Temporary cavity physical forces

[BuckskinJoe]

I am curious--does anyone know the physical forces involved in creating the temporary cavity in gunshot wounds, i.e., what actually causes the formation of the temporary cavity?

[Shawn Dodson]

It is inertial force that accelerates soft tissue mass.

[DocGKR]

Chuck a rock into a lake--notice how the water is momentarily displaced by the rock as it enters the water...same effect.

[Augusto]

Donald Carlucci, in his book Ballistics: Theory and Design of Guns and Ammunition, has an interesting explanation. He says that temporary cavity is created through the process of cavitation. It results from the adherence of the fluid molecules to the surface of the projectile and when the shear stress drops to zero on the surface, the flow separates and causes the bubble. Pg. 469.
Is someone familiar with this definition?

[BuckskinJoe]

Donald Carlucci, in his book Ballistics: Theory and Design of Guns and Ammunition, has an interesting explanation. He says that temporary cavity is created through the process of cavitation. It results from the adherence of the fluid molecules to the surface of the projectile and when the shear stress drops to zero on the surface, the flow separates and causes the bubble. Pg. 469.
Is someone familiar with this definition?

Thanks!!
That is getting real close to answering what I am asking. What I really want to know is the physics behind the formation of the temporary cavity. There is (are) force(s) operating to cause the formation and expansion of the temporary cavity, and I am seeking to understand the Newtonian and fluid mechanics of such.

[481]

Thanks!!
That is getting real close to answering what I am asking. What I really want to know is the physics behind the formation of the temporary cavity. There is (are) force(s) operating to cause the formation and expansion of the temporary cavity, and I am seeking to understand the Newtonian and fluid mechanics of such.

Joe-

If you can, try to get ahold of Duncan MacPherson's book, "Bullet Penetration". Although a bit long on math (the Calculus) at times, it provides a good explanation of the fluid dynamics involved in the production of cavitation so often seen in ordnance gelatin testing as well determining the velocity (Vc) at which a certain projectile configuration will produce (or not) cavitation in that medium.

His is a book well worth the effort to locate and a fantastic read for those interested in such phenomena.

[spdldr]

I am no scientist, but I believe that the temporary and possibly the permanent cavity is the result of water, which is a major component of tissue, being essentially non-compressible. Also, someone familiar with fluid dynamics will tell you that most liquids can move only so fast in a tube.(otherwise they may destroy the tube if it is not strong enough)

When the bullet strikes the tissue at high velocity, the water must go someplace as it cannot be compressed. Thus it is basically a hydraulic effect. In the case of a high energy round this can actually cause a blow to the adjacent tissue from the rapid movement of the water. And of course this can have an effect on the shootee.

I once constructed an apparatus to test this concept. I used 10" diameter steel well casing about 4' long with a pressure gauge about halfway down. Then I filled it with water and shot into it with FMJ .45 auto and FMJ 9MM. Both rounds had about the same hydraulic impact pressure. Needless to say, I got pretty wet!

Dave

Boonie Packer

[BuckskinJoe]

Joe-

If you can, try to get ahold of Duncan MacPherson's book, "Bullet Penetration". Although a bit long on math (the Calculus) at times, it provides a good explanation of the fluid dynamics involved in the production of cavitation so often seen in ordnance gelatin testing as well determining the velocity (Vc) at which a certain projectile configuration will produce (or not) cavitation in that medium.

His is a book well worth the effort to locate and a fantastic read for those interested in such phenomena.

Thanks! I haven't made the effort, to date, to get MacPherson's book. It looks like I need to make the effort. I am degreed in mathematics; so the calculus is not a foreign language!

[littlejerry]

Donald Carlucci, in his book Ballistics: Theory and Design of Guns and Ammunition, has an interesting explanation. He says that temporary cavity is created through the process of cavitation. It results from the adherence of the fluid molecules to the surface of the projectile and when the shear stress drops to zero on the surface, the flow separates and causes the bubble. Pg. 469.
Is someone familiar with this definition?

That sounds like the right track. In my mechanical systems course we discussed cavitation in oil dampers. It was a function of fluid viscosity and density(along with the geometry of the damper).

Wish I could remember more but I'm more of a nuts/bolts/gears guy. Any decent undergraduate level fluid dynamics book should provide some insight though- I'll look to see if mine is still laying around.

[DBR]

Try Amazon for Duncan MacPherson's book:

http://www.amazon.com/s/ref=nb_sb_no...rson&x=21&y=17