# What happened to the projectile in Hypervelocity Impact tests?

I recently saw a tweet about Hypervelocity Impact Sample and someone ask how is it possible to shoot a projectile at that speed and what happened to the used projectile when hitting the shield.

I found that it was probably shooted by a Two Stage Light Gas Guns but I didn't found anything about the projectile.

I only found this:

They got their name because hypervelocity impact produces local pressures in the target and projectile that greatly exceed the material strength of these materials, the material behaves as if it has no strength, i.e., like a fluid, or hydrodynamic behavior

Handbook for Designing MMOD Protection

### What happened to the projectile ?

Does the projectile melt with the shield ? At this speed, does the projectile melt before hiting the shield ?

EDIT: deletion of the last question, test done in vacuum.

When the collision velocity of a projectile is fast and the target hard and unyielding the impact produces forces that are greater than the compressive yield strength of the projectile and target.

So the projectile will collapse onto itself in plastic deformation while penetrating into a deepening crater in the target while converting its huge kinetic energy into heat.

This heat will liquify the projectile and crater into molten metal which can produce a cone of ejected red hot metal reflecting back and leaving traces of burn lines radiating out.

The impact force,F , must be such that:

$$\frac{F}{A_{projectile}} = m\frac{\delta v}{\delta t}/A= m\frac{v_{projectile}}{ \text{very small t}}/A> F_{\text{projectile yield strength}}$$

This is the first rough explanation. Weird things happen in a fast collision. Extensive tests have been done by artillery and shell manufacturers and designers of armory shields. Albeit the data is proprietary trade secret.

• I'm not an engineer, can you details what is the variables used in the maths ? Aug 24 '19 at 8:15

In some tests, the Livermore crew fired their projectiles into piles of sandbags, as documented here: https://crgis.ndc.nasa.gov/crgis/images/8/85/TRP00308.pdf

I seem to recall reading that in later tests, they were firing into a bore shaft in a hill downrange, and that the bore was filled with carpet scrap (that variously compressed, shredded and/or melted), but I can't find any photos of that.

• It sounds like here the test was just to see how fast they could get a 5kg projectile to go, and the sandbags were just to stop it - i.e. the sandbags were the target, in the same way that the aluminium block is above. OP's question refers to what happens to the projectile after it hits the block... Jul 23 '19 at 16:03

The projectile typically melts or vaporizes during hyper velocity impact due to the energy of impact being dissipated as heat during plastic deformation. The physics is quite involved.

• Can you details a little more ? Jul 24 '19 at 18:35
• So as to avoid link-rot, please expand your answer to include the relevant information from the link provided, at least the most essential points. Feel free to quote directly from the source.
– Wasabi
Jul 24 '19 at 23:16
• Sorry, am not smart enough to explain the details in a compact way. Removing my answer. Jul 25 '19 at 1:40
• @DorianTurba: Please send me a direct message and I can point you to the relevant literature. Jul 25 '19 at 3:31