Stories of Aerospace Engineering

Read interviews and stories of researchers and students at the Faculty of Aerospace Engineering, and discover the scientific questions on which they work and the solutions they present.

TU Delft students design new aircraft for last resort option of geoengineering

If global efforts to reduce carbon emissions fail and temperatures will rise, a last resort could be to turn to geoengineering methods, like the injection of aerosols in the stratosphere. This will produce stratospheric clouds which re fl ect part of the incoming sunlight . Students of the TU Delft have looked into the practical aspects of this option, including the design of a new aircraft to deliver the aerosols into the stratosphere and a rough cost estimation: 11 billion dollars per year. Solar Radiation Management Current models of the climate show that a possibility exists that the response of society to counteract rising global temperatures is not implemented fast enough or does not become effective fast enough to ensure temperatures remain within safe bounds. In that case, an intervention might be necessary to temporarily halt temperature increase until preventive long-term solutions are effective. Stratospheric geoengineering, more specifically, Solar Radiation Management (SRM), offers such a temporary solution. A possible implementation of SRM is the injection of aerosols in the stratosphere, producing stratospheric clouds which reflect part of the incoming sunlight. It mimics volcanoes by spraying sulfuric acid into the stratosphere. This thin, high, long-lasting haze reflects a little sunlight, keeping us cool. Sunset over Hong Kong a year after Mt Pinatubo erupted in the Philippines, showing how aerosols released by volcano’s can affect our environment (Credit: JackyR, Wikipedia) Last resort Students of the TU Delft (faculty of Aerospace Engineering) have produced a research report* to describe the preliminary technical and operational design of a fleet of purpose-built Stratospheric Aerosol Geoengineering Aircraft (SAGA) to deliver five megatons of aerosol per year to altitudes between 18.5 and 19.5 km to gain insight in the cost and impact of such a system. Dr. Steve Hulshoff, who supervised this student project: ‘I want to stress that this is not a solution we advocate to ‘solve’ the global warming issue. First and foremost, we need to reduce carbon emissions. If these global efforts fail, and temperatures reach dangerous levels, a last resort could be to use geo-engineering methods, like SRM, in order to temporarily halt the temperature increase. But only as a last resort.’ ‘There will also be severe drawbacks to SRM, like acidification of the oceans’, Hulshoff warns. ‘We will not see a blue sky as often as we do now, and ozone depletion, deposition through precipitation and climate effects other than temperature reduction, will inevitably affect the environment.’ Stratospheric Aerosol Geoengineering Aircraft Nevertheless, the group of students have looked into some practical aspects of the last resort option of SRM. The design of an aircraft delivery system for stratospheric aerosol geoengineering has provided valuable insights in the practical aspects of geoengineering. Their aircraft is designed for the job of geoengineering, and nothing else. It’s designed to go a lot higher but won’t be required to fly huge distances – so its range is only a little over half that of a jumbo. The high altitude and high payload requirements drive the design of all aspects of the SAGA mission. First of all, the operational scenario, employing a fleet of 344 unmanned aircraft, enabling 572 flights per day, is established with focus on the most efficient delivery of the required 5 Megatons of sulfuric acid aerosol to the stratosphere, which would theoretically be enough to halt temperatures rising. Isometric view of the SAGA aircraft, as proposed by the students High altitude In the plan of the TU Delft students, sulfuric acid will be ejected from the aircraft in gas phase to facilitate efficient aerosol particle formation. Transport of the aerosols at elevated temperature in combination with on-board evaporation enable gas phase dispersion, introduce a compelling power requirement. Aerosol dispersion will occur in the tropical region at altitudes between 18.5 and 19.5 km. The high altitude at which dispersion takes place, governs the aircraft design. This altitude demands efficient lift generation and considerably high thrust. The need for efficient lift generation results in a design featuring a combination with a wing surface area of 700 m2. The structural integrity of this long and slender wing is ensured with the help of a strut-braced wing design. Purpose-built engines are proposed to efficiently provide thrust and power to SAGA aircraft. Four engines, each providing over 600 kN thrust at sea level, facilitate this. Costs The costs of SAGA are estimated to amount to an initial capital cost of 93.9 billion US dollars and a yearly operational cost of 11 billion dollars, which are acceptable amounts considering the costs of global warming, according to the students. Prepare for the worst TU Delft Climate Institute is the place within TU Delft where climate researchers and climate research are brought together, ultimately to develop new scientific knowledge. Prof. Herman Russchenberg, director of the institute, applauds and stimulates the type of out-of-the-box thinking shown by the students, ‘because the world community is still not doing enough to keep climate change in check.’ According to Russchenberg we have to be very reluctant in applying techniques like these, as we don’t know their influence on the earth system, we haven’t considered legal en ethical aspects enough, and we may even increase the problem by temporarily masking temperature rise. ‘But there may come a time when we will actually be needing techniques like these, like it or not. The sooner we start investigating practicalities, potential pitfalls and consequences, the better prepared we will be.’ More information *The Design Synthesis Exercise (DSE) is the conclusion of the undergraduate part of the education in faculty of Aerospace Engineering in Delft. This report on SAGA was produced by one of the groups of students in the last edition of this DSE. Supervisor Dr. Steve Hulshoff, +31 15 27 81538, , Director TU Delft Climate Institute Prof. Herman Russchenberg, +31 15 27 86292,, Science Information Officer TU Delft Roy Meijer, +31 15 2781751, The report is available to journalists, please contact Roy Meijer.

