Most manufactured things break when you subject them to 90% strain; however Professor Xiaoyu Rayne Zheng of the Department of Mechanical Engineering at Virginia Tech has developed additively-manufactured metamaterials that completely recover from being deformed to this level. Strains are usually defined as the change in length divided by the original length and is limited in most engineering structures to less than 2%, which is the level at which steel experiences permanent deformation. Professor Zheng has developed a microstructure with a recurring architecture over seven orders of magnitude that allows an extraordinary level of elastic recovery; and then his team manufactures the material using microstereolithography. Stereolithography is a form of three-dimensional printing. Professor Zheng presented some of his research at the USAF research review that I attended last month [see ‘When an upgrade is downgrading‘ on August 21st, 2019 and ‘Coverts inspire adaptive wing design’ on September 11th, 2019]. He explained that, when these metamaterials are made out of a piezoelectric nanocomposite, they can be deployed as tactile sensors with directional sensitivity, or smart energy-absorbing materials.
Rayne Zheng and Aimy Wissa [‘Coverts inspire adaptive wing design’ on September 11th, 2019] both made Compelling Presentations [see post on March 21st, 2018] that captured my attention and imagination; and kept my phone in my pocket!
Six months ago, I wrote about ‘Finding DIMES’ as we kicked off a new EU-funded project to develop an integrated measurement system for identifying and tracking damage in aircraft structures. We are already a quarter of the way through the project and we have a concept design for a modular measurement system based on commercial off-the-shelf components. We started from the position of wanting our system to provide answers to four of the five questions that Farrar & Worden  posed for structural health monitoring systems in 2007; and, in addition to provide information to answer the fifth question. The five questions are: Is there damage? Where is the damage? What kind of damage is present? How severe is the damage? And, how much useful life remains?
During the last six months our problem definition has evolved through discussions with our EU Topic Manager, Airbus, to four objectives, namely: to quantify applied loads; to provide condition-led/predictive maintenance; to find indications of damage in composites of 6mm diameter or greater and in metal to detect cracks longer than 1mm; and to provide a digital solution. At first glance there may not appear to be much connection between the initial problem definition and the current version; but actually, they are not very far apart although the current version is more specific. This evolution from the idealised vision to the practical goal is normal in engineering projects.
We plan to use point sensors, such as resistance strain gauges or fibre Bragg gratings, to quantify applied loads and track usage history; while imaging sensors will allow us to measure strain fields that will provide information about the changing condition of the structure using the image decomposition techniques developed in previous EU-funded projects: ADVISE, VANESSA (see ‘Setting standards‘ on January 29th, 2014) and INSTRUCTIVE. We will use these techniques to identify and track cracks in metals ; while for composites, we will apply a technique developed through an EPSRC iCASE award from 2012-16 on ‘Full-field strain-based methods for NDT & structural integrity measurement’ .
I gave a short briefing on DIMES to a group of Airbus engineers last month and it was good see some excitement in the room about the direction of the project. And, it felt good to be highlighting how we are building on earlier investments in research by joining the dots to create a deployable measurement system and delivering the complete picture in terms of information about the condition of the structure.
Image: Infra red photograph of DIMES meeting in Ulm.
The INSTRUCTIVE and DIMES projects have received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreements No. 685777 and No. 820951 respectively.
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.
This week I am in the US presenting work from our EU projects INSTRUCTIVE and MOTIVATE at the Annual Conference and Exposition of the Society for Experimental Mechanics. Although the INSTRUCTIVE project was completed at the end of December 2018, the process of disseminating and exploiting the research will go on for some time. The capability to identify the initiation of cracks when they are less than 1mm long and to track their propagation is a key piece of technology for DIMES project in which we are developing an integrated system for monitoring the condition of aircraft structures. We are in the last twelve months of the MOTIVATE project and we have started producing video clips about the technology that is being developed. So, if you missed my presentations at the conference in the US then you can watch the videos online using the links below 😉.
We have been making videos describing the outputs of our EU project for about 20 years; so, if you want to see some vintage footage of me twenty years younger then watch a video from the INDUCE project that was active from 1998 to 2001.
Henry Lea Laboratory, The University of Sheffield in the 1960s
I have happy memories of teaching laboratory classes at the University of Sheffield in the mid 1980s and 1990s in the Henry Lea Laboratory. The laboratory was crammed full of equipment for experiments in mechanics of materials. We conducted the practical classes on a limited selection of test machines that stood around a set of benches in the centre of the laboratory on which were a series of bench-top experiments for undergraduates. The outer reaches of the laboratory were packed with test machines of various shapes and sizes that were the domain of the research students and staff. So, undergraduate students were privileged to conduct their laboratory classes surrounded by research activity – this was one of the advantages of attending a research-intensive university to study engineering. However, this is not the experience that modern students gain from laboratory classes. Sheffield, like Liverpool, and many other research-intensive universities has purpose-built teaching laboratories that provide modern spacious facilities for teaching and learning but also segregate undergraduates from the research business of the university. In the UK, the increase in student numbers, as we moved towards 50% participation in higher education, was probably a prime driver for the design and construction of these facilities. However, often the growth in student numbers exceeds the planned capacity of the teaching laboratories and the student experience is reduced by being in a group of five or six with only one or two of them being able to get hands-on experience at the same time. To overcome this problem, I have used practical exercises as homework assignments that can be performed in the kitchen at home by first year students. These were initially designed for the MOOC on thermodynamics that I developed a few years ago but they work equally well for undergraduate students and allow individuals to gain experience of conducting a simple experiment, recording and processing data, and write a short report about their findings [see post on ‘Blending learning environments‘ on November 14th, 2018 and ‘Slow down time to think [about strain energy]‘ on March 8th, 2017]. I have found that the participation rate is about the same as for traditional laboratory classes but different because students can learn from their mistakes in private and acquire some experimental skills . However, it is a long way from conducting labs for small cohorts in a laboratory where world-class research is in progress.