A study from the National University of Singapore has found that when a projectile is fired at a sand block at high speed, it absorbs more than 85% of the energy exerted against it. This ability to resist the impact increases with the speed of the projectile, even at high velocities.

Although sand has been used traditionally for military fortification, very little is known about the unique energy absorption capability of the material. In the study, a team of researchers from the National University of Singapore's (NUS) Faculty of Engineering discovered that steel plates have poorer energy absorption capacity against high-speed projectiles.

The ability to resist the impact increases with the speed of the projectile, even at high velocities. Credit: National University of SingaporeThe ability to resist the impact increases with the speed of the projectile, even at high velocities. Credit: National University of SingaporeThis 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 armor systems.

Led by Assistant Professor Darren Chian Siau Chen from the Department of Civil and Environmental Engineering, the research team made the discovery after conducting tests where projectiles of various shapes and masses were fired against a silica sand block. Silica sand is one of the world's most common varieties of sand.

The team also found that resistance offered by the sand block increases with the speed at which the projectile travels. Different nose shapes and masses of projectiles fired at a range of velocities were investigated.

The projectile impact also results in an extreme frictional force that could potentially break the projectile into pieces. This is due to the pressure and friction offered by the sand grains, which dilate and resist continual penetration of the incoming projectile.

In contrast, energy absorption capacity of an equivalent steel plate falls dramatically as the velocity of the projectile increases, resulting in the projectile passing through it without further obvious resistance. This is also known as the hydrodynamic effect, where steel behaves alike to a fluid without material strength with increasing velocity beyond the ballistic limit, which is the minimum velocity required for the projectile to penetrate the target.

The team says that it believes that the findings will further expand the applications of sand, which is currently used in glass making, building construction, and land reclamation.

The NUS team says it intends to carry out larger-scale trials to establish the full potential performance of sand for impact resistance. To further tap on its penetration-inhibiting property, the researchers will also explore integrating the sand layer with other compliant materials for possible application in critical infrastructure protection. In addition, the research team will look into the energy absorption capabilities of similar geomaterials such as rock rubble.

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