In this case study, we will show how to plot calculated results from Excel to nax2cell 3D View (Vizzer)
Excel file and this article can be downloaded at : https://idaerosolutions.com/media/1151/calculateplasticdeformationfromlinear_results.zip
Many times, simulation engineers we need to know the stresses values in a component, considering the plastic behaviour of the material to make our assumptions. One way to do this is by including the plasticity curve within the FEM model itself, and later launching a non-linear analysis. But this could take a long computing time, i.e.: because the model has many load cases, or any other causes, so it can become in a complicated task. Sometimes, it can be enough to us just knowing an estimation of the plastic stresses based in elastic stresses calculated. The scope of this article, is to provide a fast engineering approximated simplified method, based on Neuber criteria to estimate the plastic tensions, starting from some results in elastic analysis, and later to be able to visualize them in a 3D window to check the distribution of these tensions in our part.
Reviewing some basic concepts, Neuber establishes that the plastic energy in constant, so we make the hypothesis that:
Using the Ramberg-Osgoob curve to have a relationship between the stresses and deformation in elastic and plastic zone:
Being E the elastic modulus and Fty the yield stress allowable.
Starting with Eq2, we can define plastic deformation e plastic as e nom and plastic stress Sigma Plastic as Sigma nom.
So, it can be replaced in Eq1 e plastic with formula from Eq2, and e elastic from Eq1 can be replaced with sigma elastic divided by E, the sigma elastic is obtained from the elastic analysis run in the FEM , so now we have one equation to solve the plastic stress and the value of n.
n can be calculated using Eq1 at ultimate stress point, known mechanical properties of the material (Ftu , ultimate elongation) So now it can be calculated the plastic stress. But since solving this Equation can be complicated, it can be easy to use solver function from Excel, as shown in the Excel available for download.
PLOTTING 3D RESULTS
The second step, it is very useful for a simulation engineer, can plot these estimated plastic stresses in the 3D model back.
Using #nax2cell ® and Excel®, we can automate this task for all elements in a FEM model in a very easy way, including the extraction of the data from the op2 file from #nastran, and showing the results calculated in the Excel® directly in a 3D view dinamically.
The referenced video at header shows how to do it.
Last Edited 12 April 2019