Stress and yield in thick wall tube 1

[WJW]

Chaps,
Not my usual area of work but i've been looking at the stress in thick wall tube, when being injected with rubber at 12500psi!
As this tube has capped end's it generates longitudinal stress as well as the normal tangential and radial.
My stress values are :-
ID of tube =
(Radial) = -86.2MPa
(Tangential) = 562.4MPa
(Longitudinal) = 207MPa

At the OD of tube
(Radial) = 0MPa
(Tangential) = 476.2MPa
(Longitudinal) = 207MPa

Am fine with all the above working out, but become unstuck when trying to apply a stress criterion like "Von Mises"

Applying the Von Mises for ID = SQRT(((Sig1-Sig2)^2+(Sig2-Sig3)^2+(Sig3-Sig1)^2)/2)

I obtain a value of 562MPa !! if that looks familiar that’s because it is my tangential stress at the ID. Doesn't sound right to me, I would expect i higher value than one of the principal stress's.
Can any of you Pressure vessel people help me out or direct me.
Thanks all
WJW

 

[prex]

Tresca's failure criterion for membrane stress (the governing stress category) gives a stress intensity value very close to yours.
The calculation is:
(476.2+562.4)/2-(-86.2+0)/2=562.5 MPa
This value is what would be used in a pressure vessel calculation and would be compared with the allowable stress at temperature.

prex

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