CONTACT STRANGE WARNING

[Fabi0]

It's the first time i get this warning:

CONTACT NOT YET CONVERGED. FORCING ONE MORE ITERATION BECAUSE
CONVERGENCE OCCURRED IN LESS THAN 3 ITERATIONS AND
*CONTACT CONTROLS, AUTOMATIC TOLERANCES WAS USED.
NEXT ITERATION WILL USE THE TIGHTER TOLERANCE ON THE SEPARATION FORCE


What does abaqus want to tell me? It say that the CONTACT NOT YET CONVERGED but then it say that the convergence occurred...

Fabi0

 

[Elabbasi]

The Abaqus message is indeed confusing. The increment is not yet converged because there are large tensile contact forces.

You are using the non-default *CONTACT CONTROLS, AUTOMATIC TOLERANCES setting for dealing with "contact chatter". In general, when a contact force at a node becomes tensile, contact is released. However, with this feature, Abaqus temporarily accepts small tensile contact forces during iteration. In the first 3 iterations a loose tolerance is used to evaluate if a tensile contact force is "small".

In your model, contact is probably converged according to this loose tolerance but it's not really a good solution, so more iterations are performed.

Nagi Elabbasi

http://www.veryst.com

 

[Fabi0]

Hi Nagi, and thanks for your answer!

You're right, i'm using *CONTACT CONTROLS, AUTOMATIC TOLERANCES because i need to work with many "unstable" contacts in the same model.

Basically i need to investigate plasticity in the inner ring of a back up roller with 102 rolls....even if i've used simmetry, there's a lot of roller and contact, and many of them are difficult to be analyzed by abaqus (the one referring to the unloaded rollers).

It's about a week i'm dealing with this model, i hope contact control helps!

Thx Again

Fabi0

 

[Elabbasi]

Good luck. AUTOMATIC TOLERANCES helps with a specific type of contact problem, where nodes are going in and out of contact in successive iterations.

If that doesn't help, there are many other advanced contact features in Abaqus. Refer to Section 35.1 titled "Resolving contact difficulties in Abaqus/Standard" in the Abaqus Analysis User's Manual. It's long but quite informative.


Nagi Elabbasi

http://www.veryst.com