Is the analysis with non-linear material (plasticity) only possible with nlgeom or also with nlstat?

Rahul_P1

Hello,
I have nonlinear material (plasticity) in my Analysis and the deformation is very small. I would like to work with non-linear quasi-static Analysis. But if I start the solver Radioss 11.0 I receive the message: Non convergent nonlinear iterations for subcase 1
What is the reason for this message? Can I only solve the problem with a geometric nonlinear Analysis?

In addition their is an other problem. If I try to solve with linear Material and slide contact between two parts I receive a solution, but if I try to solve the same problem with frictional contact between the two parts (and nlstat) I receive the same message like before with the nonlinear material and additional suggestions. (The card image nlparm ninc-option 100.) I add the message and the options for the interface as a jpg-file. Do you have any ideas for my problem?
Prethanks for an answer and excuse me for my bad english.
Best regards
Kerstin

Rahul_P1

Check the constraints in your model,make sure there is not too much freedom in any one direction.

In the NLPARM card, Increase the NINC value to 15 as it might be easier to converge with more load increments. Also, increase the MAXITER as it might need a few more iterations to reach convergence (default is 25 which might not be sufficient in a few cases).

This could most likely be the solution - Change the STIFF option in the PCONT card that you show above to SOFT (or Add CONTPRM and set the STIFF option to SOFT) Try HARD also or use slide with your nlstat.

Add PARM, EXPERTNL, YES which activates a nonlinear expert system that aids in the convergence of small displacement nonlinear problems (NLSTAT).

Please get back with the results and we can discuss further 

Rahul_P1

Hallo,
with slide and PARM, EXPERTNL, YES the solver runs und I receive results with the nonlinear material. But the frictional contact doesn`t work.
Thanks for help

Rahul_P1

Kerstin,

The presence of friction, due to its strongly nonlinear, non-conservative nature, may cause difficulties in nonlinear convergence, especially when sliding is present. Therefore, solving the problem without friction can often provide convergence in otherwise failing problems. Or, in cases when presence of frictional resistance is necessary and minimal sliding is expected, enforcing a stick condition may be a viable solution, and will often lead to a better convergence than Coulomb friction (see the PGAP and PCONT bulk data card for details). Note that in cases of larger sliding motions, the stick condition may lead to divergence through a 'tumbling' mode.

Please read below topic in detail especially the Nonlinear Convergence Criteria and User's Considerations for Nonlinear Convergence

here User's Guide > RADIOSS > Bulk Data Format Input > Finite Element Analysis > Solution Sequences > Nonlinear Quasi-Static Analysis