Physicists of Duke University have developed a technique that enables them to stimulate high speed impacts in artificial soils and sand in the laboratory, and then watch what happens below the soil in super slow motion.
They found that the soil and sand get stronger when they are struck harder.
They said that this is why the ground penetrating missiles which struck the land harder and faster had limited success.
They say that the missile experiences resistance when it strikes harder and faster and finally stops.
The research is funded by Defense Threat Reduction Agency
The research helps in building better earth penetrating missile designs to destroy buried stockpiles of underground weapons and buried targets.
To imitate the missile striking soil or sand they have dropped metal projector which is having rounded tip from seven foot high ceiling into beads.
The kinetic energy of the projectile is transferred to the beads and these beads absorb the energy and strike against each other.
The researchers used beads made of clear plastic that transmits light differently when compressed, and they used polarizing filters to view the impact and they found the areas of greatest stress show branching chains of light called force chains that travel from one bead to other bead during the impact.
The projectile dropped into beads at a speed of 6 meters per second or nearly 15 miles per hour. The researchers by using beads of varying hardness were able to generate pulses ranging from 67-670 miles per hour.
To view the impact with naked eyes is not viable as it is too fast, so researchers recorded the whole experiment in the high speed video camera which can shoot 40,000 frames per second.
The force chain grows at high speed which causes the energy to move away from the point of collision must faster.
At high speeds new contacts are formed between the beads as they are pressed together, and this increases the strength of the material.
“Imagine you’re trying to push your way through a crowded room, If you try to run and push your way through the room faster than the people can rearrange to get out of the way, you’re going to end up applying a lot of pressure and ramming into a lot of angry people,” said study co-author Abram Clark, postdoctoral researcher in mechanical engineering at Yale University.