Looking backward and forward with Gijs van Kuik

On 7 December 2016 professor of Wind Energy Gijs van Kuik gave his farewell speech titled 'Wind verwacht: zet je schrap' ('Wind expected: brace yourself') in de Aula (Auditorium) of TU Delft. During his nearly forty year career, Gijs van Kuik has worked all over the Netherlands but he has started and will end his career at TU Delft. "It is my university," he says. Gijs van Kuik came to TU Delft in 1969 to study aerospace engineering. “It was the only place where I could study airplanes.” He finished his master’s degree in 1976, a few years later than originally planned. “It was the 70s” he says “so I took some time off from studying to be part of the student movements.” But he soon returned to his studies and, after graduation, he began working in the newly formed wind energy consortium under the tutelage of Theo van Holten. “I was in the right place at the right time,” says van Kuik. The oil shocks in the 1970s brought about an interest in what we now call renewable energies but were then referred to as alternative energies. However it wasn’t long before a PhD position at TU Eindhoven called him to leave Delft. He completed his PhD in 1991 and he wondered, as many recently matriculated PhDs do, if there was life afterwards. Fortunately for van Kuik, there was. He spent nearly fifteen years working in industry before returning to academia and TU Delft. In fact, for several years prior to returning to the university full time he was working simultaneously at TU Delft and Stork Product Engineering. But ultimately, two agendas proved to be too much and he decided to make TU Delft his full time home. His research while at the university has focused on the development of rotor technology for use in wind turbines. The goal of which was, according to van Kuik, “to build more intelligence into the rotor.” Wind turbines, especially those off shore, are tremendously difficult to access and improvements in their longevity can reduce the cost of maintenance. Van Kuik had the opportunity to see for himself just how difficult maintenance can be when he spent time in the nacelles of some turbine prototypes while checking certification processes. “I was much younger than,” he says of his time climbing the sixty metre high structures. Although this research may have predominantly focused on wind turbine technology, van Kuik has had a few pet research projects over the years, including a nearly decade long quest to see a Russian scientist rightly credited for discovering a constant foundational to aerodynamics. Betz’s Law, so named for German physicist Albert Betz, shows the maximum power that can be extracted from the wind. Van Kuik thought that the law had been discovered at the same time by a Russian scientist, Nikolay Zhukowsky , and, after years of digging through Russian scientific texts, was able to prove Zhukowsky had published the law the same year as Betz. Van Kuik does not speak or read Russian and could only read the maths in the articles but that was sufficient to credit Zhukowsky with the discovery as well. During his tenure at the university, he has served as the scientific director of DUWIND, a multidisciplinary research institute focussed on wind energy. Interest in wind energy has increased dramatically, At his start the introductory wind energy course would see 5-10 students per semester. Now that course attracts over 200 students. Van Kuik plans to spend his retirement, in part, sculpting. He’s been sculpting since 2001 and got into the craft after deciding he needed to do something different from his everyday work. He wanted to do something with his hands, took a sculpting course and has been creating the large stone creations ever since. He’s even given one to the Faculty of Aerospace Engineering which was unveiled in October 2016. “It was a huge thing and someone must have it. There isn’t a better place for this one than the Faculty,” he says of the work which now sits in the lobby of the faculty building. Van Kuik looks back on his time with TU Delft fondly. “I’ll miss the students, being around young people keeps you young.”

