Learning Forum

[Mehrdad Pishehgar]

Hi,
I have a model that is solved in 5 load steps. It is a static analysis with some nonlinear contacts (frictional and frictionless) and possibly nonlinear material properties.

In the first load step, the bolt pretension loads and the mass of the model (acceleration in Z direction) are applied. These two loads are present in all the solved load steps.

In the following 4 load steps, acceleration in +X, -X. +Y and -Y are also applied/added to the model in consecutive load steps. 

Now, my question is this: Is it possible to return the model to its position at the end of load step one, before starting the solution of the next load step?

So after applying the loads in load step one, the structure is in POS1.

The loads in load step two are applied (e.g. acceleration in +X) and solved. The structure is in POS2.

Before solving load step 3 (e.g. acceleration in -X), the model should be returned to POS1 and then solved. This should be repeated for all the load steps after the solution of load step two.

I hope I was able to describe the problem well enough.

Thanks in advance. 

[Erik Kostson]

Hi

If there is no plasticity (nonlinear materials) and it is all linear elastic materials, then add a dummy load step in between the steps where there are no loads on the structure and so it can go back to the original position before adding another load.

With plasticity the above does not work since we have permanent deformations (due to yield), so the best way is to define 3 different inidividual analysis systems with their separate loads.

All the best

Erik

[Mehrdad Pishehgar]

Thanks for the speedy reply. 

So, if I wanted the initial position to be the position of the structure at the end of load step one (=POS1), I just add a dummy load step in between the steps with the dummy load having the load values of load step one (bolt pretension + acceleration in Z direction)?

[Erik Kostson]

 

Actually for linear elastic material one can also just use the activate deactivate at a load step, and so to switch between loads at different steps. Then you can use this to have the loads you want at the different time steps. 

See here for activate/de-act.:

https://www.youtube.com/watch?v=lrmxV-zWqtQ

 

The dummy steps (inbetween steps) were only used to see that the structure goes back - the dummy step thus does not have any loads in it so all loads are zero there of course :) otherwise the structure would not go back to the undeformed original shape.

All the best

 

Erik