Finding strains and stresses on a hydraulic cylinder - NO external pressure?

[jrhickin]

I'm running a test simulation on a Festo rig, with a hydraulic cylinder measuring 45mm internal diameter and 54mm external diameter. The testing requires an internal pressure of 60Bar with no external pressure applied. The strain gauge and setup I'm running it on I suspect to be faulty, and I can't get any sensible principle stresses and strain answers out of it. Is there any way of working it out by hand? I want to see if it's the gauge that's at fault, the system, or if it just happens to be a strange figure.
Thinking back to my lectures, I recall Lane's equation, but as far as I know you need an external pressure to make that work. Is this the one to use? I haven't done it in ages, so any hints on how to work it out would be useful.

 

[xxChrisxx]

This is just a thick walled cylindrical pressure vessel isn't it?

 

[jrhickin]

Yes, it is. It's standard steel, 200GPa for the Young's modulus if that's any help!

 

[Shaun_W]

You don't need an external pressure to make the Lame equations work.

 

[xxChrisxx]

Then just use thick walled pressure vessel equations to find the stresses and strains.

 

[jrhickin]

You don't? I thought that was what a or b was in it?
The equation I have for Lame is a + b/r^2. How do you work it out? It's been a long while since I've had to use it, mind!

 

[xxChrisxx]

Check out engineering tool box (google it), they'll have the equtions.

They are also in Shigley - Mechanical Engineering Design if you have that book.

 

[Shaun_W]

You should know the boundary conditions. External pressure = 0 and internal pressure = 60bar.