‘We want to build aircraft as well as design them’

Aerospace expert Joris Melkert from TU Delft is one of the first four Education Fellows at TU Delft. The Delft Education Fellowships are awarded annually to lecturers who have made a substantial and valuable contribution to teaching at TU Delft. As part of the Fellowship, Melkert is going to involve students in building a real aircraft. Melkert explained, ‘Most of the problems facing the aerospace industry today concern the production side, so this is what we are going to focus on.’ The elective module that Melkert is developing fits into the faculty's ‘Pioneering Innovations’ project called ‘Building Aircraft’ and will be taught within the Master’s track Flight Performance and Propulsion and the ASM track. Melkert continued, ‘There's quite a gap between all the fantastic ideas thought up at this university and their actual implementation. As things stand at the moment, the aerospace industry focuses more on production than on design. I think lecturers should take this into account, so that our students are fully prepared when they graduate. They should hit the ground running .’ For the duration of the new module, Melkert is devising, the mezzanine in the Aeroplane Hall will be rearranged to simulate an aircraft factory. The Faculty is purchasing a construction pack for a VAN RV12. But this isn't just a game – a real aircraft will be built that can actually fly, and could be sold to a private party once it is finished. Melkert added, ‘It's a unique experience whereby students will feel what it's like to work in the strictly controlled environment of an aircraft factory. They will have to comply with airworthiness requirements, quality controls and the dynamics of working with colleagues with differing interests, while also trying to be highly innovative. In addition, they will eventually have to pass ‘their’ project on to another group.’ A challenging project The aim is to teach the module three times a year. It will last for 20 weeks and generate 6 ECTS. It is expected to start in February, providing places for around 15-20 students per round. Melkert clarified, ‘Students will be selected on the basis of a motivation video, their marks and an interview. We will also pay attention to the composition of the team: diversity is very important.’ Working as members of the team, students will not only develop good technical skills, but also gain a better understanding of the safety culture involved in producing and certifying an aircraft. In addition, they will be confronted with organisational issues, such as project and certification administration and ensuring that the project passes smoothly to the next team. Melkert concluded, ‘In short, it's a project to get your teeth into.’ As yet, no companies are involved in developing the module. ‘But,’ says Melkert, ‘that would be beneficial to both parties. We are at the beginning of a highly ambitious project and would welcome any ideas, questions and support. An initial investigation revealed that there is already a great deal of interest.’ Photo by Marcel Krijger

A guitar for the future

When Max Roest started guitar lessons at the age of four, he had no idea that, two decades later, he’d make one for his master’s graduation project at the faculty of Aerospace Engineering. Roest had long been a guitar player, even producing an album called ToneWood, which was released in 2012. He’s competed nationally in the Netherlands but ultimately, the guitar was a hobby and not a professional pursuit for Roest. After completing his bachelor’s degree in aerospace engineering at TU Delft and moving on to the master’s programme, Roest was in need of a thesis project. He was inspired by the winner of the 2010 TU Best Graduate Award. Maarten Kamphuis, an Industrial Design Engineering student, who created a training sword for Historical European Martial Arts (HEMA.) Kamphuis was a proficient HEMA longsword practitioner and Roest was attracted to the idea of combining work and his hobby. His first step was to contact Dr. Otto Bergsma, a professor in the Structures and Materials Department, who agreed to serve as Roest’s thesis supervisor. As acoustic guitar players, like Roest, are aware, while wooden guitars may produce a warmer sound, this comes at a cost. Wood is very sensitive to changes in temperature and humidity. Touring musicians know their acoustic guitars will sustain damages, even when they are being well-cared for. There are guitars made from composite materials available on the market already. But, as Roest describes, “Their sound is brittle and lacks the character of a wooden guitar.” So, inspired by a sword making IO-graduate, Roest proposed to complete his thesis on developing a composite material which would emulate the sound of a wooden guitar without the downsides of the fickle wooden material. “Wood is a lot lighter than most composites,” Roest says, “so that was the most difficult criteria to match.” He also needed a material that would match in stiffness and internal damping. He started with a polethylene material but had to abandon it due to issues with bonding. He also tried existing composite materials with foam layered in between but the damping wasn’t high enough. After three months of experimentation, he discovered that fibre-reinforced foam appeared to meet his criteria. Then, however, he had to design a testing method to verifying the acoustic properties of this new material. Fortunately, he met Farbod Alijani, a professor in 3mE who just so happened to have a master’s student starting in his group who was designing a similar testing method for another project. “I was very very lucky to meet Luka Marinangeli.” The two created a production method that resulted in panels which were very, very similar to wood. And not just any wood, moon spruce which is felled according to lunar cycles and is Roest's preferred material for his guitars. Merely producing the material did not prove sufficient for Roest’s own exacting standards. He wanted to building a complete guitar. With an estimated price tag of €10,000, however, Roest first needed to talked to Dr. Rinze Benedictus, Head of the Structural Integrity Group. “He supported me in exchange for also making the faculty a guitar.” Roest did and it now sits in his office in the Faculty of Aerospace Engineering. Once they secured funding for the project, Roest approached the technicians in the Delft Aerospace Structures and Materials Lab. “These technicians are underappreciated at the university, I never would have completed the project without their help.“ With their help, he created a guitar form out of a strong plastic and was able to attach the panels. In the interest of science, Roest tested his new guitar in the anechoic chamber also known as the “dead room” at the Faculty of Applied Sciences. It wasn’t his first trip to the space. He played in the room previously, using his traditional guitar. You can watch a video of that performance on YouTube. Museum of Sound II - Anechoic Room - Max Roest The project was more than just a fun challenge. Much of the high quality wood that is used in guitars is harvested in Alaska, in the United States, where deforestation has reduced the availability of wood. “At the current rates, we might run out of this high quality wood in ten years,” says Roest. While guitar-making is a fairly small portion of overall wood use, finding a viable alternative would be good for the industry.

