheh, (Dowson, 1998). 2. 400 B.C.: iron bearings for olive-crushing mills in ancient Greece 3. 300 B.C.: metallic bearings with lubricants and leather seals in ancient China 4. Middle Ages: studded or rimed wooden wheels for decreased wear 5. Renaissance period: Early tribological theories (da Vinci) & machines (gears, roller bearings and pulleys) 6. Industrial Revolution: steel shafts, cam-driven systems, steam engine 7. 1966: Tribology introduced as a scientific field (Peter Jost & Committee, London) Tribological elements Require contact and relative motion Many common examples: 1. Pencil and eraser on paper 2. Feet and/or shoes and the ground 3. Tires and the road (chains for snow)
2 4. Human joints tribological research of prosthetic joints Figure 2. Structure of a human knee. 5. Countless machine elements (cams, gears, bearings, etc.) 6. Energy systems (engines and motors, wind turbines, generators, etc.) Figure 3. Tribological components of an internal combustion engine (Wang, 2002)
3 Figure 4. Components of a modern wind turbine. Tribological phenomena Multiple phenomena occur typically studied individually 1. Varying and complex surface geometries Figure 5. A typical tribological interface (Wang, 2002).
4 2. Complex loading conditions elastic deformation, plastic flow of the materials (surfaces and sub-surfaces), frictional shearing (lubricants and materials) Figure 6. (a) Deformed surface and (b) contact pressure distribution obtained from a three-dimensional contact model (Liu, 2001). 3. Frictional heating chemical changes (lubricants and surfaces), thermal displacements Energy system improvements 1. Industrial Revolution: steam engine (thermal efficiency of 0.5% in 1712 17% by 1834) 2. Windmills: first reported windmill ~ 800 years ago, efficiency range of 5-10% after WWII, Dutch engineers improved bearings, efficiency now 40-50%; aerodynamic efficiency limit, Betz limit of 59% 3. Various automotive improvements Timken bearings: 2% fuel economy improvement, 30% reduction in power consumption Surface engineering of components increased energy conservation 4. Others
5 Economics of tribology High cost of tribological losses 1. Estimated annual cost of energy and material losses due to friction and wear is more than $100 billion in the US alone (Wang, 2002) 2. Worldwide, nearly 1/3 of the world s energy production is spent to overcome friction (Szeri, 1980) Figure 7. US residential and commercial energy consumption, where Losses 1 include energy lost during generation, transmission, and distribution of electricity (www.eia.doe.gov, 2001). Figure 8. US industrial energy consumption, where Losses 1 include energy lost during generation, transmission, and distribution of electricity (www.eia.doe.gov, 2001).
6 Economic savings from tribology 1. Many countries (US, UK, Germany, China, Canada, etc.) savings related to tribology improvements is ~ 1% of the GNP 2. Fuel savings: A simple example (increased savings with better tires and increased fuel economy) Figure 9. Fuel savings versus projected US consumption and Artic Refuge oil production (NRDC, 2005) 3. Fuel savings for a heavy-duty truck: Life cycle analysis 3% overall improvement in fuel consumption resulted from using fuel-efficient engine oil, gear oil and axle grease (Taylor, 2004) 4. Improved lubricants decreased wear and frictional heating (lubrication monitoring) 5. New and improved materials decreased surface fatigue 6. Surface engineering, e.g. surface coatings (decreased friction, wear and surface fatigue; improved bearings and gears) 7. Many other examples
7 Projections 1. Energy consumption and production Figure 10. US energy consumption by source from 1635 to 2003 (www.eia.doe.gov, 2003). ~107 billion equivalent barrels of oil per year by 2025 Figure 11. World primary energy consumption projections (www.eia.doe.gov, 2004). Figure 12. Projected peaking of oil production (http://www.hubbertpeak.com, 2004).
