Shortly before the pandemic started to have an impact in the UK, I went to our local second-hand bookshop and bought a pile of old paperbacks to read. One of them was ‘Daisy Miller and Other Stories’ by Henry James (published in 1983 as Penguin Modern Classic). The title of this post is a quote from one of the ‘other stories’, ‘The Lesson of the Master’, which was first published in 1888. ‘Success is to have made people wriggle to another tune’ is said by the successful fictional novelist, Henry St George as words of encouragement to the young novelist Paul Ovett. It struck a chord with me because I think it sums up academic life. Success in teaching is to inspire a new level of insight and way of thinking amongst our students; while, success in research is to change the way in which society, or at least a section of it, thinks or operates, i.e. to have made people wriggle to another tune.
One of the implications of the second law of thermodynamics is that the thermal efficiency of power stations increases with their operating temperature. Thus, there is a drive to increase the operating temperature in the next generation of nuclear power stations, known as Generation IV reactors. In one type of Generation IV reactors, known as the Very High Temperature Reactor (VHTR), graphite is designed to be both the moderator for neutrons and a structural element of the reactor. Although the probability of damage in an accident is extremely low, it is important to consider the consequences of damage causing the core of the reactor to be exposed to air. In these circumstances, with the core temperature at about 1600°C, the graphite would be exposed to severe oxidation by the air that could change its material properties and ability to function as a moderator and structural element. Therefore, in recent research, my research group has been working with colleagues at the UK National Nuclear Laboratory (NNL) and at the National Tsing Hua University (NTHU) in Taiwan to conduct experiments on nuclear graphite over a range of temperatures. Our recently published article shows that all grades of nuclear graphite show increased rates of oxidation for temperatures above 1200°C. We found that large filler particles using a pitch-based graphite rather than a petroleum-based graphite gave higher oxidation resistance at these elevated temperatures. This data is likely to be important in the design and operations of the next generation of nuclear power stations.
The work described above was supported by the NTHU-University of Liverpool Dual PhD Programme [see ‘Citizens of the world‘ on November 27th, 2019] and NNL. This is the fifth, and for the moment last, in a series of posts on recent work published by my research group. The others are: ‘Salt increases nanoparticle diffusion‘ on April 22nd, 2020; ‘Spatio-temporal damage maps for composite materials‘ on May 6th, 2020; ‘Thinking out of the box leads to digital image correlation through space‘ on June 24th, 2020; and, ‘Potential dynamic buckling in hypersonic vehicle skin‘ on July 1st, 2020.
The image is figure 5: SEM micrographs of the surface of petroleum-based IG-110 graphite samples oxidized at various temperatures from Lo IH, Tzelepi A, Patterson EA, Yeh TK. A study of the relationship between microstructure and oxidation effects in nuclear graphite at very high temperatures. J. Nuclear Materials. 501:361-70, 2018.
Lo I-H, Yeh T-K, Patterson EA & Tzelepi A, Comparison of oxidation behaviour of nuclear graphite grades at very high temperatures, J. Nuclear Materials, 532:152054, 2020.
Recently, I visited a local artist to choose a painting for a birthday present. He showed me a pair of small oil paintings in which I had expressed an interest via photographs he had sent me by email. I agreed to buy both of them and then we drifted into his studio where he showed me the pieces he was working on. There were many unfinished paintings and he described how difficult it was to finish some of them. He measured the time taken on some of them in months and, for a few, in years. I was struck by the similarity with scientists who indulge in slow-motion multi-tasking and switch between research projects in different fields, often leaving something unfinished to focus on something else and then returning to pursue the original research topic [‘Slow-motion multi-tasking leading to productive research‘ on September 19th, 2018]. I suspect both artists and scientists who indulge this approach are looking to achieve ‘a perfect balance of their conscious and unconscious life’ out of which Barbara Hepworth believed ideas are born and realized [see ‘Ideas from a balanced mind‘ on August 24th, 2016].
The studio in the photograph is Barbara Hepworth’s in St Ives, Cornwall.
The skin of an aircraft is supported on the inside by a network, or mesh, of ribs and stringers running approximately at right angles to one another; so that the skin is effectively a series of rectangular plates supported around their edges. In hypersonic flight, above five times the speed of sound, these rectangular plates are subject to vibration and to high temperatures that vary spatially and with time. The combined vibratory and thermal loading causes the plates to buckle out of plane which has two possible detrimental consequences: first, it causes the formation of fatigue cracks leading to catastrophic failure; and, second, it might influence the formation of the boundary layer in the flow over the skin of the aircraft and affect the aerodynamics of the aircraft. In my laboratory, we have built a test-rig that allows us to subject rectangular plates to random mechanical vibrations up to 1000Hz and, at the same time, to temperature distributions upto 1000K that vary in time and space. Earlier this year, we published an article in which we showed, by experiment, that an edge-reinforced rectangular plate behaved as a dynamic system in response to thermal loading. In other words, when a constant temperature distribution is applied, the shape of the plate varies with time until an equilibrium state is achieved. In addition, we found that the post-buckled shape of the plate is not proportional to the energy supplied but dependent on the in-plane temperature distribution. Probably, both of these observed behaviours are a result of differential thermal expansion of the plate and its reinforcements.
The image shows point-wise temperature and displacement measurements (centre) at the centre and edge of a reinforced plate (top) subject to a localised strip of heating over time as shown by the temperature distributions (bottom).
This is the fourth in a series of posts on recent work published by my research group. The others are: ‘Salt increases nanoparticle diffusion‘ on April 22nd, 2020; ‘Spatio-temporal damage maps for composite materials‘ on May 6th, 2020; and, ‘Thinking out of the box leads to digital image correlation through space‘ on June 24th, 2020.
Santos Silva AC, Lambros J, Garner DM & Patterson EA, Dynamic response of a thermally stressed plate with reinforced edges, Experimental Mechanics, 60:81-92, 2020.