Clark Borst: ‘Research and education need each other’

During the opening ceremony of the academic year 2016-2017 in the Faculty of Aerospace Engineering, Clark Borst, lecturer and MSc track coordinator of Control and Operations, was voted AE Teacher of the Year by the students. So what sort of teacher is he? How does he combine his teaching duties with his research? And how does he envisage the future of education? ‘Automation is a bit scary. It's impersonal, emotionless. Automation can help us to progress, but it can also make us stupid. Take graphic calculators. Pupils don’t always learn how particular answers are calculated. They skip that step. I want to create automation that makes people smarter , not stupid. This is what drives me. Learning to ask question Automation plays a major role in education. We have online education, and these days, students have fast access to all the information they need and are able to navigate their way skilfully through the digital world. But do they actually think about the information they receive? This is where our task as teachers lies. It is our job to help our students develop a critical attitude. It’s so important for their future, whether they choose a career in academia or leave university. A critical attitude will always stand you in good stead. One of the first things I try to teach students is that there's no such thing as a stupid question. To me, the stupid thing is not to ask questions. This is the atmosphere I try to create in the lecture room: one of openness. And they're allowed to laugh, too!’ Lectures becoming more valuable ‘Teachers can do great things with online education and media, although I have to say I'm not a great fan of Collegerama. I don't understand why you'd want to record a lecture just to broadcast it online. Personally, I think that lectures, and the interaction they generate, are more important than ever in today's digital, impersonal world. In a world where we are constantly bombarded with information, people are crying out for context and explanations. Students can learn books by heart, but does this mean they understand what they've read? I think that the most valuable aspect of media in education is the huge range of images we can access: we can make theory visual, which helps to make things clearer. I always thought that the best teachers were the ones who managed to simplify highly complex concepts. So this was my own ambition when I started teaching. I enjoy looking for simplicity in complicated material. For the course in Avionics, for example, I make films with animations. It's very time-consuming, but I enjoy doing it, and the films are really useful. I choose difficult subjects for these ‘tutorials’. Fortunately, the students seem to appreciate them, too.’ Boosting each other ‘Education is so important. This is a university after all! We are training the engineers of the future, and it is up to us to inspire a new generation. But education needs research to prevent it from losing touch. Your research can ‘feed’ your teaching with the latest relevant developments in the field. So it's the combination that actually generates added value. Conversely, teaching can also boost your research. We mustn't forget that we can learn from students by listening to the questions they ask. What do I do if I don't have the answer to a question? I say that I don't know, but I go away and start searching and come back with an answer at the next lecture. Difficult questions like this keep me on my toes, as a teacher and as a researcher.’ Dr. ir. C. Borst