8 2. Historical savings projections 1966 UK study Table 1. 1966 projected financial savings through tribology in the UK (Hutchings, 1992). 1977 ASME study Item Automotive Vehicle Traction CVT Low Viscosity Oils with Additives Advanced Adiabatic Diesel Wear and Metal Processing Wear Metal Processing Bearings and Seals Bearings in Gas Turbines Bearings in Steam Turbines Sealing in Gas Turbines Sealing in Steam Turbines Estimated Savings 4.5 1.8 3.0 1.3 2.2 0.4 0.1 0.1 0.1 Non-Overlapping Savings 7.4 Total 13.5 10.9 Table 2. Summary of potential savings (in percent of U.S. total energy consumption) for various tribological areas (ASME, 1977). Program Area Potential Energy Savings % U.S. Consumption Billions of 1976 Dollars Per Year 2.8 0.7 Estimated R&D Cost Millions of 1976 Dollars Benefit Ratio* Road Transportation 7.4 11.0 12.6 87 Power Generation 0.2 0.3 2.1 14 Turbomachinery 0.5 0.75 5.2 14 Industrial Machinery and Processes 2.8 4.2 3.7 113 Total 10.9 16.25 23.6 Table 3. Overview of major tribological programs for increasing efficiency (ASME, 1977). * - Benefit Ratio = 1 10 Savings R & D cost
9 3. The field of tribology Strategy for increasing energy conservation (ASME, 1977): - Assess the possible impact of tribological innovations on energy conservation and on the promotion of advanced energy technologies - Identify those areas where the application of existing or new tribological knowledge is expected to yield substantial benefits, whether direct or indirect - Recommend a research and development plan in the tribological sciences for possible implementation by government agencies and industry Principal areas considered by the strategy: - Rolling element and fluid film bearings - Continuously variable power transmission - Sealing technology - Friction and wear mitigation - Automotive engines - Metal processing - Advanced energy technologies. Future challenges to the field in regards to energy efficiency (Spikes, 1997): - Developing low friction components - Developing traction drives and high temperature engines - Improving rolling bearing elements - Develop complete simulations of engines, transmissions and other lubricated systems over their entire service life Generalized areas where tribology can increase energy efficiency: - Transportation sector - Energy generation - Materials related research - Life cycle analyses - Increasing recycling (lubricant reuse)
10 Current and priority research topics (Jost, 2005) Figure 13. Current and priority tribology research areas.
11 Views from Tribologists Based on the response of 255 readers of the tribology magazine Tribology & Lubrication Technology, STLE, January 2005 Which of the following areas do you think would yield the most beneficial results if they received more funding for research? Choose up to three. Figure 14. Results of the STLE funding survey (STLE, 2005)
12 References Books D. Dowson, History of Tribology, 2nd ed., Professional Engineering Publishing, UK, 1998. A. Szeri, Tribology: Friction, Lubrication and Wear, Hemisphere Publication, 1980. Tribology for Energy Conservation, Proceedings of the 24th Leeds-Lyon Symposium on Tribology, ed. D. Dowson, 1997. ASME Research Committee on Lubrication, Strategy for Energy Conservation through Tribology, The American Society of Mechanical Engineers, 1977. I.M. Hutchings, Tribology: Friction and Wear of Engineering Materials, Edward Arnold, London, 1992. Articles G. Liu, Q. Wang and S. Liu, A three-dimensional thermal-mechanical asperity contact model for two nominally flat surfaces in contact, Journal of Tribology, v 123, n 3, July, 2001, p 595-602. H.A. Spikes Some Challenges to Tribology Posed by Energy Efficient Technology, Tribology for Energy Conservation, Proceedings of the 24th Leeds- Lyon Symposium on Tribology, ed. D. Dowson, 1997. P. Jost, Tribology Micro & Macro Economics: A Road to Economic Savings, Tribology and Lubrication Technology, v61, n10, October 2005. Websites Natural Resources Defense Council (NRDC), www.nrdc.org/, 2006. Energy Information Administration, Annual Energy Review, www.eia.doe.gov, 2001. Energy Information Administration, Annual Energy Review, www.eia.doe.gov, 2003. Energy Information Administration, International Energy Outlook, www.eid.doe.gov, 2004. Other Q. Wang, Introduction to Tribology, Lecture Notes, Northwestern University, 2002
13 Homework 1 (Due: 09/07/2006) Choose a product or component of an energy system that involves tribology (choose a product or component used in your company, if possible). For that product or component: 1. Identify the tribological elements within that product or component. 2. Identify the key tribological issues related to the identified tribological elements. 3. Determine any recent tribological improvements made to those products or components (particularly within your company, if possible). 4. Finally, determine, if possible, the economic or energy savings (or efficiency improvements) resulting from implementing these tribological improvements. Turn in a brief, one-page typed response to the above issues and be prepared to make a 5- minute presentation in class on 09/07/2006.