Made to Measure Materials

Measuring Materials, Making Materials to Measure

Made to measure…Delaminations

Who are you?: Osman Ajmal

What is your role?: PhD Researcher

What is your work about?: Locating and measuring the growth of embedded delaminations in composite materials.

I beg your pardon?: Delaminations are one of the more prevalent forms of defects in composite materials such as Fibre Reinforced Polymers (FRPs). Non-Destructive Evaluation (NDE) is used to determine the position and size of delaminations during testing.

OK. Why?: FRPs are used in a wide variety of industries. They have applications as components of cars, aeroplanes, spacecraft and even sporting goods! By understanding how these defects in structural elements behave under different loading scenarios, these materials can be better tailored for different applications.

And?: My work compares existing and novel methods to detect these defects. Figure 1a is a finite element model of a typical specimen with an embedded defect, whilst Figure 1b shows a typical output from the real specimen, monitored by Digital Image Correlation (DIC).  Analysis of the DIC data gives, in this case, longitudinal surface strains which can be used to detect the presence of delaminations.

dic.png

Figure 1: Longitudinal strain contours of composite laminate specimen with an embedded square shaped artificial delamination in three point bending. (a) Finite Element Modelling (b) Digital Image Correlation

So what?: By comparing different NDE techniques to each other and to FEA, my work aims to determine the “resolution” of the different techniques. This is done by comparing the results of different techniques for the testing of the same structural elements and the same loading scenarios. By using artificial inserts, model defects can be created during the manufacturing process. During testing, these defects can be monitored: because the size of the delamination is known, the NDE technique can be assessed against what it   should detect, and if possible calibrated accordingly.

Final thought: The wide range of readily applicable NDE techniques are literally ‘made to measure’ defects in structural elements. It is important to determine how well they do this for delaminations in the composites used in modern cars, aeroplanes, ships and all the rest.

 

Made to Measure…Microscopy

Who are you? Rebecca Tung
What is your role? Undergraduate Medical Engineer on industrial placement in the Microstructural Studies Unit at the University of Surrey
What is your work about? I help to prepare and characterise materials using a variety of techniques, predominantly scanning electron microscopy based techniques.

I beg your pardon? Materials can be examined in a scanning electron microscope (SEM), which produces an electron image, to reveal microstructure and topography. In addition, the chemical composition of the material may be analysed which can help to determine the properties of a material.

What is a SEM? Scanning electron microscopes use a beam of accelerated electrons as a source of ‘illumination’. Electron microscopy offers a much higher spatial resolution than light microscopy and can reveal either microstructure or surface topography. When the beam interacts with the sample surface, some complex physical processes occur. This results in the emission of secondary electrons, backscattered electrons as well as X-rays. The detection of these three signals enables: (i) imaging of the surface topography, (ii) imaging of the microstructure and (iii) measuring the chemical composition. In the micrographs below, the difference between the detection of backscattered electrons and secondary electrons can be seen. Figure 1 shows the same Vickers hardness indent in a brittle material imaged with the two types of emitted electron. The behaviour of the low energy secondary electrons (Figure 1a) and high-energy backscattered electrons (Figure 1b), along with appropriate electron detectors, gives different information about the specimen.

Microscopy

Figure 1 – Comparison of Scanning Electron Microscopy modes: a) secondary electron image (the bright white areas suggest ‘charging’) and b) back scattered electron image.

And? Analysis of a material with a SEM offers not only increased resolution (therefore higher useful magnification) but the benefits of studying any combination of topography, microstructure and chemistry. Modern microscopes have multiple electron detectors that give different combinations and emphasis of information. Other possibilities include variable pressure microscopy which enables wet specimens to be studied and a focused ion beam capability which enables specimens to be sectioned and studied in 3D.

So what? The characterisation of engineering materials is essential for the goal of understanding microstructure-property-processing relationships. The SEM is arguably the most flexible technique that contributes to this goal.

Final Thought: SEM offers a variety of analytical techniques, which makes it a versatile tool for characterisation of materials. The capabilities of the JEOL 7100F SEM, at the University of Surrey, which is my favourite instrument, make it suitable for studying the whole range of engineering materials—it really is an instrument that is Made 2 Measure!

 

Made to Measure…Waste

Who are you?: Dr Jade-Ashlee Cox.

What is your role?: Currently a Senior Consultant at Ricardo Energy & Environment. Formerly I was an EngD Researcher on the University of Surrey’s, SEES programme, sponsored by Surrey County Council.