Kite power: towards affordable, clean energy

How can we produce clean and renewable energy in a more affordable way? As we are confronted with climate change and global warming, this question represents one of the greatest challenges of the 21 st century. A research team in the field of airborne wind energy of the faculty of Aerospace Engineering recently kicked off their ‘Fast Track to Innovation’ project REACH, which is funded with 3.7 million Euro by the European Horizon 2020 programme. Their ambition? To ensure cost-effective renewable energy with a low environmental footprint by using kite power, or, as it is called more generally, airborne wind energy. On 31 May 2016, the official kick-off meeting of the REACH project took place at the faculty of Aerospace Engineering. After a word of welcome by coordinator Dr. Roland Schmehl (section Wind Energy), the various partners involved gave short presentations, followed by lunch and discussions. Kitepower, a recent start-up of TU Delft, is at the core of the REACH project with the mission objective to commercialize the technology. Enevate B.V. is the technical coordinator of the project and will integrate the developed kite system, market and sell it. The goal is to have the first commercial prototype of the E100 – the name of the 100 kW kite power system – within two years, and to sell it within three. Several parties have already expressed their interest. Losing weight and reducing costs Horizontal axis wind turbines with rigid rotor blades are the most common way of converting wind energy. There are now over 200,000 wind turbines operating worldwide. But these conventional wind turbines have downsides: they are heavy, expensive, make noise and detract from the visual quality of the landscape (and so does the needed infrastructure such as high-voltage lines). The concept of a kite power system has the upper hand when it comes to these downsides. ‘Wind turbines are very robust. This means they have to deal with immense structural forces,’ Schmehl explains. ‘The tower and rigid rotor blades that take all the aerodynamic loads are heavy and expensive. The essence of airborne wind energy is to replace this heavy structure by lightweight cables and membranes. This way, we might use a tenth of the material – and thus weight – to produce the same amount of energy. This means the cost of energy would turn out dramatically lower if we use kite power.’ How does the system work? Functional components of the 20 kW technology demonstrator developed at Delft University of Technology The ground station holds an integrated ground control centre and incorporates the cable drum with a cable routing mechanism. The generator holds a 20 kWh battery. Because it houses also the central control computer, the ground station functions as the ‘brain’ of the system. The kite control unit (or KCU) determines how the kite flies by steering and depowering of the wing. The KCU is commanded by the ground control centre via several redundant wireless communication channels. Eventually, the goal is to be able to have the KCU function as a ‘brain’ as well, because it would closer to the kite and thus more reliable. Also, it would then be able to communicate with KCUs of neighbouring kite systems to avoid collision. The kite has 25 m 2 surface area and holds an on board sensor platform to continuously measure the position, orientation and velocity of the wing. The wing creates the aerodynamic lift force as turbine blades on conventional wind turbines do. Challenges ahead In the coming months, the team is set on showing the feasibility of certain features. One of the first milestones to pass, is flying during the night. This involves illumination, because aircraft need to be able to see the kite. Although every flight is registered, a back-up plan is needed, should communication fail. A second milestone would be to fly for 24 hours straight by the end of this year. The advantage the kite system has over the wind turbine – its low weight – poses a challenge. The system must be lightweight, but also strong enough to be reliable and durable. One particular difficulty in this is securing automatic launches and landings for the system: ‘If there is a thunderstorm coming, or troubles occur with a wind turbine, you can simply push a button and it will stop rotating. A flying system is very different, as you will need to land it. You cannot just stop mid-air.’ Lastly, there is currently an ongoing debate on whether a kite power system should be considered an aircraft or an obstacle. Certification of the E100 is therefore also something that will be handled in the near future. Schmehl: ‘By the end of 2017, we want to have a commercial prototype of the 100kW system.’ The 20 kW kite power system of TU Delft in operation at the former naval airbase Valkenburg, The Netherlands Dr. Roland Schmehl Johannes Peschel TU Delft : general coordinator, contributes research Kitepower : associated start-up, technical coordinator Dromec B.V. : ground station Maxon Motor GmbH : control drive trains Genetrix : kite development and production

