ASME formula t=PR/(SE-0.6P) - consideration of end load

[jbesson]

Hi engineers,

A quick one, t=PR/SE-0.6P to calculate thk under internal pressure (circumferential stress).
Why ASME doesn't combine this circumferential stress with the longitudinal stress generated by the end load which is around 1/2 the circumferential stress ?

 

[TGS4]

Primarily because those stresses are in different directions/orientations.

And that formula is based on a failure theory of maximum principal stress. of which the hoop stress is.

Make sense?

 

[jbesson]

TGS4 thanks for your reply.

Yes and no, if we consider a small piece of shell the two forces are working in the same plane and should be combined by the square root of the sum of the square for example ?

 

[TGS4]

No. There are multiple theories of failure: maximum principal stress, maximum shear stress (Tresca), maximum distortion energy (von Mises) that are meant to correlate uniaxial stress results to multi-axial stress states.

In VIII-1, the maximum principal stress theory is used. In VIII-2, for pressure only, the same is used, but for combined loadings (or design-by-analysis) the von Mises theory is used. (Old VIII-2 and current Section III used/uses Tresca).

 

[jbesson]

Ok TGS4,

It does make sense.

Thanks for your expalantions.