I wrote a couple of weeks ago about ‘Our last DIMES’ meetings (on September 22nd, 2021). They were hybrid meetings with about half the participants attending in person and the remainder on-line. When the pandemic started we had to master the skill of conducting discussions via our laptops while sitting on our own. Now, we are learning how to include everyone in a discussion when only half of the participants are in the physical room. One of our first steps was to re-equip our meeting rooms with higher quality video conferencing facilities so that we can see and hear one another more clearly. Unfortunately, our new equipment revealed the poor quality of the video clips we have produced during the DIMES project. Nevertheless, if you have never been present during a wing-bend test or a fatigue test on a large composite panel then you might find these clips interesting (see also the video of ‘Noisy progressive failure of a composite panel’ on June 30th 2021). We also produced an introductory video for the DIMES project which was to be first in a series of video shorts but the pandemic intervened and we have never been in the same place as our camera crew so we have not made anymore. Maybe that’s a good thing because 500 hours of video are uploaded every minute to YouTube so you will not have time to watch our DIMES videos 😉.
You would not think it was difficult to build a thin flat metallic plate using a digital description of the plate and a Laser Powder Bed Fusion (L-PBF) machine which can build complex components, such as hip prostheses. But it is. As we have discovered since we started our research project on the thermoacoustic response of additively manufactured parts (see ‘Slow start to an exciting new project on thermoacoustic response of AM metals‘ on September 9th, 2020). L-PBF involves using a laser beam to melt selected regions of a thin layer of metal powder spread over a flat bed. The selected regions represent a cross-section of the desired three-dimensional component and repeating the process for each successive cross-section results in the additive building of the component as each layer solidifies. And there in those last four words lies the problem because ‘as each layer solidifies’ the temperature distribution between the layers causes different levels of thermal expansion that results in strains being locked into our thin plates. Our plates are too thin to build with their plane surfaces horizontal or perpendicular to the laser beam so instead we build them with their plane surface parallel to the laser beam, or vertical like a street sign. In our early attempts, the residual stresses induced by the locked-in strains caused the plate to buckle into an S-shape before it was complete (see image). We solved this problem by building buttresses at the edges of the plate. However, when we remove the buttresses and detach the plate from the build platform, it buckles into a dome-shape. Actually, you can press the centre of the plate and make it snap back and forth noisily. While we are making progress in understanding the mechanisms at work, we have some way to go before we can confidently produce flat plates using additive manufacturing that we can use in comparisons with our earlier work on the performance of conventionally, or subtractively, manufactured plates subject to the thermoacoustic loading experienced by the skin of a hypersonic vehicle [see ‘Potential dynamic buckling in hypersonic vehicle skin‘ on July 1st 2020) or the containment walls in a fusion reactor. Sometimes research is painfully slow but no one ever talks about it. Maybe because we quickly forget the painful parts once we have a successful outcome to brag about. But it is often precisely the painful repetitions of “try and try again” that allow us to reach the bragging stage of a successful outcome.
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.
While pandemic lockdowns and travel bans are having a severe impact on spontaneity and creativity in research [see ‘Lacking creativity‘ on October 28th, 2020], they have induced a high level of ingenuity to achieve the final objective of the DIMES project, which is to conduct prototype demonstrations and evaluation tests of the DIMES integrated measurement system. We have gone beyond the project brief by developing a remote installation system that allows local engineers at a test site to successfully set-up and run our measurement system. This has saved thousands of airmiles and several tonnes of CO2 emissions as well as hours waiting in airport terminals and sitting in planes. These savings were made by members of our project team working remotely from their bases in Chesterfield, Liverpool, Ulm and Zurich instead of flying to the test site in Toulouse to perform the installation in a section of a fuselage, and then visiting a second time to conduct the evaluation tests. For this first remote installation, we were fortunate to have our collaborator from Airbus available to support us [see ‘Most valued player on performs remote installation‘ on December 2nd, 2020]. We are about to stretch our capabilities further by conducting a remote installation and evaluation test during a full-scale aircraft test at the Aerospace Research Centre of the National Research Council Canada in Ottawa, Canada with a team who have never seen the DIMES system and knew nothing about it until about a month ago. I could claim that this remote installation and test will save another couple of tonnes of CO2; but, in practice, we would probably not be performing a demonstration in Canada if we had not developed the remote installation capability.
The DIMES project has 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.