What is your work about?:A decision making framework for the sustainable management of household waste.

I beg your pardon?: Every week we throw away food, packaging, things that we’re done with – waste. But is the stuff that makes its way into out bins really waste? Our consumer goods, clothing, food and everything that we trade, requires resources to be grown and manufactured as well as energy, water and time. The term ‘waste’ has long been associated with disposal, and this might be part of the problem, as only 44% of household waste in the UK is recycled. Yet, if we were to think of household waste as a resource, it may be possible to extract its ‘value’. Items that householders no longer require should not simply be discarded of as waste, but instead should be appreciated for the inherent value they possess and the new products they can become. However, implementing this paradigm is complicated by the variety of different materials in the waste stream, and the number of stakeholders responsible for its management. A central theme of the work presented in this thesis is the paradigm shift ‘From Waste to Resource’.

Why?: There are two key issues that need to be addressed. Firstly, we need to understand what is present in the resource stream, and in what quantities. This then allows waste managers to make informed choices about collection strategies and investment in reprocessing infrastructure. Not all constituents of the resource stream will be present in economically viable quantities – at least not in one collection authority. Sometimes it is necessary to pool resources with other councils, if you know how much of something you have got. Secondly, in some cases there is ‘more than one way to skin a cat’. For most materials that we would want to deal with there are multiple options, and the inevitable default of landfill or incineration. These different reprocessing options will have their own costs, benefits and implications: is it better to ship something across overseas to the most efficient reprocessing plant, or keep it local but get a minimal return? This is not always a straightforward question to answer.

And?: This is important both for issues of resource security and sustainability. Indeed, whilst the times of ‘make do and mend’ can appear to be in the past, there is a great deal of interest in reusing and recovering material resources, especially if components or assemblages can be refurbished or ‘upcycled’. This research has developed a decision-making tool, which can enable local authorities to assess the best way of managing their household ‘waste’. This takes the user through the identification and quantification of the materials of interest, the determination of viable treatment options, and an options appraisal.

Waste supply chain-1

Figure 1 – Complexity of the waste supply chain network. Direct relationships are represented by solid green lines. The dotted lines represent future relationships and solid black lines represents influences. (After Cox and Jesson, 2015.  Artwork produced by Materials World from an orginal diagram).

So what?: By understanding the composition, amount and value of ‘waste’ available to them, local authorities can take a more proactive approach in the ‘Waste Supply Chain’ to prevent the implementation of ‘sub-optimal’ management practices and the loss of valuable resources.

Final Thought: Using something once and letting it end up in landfill is the real waste. We can all do our bit at home like taking our old clothes to the local charity shop, but that will only take us so far. Crucially, we need to make sure that our resources stay out of landfill and remain in the cycle.

If you’d like to read more about assessing the resource stream, you might like to check out our award winning paper (ICE Telford Premium, 2016), here, for free.

 

Made2Measure Heaven: Plasma FIB

Who are you? Dr Mark J. Whiting

What is your role? I’m an Academic in the Department of Mechanical Engineering Sciences at the University of Surrey.

What is your work about? My research centres on the role of microstructure and especially interfaces in the manufacture and performance of advanced metallic materials. One way to study interfaces is to use a plasma focused ion beam or PFIB.

I beg your pardon? The engineering performance of many materials depends on the nature of interfaces as well as the physical processes that occur at these boundaries. Many current and next-generation structural materials bring together diverse materials in composites, combing a metal and an inorganic material. These include glass-to-metal seals, previously featured on this site. Another example, also featured here, are SiC monofilament reinforced titanium matrix composites. The interfaces not only determine some aspect of performance, but their exact nature depends on processing and manufacture. Even monolithic materials owe some of their performance to interfaces created during manufacture—additive manufacturing processes for metallic materials have a molten metal/gas interface throughout production. Gas absorption and oxidation etc. can all alter this interface prior to its becoming part of the bulk.

A new method for studying interfaces as well as other microstructural features is plasma focused ion beam, PFIB, technology. My two colleagues, Professor John Watts and Dr David Cox, and I were recently awarded an EPSRC grant to purchase such an instrument for the University of Surrey. This venture is in partnership with the NPL who are interested in the materials metrology capability the instrument.

