MMaterialsgateNEWS 2008/08/20

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Light metals against bombs and grenades

A cheap and simple structure made of aluminium can mean the difference between life and death the day the bombs go off.

A soldier in a war lives a life exposed to danger – both inside the compound fence and on assignment on the outside. If the container he lives in is struck by a direct hit, it can be transformed into a clump of twisted metal in a matter of seconds. If he drives over a land mine, he and his vehicle can be blown sky high.

War is never safe. Nevertheless, it’s possible to protect soldiers from at least some of the dangers. Tank steel and armoured concrete provide good protection, but structures made from steel or concrete are quite heavy, and can be difficult to move. Aluminium, on the other hand, is a light product -- in a number of different ways.

One of the Norwegian University of Science and Technology’s three Centres for Research-based Innovation is called SIMLab (Structural Impact Laboratory). Here, researchers are working with aluminium structures for protection against impacts, metal-piercing projectiles and explosions from everything from small stones to bombs -- in war or in peace.

“We have developed a light, cheap and flexible solution to protect fences, buildings, ammunition dumps and containers”, says the lab’s leader, Magnus Langseth.

Stands against most

The solution has grown out of a close co-operative effort between the Norwegian Defence Estates Agency (NDEA), a branch of the Norwegian Defence Ministry, and NTNU. NDEA is responsible for the Norwegian camps and compounds that are involved in international operations, and has over a number of years financed the centre’s research on protective structures for both military and civilian use.

The structure is made from a type of double panel filled with a heavy substance found on site, such as dirt, sand, gravel or small stones. The panels are pieced together from aluminium shapes that have cavities in them, which are shaped out of internal division walls. These aluminium shapes are easy to produce by extruding them through a kind of mouthpiece that gives them the desired cross-section. They are also easy to move, and are pieced together using a click-together system. A panel is placed in a lifting device and is mounted on a container wall, for example. Afterwards it can be filled from the top with weight, which then can be drained out of the bottom when the panel needs to be unmounted and moved to another area.

Two men can completely secure a container in this manner in the course of a morning.
“These filled aluminium shapes can stand against projectiles and explosives” explains Tore Børvik, who works with NDEA and is an adjunct lecturer at NTNU, with a position at SIMLab.

Survived the test

The system was tested in a full-scale explosion and demonstrated its effectiveness: the panelled container received just minor damage from an explosion that was equivalent to 4 tonnes of TNT detonated from 120 metres away. Without the light metal protection, the container would have been blown to smithereens. But there remain a few details that have to be improved, so the system isn’t on the market yet. Nevertheless, a number of NATO countries have already shown interest in it.

“We at NTNU aren’t in the business of producing these things”, Langseth says. “Our job is to develop work tools that product developers need. We make computer models for design, and experiment with alloys, dimensions and construction. The tools for this type of protection need just a little more work before they’re ready.”

On dangerous roads

Only a few of the vehicles used for peacekeeping forces are protected from land mines. Tank steel is expensive, but first and foremost it’s heavy – and many places are inaccessible to a four-wheel drive that’s been armoured with tank steel. A vehicle needs lightweight protection.

Aluminium is a light metal. But a gravel-filled panel is quite heavy, and isn’t suited as either a bottom plate or as a canopy. So SIMLab’s researchers are working to develop light plates made from aluminium foam that in time may be used to solve the dilemma.

“This is an extremely complex problem”, Langseth emphasises. “When a landmine explodes, the combination of sand and air pressure tosses the vehicle and the driver up in the air. We have to find a method to absorb the pressure, something that is lightweight and doesn’t take up much space. We don’t yet have the technology, but we’re working with the design tools that we have already developed.”

SIMLab has now been invited to join an international co-operative effort comprised of the world’s leading researchers in mechanics and materials where the theme is protection of vehicles in war zones.

Lisa Olstad/The norwegian research magazine Gemini

Investigated and edited by:

Dr.-Ing. Christoph Konetschny, Inhaber und Gründer von Materialsgate
Büro für Material- und Technologieberatung
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