Shaped Charge Physics

Question

It seems that I have a problem understanding the physics behind shaped charge.

I was told that shaped charges are the way they are because a hollow conical shape in the middle of an explosive will concentrate the explosive energy to the center (i.e. the tip) of the hollow cone.

How is this possible?

My teacher provided me with this explanation: For example, if, let's say I have a cube with explosives inside. The explosion will blast all the sides of the cube (hence dissipating energy to all sides). Yet for shaped charge, the explosion will concentrate itself at the tip of that cone.

But this doesn't make sense to me. If an explosion will blast off all the sides of the surfaces of the container holding the explosive, then it should not matter what the container's shape is, right? The explosion will still blast off all the sides of the container no matter what. That is, the explosion will still explode everywhere; not just concentrated at a single point.

P.S. I have tried to consult wikipedia on Munroe Effect and Shaped Charge, but the page simply stated that "Explosion will be concentrated"; it does not explain why that is the case.

Thank you!

Answer 1

I suggest that you look up Huygens Principle for wave propagation. If you apply it to explosives on the surface of a sphere, you will see that two waves are launched: one that expands in all directions, and one that converges to the center. In the case of a cone, one wave will expand outward perpendicularly from the surface of the cone, while another wave will converge toward the axis of the cone. So, half the energy is lost in either case unless a container is provided to reflect the expanding wave and convert it to a converging wave. What happens when the converging wave reaches the axis is a different story, depends on the nonlinearity of the behavior of the colliding materials, and is NOT well described by Huygens Principle.