Tag Archives: experimental mechanics

Enduring, authentic, ancient and modern

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Decorative photograph across SevernTwo weeks ago, over a period of forty-eight hours, I visited four churches. An unusual event for me.  We travelled from Liverpool to Bristol one afternoon to attend a Thanksgiving Service the following morning for an extraordinary engineer and a lovely man, Eddie O’Brien.  The evening before the service, we stayed in a village pub in Oldbury-on-Severn and after dinner walked up the hill to the 13th century church dedicated to St Arilda.  It was locked so we strolled around the overgrown churchyard along a narrow mowed path and enjoyed the view across the Severn to Wales.  The following morning we drove into Bristol city centre to attend the Thanksgiving Service which was held in the Zetland Evangelical church.  The church was plain, unpretentious and packed.  The service was led by a retired pastor who preached with a gentle, thoughtful passion about Eddie’s life and its meaning.  I knew only one, possibly two, facets of his life: his professional life as an engineer and leading exponent of experimental mechanics; and his life as a student.  Eddie was twenty years my senior and thirty years ago I supervised his MPhil and PhD in experimental mechanics.  He was in his fifties and I was in my thirties – it was a challenge for both of us and we learnt from each other.  When he graduated he presented me with a copy of his PhD thesis that he had hand-bound in leather himself.  We left Bristol after the service and drove north across the Severn Bridge to Tintern Abbey where we stopped for lunch looking out over an empty cricket pitch across a green enclosed valley before exploring the ruins of the Cistercian abbey.  The abbey was founded in 1131 and in 1536 it was surrendered to Henry VIII during the dissolution of the monasteries.  The lead from the roof was removed and five hundred years of decay started creating the ruins you can wander around today.  Back in Liverpool, the following evening we went, with our neighbours, to a ‘Music at the Met’ concert at the Liverpool Metropolitan Cathedral called ‘Music for a King’ and featuring uplifting pieces, including ‘Zadok the Priest’ and ‘Crown Imperial’.  The bold grandeur of the concrete structure, richly coloured stained glass, thunderous organ and combined choirs of the anglican and catholic cathedrals contrasted starkly with the simple service of Thanksgiving for Eddie O’Brien we had attended the previous day when we sang hymns recalled from childhood, including ‘The Lord’s My Shepherd’.

Image: view across River Severn to Wales from St Arilda’s churchyard.

Reasons I became an engineer: #2

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Decorative photograph showning the entrance to the Engineering Faculty at the University of SheffieldThis is the second in a series of posts reflecting on my route to becoming an engineer.  In the first one I described how I chose a degree in mechanical engineering so that I would have appreciation of the technical difficulties that engineers might cite when requesting operational changes for a ship that I hoped one day to command [see ‘Reasons I became an engineer: #1’ on April 19th, 2023].  I think I selected mechanical engineering because it provided a broader engineering education than other engineering degrees and I did not know enough to choose any other branch of engineering.  I went to the University of Sheffield and during vacations returned to the Royal Navy serving onboard HMS Active and flew out to join her wherever she was in the world, except when I went to the Royal Navy Engineering College at Manadon outside Plymouth to undertake engineering applications training.  I cast a brass nameplate, which I still have in my office, and made a toolbox that I also still have at home.  After graduation, I returned full-time to the Royal Navy as a sub-lieutenant and started my career as a naval officer in the executive or seaman branch.  However, I did not settle and missed engineering so I asked for and was refused a transfer to the Royal Corps of Naval Constructors who work on the design and development of warships.  As a result, I resigned my commission in the Royal Navy and got a job as a research assistant in the Department of Mechanical Engineering at the University of Sheffield where I registered for a PhD in engineering.  I had taken a positive step towards becoming an engineer but perhaps on the premise of what I did not want to do rather than what I did want to do.

