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I am designing a vacuum chamber made of a vertical glass cylinder free of contact from any other structure, except by the top and bottom where aluminum disks seal the device.

Temperature is the same inside and outside.

I found on several books the following formula for the hoop stress:

s = p * r / t

s = stress

p = pressure

r = cylinder radius

t = wall thickness

They say the formula is the same for external or internal pressure.

But I assume the strength for internal pressure is tensile and for external pressure is compressive.

Glass compressive strength is 10^9 Pa.

The diference of the pressure inside and outside is 10^5 Pa.

Cylinder radius is 0.15 m

So...

10^9 = 10^5 * 0.15 / t

t = 1.5 x 10^-5 m

This doesn't make any sense. This pressure from outside the cylinder would break the glass.

What is wrong here?

Please, does anyone have any reference on calculating a "

**brittle material thin-walled cylinder subject to external pressure**", even better if glass specifically.

Von Mises is not applicable since glass is a brittle material.

Any help would be highly appreciated. ;-)