Engineering Auxetic Materials and their Implications for Security 

Engineering Auxetic Materials and their Implications for Security 

PaCCS Communications Officer Kate McNeil sat down with University of Exeter’s Professor Ken Evans to discuss his work on engineering auxetic materials and the potential applications for these technologies in the security domain. 

Can you tell me a bit about your work, and how it links to issues in crime and security? 

I work in a new area called auxetic materials, which are materials with very unusual properties. If you take a normal material like a rubber band and pull on it, it gets longer and thinner. The types of materials I work on, are unusual because when you pull on them, they get longer and thicker. So, they are extremely unusual, which results in differences in their overall mechanical properties, and creates opportunities at the atomic, micro-structural level and the macro-scale. We can then put different types of geometry into materials, and people have tried to make auxetic materials in different ways and by using different materials. One of the earliest areas of work with auxetic materials were foams – you can make these foams condense and increase their density when squashed, for example. That has massive potential in terms of impact protection, knife protection, ballistic performance, acoustics and any other impact situation where materials react to impact.  

This technology has now expanded beyond foams – so you could use auxetic ceramics for ballistic protection, or foams for knife protection, or auxetic textiles for blast protection. We are also using ‘honeycomb’ structures and are also making geometries with textiles through specific types of knitting, yarns, and weaves. You can thus create materials with unusual geometry and unusual behaviours, such as improved energy absorption. That could be useful for changing the suspension in a vehicle so that it can be soft of hard depending on the circumstances. Meta materials are another area of development here, where at a nano scale you can create things which have negative thermal expansion (materials which get smaller when they get hot), negative stiffness, etc. However, auxetic materials have been around the longest in this field, more than 20 years now, and that has created opportunities for commercial development.  

Have you sought to commercialize this technology or to develop products based on your findings? 

We did some work with the Home Office a few decades ago, which then turned into some work with the Ministry of Defence. The Home Office work was to make auxetic blast curtains which would be protective when there was a terrorist explosion – the curtains wouldn’t be lacerated by the glass, instead, it would collect the glass shards, which would reduce damage. We also looked at improving helmet design for people travelling in tanks – we could make the helmets smaller while getting better protection, which is great for soldiers operating in confined spaces. In both cases, the proof of concept for the technology worked, but we struggled at the commercial development stage.  

The Home Office and MoD didn’t have the means to continue to fund the research, and because they were interested in security and protection, there were complications when it came to possibly bringing in commercial partners which had venture capital funding. For example, there were patent protection concerns which got messy. I was hopeful that the innovation unit within the university would be able to help – this was earlier in my career and perhaps I still had rather naïve expectations – but it didn’t work well, with relatively limited funding for patenting. The US seems to be doing better than the UK at commercialization in this way, with the US Defense Department appearing to be more open to the possibility that technology associated with it might be also commercially developed.  

Is this field continuing to grow, and are there other opportunities for this technology to be applied? 

These materials have massive opportunities in terms of protection, and research has been growing in this area for 30 years now. But where we’re seeing the most growth in research is in China. The Chinese research groups are very well funded, and it’s very difficult to know where they are going with it. China puts an enormous amount of funding into research, and while what they are trying might not yet be quite as innovative as the research going on in Europe and the United States, China is protective enough that it’s hard to say what is happening commercially. There’s a possibility that we may lose out relative to the investment China is putting in, and we wouldn’t know until it’s too late.  

Have there been more successful attempts at applying this technology in other areas? 

In the United States, there has been a textiles company that has been set up which is interested in blast curtains for the oil industry, though I’m not sure how far that has gotten. The big area of commercialization for this technology at present is in sportswear,Nike have done things on the soles of shoes, for example and another company is doing work in Florida looking at auxetic foam protection for the American football market. But it’s easier to get a sporting good on the market as opposed to a product designed for security and protection. 

What are you working on now? 

I spent some time in management and leadership roles within my university but was very lucky that I have a good research group and publication has carried on. Now, I’m on study leave, and I’m getting back to textiles and composite materials. I’m interested in the behaviour of auxetic carbon fibre reinforced composites, which can be used in industries like aircraft design. The direction of the fibres can be oriented to make them auxetic. Though this is a heavily regulated industry so there are restrictions on how the fibres can be designed, I do think there are potentially exciting things that can be done here. I’m also working with chemists on molecular level auxetic compounds, but I’d say that scaling things up in chemistry is probably 5-10 years away, while in other areas, things are ready to take off and it’s just a question of which country gets there first.  

What does work in the textile area look like? Where do ideas for new patterns come from, and how does the knitting and weaving actually get done? 

We have worked with a textiles group at Drexel University in the US. It’s a classic example of taking an odd idea, and then trying to find someone who can understand it – in the UK it’s harder to find people who do fundamental work on textiles anymore. It’s not our industry anymore.  So, it’s a question of finding people who can do it. I came up with the conceptual ideas about geometry, and then I had to find someone in the world of textile research who knows about the knitting or weaving machines to make it. They also sometimes bring in people who know about the unique properties of yarns, for example, and then we have to figure out if we can actually make a machine do the thing we want it to do. It’s been relatively conceptual, in exploring the ways of predicting unusual properties in knits and weaves, but you have to be able to work with people who know the computer control of the equivalent textile equipment. It’s also not a million miles away from additive manufacture – things like 3D printing. All of these technologies are coming of age and will be used in future production.  

What do you want policymakers of industry to know about this area of work? 

If you do a commercial development, right now it’s easy to get to a development stage but making innovation commercially possible still seems to me to be hard and slow in the UK. We don’t bring the people together soon enough, whereas in the US they are more flexible – people give “wacky” academics money there and hope that something might become a commercial development and expect a reasonably high margin of failure at the early stages. Meanwhile in Europe and the UK, the research councils fund the “wacky” ideas, and the innovation and industry steps are seen as later, separate processes. There’s a lack of join up between the different stages of development and it would be nice to build relationships earlier, especially where academics have great ideas but no commercial backgrounds. Innovate UK does a really good job at what it does of course, but I think it needs to find a way to support innovation earlier in the game. That might involve clashing with the research councils, but an academic doesn’t care about that – when we have good ideas we just want to run with them as quickly as possible.  

I also think that there are bigger picture questions and challenges in security right now. Security from a software and data protection side is flourishing as a set of commercial developments – people have bright ideas which can come in from a commercial perspective. Meanwhile, in materials and manufacture, talking about security seems to mean secrecy and not being able to commercially develop in the same way. Maybe our sector needs to learn more from the data protection people, about how to do security-related research in a way that doesn’t discourage commercialization or dissuade individuals with good ideas from getting involved.