What is Tribology ?

Mention the word ‘tribology’ to most people, and you’ll likely be met with a blank stare in response. However, the discipline of tribology is something that many people rely on (even if they don’t realise it) for the smooth functioning of their day-to-day lives. Keep reading and join Brookes Bell as we dive into the fascinating world of tribology…

Tribology: a definition

So, what exactly is tribology? Put simply, tribology is defined as the ‘study of interacting surfaces in relative motion’.

Considered to be an interdisciplinary field of study, in practical terms tribology focuses on friction, lubrication, and wear. However, tribology also encompasses other areas such as contact mechanics, surface damage processes and surface optimisation processes.

However, this only describes the scientific aspects of the subject. There are also many practical aspects, specifically the design and operating principles of the moving parts of machinery. If we take just one such moving part, a “bearing”, there are numerous types of bearing, operating on a range of different principles, and each type has its own advantages, limitations, and development history. The tribological science aspect is key to the successful operation of a bearing, but the practical matters of design, operating limits, and experience of what can go wrong, are the “engineering tribology” aspects. In order to design a machine moving part, or to diagnose a problem with a machine, these practical aspects are just as important as the fundamental science side.

The above example of “bearings” is just one of many generic types of tribological component or system. Others include gears, rotary seals, sliders, pistons and piston rings, cams and followers, and various drive systems such as roller chains and belts. Even more basic parts such as wire ropes and pulleys, or anchor chains and winches, are tribological components.

A (very) brief history of tribology

Although friction, wear, and lubrication have been issues since the dawn of the industrial revolution, tribology didn’t become a distinct field of study until the mid-1960s.

The term ‘tribology’ emerged from the 1966 Jost Report, the result of a working group - chaired by Dr Peter H Jost - that was invited by the UK Department of Education and Science to investigate the state of lubrication education and research.

Aside from naming an entirely new discipline - the word tribology being based on the Greek ‘I rub’ - the result was a report with some startling findings.

It was estimated that friction, wear, and corrosion cost the UK economy a substantial 1.1% to 1.4% of GDP on an annual basis.

From there, efforts proliferated to ensure that tribology best practices were embraced by industries of all stripes.

The importance of tribology

Perhaps the most important achievement of tribological knowledge has been the progressive improvement of reliability of machinery, equipment, and other moving devices, ranging in size from large power station turbines and ship main engines, to small yet important mechanisms such as artificial hip and knee joint implants. Tribological understanding and research has led to improved designs and improved operating practices, resulting in an order of magnitude improvement in reliability (and some improvements in efficiency and energy consumption).

Think of pretty much any mechanical component that has two or more moving parts, and you’ll have an example of tribology in action. Those moving parts will be moving in relation to another surface - and therefore may potentially suffer from wear and / or friction.

This means that the application of tribology best practices can result in many benefits.

The benefits of tribology include:

• Extending the service life of critical components and machinery
• Improved energy efficiency and reduced energy losses
• Improved productivity
• Improved safety in relation to machinery and plant operation

Each of these points are very distinct benefits, however they are somewhat abstract. So, let’s quantify them with some tangible numbers. We’ve taken a look at each one in turn below.

Extended service life

The average piece of machinery or plant is dependent on the interaction of multiple small components acting together as part of a system.

How these components behave in relation to each other affects the overall operation and health of the piece of machinery.

As these components interact, they can be subject to wear and friction. According to one study conducted by Emeritus Professor Ernest Rabinowicz, which looked at the factors that caused the ‘loss of usefulness’ of machinery, surface degradation was the cause of over 70% of loss of usefulness.

As such, the application of tribology best practices can significantly reduce ‘loss of usefulness’ and therefore extend the service life of important pieces of machinery.

Improved energy efficiency

With concerns around climate change becoming more pressing, tribological improvements are a potential way of saving energy in industry.

Why? Because the implementation of tribology best practices can reduce the amount of unnecessary energy utilised by machinery.

Think of it this way; the more friction is present between the interaction of two components, the more energy will be required to maintain that interaction.

To give you an idea of the total amount of energy that’s at stake here, consider that according to one study, approximately 23% of the world’s total energy consumption originates from tribology contacts.

Of course, much of this energy loss at tribological contacts is inevitable, but it is reasonable to suppose that further optimisation of designs and operating conditions could reduce it by something of the order of 10%, corresponding to an overall reduction in energy consumption of around 2%.

Improved productivity

Tribology can have a direct economic impact through improved productivity.

According to the book Industrial Tribology: Tribosystems, Friction, Wear and Surface Engineering, Lubrication (2011), the gross domestic savings that could be achieved by the application of tribology best practices could be as much as 1.3% to 1.6% for an individual nation.

This would be as a result of reduced downtime, fewer maintenance costs, fewer replacement costs and more.

Improved safety

Tribology also has an important contribution to make to the safety of machinery, vehicles and other assets.

Where tribology best practices haven’t been implemented, the consequences can be severe.

Take, for example, the case of Alaska Airlines flight 261 which crashed in 2000 killing all 88 passengers on board.

Investigations found that the crash was caused by the complete failure of the plane’s jackscrew assembly, which formed part of the flight control system. The assembly failed as a result of excessive wear, which occurred due to insufficient lubrication.

What are the most recent advances in tribology?

Like any discipline, tribology is continually evolving. As a multidisciplinary field, tribology has inputs from a broad range of areas, meaning it is always subject to new findings and developments.

To give you an idea of how tribology is developing, we’ve outlined some of the most recent advances below.

Superlubricity

Superlubricity is an emerging area of tribology that focuses on systems that involve motion with little to no rubbing.

Because superlubricity methods and materials hugely lower the friction coefficient, they greatly reduce friction-related wear and noise. Examples of superlubricity materials include DLC (diamond-like coating) films.

Biotribology

Tribology is increasingly being applied in biological scenarios. For example, the interactions of joints (e.g. hip replacements).

Dubbed ‘biotribology’, this is an area of tribological development that is being applied across the medical sector, leading to the rise of subsets of biotribology such as ‘skin tribology’ and ‘oral tribology’.

High-temperature tribology

As the name suggests, high-temperature tribology is concerned with the study of how surfaces (and lubricants) interact at high temperatures.

High-temperature tribology is typically defined as occurring from 300-350ºC, where base oils and polymers will begin to decompose, up to about 1000ºC.

The main thrust of high-temperature tribology research has been to identify and create both materials and surface solutions that will reduce friction and wear within the temperature range mentioned above.

Computational tribology

In an attempt to model and anticipate tribological problems in system, component and material designs, computational tribology has arisen.

Computational tribology aims to model the behaviour of systems and materials via multiphysics simulations. Computational tribology also incorporates related models and simulations, such as computational fluid dynamics.

Make your business more efficient with tribology

No matter what industry you operate in, if you make use of machinery, vehicles or any type of system that incorporates interacting components, surfaces, and lubrication - you can benefit from expert tribology advice.

Here at Brookes Bell, we possess decades of tribology expertise, having advised companies large and small across a broad range of industries on how to implement tribology best practices in the design and operation of machinery.

Find out more about our tribology consultancy services

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