Thirty-three months ago (see ‘Finding DIMES‘ on February 6th, 2019) we set off at a gallop ‘to develop and demonstrate an automated measurement system that integrates a range of measurement approaches to enable damage and cracks to be detected and monitored as they originate at multi-material interfaces in an aircraft assembly’. The quotation is taken directly from the aim of the DIMES project which was originally planned and funded as a two-year research programme. Our research, in particular the demonstration element, has been slowed down by the pandemic and we resorted to two no-cost extensions, initially for three months and then for six months to achieve the project aim. Two weeks ago, we held our final review meeting, and this week we will present our latest results in the third of a series of annual workshops hosted by Airbus, the project’s topic manager. The DIMES system combines visual and infrared cameras with resistance strain gauges and fibre Bragg gratings to detect 1 mm cracks in metals and damage indications in composites that are only 6 mm in diameter. We had a concept design by April 2019 (see ‘Joining the dots‘ on July 10th, 2019) and a detailed design by August 2019. Airbus supplied us with a section of A320 wing, and we built a test-bench at Empa in Zurich in which we installed our prototype measurement system in the last quarter of 2019 (see ‘When seeing nothing is a success‘ on December 11th, 2019). Then, the pandemic intervened and we did not finish testing until May 2021 by which time, we had also evaluated it for monitoring damage in composite A350 fuselage panels (see ‘Noisy progressive failure of a composite panel‘ on June 30th, 2021). In parallel, we have installed our ‘DIMES system’ in ground tests on an aircraft wing at Airbus in Filton (see image) and, using a remote installation, in a cockpit at Airbus in Toulouse (see ‘Most valued player performs remote installation‘ on December 2nd, 2020), as well as an aircraft at NRC Aerospace in Ottawa (see ‘An upside to lockdown‘ on April 14th 2021). Our innovative technology allows condition-led monitoring based on automated damage detection and enables ground tests on aircraft structures to be run 24/7 saving about 3 months on each year-long test.
Last month when I was in Taiwan [see ‘Ancient Standards‘ on January 29th, 2020] , I visited Kuosheng Nuclear Power Plant which has a pair of boiling water reactors that each generate 986 MWe, or between them about 7% of Taiwan’s electricity. The power station is approaching the end of its licensed life in around 2023 after being constructed in 1978 and delivering electricity commercially for about 40 years, since the early 1980’s. There is an excellent exhibition centre at the power station that includes the life-size mock-up of the reinforcement rods in the concrete of the reactors shown in the photograph. I am used to seeing reinforcing bar, or rebar as it is known, between 6 to 12mm in diameter on building site, but I had never seen any of this diameter (about 40 to 50mm diameter) or in such a dense grid. On the other hand, we are not building any nuclear power stations in the UK at the moment so there aren’t many opportunities to see closeup the scale of structure required.
Earlier this summer, when we were walking the South West Coastal Path [see ‘The Salt Path‘ on August 14th, 2019], we frequently saw kestrels hovering above the path ahead of us. It is an enthralling sight watching them use the air currents around the cliffs to soar, hang and dive for prey. Their mastery of the air looks effortless. What you cannot see from the ground is the complex motion of their wing feathers changing the shape and texture of their wing to optimise lift and drag. The base of their flight feathers are covered by small flexible feathers called ‘coverts’ or ‘tectrix’, which in flight reduce drag by providing a smooth surface for airflow. However, at low speed, such as when hovering or landing, the coverts lift up and the change the shape and texture of the wing to prevent aerodynamic stalling. In other words, the coverts help the airflow to follow the contour of the wing, or to remain attached to the wing, and thus to generate lift. Aircraft use wing flaps on their trailing edges to achieve the same effect, i.e. to generate sufficient lift at slow speeds, but birds use a more elegant and lighter solution: coverts. Coverts are deployed passively to mitigate stalls in lower speed flight, as in the picture. When I was in the US last month [see ‘When upgrading is downgrading‘ on August 21st, 2019], one of the research reports was by Professor Aimy Wissa of the Department of Mechanical Science & Engineering at the University of Illinois Urbana-Champaign, who is working on ‘Spatially distributed passively deployable structures for stall mitigation‘ in her Bio-inspired Adaptive Morphology laboratory. She is exploring how flaps could be placed over the surface of aircraft wings to deploy in a similar way to a bird’s covert feathers and provide enhanced lift at low speeds. This would be useful for drones and other unmanned air vehicles (UAVs) that need to manoeuvre in confined spaces, for instance in cityscapes.
I must admit that I had occasionally noticed the waves of fluttering small feathers across the back of a bird’s wing but, until I listened to Aimy’s presentation, I had not realised their purpose; perhaps that lack of insight is why I specialised in structural mechanics rather than fluid mechanics with the result that I was worrying about the fatigue life of the wing flaps during her talk.
I have been resolving an extreme case of Tsundoku [see ‘Tsundoki‘ on May 24th, 2017] over the last few weeks by reading ‘A short walk in the Hindu Kush‘ by Eric Newby which I bought nearly forty years ago but never read, despite taking it on holiday a couple of years ago. Although it was first published in 1958, it is still in print and on its 50th edition; so, it has become something of classic piece of travel writing. It is funny, understated and very English, or least early to mid 20th century English.
It felt quite nostalgic for me because about thirty years ago I took a short walk in Gilgit Baltistan. Gilgit Baltistan is in northern Pakistan on the border with China and to the west of Nuristan in Afghanistan where Eric Newby and Hugh Carless took their not-so short walk. I went for a scramble up a small peak to get a better view of the mountains in the Hindu Kush after a drive of several days up the Karakorum Highway. We were driven from Islamabad to about a mile short of the border with China on the Khunjerab pass at 4730 m [compared to Mont Blanc at 4810 m].
I was there because the Pakistani Government supplied a small group of lecturers with a mini-bus and driver to take us up the Karakorum Highway [and back!] in exchange for a course of CPD [Continuing Professional Development] lectures on structural integrity. This we delivered in Islamabad to an audience of academics and industrialists during the week before the trip up the Karakoram Highway. So, Eric Newby’s description of whole villages turning out to greet them and of seeing apricots drying in the sun on the flat roofs of the houses brought back memories for me.