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Reducing the environmental impact of human activity has become imperative in nearly all areas of engineering science. Recycling, minimizing waste, and increasing efficiency are as equally important as the moves towards developing sustainable energy sources.
What is Friction?
In all moving things, organic or mechanical, the friction between surfaces in contact causes wear and eventual failure. In terms of friction in mechanical moving parts, the first and most obvious solution is to lubricate and perhaps the second is to use materials substantial enough to withstand wear for as long as possible.
Tribology is the “science of interacting surfaces in motion” and it aims to reduce friction, wear and increase efficiency with strategies that encompass design, lubrication and material technology. The term ‘tribology’ was probably first used in 1966 by Prof. H. Peter Jost in his report for the UK Department of Education and Science. He believed that huge sums of money had been lost in the UK as the consequences of friction, wear, and corrosion.
In their 2012 conference paper “Green tribology and quality of life” tribologists Emilia Assenova, Majstorovic Vidosav, Aleksandar Vencl, and M. Kandeva proposed that:
“Nowadays, losses resulting from ignorance of tribology amount to about 6% of the gross national product (GNP) in the United States alone. This figure is around USD 900 milliard annually. As far as China is concerned, they could save above USD 40 milliard per year by the application of tribology or more than 1.5% of the GNP ”
Inevitably, this is an area of specialty that has been identified as one that can offer solutions and strategies that address the environmental impact of current tribological approaches.
The term “green tribology” evolved from concepts put forward by tribologists in the late 90s when they spoke about “tribology for energy conservation” and “environmentally friendly tribology”. Tribology was recognized as an area of engineering science that could move beyond its original remit of increasing efficiency through the reduction of friction and wear into the realms of saving energy and resources, minimizing noise pollution, developing novel bio-lubrication and generally being a positive contributor to reducing environmental harm. More recently the term “green tribology” is talked about in the context of quality of life.
Use of Bio-Lubricants
There are several important areas that green tribology is actively researching in which significant impact can be achieved. The investigation and implementation of the use of bio-lubricants is one. Lubricants used in the earliest of applications would have been derived from organic sources and as such, they would have fulfilled the definition of a bio-lubricant in that they would have been bio-degradable.
Mineral oils whose use dates from the late 18th century are derived from non-renewable fossil sources and do not degrade. They also contain a range of complex and potentially harmful chemical components and have been used extensively in all forms of systems lubrication, particularly in combustion engines.
Finding bio-lubricants that can equal or surpass the performance of those derived from crude oil is a key objective, especially in applications that we would consider to be environmentally friendly such as wind turbines. Creating bio-lubricants from bio-mass waste materials is an even more sustainable approach.
Bio-Mimetics Design for Tribological Applications
Another area of research is Bio-mimetics design for tribological applications. It is the study of how nature solves the problems of friction and lubrication. In one application the unique anti-drag properties of shark skin know as the Riblet effect has successfully been used in the design of the wing skin of Airbus aircraft leading to a 6% reduction in air drag and significant savings in fuel costs.
The properties of the skin of the lizard commonly known as the "sand fish" also inspired the design of textured surfaces on bearings. In tests of unlubricated sliding conditions, the sand fish inspired texture reduced friction by more than 40% of the untextured surface.
These findings could be applied to the design of artificial joints and nano devices that cannot be lubricated conventionally. There are many other areas where the study of surfaces in nature is pointing researchers to solutions that can fulfill the ultimate aim of tribology and eliminate the need for lubrication.
As Professor Jost the man credited with much of the development of this area of engineering noted in his 2010 Moscow seminar
“…the cause of Green Tribology is indeed a worthy cause for all tribologists and their organizations to pursue, as it will help tribology to play its rightful part, not only for the benefit of science and technology, but much more importantly, for the benefit of mankind...”
It seems that this little known area of engineering research is making a far more significant contribution to reducing environmental harm than they have, to date been given credit for.
- Assenova, E & Vidosav, Majstorovic & Vencl, Aleksandar & Kandeva, M. (2012). Green tribology and quality of life.
- Jost H P. Development of green tribology—An overview.
Seminar—New Direction in Tribotechnology, Moscow, 2010.
- Green tribology: Fundamentals and future development
- Si-wei ZHANG*