Simple measurement of blast overpressures

I'm looking for a simple, and hopefully reasonably accurate way to measure explosive overpressure (and/or impulse) at a distance.

The way the pros do it involves lots of fancy electronics, piezoelectric transducers, accelerometers, various outrageously expensive computer programs, etc. I'm hoping to avoid as much of that as I can, while still retaining as much accuracy as possible. Obviously there are many ways to qualitatively measure blast overpressure/impulse, but I'm hoping for something more quantifiable.

I'm not looking to try to measure very high pressures. I'd say in the range of 10 to 1 psi is a reasonable area.

I'm currently most interested in comparing conventional high explosives with thermobaric and fuel/air systems.

My first idea was some kind of spring loaded mechanism that can somehow record its maximum deflection from the shock wave. It would also be possible to film the deflection at 1200 fps (which I fortunately have access to). Unfortunately that camera may be better used by actually filming the detonation... and I don't have two . Either way, it seems that it would be hard to achieve decent accuracy with such a rig... I'll have to think about it more..

Any ideas? There must be unconventional ways of doing it that could work?

USP 7162919 seems essentially a ballistic pendulum with a spring loaded plate substituting for the simple pendulum wieght.Personally Id rather fabricate a ballistic pendulum from wood or steel assuming you have a welder and cutting tools besides the math needed is already there and waiting.And more important as far as Im concerned Is availability/simplicity math involved as well as fabricating the pendulum from steel or wood.Some imagination and the pendulum will indicate its maximum deflection via a fixed marker on the pendulum and surface for the marker to inscribe.Simplicity of fabrication ,equations already done with the addition of an appropriate timer an equation for overpressue should be able to be found.
After all it would just be unused technology a few searchs should reveal.A 5 minute google search revealed the formula for velocity @ the pendulum, including pendulum wieght,movement etc.Charts/formula must still exist for
use of the ballistic pendulum as it must have been in use
until the early 20th century @ minimum for both projectiles/explosives revealing velocity and energy of both.

The other patent mentioned seems far from simple..." a pressure sensor located inside the tube...also includes a data processor and computer connected by wires to the accelerometer... "The Title was simple methods wasnt it?

Regards,

Don't mind me Im still searching for the formula for the layout for a simple cone.

[Edited on 23-4-2009 by grndpndr]

[Edited on 23-4-2009 by grndpndr]

[Edited on 23-4-2009 by grndpndr]

My dementia ravaged brain cells without a calculator within reach and guessing a std brick to be 8-9 long x3-4in wide?
That would be looking at approximately1.056 lbs-1.584 lbs
over what period of time.Sounds plausible, but if correct is that the max overpressure your safisfied with learning .044psi?I suppose you could fabricate a universal stand for using various dimension/wieght for different PSI but that would require multiple detonations !Again with the pendulum though I havent yet found the correct dimensions, pendulum wieght or mathematical formula to find velocity/psi im sure there not uber difficult to find and would require only 2-3 detonations, baseline and actual device to be tested,another advantage is you dont have to focus the camera on the pendulum a simple marker can be fixed to the pendulum to graph its movement saving your camera for detonation and ideally an adequate timing device in the frame.Calculate time /distance =velocity?PSI shouldnt be hard to find after that particularly with pendulum data. Of course my medications havent yet
kicked in so its possible this is all BS.
Would you mind my asking what design is your theoretical device? proposed wieght?Very anxious to hear of the results.
And if you would kindly share the design and calculations decided on for finding the theoretical blast wave PSI? regards

[Edited on 23-4-2009 by grndpndr] Multiple edits due to ravaged though processes.

[Edited on 23-4-2009 by grndpndr]

[Edited on 23-4-2009 by grndpndr]

[Edited on 23-4-2009 by grndpndr]

I just find an other way to mesure over pressure, it is very easy to make and price less.
It consist of a alluminium foil stock between to metal of wood sheet. The wood/metal sheet are pre holeded of different size hole and the alluminium foil is put between there.
If you have see the mythbuster episode of (blowing up a shark with some flare)(finish with a lot of high explosive), it is the same principe of the thing that they put in the water to know if the hero will be alive or not.
The only difference, is that we have différence size of hole to know more exactly what is the pressure.
some literature on it: page 14

http://dspace.dsto.defence.gov.au/dspace/bitstream/1947/3630...

The only thing that i am not sure is the way to calibrate the gauge. I think of calibrate it with a compresser but i am not really sure if it can be compare to an explosion.... My idea is to make a pressure box and close one end with one of the hole of the gauge and slowly put more pressure. went the hole blow, it is the pressure that it will blow if the explosion reach this point. (bigger hole, more easy to blow and smaller hole harder to blow).

the only probleme with this way of mesurement is the proble of the srapenal.... because if some piece of the explosion go in somme hole, it will change the result...

i think that the best way to know if it work is to try it

i find somethink else...

http://www.mne.psu.edu/psgdl/HargatherAviationMtg2006.pdf
it is call (shock hole)

[Edited on 23-4-2009 by Bikemaster]

I still lean to the pendulum method, well used and understood with a myriad of supporting math . Plus instructions as to exact dimensions and wieght of the pendulum.The ballistic pendulums made from simple cardboard boxes of a given diameter/wieght and dimensions along with the mathematical equations needed.The same could just as easily be made for a det/vel-energy pendulum with the same support already easy to find and fabricate from at most wood components with the pendulum a box so the exact wieght needed could be loaded.

