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Aluminum failure characteristics

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: jeepkahn » Sat Oct 10, 2009 1:46 pm

hydrostatic won't work for the testing he's trying to do, it won't show the catastrophic damage that occurs when the materiel fails with stored energy... Hydrostatic is great for testing failure strength, but lousy for testing catastrophic failure characteristics...
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Unread postAuthor: Moonbogg » Sat Oct 10, 2009 6:29 pm

I can't be the first person in history to have a desire or need for this type of testing. The data simply has to exist somewhere, its just a matter of finding it.
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Unread postAuthor: btrettel » Sat Oct 10, 2009 6:47 pm

With aluminum, you'll see noticeable strain (i.e. stretching of the material) before failure assuming the material lacks any serious inherent flaws. That answer might not be good enough for you.

The ductility also means that aluminum's much more likely to tear than fracture like ABS.

I think it would be hard to know precisely how aluminum will fail without some detailed analysis and more knowledge than I have. I'd feel fine if the FEA said it had a good safety factor.
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Unread postAuthor: Moonbogg » Sat Oct 10, 2009 7:49 pm

btrettel wrote:With aluminum, you'll see noticeable strain (i.e. stretching of the material) before failure assuming the material lacks any serious inherent flaws. That answer might not be good enough for you.

The ductility also means that aluminum's much more likely to tear than fracture like ABS.

I think it would be hard to know precisely how aluminum will fail without some detailed analysis and more knowledge than I have. I'd feel fine if the FEA said it had a good safety factor.


Yes, I always thought the aluminum would fail in an ABS-like manner. The FEA factors are adequate, ranging from 3-5 and thats at maximum theoretical pressure (closed chamber). I feel sort of like a pilot after buying a new airplane. He will want to stall the airplane on purpose so he can get a feel for its limits. I know what the FEA sais, and I know what my best judgement sais, but theres just nothing like real data.
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Unread postAuthor: broken_system » Tue Nov 17, 2009 2:17 pm

Sorry if this is a little OT but if you had a smaller aluminum cylinder, say 2"d and say 1/8" thick, and were dealing with very small amounts of propane/air fuel combusting inside with a clear passage for the expanding gas to take by pushing a projectile, would there be any chance of failure? Or for that matter any chance of warping/stretching/cracking/etc the tube?

Or would a small about of fuel not be concidered enough to affect the aluminum cylinder.

Also, would it be practical to install a burst disk of a different material with a lower breaking point, and position it so that if failure does occur, it would just break apart away from you? (Safety, safety, safety!).
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Unread postAuthor: SpudBlaster15 » Tue Nov 17, 2009 3:59 pm

broken_system wrote:Sorry if this is a little OT but if you had a smaller aluminum cylinder, say 2"d and say 1/8" thick, and were dealing with very small amounts of propane/air fuel combusting inside with a clear passage for the expanding gas to take by pushing a projectile, would there be any chance of failure? Or for that matter any chance of warping/stretching/cracking/etc the tube?

Or would a small about of fuel not be concidered enough to affect the aluminum cylinder.

Also, would it be practical to install a burst disk of a different material with a lower breaking point, and position it so that if failure does occur, it would just break apart away from you? (Safety, safety, safety!).


2" Aluminum pipe (Probably the standard 6061-T6 alloy/heat treatment) with a 1/8" wall thickness will have a burst pressure far above what stoichiometric propane/air at atmospheric pressure can produce.

As for the original post, I don't know which particular alloy you are working with, but most are very ductile and will tend to stretch and tear rather than fragment. I have done some testing with aluminum vessels and very high pressures (Can't discuss the methodology here), and I have found that if you apply stress relatively slowly (As in a propane/air mixture at a few times atmospheric pressure), the vessel remains in one piece, much like the ABS pipe characteristics we are all familiar with.
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Unread postAuthor: Moonbogg » Tue Nov 17, 2009 11:12 pm

Right. Basically what i'm getting at is I want to know how much the Venom can take before blowing up. There are things that need to be taken into account and they are filled with variables. Such as weld type and size. The welds are done clean and are pretty fat looking (pretty scientific of me, I know). The first thing to go on the venom, I believe would be the back plate bending outward. It would have to force the return pipe back as well and the return pipe would have to cause the gusset to buckle in on itself. That would be hard to do lol. But I am curious and want to know. I am not an expert in welding so I wonder if the welds are more brittle than the base material. Would a weld crack be the first sign of failure? If I had the money i'd make another one and crank up the X values with a camlock plug in there and wait for somethign to give. Now that would be educational and fun.
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