Structural damage assessment using infrared detectors in fusion environments

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Schematic representation of plasma flux in a fusion reactorAbout six months ago, I described the success of my research group in detecting the early stages of the development of damage in structural components using small, cheap devices based on infrared measurements [see ‘Seeing small changes is a big achievement‘ on October 26th, 2022] after it had been reported in the Proceedings of the Royal Society.  The research was motivated by the needs of the aerospace industry and largely supported via the European Union’s Horizon 2020 research and innovation programme.  We are planning to extend the research to allow our technology to be used for diagnostics in future fusion power plants.  Plasma facing components in these powerplants will experience significant structural and functional degradation in service due to the extreme condition in the reactor.  Our aim is to develop systems based on our infrared monitoring technology that can identify and track material degradation without the need for plant shutdown thereby enabling unplanned maintenance to be undertaken at the earliest sign of component failure.  We are collaborating with the UKAEA and are looking to recruit a PhD student to work on the project supported by the GREEN CDT and Eurofusion.  If you are interested or know someone who might be interested then please follow this link for more information.

Reference:

Amjad, K., Lambert, C.A., Middleton, C.A., Greene, R.J., Patterson, E.A., 2022, A thermal emissions-based real-time monitoring system for in situ detection of cracks, Proc. R. Soc. A., 478: 20210796.

Seeing small changes is a big achievement

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Figure 8 from Amjad et al 2022Some years ago I wrote with great excitement about publishing a paper in Royal Society Open Science [see ‘Press release!‘ on November 15th, 2017].  This has become a routine event; however, the excitement returned earlier this month when we had a paper published in the Proceedings of Royal Society of London on ‘A thermal emissions-based real-time monitoring system for in situ detection of cracks’.  The Proceedings were first published in February 1831 and this is only the second time in my career that my group has published a paper in them.  The last time was ten years ago and was also about cracks: ‘Quantitative measurement of plastic strain field at a fatigue crack tip’.  I have already described this earlier work in a post [see ‘Scattering electrons reveal dislocations in material structure’ on November 11th, 2020].  This was the first time that the size and shape of the plastic zone around a crack had been measured directly rather than inferred from other measurements.  It required an expensive scanning electron microscope and a well-equipped laboratory.  In contrast, the work in the paper published this month uses components that can be purchased for the price of a smart phone and assembled into a device not much larger than a smart phone.  The device detects the changes in the temperature distribution over the surface of the metal caused by the propagation of a crack due to repeated loading of the metal.  It is based on the principles of thermoelastic stress analysis [see ‘Counting photons to measure stress‘ on November 18th, 2015], which is a well-established measurement technique that usually requires expensive infra-red cameras.  Our key innovation is to not aim for absolute measurement values, which allows us to ignore calibration requirements, and instead to look for changes in the temperature distribution on the metal surface by extracting feature vectors from the images [see ‘Recognising strain‘ on October 28th 2015].  Our approach lowers the cost of the equipment required by several orders of magnitude, achieves comparable or better resolution of crack growth (around 1 mm) and will function at lower loading frequencies than techniques based on classical thermoelastic stress analysis.  Besides crack analysis, the common theme of the two papers is the innovative use of image processing to identify change, based on the fracture mechanics of crack propagation.

The research reported in this month’s paper was largely performed as part of the DIMES project about which I have written many posts.

The University of Liverpool was the coordinator of the DIMES project and the other partners were Empa, Dantec Dynamics GmbH and Strain Solutions Ltd.  Airbus was the topic manager on behalf of the Clean Sky 2 Joint Undertaking.

Logos of Clean Sky 2 and EUThe DIMES project received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 820951.

The opinions expressed in this blog post reflect only the author’s view and the Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains.

References:

Amjad, K., Lambert, C.A., Middleton, C.A., Greene, R.J., Patterson, E.A., 2022, A thermal emissions-based real-time monitoring system for in situ detection of cracks, Proc. R. Soc. A., doi: 10.1098/rspa.2021.0796.

Yang, Y., Crimp, M., Tomlinson, R.A., Patterson, E.A., 2012, Quantitative measurement of plastic strain field at a fatigue crack tip, Proc. R. Soc. A., 468(2144):2399-2415.

Image: Figure 8 from Amjad et al, 2022, Proc. R. Soc. A., doi: 10.1098/rspa.2021.0796.