Learning Forum

[Dennis Chen]

How does ls-dyna handle contact after a pre-stress in a modal analysis?   Based on my simple model test, it doesnt' seem to register the contact status at the start of an eigenvalue analysis.   I use control_implicit_eigenvalue with a negative load cuve ID to define when to extract the modes. 

Ansys Mechanical/MAPDL has options to treat the frictional contact as bonded.    Does this option exist inside LS-Dyna?  I can't find it but I want to ask to see if others know. 

Thanks 

[Ram Gopisetti]

Hi Dennis, 

If the contact is closed, it is like inserting a stiff spring between the segments (for Mortar contact), Normal stiffness, and tangential stiffness depending on the coefficient of friction.

If the contact is open, the tie is not enforced. 

Cheers, Ram 

 

[Dennis Chen]

 

Hi Ram, I couldn’t reproduce this in a simple example model.    I start with an automatic_surface_to_surface contact and at the end of t=1s, the contact is established and then I do the modal analysis but I can see the contact is is tied.  

Is there an example problem I can find?   Must I use mortar contact?

 

[Dennis Chen]

Hi Ram, I used Mortar contact and suddenly and magically, it aligned much better with Ansys Mechanical results.   I can adjust a few parameters to see how it affects the alignment.

MAPDL uses these force bond method to treat contact and I just want to understand the logic in LS-Dyna for accomplishing similar things.

I have to ask:  where in the documentation do I find that Mortar contact would be better suited for intermittent modal analysis?  I want to find the source of the knowledge.

THank you