DHO

I am at a loss to understand Your question. I work with aerospace pneumatic and fluid system components and have never heard of a "convoluted capsule diaphragm"!?!?

Photos/sketch of the component MIGHT help us understand what it is.

Regards, Wil Taylor

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here is a very thin diaphragm. pressurized on one side, pushed by on the other side. what is the stress at the position shown?
thanks.

• http://files.engineering.com/getfile.aspx?folder=7ae67dae-dc38-433e-a9b5-e2

Is this a pressure switch?
Or a diaphragm pump?
Does the cavity that the diaphragm moves in have a function other than being the surface the diaphragm rests against?

I suspect you're looking for the load or pressure that causes it to invert. Can a test be done?

STF

yes. it is a pressure switch. the curved back on upper part is for the diaphragm to rest for proof, burst pressure purpose.
also, it "is" also a diaphragm pump, when the diaphragm is pushed down (as a ground check when installed on fire extinguisher).
i am looking for the cycle life when the diaphragm is pushed down (and let it up) when a constant pressure is applied.
thanks.

An estimate can be found in Roark's Formulas for Stress and Strain. Look for the cases of circular plate loading, for an "annular" shape.
Anything more profound than that, and you may need to go down to the basics: Timoshenko et. al.
One thing that might help, since the disk is circular, is that you can assume the stress in any "dr" ring is uniform, so it's a one-dimensional integral.

STF

Try this link: http://www.google.com/url?sa=t&rct=j&q=&am...

You may try Finite Element Analysis; probably, any standard software would do.

dho-

Based simply on what your sketch shows, I don't see how the applied upward pressure force and the axial travel of the piston will overstress the metal diaphragm. The piston and thin metal diaphragm will simply unload once they contact the upper housing surface. However, if pressure is applied to the thin metal diaphragm to drive the piston downward, then you need to look at the stresses in the weld joint between the thin diaphragm edge and the thicker piston edge. This is where it will likely fail when the piston stops against the lower housing surface.

SPM, i have no idea if FEA can handle such case, a .002" diaphragm. have you any experience?
(i have no access to FEA.)

you are right, the stress will be gone when the diaphragm rests against the upper housing. as a pressure sensor, the diaphragm will move up and down under applied variable pressure (against a loaded spring on the stop/piston which is not shown). as another requirement, customer wants to apply motion to the stop/piston against the system pressure to verify the operation of the pressure sensor. seems the calculation of the stress is not an easy job (to me), i ran a test, it passed my life cycle target. thanks. to all.
ps, the diaphragm is not welded to the stop/piston.