Breaking a paintball

[SLICEnDICE]

I believe this is a good question for the deep blue area. Does anyone really know what it takes to break a paintball. I do not know what are the proper units are for this measurement(force?) I would like to figure out what what it takes for a bolt to break a paintball. Thanks for any help.

[thevilduk]

take a paintball and stack weights on top till it breaks and record the weight then take the surface area of the paintball and divide it up? i really have no idea what im talking about.. hell im only in geometry... please don't beat me up too much:(

[Coaster]

you should take into consideration that most paintshells are different based on how thick/thin the manufacturer wants them to be. Also, paintballs arn't to consistent in their size, so in a batch they could be slightly different.

[Redkey]

I ran these tests back in feb of 02, only one type of paint was tested so I cannot compare the results to anything. I asked a friend to bring home samples of paint from a local tourny but he forgot.

paint: banana banshee (zap I think)
load cell: 50lbs max capacity
load rate: 0.50 inches per minute
data rate: 20 points per second
specimens: 12
average load at failure: 27.8 lbs
std dev of load at failure: 9.6 lbs

the orientation of the paint does have an effect on the crush load of the ball. The paper towel was to keep the paint off the equipment. The crushing surfaces were flat and parallel to each other. The paint wasn't exactly fresh but had been stored sealed in a cool location.

Only one loading rate was used, I assume the failure loads will be influenced by the rate.

If people are interested I could run more tests... Since I only play PB about twice a year anymore, my supply of paint is very limited.

To do this correctly you would need to compare 4 or 5 popular types of paint over several weeks or months of production. This way you would be able to meaure the trends over time with each type of paint, allowing you to make a more accurate comparison.

Also, it would be nice to measure the shell thickness, weight, and diameter (in several orientations) of each ball tested. If the ball manufactures had a quality control lab these are some of the tests they *should* be performing on an hourly basis.

[SlartyBartFast]

Remember that compression strength is not the same as impact strength.

When a paintball is handled, compression strength is most important. When fired impact strength is the most important. Impact strenth has to be high enough so that the ball does not break due to impact with the bolt/initial air blast and low enough that it breaks on players without causing injury.

As noted by Redkey, there is a difference whether the force is applied on a paintball's seam or not.

[Redkey]

but, the impact is compressing the ball, it's just doing it at a much higher rate.

Yes, there are differences between the actual forces placed on a ball during firing/impact and squashing the ball between two flat plates. The compression test is a basic starting point for comparisons. What good would it do to build a complex test system to measure the breaking forces of a ball at velocity only to find out there is so much variablility in the balls themselves that a comparison is impossible.

I prefer to start with the quick and cheap method to take an initial stab at the testing. If the results look promising, then move onto the more complex testing.

But, you are right, a compression test isn't exactly representative of an impact.

[ShooterJM]

Interesting data, I'd be interested in seeing what results a few other paint kinds would give.

[SlartyBartFast]

Originally posted by Redkey
but, the impact is compressing the ball, it's just doing it at a much higher rate.

Not so. It all has to do with the differences between elastic/plastic strength and brittleness if my Engineering materials class memories are correct. If memory serves, compression strength does not equate to impact strength with any type of formula.

If you already have access to a compression tester, is there not an impact tester in the same lab? Basically, it's a mass on a pedulum. That's as far as my engineering lab memories from university go.

[Redkey]

hmmm... I think we are on slightly different paths. You are probably correct in saying that impact strength and compression strength are not related for a thin shell material. When you start looking at thickner materials this may not be true.

Going back to the original question... "What does it take to break a paintball?" In my first post I say nothing of the compression strength... because that is not what I measured.

My test was to see what it takes to crush a ball. I decided to start with a very basic and simple test but, with oldish paint the results are not very useful. I intend to repeat the tests with fresh paint to see how consistant a particular type of paint is. If things look promising I may look at other types of fresh paint or perhaps look at the effects of aging on the paint. There are so many variables that need to be considered to make the test meaningful it gives me a headache. Running some intial fact finding tests will make it clear what variables are important to consider for future testing.

A pendulum tester would only provide limited data... ie the amount of energy absorbed when the impact head swings through the ball.

