Unconstrained model 1

[mel08]

I am trying to compress a piece of bone between 2 stainless steel plates. I have fully constrained all dof's of the bottom plate and apply a constant surface load to my top plate. The plates are made of shell elements and the bone of bricks.
I have created contact elements between the faces of my bone and of the plates.
However when I solve, i keep getting an error that one of the nodes on the edge of the top plates has UZ = a massive number. Ie i haven't properly constrained my model. I'm not sure why this is happening. Can anyone help??

 

[cranisch]

Do you have initial gaps between the components? Sometimes when your substep size is too big and you have gaps between the bodies you get a situation where no contact is established because the displacements of the surfaces are larger than the pinball radius between two iterations.
To check if you have gaps or too much penetration use the contact tool (connections > contact tool).

If you have no initial gaps, there are three possibilities to avoid rigid body motions in this case (maybe there are more but these are the ones that I found out):
1. Reduce the initial substep size tremendously (can be increased for further substeps automatically)
2. Use higher Normal Stiffness Factors for the contacts
3. Sometimes most useful: Insert springs between the contacting bodies with an adequate low stiffness on your own. So that they act somehow like "weak springs"

Tell me if those suggestions help.

 

[mel08]

Thanks so much. I'll check the initial gaps and go from there.