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Hydrotesting Vs. Shock Pressure

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: D_Hall » Thu Apr 08, 2010 7:19 pm

Coming to this thread way late but....

2) 3:1 safety margin on a dynamically loaded system? You'll *PROBABLY* be OK, but I won't be standing next to you when you shoot it. At least in my life as a Mech Engineer, 3:1 is the rule of thumb for static loads, but for dynamic loads it's 5:1.

1) Also, are you using thin walled pressure vessel equations or the "real" equations? After all, I'm assuming you're using some pretty heavy stuff which means the thin wall equations are no longer valid. Worse, the thin wall equations - if applied to a thick walled vessel - will overstate the actual strength.

1 + 2 = You may not have a safe system on your hands.
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Unread postAuthor: randompkguy » Thu Apr 08, 2010 7:51 pm

well this is good, obviously you don't assume deformation like you said, but i have some of this: http://www.mcmaster.com/#8980k54/=6ksz6v
so i don't think i'll get too much deformation before it bursts. i'll have to read that other analysis too.

EDIT: dHall, I'm using 80% of the yield strength, and then dividing that by 3, so its closer to 4:1. And yes, i used the thin walled assumption for hoop stress because the inner radius to wall thickness ratio is almost 5:1 (its about 4.32:1)

this is the steel i got: http://www.onlinemetals.com/alloycat.cfm?alloy=A513
but i don't trust these numbers, so i worked form the lowest yield strength i could find for 1026 which was about 50800 psi

And finally, i pressure tested it to 3500psi for at least an hour and measured no deformation afterward. (this was with the barrel plugged, so the entire cannon was pressurized)
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