Calculating Vacuum Pressure within a Cylinder??? 1

[Superslinky]

Hi all,

lets say I have a tube of material (any) and I cap both ends. Now I drill a hole in one side (end or whatever) and draw a vacuum. How do I determine the strength of the material being used on either end and the "tube".

For the sake of the question let say the cylinder was 6061 alum and measured 20" dia. by 25" tall with a 1/4" wall thickness and each end was capped with 1" thick lexan.

I would be drawing a vacuum to around a negative 10 psi.

Any help would be appriciated. Maybe even a reference website where I could read about it would be helpful as well.

Thank you all...

 

[rb1957]

"[ R^2 - (R-t)^2 ] / [ R^2 - (R-t)^2 ]" = 1, no?

i'd've thought it'd've been pR/t = p*(Ro-t/2)/t

 

[chicopee]

The above formula that I submitted is for longitudinal stresses. For thickness of end flat round cover plates, use formula for simply(or rigidly) supported under uniform load; such formula is found in any ME handbook.

 

[DRWeig]

rb1957, I agree.

Chicopee, did you perhaps leave out parentheses around the last two terms?

Goober Dave

 

[chicopee]

Sorry I see the problem and I should have checked the equation prior to submission. Probably did misplaced a parentheses since these are old notes. Check pg 6/9 where internal pressure =0 and external pressure prevails on the following link:
courses.washington.edu/me354a/Thick%20Walled%20Cylinders.pdf

 

[Ron]

Put a few bonded strain gages on it, pull the vacuum and erase all doubt.

 

[chicopee]

Did find a general equation for determining stresses in thick wall cylinder. Reference is included .See attachment.

 

[flash3780]

It's a bit of a sidebar issue, but there's been a lot of discussion about absolute pressure versus gage pressure. To be clear, it's best to explicitly state whether you're talking about absolute, differential, or gage pressures. PSIA, PSID and PSIG are commonly used, or you can spell it out.