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Posted: Mon Dec 20, 2010 9:09 pm
by Insomniac
Ok, it may have been mechanical impact that did it. But it's still not a BLEVE, in the strictest sence (boiling liquid expanding vapour explosion). Nonetheless, you are right... We will never know for sure.
Posted: Mon Dec 20, 2010 9:56 pm
by velocity3x
Moonbogg wrote:
I have never tested a cannon to failure, so I don't know how dangerous a 2x hybrid failure would be, especially hand held. I don't know how the aluminum would behave if it failed.
I know you're a SolidWorks user. Have you ever static tested the cannons components in COSMOS to determine the approximate FOS?
Posted: Mon Dec 20, 2010 10:36 pm
by Moonbogg
velocity3x wrote:Moonbogg wrote:
I have never tested a cannon to failure, so I don't know how dangerous a 2x hybrid failure would be, especially hand held. I don't know how the aluminum would behave if it failed.
I know you're a SolidWorks user. Have you ever static tested the cannons components in COSMOS to determine the approximate FOS?
Yes. The FOS of the weakest area was about 4.2 @ 200PSI. But this was assuming a solid part. My cannon is welded. It was heat treated to regain some strength, but not all strength can be expected to be regained. Maybe 80-90% or so from what i've read. The mechanical properties of the weld are also different in some ways than that of the base material, so there is more uncertainty there. So things like ductility and resistence to stress cracking come to mind, so its not only the yield values that are concerning me.
Also, the yield strength of 6061-T6 is about 40,000psi while the ultimate tensile strength is only 45,000psi! This leads me to suspect that if a design approaches yield, it is also approaching ultimate failure. Its not like steel where the yield is way below the ultimate tensile, allowing for more deformation before failure. Aluminum just doesn't seems to be very ductile at all in the T6 condition.
Combine that with the variables that the welding process introduces and its enough to cause this cannon builder some anxiety and second guessing of the cannons true FOS.
Then ontop of all that is the fatigue factor. How many cycles can it take? Without a thorough understanding of all of these variables AND extensive testing it is impossible to assign an end of life date. I wish Solidworks was that good, but it can't predict every variable. It will put you in the FOS ballpark as a reference starting point, but thats about it.
In addition, my son was just born two weeks ago and I find myself full of overly conservative though processes that are a stark constrast to my thinking just a few months ago.