Learning Forum

[Andrei F L]

Hello. I am studying biaxial elastoplastic buckling, and I am having convergence issues. I am receiving the following error:

*** ERROR *** CP = 57.703 TIME= 16:45:19
Solution not converged at time 11.1825 (load step 1 substep 1).
Run terminated.

*** WARNING *** CP = 57.703 TIME= 16:45:19
The unconverged solution (identified as time 4473 substep 999999) is
output for analysis debug purposes. Results should not be used for
any other purpose.

My case study is elastoplastic buckling of stiffened plates, in which I use Bilinear Isotropic Hardening.

I am using PyMAPDL 0.68.4 and ANSYS Mechanical APDL 2024R2 Student Version.

The generated APDL script is attached.

I tried to introduce CNVTOL as a way to reach convergence, but without success.

How can I modify the script above in order of it to work?

Since now I thank very much for any piece of advice.

The APDL code is given below:

/SOL
ANTYPE,0
NLGEOM,ON
NSUBST,200,400,100,
CNVTOL,F,0.1,,,
CNVTOL,U,0.1,,,
PSTRES,1
TIME,4473
SFL,lines_contorno_placa_ts,PRESS,4473,,,
SFL,lines_contorno_placa_ls,PRESS,4473,,,
SFL,lines_borda_ls,PRESS,4473,,,
SFL,lines_borda_ts,PRESS,4473,,,
SOLVE,

 

[Erik Kostson]

Hi

This chapter is about buckling/unstable structures.

Search in the apdl help for :

Unstable structures:

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v242/en/ans_str/Hlp_G_STRUNST.html

It is in APDL help, structural guide, and chapter 8.11 Unstable structures.

Hope this helps

Erik

 

[Andrei F L]

Hello, Erik. I don't have access to this link. I tried to register here, but it asks for a Account Number(Customer Number), which seems to be related to a paid subscription, but I am using the ANSYS Student version.

Is there a way for me to access it?

Since now, I thank you very much for the help.

[Erik Kostson]

 

 

Hi

Just open the help manual say from APDL UI, or the Start menu (Ansys Help 2024 R2 say) and then search:

Search in the apdl help for :

Unstable structures

 

It is in APDL help, structural guide, and chapter 8.11 Unstable structures.

 

All the best

Erik

 

[Andrei F L]

 

Thank you for pointing that reference. It is helping a lot in the understanding of the problem.

I did some modifications on the script, and now I am receiving the following errors:

 

 *** ERROR ***                           CP =     141.031   TIME= 19:48:41
 Element 3763 has excessive thickness change.

 *** ERROR ***                           CP =     141.062   TIME= 19:48:51
 Element 1499 has excessive thickness change.

 *** ERROR ***                           CP =     141.094   TIME= 19:48:52
 Element 3486 has excessive thickness change.

 *** ERROR ***                           CP =     141.094   TIME= 19:48:53
 Element 3925 has excessive thickness change.

 ************************************************************************
 The number of ERROR and WARNING messages exceeds 5.

 Additional messages suppressed.

The Absolute Convergence Norm vs Cumulative Iteration Number plot is this:

The updated nonlinear snippet of my script is this:

 

ANTYPE,0
NLGEOM,ON
PSTRES,1
pred,off
AUTOTS,ON
NSUBST,200,400,100,
OUTRES,ERASE
!OUTRES,ALL,1
OUTRES,ALL,ALL
TIME,6390
NEQIT,100
SFL,lines_contorno_placa_ts,PRESS,1980.9,,,
SFL,lines_contorno_placa_ls,PRESS,1980.9,,,
SFL,lines_borda_ls,PRESS,1980.9,,,
SFL,lines_borda_ts,PRESS,1980.9,,,
STABILIZE,CONSTANT,energy,0.0001
SOLVE,

Is there anything else that I can do to get rid of the ”Element 3925 has excessive thickness change” error?

Since now I thank you very much for all the help