Designing better body armour
It's not only vehicles that need protection, body armour is a key weapon in the fight against explosives. It not only has to protect the wearer, but also be lightweight enough to allow them to do their job effectively. This has led to all kinds of creative solutions over the years, from liquid body armour to the use of natural materials such as spider silk. Adam Healey researches this field at the University of Surrey...
Kat - What is the kind of body armour that soldiers or police would be wearing nowadays?
Adam - Well, the typical kind of armour you see on troops on the ground, if you consider typical flat jackets they kind of wear, the fabric itself is usually made of things like Kevlar or nylon - very strong fibres. They have pockets in the fronts and the sides and the back into which slot hard plates, designed to stop very high energy impacts like armour piercing, bullets and things like that which are commonly made of a combination of ceramic and composites. There are several advantages that ceramics have over other kind of materials. I mean for example, one of the the main things is weight. Weight for weight ceramics and composite systems are able to stop higher energy impacts than almost any other materials such as metals. It takes a much thicker metal sheet to stop the same kind of burst that ceramics can. It's quite difficult to nail down specific material properties that can be linked to "bulletproofness" if there is such a word. High hardness is commonly used as an indicator in this respect. Although something else that armour development is constantly trying to improve is costs. We could try and armour all soldiers with diamond if we could, but it's very, very expensive.
Kat - It would be really blinging though.
Adam - I'm not sure that's a primary concern but yes, it would.
Kat - Maybe not. So, tell me about the kind of work you're doing. You work with ceramics. Whats working in their structure to make them protective against high impacts?
Adam - The way a common ceramic armour system works is a sheet of ceramic and a sheet of composite. The job of the ceramic is to destroy the bullet and the job of the composite is to catch all the bits that are left. The ceramic does it in a variety of different ways. It's very hard so the bullet is fractured against it. As it breaks, it starts eroding the bullet as it pushes through the system. Fragments fly off, they take energy with them and we're examining the fragmentation and trying to work out what's actually happened. Like, how have these fragments formed. Normally, when you shoot something, the fragments end up behind the gun that shot it, it will go all over the range. But I've been using different methods to catch all the fragments and I've been trying to characterise these fragments and also, look for similarities between what's happened to fragments generated from ballistic events and fragments generated from other tests that are available to us.
Kat - So, you're kind of trying to put all these information together to work out almost a prediction of how materials would respond?
Adam - Pretty much, yes. It's a very large, vast and difficult jigsaw.
Kat - I can imagine that. Where are the ceramics of the future heading in this kind of body armour?
Adam - Well, what a lot of people are working towards at the moment are ceramic composites. They've got a solid plate of ceramic and they have different particles in here that change the way the ceramic behaves under impact. Like it might change the direction of cracks or generate fragments in different ways which will have an effect on how balistically powerful a material is. Or even materials which have a change, even down at like an atomic level that changes the behaviour of the ceramic under high magnitude impact.
Kat - I was going to say, we just heard Graham talking about the issues of flexibility and the kind of ways that he's structuring the materials that he's working on. I mean, with ceramics presumably, they're very hard and not very flexible.
Adam - Yes, that's true. Sometimes you hear of soldiers just foregoing those hard armour plates altogether, just taking them out of the flat jacket. Sometimes people try to develop new ceramic plates which are actually made up of loads of little plates like in a mosaic pattern. But they're not as balistically strong as like a solid ceramic sheet.
Kat - So, it's always going to be a toss-up between the flexibility you need and the strength, the hardness to withstand those kind of impacts.
Adam - It is the kind of areas that body armour development is trying to improve on.
Kat - We've heard about some new ideas in body armour. There's an idea of liquid body armour. I mean, what would that be about?
Adam - I take these kind of developments with a pinch of salt because I haven't found any academic papers on them. But the way it works is that the molecules in these liquids they rearrange under high impact and they stiffen up. My current understanding is that it can't harden quick enough or strong enough to stop bullets. It's mainly used to treat Kevlar vests to increase their stab resistance.
Kat - What about using the natural world as a source of inspiration to inform us about the development of body armour?
Adam - Biomimetic armour which is inspired from structures found in nature is a very very exciting subject. A very interesting paper I read looked at mantis shrimp, they scuttle around, do their thing and basically spend their entire life punching crabs to death.
Kat - Okay, they're strong.
Adam - You can imagine the kind of power behind the clubs that they use to do this and the incessant impacts that they had to do over and over again their entire lives. The materials involved in making these clubs must be very excellent at absorbing impacts. So some people look into how they do that and seeing whether it can be transmitted into armour applications.