Stress Intensity determination through FEA 1

[phodgson]

Hey,

I am performing a pressure vessel analysis using ASME boiler code Section VIII Division 2 and Algo's FEMPRO (latest edition). This requires examining the stress intensity. The stress linearization software provides an average value of the stress intensity Pm + Pb, but the code requires finding the greatest intensity through a section; not an average.

However, the Tresca value is define as a measure of the maximum shear stress. Stress intensity is defined as 2*maximum shear. Therefore, is the Tresca*2 stress result output a good approxiation of the stress intensity at a node? It's logical, but I'm still not sure whether this is a correct assumption.

Thanks,

Pat Hodgson
Mechanical Engineer, E.I.T

 

[jte]

Pat-

Yes, your assumption is correct. You can directly substitute your "2*Tresca" value for "Stress Intensity".

jt

 

[corus]

From memory, the Von tresca stress is the absolute maximum of the difference of principal stresses and is the stress intensity. This is a conservative means to obtain the stress intensity. Von Mises is the stress intensity usually used with ductile material. You don't use twice Von Tresca's for the stress intensity at all.

Here's a site to explain it

http://engr.bd.psu.edu/ansysug/strs_class.html

corus

 

[GBor]

Corus,

Nice site, but, and I'm not ASME B&P Expert, the site describes "Stress Intensity" as "Difference between maximum and minimum principal stress". If I'm not mistaken, Tresca in Algor is defined as 0.5*Max[ABS(S1 - S2), ABS(S2-S3), ABS(S3 -S1)], so 2*Tresca would be the definition of Stress Intensity on the site you list.

 

[rb1957]

isn't the "Difference between maximum and minimum principal stress" the max shear stress *2 ? (remembering my mohr's circle) ...

 

[johnhors]

rb1957

Yes !

Though Mohr's circle only applies to a two dimensional stress system, but the difference between the maximum and minimum principal stresses is still twice the maximum shear stress in 3D as well.

 

[rb1957]

i learnt (many years ago) that you could plot all three planes (and determine all three principal stresses) ...
i'll accept that tresca is a 3D failure criteria, i was just responding to the quote.

btw, (i posted on the other thread) this "stress intensity" has nothing to do with fracture mechanics stress intensity, does it ... that's confusing !?