ASME VIII div 2, 2007 1

[Framestedt]

Hi,

I´m working with an elastic analyse of a pressure vessel and according to section 5.3.2 in ASME VIII div 2 2007 the following criterion shall be checked:

S1+S2+S3?4S

What is this criterion and what do I check applying this? Shall I use the absolute values of the primary stresses when adding them?

Regards

 

[gr2vessels]

Read the entire Clause 5.2 and 5.3.
Cheers,
gr2vessels

 

[TGS4]

The criteria is called Local Failure (as indicated by the title of Article 5.3). It is a real failure mechanism - under the right set of conditions, a material can rupture without prior plastic deformation - usually under a tri-axial (tensile) stress state. Note that in calculating the invariants stresses (von Mises for example), the calculation is based on the DIFFERENCE between principal stresses. However, if all of the principal stresses are essentially equal, failure would not be predicted by the plastic collapse method. This is a rare, but very real failure mode that needs to be considered.

You do NOT use the absolute value of the local primary membrane plus bending principal stresses, but the algebraic value.

 

[Framestedt]

Thanks for your explanation TGS4. I have read Article 5.3 in ASME VIII but I didn´t understand how/why to to apply this code check. Now it makes sense.

However, I still wonder how I can sum three orthogonal principal stresses (S1+S2+S3) when they obviously aren´t pointing in the same direction?

Thanks again

 

[jte]

Framestedt-

Just treat S1 S2 and S3 as magnitudes, not vectors. This is no different than determining the old Stress Intensity by taking the max algebraic difference of the principal stresses. No vectors involved there either.

jt