Stresses in beam models 1

[julij]

i made a beam model, calculated and now i have problem. in old program which i used, as results i could get normal stresses, shear stresses and von Misses.
sigma_Misses=sqrt(sigma_normal+3*sigma_shear^2)

in Femap i can obtain only normal stresses and "combined stresses" which i don't even know what they are.

is it possible to get shear and von Misses stresses in Femap?

 

[rb1957]

i think FeMap (like most FEAs) will give you beam loads (axial, shear, moments) and stresses recovery points (as defined on your section).

An observation i would make is that peak bending stresses don't coincide with peak shear stresses, so combining them (as i read your post) is conservative.

 

[ThomasH]

Hi

The results varies with what solver you are using. Exactly what you get and now it is computed you can probably find in the manual.

One way to figure it out if the manual isn't there is to start with a simple axial force. What resulöts will that produce. Then you use pure shear and so on ....

Good Luck

Thomas

 

[BlasMolero]

If you run bundle "FEMAP with NX Nastran" the stress results you get for CBAR/CBEAM elements are axial stress, bending stress and max./min. combined stresses, i.e., axial + bending stresses, in both EndA and EndB, and in the four stress recovery points of the beam cross section, as well as margins of safety (MS-T & MS-C) in tension and compression if you enter stress limits on the MAT1 entry.

NX Nastran computes the bending moments End-A & End-B at plane1 & plane2, shear forces (in both plane1 & plane2), axial force and torque, but do not compute torsional stress neither shear stress.

Since there’s no torsional stress recovery for the CBEAM element, the margin-of-safety computation does not include the torsional stress. If the torsional stress is important in your stress analysis, use the torsional force output to compute the stress outside of NX Nastran. The torsional stress is highly dependent on the geometry of the CBAR’s cross section, which NX Nastran doesn’t know.

In summary, with NX Nastran only the longitudinal stresses ara available as complex stresses; hence, any stress due to torsional or warping is not included, is up the user to check that values.

Best regards,
Blas.

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Blas Molero Hidalgo
Ingeniero Industrial
Director

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