# Tangential stresses on shell using Karamba 3D

Hi Everyone! I’m having a small problem in calculating the tangential stresses on a shell.
I want to apply the following (von mises)criterion:
sqrt{\sigma_max^2*(z*)+3tau^2*(z*)}<sigma_{id}
but I really don’t know how to extrapolate tau (tangential stresses).

There is someone that can help?

Thanks a lot.

Hello @laura.sardone,
you formula for the Von Mises stress is not correct (see e.g. https://en.wikipedia.org/wiki/Von_Mises_yield_criterion). The in-plane shear stress ‘tau’ is sometimes denoted as ‘sigma_12’.
In Karamba3D 1.3.3. you can get the stresses in a certain layer of a shell from the cross section forces via the ‘Shell-Forces’-component. In Karamba3D 2.0.0 WIP you could use the ‘Shell Section’-component for retrieving the stresses along an arbitrary section through you shell.
– Clemens

Thank you so much, Clemens!

Yes, I’ve realized it a few moments after the question!

I’ve solved it using python by imposing the problem as follow:
vonMises = ( (sigma12)+(sigma22) - (sigma1*sigma2) )0.5
where sigma 1= ((x
2)+(y2)+(z2))0.5
and
sigma2 = ((u
2)+(v2)+(w2))**0.5

by connecting Sig1_vec and Sig2-Vec from ShellVecResults as input I’ve obtained what I needed!

Thanks a lot.

l.s.

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