I'm doing forensic ballistic research. I want to measure the heat generated by a orthagonal bullet impact upon a steel object.

My plan is to have a setup something like this: A 2 inch (or so) diameter round "core" will be removed from a 1 inch thick steel plate. The core will have some sort of heat insulation tape on the sides and the back. It will then be replaced into the hole in the steel plate for lateral support and an insutated backing material (big block of weighted wood, etc) will be behind the core.

The idea is that most of the heat from the collision will heat-up the core, not the supporting objects.

A bullet will be fired (at close range) into the 2 inch core. The bullet will be stopped by the steel core. The temperature rise of the core will be measured (somehow) and recorded over time.

Any thoughts on what sensors or other instruments could be used to make this as simple and effective as possible ?

Thanks,

Alex Jason

 

If the bullet is stopped by the core, you will get a false reading, due to the heat of a fired bullet. Going several times the speed of sound heats them up a good deal, well past the point you can touch one without getting a mild burn.

I do know that somewhere between 1500 and 2000 rounds in a short time into the same areas on a vehicle (under 20 seconds) creates enough heat to set a car on fire though, if that helps. Bullets in that case are 30 caliber from a minigun.

What part of the ballistics are you trying to understand/measure?

 

The fact that a bullet gets heated by the gunpowder combustion and the friction of the gun barrel does not affect the experiment.

I am only trying to find a way to measure the heat rise caused by the impact. The temperature of the bullet before impact is not relevant to this project.

I don't want to get off track into a general discussion of bullet dynamics. But I do know much about bullets and ballistics. A standard (non-tracer) bullet does not get hot enough to ignite other objects. Fire a bullet into a phone book there will be no fire and no singing of the paper. A bullet does not get hot enough to burn one's fingers -- or the bodies of those who have been shot.

Thanks for reading about my project.

Alex Jason

 

If you are measuring temperature rise caused by the bullet's kinetic energy, it seems logical that its temperature at impact would affect the result, unless the target was at the same temperature. In any event, if you know the speed and mass of the bullet, can't you just calculate its kinetic energy and convert from joules to calories, if needed?

Your design sounds fraught with sources of error. Most obvious, it seems some of the energy will be transmitted to the supports. Second will be finding the perfect insulating tape that will transmit neither any motion nor heat.

John

 

I don't know but, could you be looking for this....

http://www.omega.com/temperature/z/InfraredPyrometers.html

 

Yes, the heat can be computed from the mass and velocity of the bullet but I want to actually measure the heat created.

It doesn't matter that the temperature is of the target material -- I just want to determine the temperature increase after impact.

I realize that there are many reasons why this cannot be a "perfect" experiment. That's okay. I want to see what temperature I can measure.

Thanks,

Alex Jason

 

Yes, I've thought about these but I need to record the data (temp). I'm still reading about all the models.

Thanks --

Alex Jason

I don't know but, could you be looking for this....

http://www.omega.com/temperature/z/InfraredPyrometers.html

 

The best way may be using several rounds quickly, and measuring the steel plate's heat rise. The mass of the steel compared to the mass of the projectile is rather huge. This means that a single bullet striking the target would change the temperature in a way too small to measure accurately.

When I was talking about the heat of bullets, it's from picking them up around me, they are quite warm, but the duration of contact is very short when moving that they won't start anything on fire singularly, I'd guess 250 degrees or so, like a very hot transistor. Depending on the round, mainly jacketed high velocity, or low velocity handguns, actually capturing the bullet could be an issue, as well as movement of the target. All major calibers have a foot-pound average table for energy at various distances. Are you trying to calculate how much of the terminal energy of the projectile is transferred to the target as heat?

What often is used to measure a small quantity is to use a large quantity in several tests to get a solid guess of the ranges the small quantity will be, then perfect an experiment in an extremely well controlled environment to verify.

Similar to quantum mechanics, where the concepts were known on the macro scale to estimate the micro scale, but couldn't be proven until colliders with sensitive enough sensors were made.

 

Will the temperature in your steel target be homogeneous? During the period in which the temperature in the target equalizes, it will be losing heat to the surroundings.

Will it be in a vacuum? Will you put the target into a thermos of water?

Other than simply wanting to do it, it is unclear what the purpose of this experiment is, particularly when you consider there are so many sources of error.

