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A study led by Assistant Professor Darren Chian Siau Chen from the Department of Civil and Environmental Engineering at the National University of Singapore's Faculty of Engineering has found that when a projectile is fired at a sand block at high speed, it absorbs more than 85 per cent of the energy exerted against it. This ability to resist the impact increases with the speed of the projectile, even at high velocities.
While sand has been used traditionally for military fortification, very little is known about the unique energy absorption capability of the material. In a recent study, a team of researchers from the National University of Singapore's (NUS) Faculty of Engineering found that sand can absorb more than 85 per cent of the energy exerted against it, and its ability to resist the impact increases with the speed of the projectile, even at high velocities. In contrast, steel plates have poorer energy absorption capacity against high speed projectiles. This novel finding suggests that sand can potentially be used as a cheaper, lighter and more environmentally friendly alternative to enhance protection of critical infrastructure as well as armour systems.
[Editor's note: We've previously discussed an impending shortage of sand..]
(Score: 2) by hamsterdan on Tuesday December 13 2016, @03:17AM
Isn't the ground used to create a bigger shockwave ? I seem to remember reading something about why US H bombs didn't need to be as big because they could blow at a more precise height.
(Score: 2, Insightful) by Francis on Tuesday December 13 2016, @03:42AM
I hadn't heard that, but that's right. While the blast energy dissipates in relation to the radius squared, if the blast is at ground level, you're only using the edge of the blast with most of it being directed up and down. If the bomb gets embedded in the ground, then it's even worse as the blast has to dissipate a lot of material before reaching any of the buildings. Plus, as the AC mentioned, that debris is radioactive and can stay in the air for a prolonged period.
There's a height that maximizes damaged based upon keeping the radius as small as possible, but maintaining as much of the surface area of the blast at an optimal level as possible. And anybody that could do that more accurately, would be able to use smaller bombs to cause the same amount of damage.
(Score: 3, Informative) by Spook brat on Tuesday December 13 2016, @05:37PM
Another benefit to air bursts is shockwave reflection off the ground. Check out the Nevada test blast videos on Youtube, the blast front travels across the ground with a "V"-shaped profile. Objects in its path get hit by the leading edge compression wave, decompress as the leading edge passes them by, then compress/decompress again in the reflected trailing edge wave. Amazingly, some of the trees in the video survive this. Few man-made structures do.
From a targeting perspective, air burst is also better because you're more likely to have line-of-sight to points on the ground from above than from a ground burst. Ground bursts get deflected upward and dissipated by things like hills and structures closest to the blast point. An air burst, in contrast, is likely to have open air between the detonation point and any given point on the ground - no losses due to terrain shape.
Incidentally, the same principles are used for conventional bombs and artillery. Daisy Cutters / MOABs are also typically detonated above ground for best line-of-sight to a large target area.
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