Theres no doubt the diaghragm Idea isnt elegant in its simplicity I only question will the tensile strenghth of a sq in of Al foil be easily found and its varying degrees of failure.What will constitute failure a tear?Puncture?, a complete puncture of the entire sq in?Are mathematical equations available to plagarize LOL like the ancient pendulum method? the simplicity of a box type pendulum made of wood also means you could make a good # so many shots wouldnt be required OT the important Enhanced Blast experiments and hopefully 1 baseline HE only test shot.

In any event as the experiment progresses a progress report complete with success and failures as well as( if youll share) not just PSI overpressure reports but actual construction and math equations youve used would be of great interest at least to myself as well as Id bet many others.The Idea of the Enhanced blast warhead whatever form it may take is becoming perhaps the new frontier for explosives and HE patents.What with increased precision bombing and minimal collateral damage it seems the EBX warhead is one of the waves of the future. respectfully, grndpndr.

And if a brief description of the EBX Warhead youve devised wouldnt reveal any info youd rather secret, that would be greatly appreciated as well. Regards.

[Edited on 28-4-2009 by grndpndr]

It's true the pendulum setup would be much easier to calculate..

It doesn't really matter either way, the blast I was hoping to measure is over and done with. It ended up that we didn't have time to set up any sort of overpressure measurement at all.. Very unfortunate. The only measure I have is that I felt a decent thump on my chest from at least 600-800 feet away (estimate). And another person who was probably 100 feet closer to it than me said his chest was in a little pain for a while afterword.

Here it is. http://www.youtube.com/watch?v=h7YJxsKD5jw&feature=chann... Enjoy

I was surprised at how little was left, and how far it threw the pieces. A few pieces of mangled sheet metal were landing at least 1000 feet from it, although I suspect most fell within about 250 feet.. No idea where the engine went, must be off in the woods somewhere.

The charge consisted four seperate containers of NH4NO3/(NH4)2SO4 fertilizer, ~15% -300mesh Al, and a touch of methanol/nitromethane RC fuel. Boosted with cast ETN, connected with ETN detcord.

One charge, consisting of roughly 50kg of the above mixture was placed directly on top of the engine. A second smaller one (maybe 30kg) was placed where the drivers feet would go. A third one (also about 30kg) was set one the right rear seat. A fourth one of similar size was in the trunk.

[Edited on 28-4-2009 by 497]

Dude this is huge!!!! How can you find that much ammonium nitrate.
Are you a professionnal of an amature pyrothecnitian

With all this unlimited ressourses, it should be easy to calculate the overpressure because more it has explosive, more it is easy to get precise result.
For the next explosion, just go read about overpressure possible hurt. It can happen bad thing if you receive a lot of overpressure...an other thing, chech the humidity before make those test because, humidity help to make travel the shockwave true you.

But...wath a hell of a bang

Quote: Originally posted by Bikemaster

How can you find that much ammonium nitrate. Are you a professionnal of an amature pyrothecnitian With all this unlimited ressourses, it should be easy to calculate the overpressure because more it has explosive, more it is easy to get precise result.

I got the ammonium nitrate as fertilizer, its roughly $1/kg. Pretty easy to buy a few hundred kilos for not that much

I'm an amateur, I prefer the term hobbyist. Sounds more harmless ^_^

While there is some logic to large charges being easy to measure, the fact that they're large charges make them difficult to repeat. There's quite a lot that goes into a blast over 50kg, so I can't just go blow off a hundred pounds every weekend for overpressure readings

And I'm leaving for my job all summer at the beginning of May, so I won't be able to do anything at all until fall, unfortunately.

Quote: Originally posted by hissingnoise

Was it a joint effort with you guys?

All of our projects are something of a joint effort to one degree or another

"IMO, sulphate-free AN (available as C.A.N fertiliser) would have given an even more powerful blast."

Sulfate free would be great, I'm sure it would increase power. Feel like finding a supplier in Alaska that anyone can purchase from, over the counter, with cash? ^_^ I've looked pretty extensively.

"You could gather up all the fragments, weld them together after a fashion and put the "finished" vehicle in an art exhibition with the title "Afghanistan"."

No offense, I seriously hope that's a joke

1. It's spread out over a massive area, say 300m in all directions, some pieces found even farther than that.
2. Most of the pieces are tiny, many of them only a couple cm across.
3. The whole idea is to stay AWAY from the scene as much as possible- this would require literally hundreds of hours of scouring the woods right at the blast site.

Admittedly, it would be a pretty epic art display... sadly I would rather not display it for security reasons even if I COULD do it...

Self contained executable