Had I taken a photo in the other direction you would have seen our instrumented impact tester. Using optical gates and a series of strain gages in the impact head we record impact velocities and load vs time curves for impacts. Unfortunately this machine is setup to break big things... The impact head measures upto 3500 lbs. Trying to measure the impact force on a paintball would be impossible. Like trying to weigh yourself on a truck scale.

Anyhow, I like your questioning... it's good when people think about what they are seeing instead of just assuming it is correct.

[athomas]

Most of the time the bolt force required to break a paintball is the shear force not the impact force. This is chopping that is the main concern of most gun breaks.

Think of it like an egg. If you cup an egg in your hand, you can exert a high force on it before it breaks. This is much like a bolt pushing a ball into the barrel of a gun. Now take an egg and squeeze it between two fingers. It'll break much easier. This is much like the bolt catching the ball half way into the breach and chopping it.

The total force of the bolt on the ball is concentrated on one spot on the ball in the chopped ball/egg scenareo as opposed to being spread out over the entire surface in the pushed ball/cupped egg scenareo.

In measuring the actual breaking force of the balls you should use a scale and pressure device capable of measuring peak values. That way you actually measure the peak pressure exerted before the ball actually broke. You should also test balls on edge(seam vertical) and balls laying flat (seam horizontal). This should be a good indicator of the forces and relationship of which balls break easier than others. The rate at which the load is increased should be small enough as to not create an "overshoot" on the readings. The crush forces should be indicative of real world valvues.

In the real world the total force is made up of velocity and mass. The combination of the two make up a value of energy. In the experiment, the only energy comes from pure force and no "measure" velocity. The resulting forces are approximately equal in both cases. I say approximately because there are velocities involved in crushing and other things that affect as well, but not that we can or need to measure them.

Have fun and post any findings you may come up with. It would be interesting to see actual crush numbers associated with paintballs.

[zach rumchak]

hey i tried this not as well as the one guy but i got 15 pounds on zap chronic

[zach rumchak]

athomas .. correct me if i am wrong but i kind of got that you a re saying in your 1st paragraph that is this
kind of like a bed of nails trick put 170lbs of body weight on your foot and step on a nail bed you get alot of peircings
but distribute thatweight and you will just get poked

example on foot-you may have somewere around 20lbs of pressure per square inch
but if you lay on the nails you may only have like 2lbs of pressure per square inch

[sniper1rfa]

i might make a little device to measure a ball's shear strength.

im thing a tube with a rod in it, to simulate the bolt chamber. stick the ball halfway into a hole in the side and pinch it. then just press the rod slowly onto a scale till the ball breaks.

[athomas]

zach rumchak: I think you are correct in your assumption of my explaination.

[Redkey]

How about strain gaging a thin (.125" or so) metal disc and then shooting a paintball into it. The resulting deflection of the metal will cause a spike in the strain gage output. The metal disc could be calibrated by stacking weighs in the center of it to see what load levels produce which strain levels.

Or... if you were really clever you could calculate the stress on the disc based on the amount of strain and the modulus of the disc material. Once you had the stress levels (psi) and the proper calculations for the geometry of your plate you could calculate the load supplied by the ball impact.

I perfer the first method... I suppose you could use it to check the second.

Anyone want to give this a shot? It's actually a very good excercise in instrumentation and materials science... since you're basically building and calibrating your own load cell.

Also... I've smashed a bunch more paint but have been too busy to put the results together in a useful format.

[joeyjoe367]

Why don't you just fire paintballs at the ground?

Set up a mag or other gun to shoot at like 100 fps or lower. Point it straight at the ground, maybe 1" of clearance, and shoot the gun.

slow down the FPS until a shot DOESN'T break, and that's about how fast the paintball needs to be going in order to break.

This way, you've got your data in a medium that matters: How many FPS does the ball need to be going in order to break on someone/something?

[athomas]

Different materials absorb or deflect energy at different rates. By measuring the actual force used to cause the break we can get more accurate information. I agree with Redkey in the measurement of the stresses to produce a recordable output.

Here's a thought. How about firing the ball into a calibrated lcd type of stress meter. Analyzing the resulting color of the lcd indicates the force applied at various points of impact. The total force could be measured by deflection at the same time.

[AGD]

I wanna go play with Redkey! He's got cool toys.....


AGD