John

 

A bullet does not get hot enough to burn one's fingers -- or the bodies of those who have been shot.

Alex Jason

This thread worries me. The physics of heat production and temperature of projectiles has been studied extensively.

Here are two textbook links:
http://www.math.upenn.edu/~chai/319/319damage_patterns/node10.html
http://cambridge.org/us/engineering/author/nellisandklein/downloads/examples/EXAMPLE_4.9-3.pdf

The first link states that a typical bullet had a measured surface temperature of 150 °C. That would certainly feel hot to the touch in clear distinction to what the OP asserted.

Second is the OP's claim that he is doing forensic ballistics research. It is easy to assume that he is in a well equipped licensed laboratory, but that is just an assumption. Absent a clearly stated purpose and the OP's failure to consider the many uncontrolled variables, I am wondering whether this is not just a school science project.

In any event, some good suggestions have been given on how to measure temperature of the target. I suspect further discussion of these experiments will not be productive and may give the appearance that AAC participated in and aided such a potentially dangerous experiment.

John

 

Depends, if he is the Alex from Second Chance Body Armor.

Then he more than likely has a legitimate project.

 

You mean this one: http://www.youtube.com/watch?v=aaS_2l8nGdg

Thank goodness they are only shooting at each other and not trying to fix their brake lights.

In any event, the science of what is proposed is too vague.

The e-mail addresses for Second Chance Armor inquiries are all to BAE Systems. I suspect a military contractor of that size would have access to quite sophisticated temperature measurement systems.

John

 

I'm with considering this bogus until proven otherwise.

For one thing, very few things are as certain as the physics involved here. The speed and mass of the bullet are known, and 100% of that kinetic energy will be converted to heat in a capture-collision. Period. It's not necessary to measure it, the laws of physics are not in question.

You could spend a long time refining the measuring device, but your ultimate guide to success would be that you were able to validate the basic physics that you knew when you started.

One huge problem with any such device, and any interpretation of the data, is that, while you might be able to thermally insulate a "chamber", I can't see how you can "insulate" mechanical energy. Any vibration leaving the capture area transmits energy away from that area. Perhaps in the lab you can essentially immobilize it, but what good is the data when compared back to the real world? A LOT of the impact energy travels quickly away from the impact site. Maybe a calorimeter (to catch the heat) on the end of a pendulum (to capture the mechanical energy).

 

The biggest problem I see here is that the most of the heat from the deformation of the bullet stays in the bullet, and only a small and variable fraction will be transfered to the steel target, depending on how the bullet shatters and how quickly it ricochetes.

 

I agree with kubeek, the bullet will be long gone before any real heat transfer takes place. I don't even think an infrared thermometer would have enough time to capture the spike.
my $.02

 

Just a thought, have you thought about starting off smaller scale?

I'm thinking airgun (not a Daisy, but the high powered type), hitting a 55 gallon drum with pellets will go through the steel when supersonic, but only make a very large dent when subsonic. The pellet in the latter case tends to flatten into a lead disc.

There would be three different temperatures to measure:
1) Temperature rise from steel stretching.
2) Temperature rise of pellet while deforming.
3) Actual temperature rise of steel due to being in contact with the pellet for a fraction of a second.

If 3 is the quantity you are trying to measure, factors 1 and 2 would make 3 very hard to detect. Think of bending a coat hanger back and forth until it breaks, a pretty fair amount of heat is generated with just a few bends.

 

Looking at these high speed videos it's hard to tell where and what to measure. For hard targets most of energy seems to used up by the bullet deforming.

http://www.youtube.com/watch?v=QfDoQwIAaXg

 

Any thoughts on what sensors or other instruments could be used to make this as simple and effective as possible ?

IR guns and/or IR videography. This would allow a sensor at a safe distance to "see" the full thermal picture (literally) of the impact. You wouldn't need to worry about insulation or other things that might introduce artifacts. There may be some challenge in getting the camera calibrated to the temperatures relevant to the experiment. The laser-guided IR gun might be handy for determining the peak temperatures reached.

 

Moderator: We don't need this link.

 

It looks as if this whole thread may have been stealth spamming. The OP's site appears not to be particularly scientific, although it does have any number of bloody videos for sale.

Tracecom ran the site down, and I deleted the link and closed this thread after taking a look.