Research challenges in wind energy

Can supercooled generators improve the efficiency of offshore wind turbines? How can ‘big data’ from sensors mounted on wind turbines help in the maintenance of wind farms? How can we calculate the effects of waves on floating wind turbines? Is it possible to forecast wind power at the height of wind turbines? Is it a good idea to combine offshore wind turbines with wave or tidal energy generators? These are some of the questions included in this research agenda for wind energy drawn up for the European Academy of Wind Energy by TU Delft professor of wind energy Gijs van Kuik and his colleague Joachim Peinke from the Carl von Ossietzky University of Oldenburg, Germany. They are fundamental scientific questions from researchers working in 11 different fields, ranging from material sciences to energy conversion, and from environmental impacts to aerodynamics. Van Kuik: ‘Most wind energy agendas, such as that of the International Energy Agency, focus on technologies for application in the short term, for example to reduce the costs of wind energy. However, this agenda looks to the future.’ Why do we need to do this? ‘The biggest wind turbines currently in use are the largest rotating machines in the world, wind turbines are more and more often used in large offshore wind farms, and the contribution of wind energy to the global energy mix is increasing. This increase in scale means there are new scientific challenges to be solved. As scientists, we are of course interested in the answers, but the main reason for coming up with answers to these long-term challenges is that they can result in game changers – radical new technologies that make it possible for wind energy to become a significant component of the energy mix.’ Paper encourages discussion Under the banner of the European Academy of Wind Energy, TU Delft professor of wind energy Gijs van Kuik and his colleague Joachim Peinke from the University of Oldenburg have drawn up a long-term research agenda for wind energy. Researchers working in 11 different fields in Europe and the US submitted their fundamental research challenges for inclusion in the agenda. The agenda will initially be published as a scientific paper with the title ‘Long-term research challenges in wind energy’, in the new open access journal Wind Energy Science. It will also be published in book form later this year. Gijs van Kuik: ‘The aim of this paper is to show that wind energy is more than just an engineering discipline that comes up with short-term solutions. Answers to fundamental research problems can help in the future development of the wind energy sector.’The main aim of the paper is to encourage discourse amongst colleagues. Van Kuik: ‘I hope that many people who read the paper disagree with our views, so that we encourage a lively scientific debate.'The EAWEwind energy research agenda will also be published in book form by Springer later in 2016. Further information For further information please contact professor Gijs van Kuik at +31 15 27 84980 or via . Article published in Wind Energy Science 9 February 2016: van Kuik, G.A.M., J. Peinke ‘Long-term research challenges in wind energy’ . The new Wind Energy Science journal

One way to make composite aircraft lighter: stop riveting and start bonding

Provided it’s manufactured and applied correctly, adhesive bonding (using glue for non-material scientists) is a safe and efficient way to join aircraft parts together. “Adhesive bonding has been used for several years instead of or together with rivets in conventional metal aircraft. But now that aircraft fuselages are increasingly made from composites we need to know more about how we can use adhesive bonding to join composite parts optimally." "At the moment we apply similar design methodologies used up to now in metal bonding to adhesively bond the new material composites. This penalizes significantly the weight saving potential of composites”, says structural joints researcher Sofia Teixeira de Freitas of the faculty of Aerospace Engineering, TU Delft. ”The design of bonded joints has to be re-invented in order to efficiently join composites, both in term of shape and in terms of material properties optimisation (fibre direction and layup).” In July Teixeira de Freitas was awarded a NWO Veni-grant. The grant gives her the opportunity to come up with a new design methodology with which the aircraft industry can determine the optimal properties of the composite material and the optimal geometry to join the different aircraft parts together safely and efficiently. Drilling holes and fitting rivets Since about the time Boeing introduced the Dreamliner, aircraft manufacturers have predominantly used carbon fibre composite materials for parts of aircraft as a light and strong replacement of aluminium. On aircraft leaving the production lines now, about half of the materials used are composites. It’s understandable that composites are popular with the manufacturers: lighter aircraft have lower fuel consumption and lower CO2 emissions for example. Aircraft consist of many small parts that have to be joined together. In traditional aluminium-made aircraft fasteners such as rivets were used to do this. Teixeira de Freitas: “We have only slightly adapted the old joining methods used for aluminium to fit modern airplanes that are made from both aluminium and composites. Basically, we still drill holes and fit rivets. This is far from optimal. Drilling holes cuts the carbon fibres of the composite and significantly destroys their load bearing characteristics. To compensate that more material is used, which makes the airplanes heavier again.” Joints between the wing skin and the stiffener, aircraft wing Zooming in on the adhesive bond solution Adhesive bonding – glue Using just adhesive bonding could solve this issue, but much more knowledge is needed about the ’glue’s’ behaviour in the longer term and we need to know better how to shape the composite’s fibres and what geometry is needed to connect the two parts together. Teixeira de Freitas: “Composites are not like metal that has fixed properties. The fibres that make up the composite can be placed in different directions, making it possible to adjust material properties. We need to find out how to create optimal properties to build a stronger and safer adhesive joint. Also we need to know what the optimal geometry is of connecting the two parts together, whether it’s linking composites together or whether it’s connecting composite and metals.” Teixeira de Freitas faces an interesting scientific challenge: “Composites already exist as highly efficient materials, but they need to be optimised to become very efficient structures as well. What we need to do is scale up to larger structures. Adhesive bonding plays a pivotal role in this”. Is the future made of glued composites? Will all aircraft – or any other metal structure – consist of bonded composite parts in the future? Teixeira de Freitas believes in the future every part of a structure will be made from the best material tailored to its purpose and that new solutions will be found for joining these together safely and efficiently: “Interfaces in hybrid structures will become increasingly important. In the future we will need joints that do not reduce the performance of material parts. Adhesive bonding is a very promising candidate for this, but other options are also researched (for example by my colleagues at the faculty), such as welding plastics or even using a type of Velcro.” Veni The Innovational Research Incentives Scheme Veni is a grant from the Netherlands Organisation for Scientific Research (NWO) for researchers who have recently obtained their PhD. It allows them to conduct independent research and develop their ideas for a period of three years. The researchers receive a maximum of 250.000 Euros. Teixeira de Freitas: “I am planning to use the grant mostly to collaborate with experts at other universities and build bridges between disciplines.” Offshore industry This summer Teixeira de Freitas received another piece of good news: she – and her colleagues in a broader consortium – also received a grant of 500.000 Euro from the Top Sector High Tech Systems and Materials for research on using composites in the offshore and maritime industry. Sofia Teixeira de Freitas Sofia Teixeira de Freitas is a civil engineer with a Master’s degree from the University of Lisbon in Portugal. In her PhD at the faculty of Civil Engineering at TU Delft shedeveloped adhesive bonding technology for reinforcing steel bridges. She currently holds the position of Assistant Professor in the department of Aerospace Structures and Materials at the faculty of Aerospace Engineering at TU Delft. Sofia: “My multi-engineering background gives me a broader perspective, an overview of disciplines which I find very useful. What really motivates me? To expand my knowledge and pass it on to new generations.” The banner photo pictures the composites laboratory at TU Delft

