Divergence and error: increment size smaller than minimum

1

I am not much experienced with CalculiX. I have a hyperelastic Ring to which a large prescribed displacement is given.
The model converges till a diplacement of 15, but as soon as I give displacement above 15 or 20, the model shows divergence and error stating the increment size is smaller than minimum

This is the surface interaction between the Ring and the moving metal part that stretches it

*SURFACE INTERACTION, NAME=tensile
*SURFACE BEHAVIOR, PRESSURE-OVERCLOSURE=linear
200, 0.00639, 1e-3
*FRICTION
0.9, 0.055

and this is the step part:

*STEP, NLGEOM, INC=200
*STATIC
0.1,1,1e-100,1e30
Ndisplaced,1,-15.467

Could anyone help me with this. What could be the problem ? should I improve the mesh or change something in the input file ?

2

is your model running with a tied contact ?

3

It’s a node to surface contact

*SURFACE INTERACTION, NAME=tensile
*SURFACE BEHAVIOR, PRESSURE-OVERCLOSURE=linear
200, 0.00639, 1e-3
*FRICTION
0.9, 0.055
*CONTACT PAIR, INTERACTION=tensile, TYPE=node to surface

4

Try tying the surfaces. If the analysis completes with this setting, the reason for non-convergence lies somewhere else, not in contact (which often causes problems). Try also changing the material model or adjusting its properties, refining the mesh (if needed) and using different element type. You can also try running the study with the dynamic analysis step.

6

If that’s compatible with your simulation, you could also try to constrain displacements in the orthogonal directions. It may help the convergence.

*BOUNDARY
Ndisplaced,2,3