Nano Stops the
Shock Wave


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The blast wave that comes with an explosion does far more damage—to bodies, buildings and vehicles alike—than any projectiles or fragments that come along with it. Thickening an exterior with armor or anything else will cut down the impact of a blast, but it comes with heavy economic and weight costs.

Now, researchers at the City College of New York’s Experimental Fluid Mechanics and Aerodynamics Laboratory have shown that a thin coat of porous nickel or copper, carefully designed at the nano-level, can cut down the force of an explosion by more than 30%. The material is designed to be as porous as possible so that the surface area to volume ratio is as large as possible. In essence, the elasticity of the porous nanomaterial bounces a portion of a blast’s energy back in the direction from which it came. 

Professor Yiannis Andreopoulos. Image: CCNY

 

Normally, when a blast hits a wall all of its energy is transferred into and beyond the wall. After it’s hit, there is no longer any flow in whatever gas the blast wave has passed through. “The flow behind the shock is zero velocity, because that’s the velocity of the wall,” says Yiannis Andreopoulos, a professor of mechanical engineering at the school, who lead the project. “But now there is a velocity to the wall, so the flow goes in the opposite direction. Without the nanoparticle there’s no reversal.”

Stress and Strain

To test the effectiveness of their nanoparticle material, Andreopoulos ran both a real world macro scale experiment and a model. The later abandoned Navier-Strokes equations usually used to look at the flow of fluid and instead turned to molecular dynamics simulations. “When we go to very small sizes, the classical continuum mechanics doesn’t work anymore,” says Andreopoulos. “We have to come down to individual interactions between atoms and molecules.”

Diagram showing the velocity, temperature and stress fields. Image: Yiannis Andreopoulos/CCNY

 

The model allowed the team to look at stress and strain, usually bound by constitutive law, separately.

The nano-coating also shows high strain rate effects. Compress a dog bone slowly and it will endure a certain amount of stress and strain. But if the same force is applied suddenly the bone becomes temporarily stronger. Andreopoulos’s material exhibits this effect to the tune of 30%.

Right now the layer that Andreopoulos is experimenting with is a single micron thick. Once it’s become a commercial product he expects that the layer will be 50 microns. The increase in effectiveness that might come with an increase in thickness has yet to be explored.

Military Applications

The fruits of Andreopoulos’s research are not limited to potential applications. His model and experiments offer insight into how waves propagate through porous material. They may help explain how an ultrasound’s waves are dissipated by small pores in human tissue and help us better understand the effects of underground gas stored in the tiny pores of rocks.

But the high performance of the material, its relative low cost of production, and the ease with which it can be applied, does suggest that much of the world will soon be coated in the new material.

Put it on the outside of a bus, for instance, and the vehicle and people inside will be more likely to survive an explosion. “It’s going to dissipate,” says Andreopoulos. “There are some ideal cases where the subject would be protected by it.” Fuel tanks or other parts susceptible to shockwaves could be coated as well. Passengers wearing coated clothes would be more greatly protected from an internal explosion.

The military applications are myriad. “They can coat everything,” says Andreopoulos, who has indeed received calls from the army. The next generation of airplanes, which are already slated to have a porous coating for sound absorption, could combine it with the nanomaterial to help mitigate potential blasts.

It’s understanding elasticity at the smallest scale that will protect us from dangers at the largest.

Michael Abrams is an independent writer.

When we go to very small sizes, the classical continuum mechanics doesn’t work anymore.

Prof. Yiannis Andreopoulos, City College of New York

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Comments(3)
  • Quality Engineer Assist. CSSBB (Manufacturing & Processing)
    If it absorbs shockwaves does it also absorb sound waves? If so the coating would be an easy way to sound proof a room or the shared wall of a duplex. If I put it on the bottom of my shoe will the coating absorb a little bit of the energy of my steps so my impact with road isn't as hard on my joints?
    Feb 06, 2015 at 02:15 PM
  •  (Researchers)
    As you said it can cut down force upto 30% but if we use it on humans body it will be of no use as people will still get hurt.
    Aug 22, 2013 at 12:19 PM
  •  (Aerospace & Defense)
    Is this applicable to windows as well, perhaps as part of low emissivity coatings? Seems like in most explosions (and I'm thinking Boston and Chelyabinsk here) many of the injuries are due to broken glass, primarily windows.
    Aug 07, 2013 at 04:13 PM

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July 2013

by Michael Abrams, ASME.org