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# What is the formula/equations behind Max stress in post processing

Creator

Hello,

I am wondering what Max Shear calculates, when I calculate a cantilever beam with a bending force, this is not the value  expect.

Regards,

Olaf van Buul

2 REPLIES

# Betreff: What is the formula/equations behind Max stress in post processing

Gears Phenom

Hello Olaf,

did you keep in mind the difference between Euler-Bernoulli beam theory and Timoshenko beam theory?

(If you create your model with real beam elements.)  I believe that NX is using Timoshenko beam theory and mostly analytical solutions only reproduce Bernoulli beam theory.

I guess, maximum shear stress is according to the theory of Mohr's circle half the difference between maximum principle stress and minimum principle stress at a grid point. But keep in mind that if you calculate only 2 of the 3 principle stresses the third one is zero and can redefine maximum or minimum principle stress values depending on signs of your stress values.

Edit:

Keep in mind:

- to switch off nodal combination,

- that nodal values are extrapolated values and sometimes they do not describe the stress tensor at grid point position correctly but only in average because extrapolation can made for stress components directly or may be for all invariants of stress tensor, too. Therefore try to use stress tensor values at integration points, i.e., centroidal values. They are calculated directly without extrapolation.

May be it helps,

Michael

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# Betreff: What is the formula/equations behind Max stress in post processing

Creator

Hello Michael,

I now I bit to busy to verify what you said in postprocessing, but it is planned to verify this in the near future.