Tribo-Acoustic Sensors for In-Situ Performance and Inspection of Machine Components

Lead Research Organisation: University of Sheffield
Department Name: Mechanical Engineering


Engineering machines, from car and planes, to power stations and production lines, have lots of moving parts. The reliability of these parts is key to the function and energy efficiency the machine. It is often these moving parts that fail and frequently that failure is associated with the rubbing surfaces. Machine elements like bearings, gears, seals, and pistons often wear out, exhibit high friction, or seize.

Knowing if a machine element is performing at its optimum can save energy and lead to long life. Being able to monitor the components in-situ in a machine can speed up the development cycle time. Further, monitoring performance rather than failure, allows allows the machine operator to plan maintenance. This is particularly important for high capital cost machines, in remote locations, like offshore wind turbines.

Current monitoring methods are based around measuring excessive vibration or the noise emitted by a failed component (acoustic emission AE) or by counting wear debris particles in a lubricant. Sensors that measure performance rather than failure, and so can be used to optimise operating parameters would be much more useful. This also opens the possibility of using advanced control based on sensor readings, Many machine components are commodities, and integrating sensors provides a way to add value to what would otherwise be a commodity product.

The Leonardo Centre at Sheffield has developed unique methods for measuring machine contacts in-situ. The approaches are based on ultrasonic technologies adapted from the NDT and dynamics communities. By sending ultrasonic pulses through machine components and measuring transmission and reflection we have been able to non-invasively study various tribological machine components. In early work we developed methods to measure the oil film thickness, and the amount of metal contact. This has been well established, validated in laboratory experiments, and applied to journal bearings, trust pads, rolling bearings, pistons, and seals. Several industrial companies have adopted these approaches in their product development cycles.

This fellowship seeks to explore new methods to learn more about contacts. Buy using different kinds of ultrasonic waves, transducer topologies, and signal processing we will develop methods to measure contact load, stress history, oil viscosity, and friction. These will be prototyped in the laboratory and we have industrial partners ready to provide field applications. In addition the fellowship seeks to collaborate with academic institutions; firstly to learn new acoustic sensor techniques and secondly to support research into machine element research with the provision of new measurement methods.

This will support the Leonardo Centre aim to be, not only the leading centre for ultrasonic measurement in tribology, but to be a key part of the UK's research infrastructure in machine component research and development both in industry and academia.

Planned Impact

The industrial beneficiaries of this research will be machine element manufacturers and major equipment suppliers, owners and operators. Potentially this could be across all industrial sectors; but principally high value products where sensor installation is cost effective, for example offshore wind, power generation, offshore oil and gas, and aerospace.

Five examples are given:
1. Wind Energy Industry. Wind power is still relatively expensive and much of this cost is associated with on-going maintenance. Wind turbine bearings for example are subject to complex loading and current lifetimes are short (5 years typical for gearbox bearing). Advanced sensor system could be used to monitor film thickness and load and detect when failure is likely and remaining useful life.

2. Power Generation. Load and air based gas turbines transit thrust through hydrodynamic bearings. These are unmonitored and their operation is not optimised during running. Sensing the bearings on the test stand could help to reduce size and weight by ensuring the individual elements carried exactly the right load at the right lubrication condition. In the longer term sensing during flight could be used to optimise their performance and hence fuel efficiency.

3. Aircraft Landing Gear - pin joints that allow articulation of the structural parts. When are the joints likely to fail, how can they best be monitored in the event of a hard landing.

4. Combustion Engines Industries. There is a global drive to improve engine efficiency and reduce emissions. Sensing of machine parts (engine bearings, piston/liner) has great value in optimising engine performance. For example, large marine diesel engines consume (i.e. burn) as much as 1 tonne of lubricating oil and 250 tonnes of fuel per day. Building a sensor system that exactly regulates lubricant flow just when it is need could significantly reduce the financial and environmental costs of operation.

5. Metal Rolling Industry. Metal rolls are largely commodity products; most R&D in the industry is based around material improvements that marginally increase wear resistance. The provision of internal sensing capability into a metal roll to monitor load, stress, lubrication, wear and surface roughness would create a functionally more useful product and add value through technology.

Impact to the nation is through increasing the competiveness of UK products. Many machine components are commodity products. One way to add value to the component is to through embedded technology. This might be in terms of component design features, or by using advanced materials. Alternatively it can be through the use of on-board monitoring and feedback. Commercial value can be added by selling a monitoring and control system along with the low-cost machine element. This requires the in-situ sensing capability that is a deliverable of this fellowship.