Fighting corrosion with algae

If algae and specifically diatoms can be used to increase the efficiency of environmentally friendly anti-corrosion coatings, we could protect all kinds of structures – aircraft, trains, military tanks and so forth – without using toxic and expensive materials. The use of coatings is one of the most widespread approaches for protecting metallic structures against corrosion. Such coatings use passive and active protective methods such as barrier against corrosive species and corrosion inhibitors. For almost 100 years, corrosion inhibitors based on chromium VI have been used in coatings to maintain the protective function even after damages have occurred. Though efficient, these particles are highly toxic and carcinogenic. As a consequence, the consumption of chromates has already been banned in many applications and is a constant target for the highly demanding aerospace sector where its banishment has been delayed several times due to the lack of sufficiently good alternatives. The use of algae, and specifically the exoskeletons of the algae group known as diatoms, might help us create the alternative the world is looking for. Along 2015, Assistant Professor Santiago Garcia at the Novel Aerospace Materials group, set up a project to explore the potential use of diatom exoskeletons (or: frustules) to protect aerospace structures. Garcia: “In 2015 we made the first proof of concept to demonstrate that algae can be used for active corrosion protection and self-healing applications. I believe this could potentially have a huge impact.” Why diatom frustules? There are already a few examples of promising corrosion inhibitors that might replace chromate. However, studies have shown that unwanted reactions occur between these inhibitors and the surrounding coating matrix thereby minimizing their inhibiting efficiency. A way to avoid this is to encapsulate the inhibitors inside carriers. Using a carrier reduces the interaction between the inhibitor and its surroundings, and in addition it can be used to control the release of the corrosion inhibitors. This strategy can theoretically result in much more efficient anti-corrosive coatings. Frustule of the Aulacoseira type diatom (diatom exoskeletons) The frustules can function as such a micro-sized carrier. Why is their specific architecture suitable for the task? PhD researcher Paul Denissen explains: “Frustules are hollow nanoporous silica microparticles referred to as ‘pill-box’ structures. They have a cell wall made of silica, a strong structure with pores. Luckily for us, these pores are big enough to allow the corrosion inhibitors in and out.” Studying individual particles After his MSc thesis on this topic Paul Denissen started his PhD research last January and is looking into the isolation and study of individual frustule particles by means of advanced characterization techniques. Garcia: “Frustules show a wide diversity in shapes, sizes and porosity (namely architecture). Dedicated tests need to be performed to find out how the individual particles behave and how we can influence that behaviour. In short, we want to: Explore the potential use of diatom exoskeletons and demonstrate that they can be used for doping and controlled release of functional species in coatings such as corrosion inhibitors. Evaluate what the effects of the architecture and geometry are on the release and efficiency of corrosion inhibitors. Modify the surface of diatom exoskeletons and apply certain triggers such as changes in the pH level to control the release of corrosion inhibitors. If we understand this, we can start making coatings that only release the required amount of corrosion inhibitors at the right time using highly available raw materials. “ Corrosion protection mechanism of coatings containing inhibitor-doped diatom exoskeletons Nature’s solution to an industrial problem The NovAM group is now specifically looking at high strength aluminium alloy 2024 used in aerospace manufacturing, which is very susceptible to corrosion but the trick can be used to protect all kinds of metal alloys. Denissen explains that this self-healing mechanism could also be used for other applications in the future: “Every inhibitor has certain characteristics which have certain effects when encapsulated in a carrier. Once we have quantified individual particles and measured how they behave, we can decide on which particle is best for a specific application, such as aircraft.” If algae and specifically diatoms can be used to increase the efficiency of environmentally friendly anti-corrosion coatings, we could protect all kinds of structures – aircraft, trains, military tanks and so forth – without using toxic and expensive materials. Garcia: “Diatoms occur in virtually every environment that contains water. Reproduction among diatoms is by spores and asexual by binary fission and they have a very high growth rate. Using frustules to make active anticorrosive coatings would not only present a healthier solution to current synthetic approaches, but it would be up-scalable, sustainable and inexpensive as well. This new concept follows the line with our ongoing research on self-healing polymeric systems and new functional micro and nano fibres for composites and coatings made out of algae.”

