Nonlinear analysis results for shell+solids element model

Question:

There is model from shell elements attached where some parts has solid elements. User defined plastic material properties and nonlinear material analysis is done. AFter this calculation user switched to linear analysis. She removed plastic material properties but „Analysis Control Data“ remained unchanged.
After that she removed also „Analysis Control Data“ and the results are differend.
Why the results are different once (Remove Nonlinear Analysis) is removed and for 2nd timeit is not but there is no plastic material assing in model.


Answer:Dear User,

It seems more of a limitation to use material non linearity with out considering plastic materials.

" In the model, there is one plastic material property and it is only assigned to the "S355_plastic" material, but the "S355_plastic" material is not used to a element. As a result, there is no element having plastic material property and thus the user defined plastic material has no effect the material nonlinear analysis results. If the user would like to use material nonlinear analysis, the plastic material property should be assigned to the other materials "S355" and "S355_nehmot".

In addition, although the plastic material is assigned to the all material, if the stress is in the elastic region, the plastic material has no effect the analysis results. In this model, it seems like that the stresses of all elements are in elastic region in all load cases.
One more thing, stresses of linear and material nonlinear analysis results are generally different, because several techniques used in linear analysis can not be applied to material nonlinear analysis. The exactness is better in linear analysis than material nonlinear analysis.

In linear analysis, many schemes are developed to enhance the performance of the plate element.
Therefore, so many element of a plate are developed in linear analysis.
On the contrary, in the nonlinear analysis, generally, basic formulations are used due to the difficulty of a plasticity handling.
Therefore, the linear analysis have better performance in elastic region. "
Creation date: 10/31/2017 3:23 AM ()      Updated: 10/31/2017 12:55 PM ()