Indirectly, nationwide impact is achieved through the availability of lower cost energy and reduced greenhouse gas emissions. This is through the more efficient use of natural resources. A well-designed machine element operating at its optimum point is smaller, lighter, lasts longer, and consumes less energy. In-situ sensing enables that design and operating optimisation.


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Carretta Y (2017) Ultrasonic roll bite measurements in cold rolling - Roll stress and deformation in Journal of Materials Processing Technology

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Carretta Y (2017) Ultrasonic roll bite measurements in cold rolling: Contact length and strip thickness in Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology

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Fuentes R (2016) Observations on acoustic emissions from a line contact compressed into the plastic region in Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology

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Leonhard, L (2017) Film Thickness Measurements in a Running Hydrostatic Unit Using Ultrasound in Tribologia - Finnish Journal of Tribology

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Suzuki H (2016) Design and implementation of a non-resonant vibration-assisted machining device to create bespoke surface textures in Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

Description 1. We have developed a new sensor for measuring the viscosity of oil samples inside vessels, tanks, and pipes. The method uses the reflection of ultrasound with a matching layer (acting like a non-reflective coating on sunglasses) to enhance transmission. The sensor has been used to measure the oil film that forms inside an operating bearing, and to measure the viscosity of the oil in a car engine sump during a trip around the Peak District.

2. We have built a spectroscopic approach to the measurement; by changing the frequency we can excite different parts of the oil and so measure the constituent parts.

3. We have invented a new method for measuring very thin surface layers by using multiple superimposed ultrasonic reflections.

4. We have invented a new method for measuring friction at an interface by using high power non-linear ultrasound
Exploitation Route To monitor engine oils for degradation - so they can be changed when only when needed and not at regular service intervals.

To assist in the design of beings - ensuring that oil viscosity is maintained in the places where it is needed.

To assist in measurement of lubricant degradation.

To measure deposited liquid and solid layers on a free surface

To measure friction in-situ in machine parts
Sectors Aerospace, Defence and Marine,Energy,Transport

Description Several sensor systems have been installed on industrial equipment for the purpose of monitoring or product development. We have developed methods for measuring load in rolling element bearings with ultrasonic sensors. These have been installed on a wind turbine in Northern Ireland owned by Scottish Energy. This has been done in a project joint with Ricardo - they are using the data to verify perforce of their novel 'Multi-life' bearing design, and to validate their codes for wind turbine transmissions. We have worked with Wartsila WinGD to install sensors on a marine diesel engine at Winterthur, this has been used to develop a control system for the flow of oil into the cylinders.
First Year Of Impact 2017
Sector Energy
Title A New Device for In-Situ Measurement of Lubricant Viscosity using a Matching Layer 
Description A device that allows measurement of viscosity inside a vessel, tan, or pipeline with no direct contact between the sensor and sample. Based on the reflection of shear polarised ultrasound and the use of a matching layer to aid transmission. 
Type Of Material Improvements to research infrastructure 
Provided To Others? No  
Impact In progress 
Title Continuous Wave Ultrasound for Analysis of a Surface 
Description A method using continuous ultrasonic waves to measure the properties of surface coating and layers. Normally the layers are so tin that they comely reflect sound. But using continuous waves we can amplify their effect. This means we can measure the viscosity, thickness, and presence of thin films on solid metal surfaces. 
IP Reference GB1522677.2 
Protection Patent application published
Year Protection Granted 2016
Licensed No
Impact Still in progress
Title Deriving Contact Stress or Contact Load using Ultrasound Data 
Description A method to measure the load imparted between the balls or rollers and raceways in a rolling being. This has application to wind turbine bearings where highly variable wind loading and gearbox dynamics leads to uncertainty in bearing loading. 
IP Reference GB1414998.3 
Protection Patent application published
Year Protection Granted 2015
Licensed Yes
Impact Licensed to Ricardo Innovations Ltd
Company Name Leonardo Testing Services Ltd 
Description A consultancy company to provide tribological testing services. 
Year Established 2016 
Impact Support for several industrial companies (Ivista, BPC, Lubricants UK, WD40, Wrekin, Ricardo innovationsLtd, Rolls-Royce) in product design and development.