Mark

Figure 1 – The author discussing plasma technology with a Cyberman (Cyber-leader 768HY98)

What is a PFIB? FIB, or focused ion beam, techniques have become firmly established in the last decade as ways to make both devices and specimens for characterisation. In these traditional FIB methods liquid gallium is ionised and used to remove material. In this way, thin slices of many functional and structural materials can be made for study by techniques such as transmission electron microscopy. The selective removal of material down to the nanometre scale means that very small devices can be fabricated from a multiplicity of materials. The study of interfaces by electron microscopy and allied advanced characterisation techniques requires greater effort to gain nanometre-scale information reproducible over reasonable length scales. The use of gallium to remove material poses some problems. Gallium can react with many metals, in some cases forming low melting point eutectic alloys. More fundamentally, there is a limit to the ion current and therefore speed with which a gallium ion beam can remove or ‘cut’ material. The recently commercialised plasma FIB uses xenon ions. Xenon is not only inert but can also offer significantly increased ion currents and sputter yield. The two current manufacturers both quote at least a sixty-fold increase in throughput. In most cases this enhanced milling speed will offer the opportunity to fabricate bigger devices with nanometre-scale detail or the production of larger more representative samples.

And? Much materials characterisation studies specimens which are so small that there are often significant doubts as to whether the specimen is representative of the bulk material. Rather than study a handful of grains and three grain boundaries, PFIB means that hundreds of grains and thousands of boundaries can be studied. The speed of PFIB also makes possible the 3D characterisation of materials on a sensible timescale.

So what? The University of Surrey’s PFIB will be used for a multiplicity of engineering projects. The work that I will do with it offers science which will enable (i) the manufacture of lighter, stronger and stiffer structural materials, and (ii) the additive manufacture of advanced structural materials which produce less waste than materials made by subtractive manufacture.

Final Thought: Plasma FIB offers the ultimate in Made2Measure Materials. It offers new possibilities for the manufacture of devices, new capabilities for materials metrology as well as being a technique that offers characterisation capability informing the science underpinning modern materials manufacture.

Made to Measure… Printed Solar Cells

Who are you? Harry Cronin

What is your role? I’m an EngD Research Engineer at the University of Surrey and DZP Technologies

What is your work about? I’m working on the scale-up of printable solar cells based on organic-inorganic halide Perovskite materials.

I beg your pardon? Perovskite materials have the general formula ABX3. By changing the atoms or molecules which sit at the A, B and X positions these fascinating materials can be designed to have a wide range of optical and electronic properties. Recently, it has become clear that halide Perovskites are an excellent material for making solar cells. These materials use a small organic molecule on the A site, a metal like lead or tin on the B site and a halide such as iodine on the X site. The efficiency with which the best Perovskite devices convert sunlight into electricity has been pushed from 3.8% in 2009 to over 20% today. But the real advantage of Perovskite solar cells is that they are simple to make – simply deposit a precursor solution, and the Perovskite forms on drying. This property makes them ideal for printing, but owing to a number of unsolved challenges a printed Perovskite cell has yet to be commercially demonstrated.

Solar Harry

Figure 1 – The author, grinning inanely, prepares to coat a conductive silver substrate with a second layer using doctor blading.

Why? Solar cells could potentially play a major role in reducing carbon emissions, but are currently too expensive to compete with fossil fuels in many applications. By using cheap, high-throughput printing technologies, similar to those used to produce newspapers, cell prices could potentially be slashed. This is part of a wider trend in electronics manufacturing, in which people are trying to make all sorts of ultra-low cost devices by means of printing. Previous work at DZP Technologies has produced prototype printed cells, and the aim of my project is to improve the efficiency of these prototypes by the introduction of Perovskites. There are many challenges to be overcome with the scale-up of this technology.

And? Printed solar cells consist of multiple layers, each of which must be simultaneously optimised and controlled both in terms of materials and processing. In my research I have looked at a method for increasing the conductivity of several of these layers using high intensity light pulses. Put simply, more highly conductive interlayers will mean better-performing solar cells. In parallel to this I have investigated the behaviour of the Perovskites under different processing conditions, which will be vital knowledge as we work towards scaling up the technology.

So what? If this technology can be taken from the lab to commercial scale, we could start to see solar cells in many new places. As well as being cheaper, printed solar cells open up a range of new applications due to their light weight and mechanical flexibility. For example, flexible solar parking shades could be used to charge electric vehicles parked underneath them. Or, highly portable rolls of solar cells could be developed for camping or use in disaster zones.

Final Thought: Made to measure printed solar cells have the potential to offer a step change in the affordability of solar power, alongside flexibility, low weight and large area. Coming soon to a rooftop near you (we hope)!

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