Glue for art’s sake

Hans Poulis (TU Delft Adhesion Institute) recently received funding from the NWO for his research proposal in the field of adhesive aging. The proposals were accepted in the first round of funding of the Netherlands Institute for Conservation, Art and Science (NICAS). Poulis: “This is the first time that the Adhesion Institute will be developing a new type of adhesive from scratch.” There are currently all sorts of standard adhesive types in use for the restoration of works of art. Synthetic adhesives are often more stable than natural adhesives, but are not always entirely suitable. They were not developed for restoration purposes and therefore never have all the necessary characteristics. So we usually don’t know how they will alter over time, either chemically or mechanically. In other words, how the substances age over time under environmental influences. They might turn yellow, for instance, or the qualities of the adhesive bond may alter. Hole in the market It is a niche market, and not really commercially viable for businesses. Recanvassing paintings requires relatively large amounts of adhesive, but you can imagine that for repasting tiny paint flakes only tiny amounts of adhesive are needed. The Adhesion Institute will be looking into that latter process, and particularly into reverse glass paintings and compositions in oil paint and gouache. These works are typical for many works of art that will need restoring in the short term if we want to preserve them for future generations. Developing a specific adhesive for this purpose is not cost-effective for a company, if only for the high costs of the research involved. Poulis: ‘Firstly we’ll take two post-doc researchers into the field. I hope to organise a brainstorm session in March with professionals who have years of experience, including curators. They know exactly which requirements the adhesive must meet. Based on the outcome of that session, we will determine the start phase of our research. That will centre on the question: what chemical substance will we base it on? That will be our main ingredient. We will then create different mixtures and depending on the requirements, adapt the recipe accordingly. Using various lab tests we will determine how the mixtures react, initially and over time.’ From test to product By carrying out aging tests, we aim to find out how mixtures react after a certain number of years. For instance, light exposure tests will enable us to see to what extent such a substance turns yellow over time. For these tests, Xenon lamps are used. They generate UV light and initiate an accelerated aging process. Poulis: ‘Ultimately, we will also test the adhesives on works of art (mock-ups). Of course, in practice you never know precisely what will happen to the adhesive, because of the numerous circumstances that could influence it. Moreover, there are no data available which can link accelerated aging tests to actual conditions.’ The Adhesion Institute has set itself a two-year time limit in which to develop an adhesive which is suitable and stable in the long term when it comes to mechanical and visual performance. The consortium for this research project includes a commercial company specialised in the manufacture of small quantities of adhesive. They would be able to put it into production. Poulis: ‘And who knows, it might generate a spin off.’ --- The NICAS is an interdisciplinary research centre aimed at the conservation of cultural heritage. It works in collaboration with the Netherlands Organisation for Scientific Research (NWO), the Rijksmuseum, the University of Amsterdam (UvA), the Cultural Heritage Agency of the Netherlands (RCE), and Delft University of Technology (TU Delft). Click here to visit the NICAS website.