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      Please click here for a short but important announcement   03/26/17

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Rahul Ponginan

Contact problem in two different sub-cases.

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Dear Administrator,

I would like to know how can I properly use multiple sub-cases in a contact problem.
I have done a simple example (attached) in which in the first sub-case I apply a load that closes the contact, in the second loadcase I would like to study how this contact will react to an horizontal force.
I have used the CNTNLSUB card in the second loadstep however the contact is not performed in the second analysis.

I tried to applied the same vertical load in the second loadcase as well and also did not worked, how could I perform the analysis in such a way that:
Loadstep 1 : the contact is closed (using a vertical force)
Loadsetp 2 : An horizontal force is applied to the contact is already closed

Sorry for the simple question.

Thank you for the help.

Best regards
Vitor

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Hi Vitor,

What should the results actually look like? can you please describe the expected results?

Secondly you do see that the loads in the horizontal direction are unopposed and will create extensive deformation or in fact just displacement as the top component is not constrained in that direction at all. what is the reasoning behind such boundary conditions?

See image below where I compare results for different run parameters, see top left window where in the loadstep I have used cntnlsub with scid and in scid I have referred the previous loadstep, in this analysis I have also removed the load on the top plate in the vertical direction leaving only the horizontal load.

Just below that , i.e. bottom left i run the analysis with the load in the vertical direction in the top plate again using the scid option

The results on the left are from analyses run as you have sent it. cntnlsub in all conditions seems to give us similar results.
l5df2-23.png

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Hello Rahul,

First of all I would like to thank you for the help.

About the contact I am sending you a simplified analysis in which I have two identical loads in two different load steps. What I expect in the results is that:

In the beginning of the first load step the contact is open, then in the end of this loadstep the contact is close due to the application of the first force F1.
In the beginning of the second step the contact should be closed (as in the last step of the first loadcase) and then the second load F2 would keep the contact closed during the second load-step.

The motivation is to understand how OS leads with multiple load-cases when using NLSTAT.

The problem that I am facing is that, in the beginning of the second step the contact is open, and I cannot understand why this is happening once that in the last step of the first loadstep it was closed. In addition, the results indicate that the displacement in both cases was 0.5 mm, which means the gap was closed two times. However the stresses in the second loadstep are double than in the first icon_eek.gif . I cannot understand why this is happening, once that OS uses Newton-Method for NLSTAT, then I would expect that the second loadstep should use the geometric stiffness matrix from the last iteration of the first load-step in which the gap is closed and to run the second loadstep.

Thank you again for your help
Regards
Vitor

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Hi Vitor,


We should not expect the 2nd subcase to start from the end position of the first one.


CNTNLSUB only carries over the nonlinear evolution data, for example, the gap status or plastic deformation, but not displ/stress, loading, boundary conditions, etc.


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