An explosive filled with gaps can only detonate after a liquid is poured into it, which could make it unusually safe for transportation and storage

A Swiss cheese-like structure made from an explosive material offers a promising way to safely store and transport explosives. The 3D-printed design detonates only when the holes in it are filled with a liquid.

Explosives are useful in industries like mining, but they are also hazardous because there is always a risk of accidental detonation, like when they are exposed to heat or shaken up in transport. Alexander Mueller at Los Alamos National Laboratory in New Mexico and his colleagues created an explosive that cannot accidentally blow up – so long as it is kept dry.

The researchers used a paste-like explosive material called HMX as ink in a 3D printer to create a cubical structure full of voids. Specifically, the cube consisted of tiny cylinders of HMX spaced just a little bit apart from one another, stacked up in layers like Jenga blocks.

To test this holey structure, the researchers placed it between two aluminium plates and two transparent pieces of thick plastic and added a detonator. They then poured either water, mineral oil or a salt solution into the cube or left it dry, and started a detonation. A high-speed camera recorded how the material behaved and how fast the aluminium plates moved away from it.

When the cube was dry, the plates moved slowly because the HMX combusted instead of exploding. But when the cube was filled, the detonation resulted in an explosion that pushed the plates out rapidly. From the speed of the moving plates, the researchers calculated that the explosion produced 50 times more energy than the burn.

Mueller says the structure’s holes changed how much energy stayed with the cube after detonation. When they were empty, lots of energy left the explosive through them. But when liquid plugged them up, more energy stayed inside the cube and that helped it build up into a explosion, he says.

According to the Small Arms Survey,unplanned explosions at munition sites cause hundreds of casualties every year. Mueller says that because the new explosive is barely an explosive until liquid is added to it, it is unlikely to cause similar incidents. He and his colleagues are now fine-tuning their design by determining how the structure’s geometry and the density of the fluid affect the strength of the explosion.

Journal reference: Physical Review LettersDOI: 10.1103/PhysRevLett.130.116105