 # Obtain nodal stress and strain vector & poisson ratio

Could someone please point out how I can obtain the stress and strain for each node.

Stress: With reference to the picture below I can get a Stress vector per face, is there an better to get a vector per node than taking the average?

Strain: At the point input I’ve use the list of nodes, I get 0 vectors. Any ideas?

Poisson Ratio: What’s the reason for having no poisson ratio as an input the MatProps component?

Dear Charles,

instead of taking the average you could add the opening angle of each element corner as a weighting factor.

The ‘Principal Strains Approximation’-component takes an undeformed and a deformed model and computes the principal strains based on the differences of the nodal displacement. The applied procedure is a rough approximation. See the manual for details. There are two definitions (‘Principal_Strains_Approximation_LargeExample.gh’ and ‘Principal_Strains_Approximation_SmallExample.gh’) in the Karamba3D examples. You get there by double-clicking on the Karamba3D desktop icon and selecting ‘Examples\TestExamples’.

The Poisson ratio ‘nue’ is implicitly given via Young’s Modulus E and the in-plane shear Modulus G12: G12 = E/(2*(1+nue)).

Best,
Clemens

Thanks Clemens, it’s now clear how the def.Model is to be used. However, the amplitude of the strain vector is dependant upon an arbitrary displacement multiplier. Am I right that the true strain can be obtained by using the “Nodal Displacements” component to deform the mesh and using this as the input to the “Principal Strains Approximation” component?

Is there a way/formula that’d allow me to define nue explicitly? I have a database containing these which I’d like to use.

Hi Charles,
the def.Models displacements depend on the ModelView-component’s ‘Deformation’ slider. The “Nodal displacement”-component has nothing to do with it. Please read section 3.6.4 of the manual (see Karamba3D User Manual 1.3.1).

If you have nue then calculate G according to this formula: G = E/(2*(1+nue)).

Best,
Clemens