convergence problem

[squiddi]

Hi, I have a big problem with abaqus cae. I have to verify stresses in a beam under different load (from 1000N to 9000N). Everithing is fine until I reach 7000N and 8000N. In those cases abaqus doesn't find a solution to the problem (if I put 9000N everything's fine again). What is the problem? Maybe a mesh problem?

 

[rstupplebeen]

Providing the error message will greatly help with diagnosing the problem. My best guess is that the minimum time increment was reached or too many attempts made. If so go into the step definition and allow a smaller increment and increase the maximum increments. I hope this helps.

Rob Stupplebeen

https://sites.google.com/site/robertkstupplebeen/

 

[IceBreakerSours]

Few things for you to think about:

A) Are there any error messages in the .log/.dat/.msg files? If so, what do they say?
B) If an .sta file was generated, what does the last line say?
C) Open the ODB, look at the displacements. Are there any distortions?

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[squiddi]

First of all thanks for the answers, I really appreciate.
error message: Too many attempts made for this increment
.sta file: THE ANALYSIS HAS NOT BEEN COMPLETED
I tried what "rstupplebeen" suggested with no results. I can not see any displacement because abaqus can not start the step1's analisys.
I wonder why I have problem with 7000N and 8000N and everithing goes fine with 9000N.

 

[burningDiesel]

That's indeed very strange, because to get to 9000 you have to pass through 7000 and 8000.
Are you using a dynamic implicit? Probably not.
So what rstupplebeen suggested was probably correct.
Try limiting the maximum allowable time increment (the 4th number at *static) as well.
So use something like 1e-3,1,1e-7,1e-2. (<--- this is VERY dependent on your problem, it's just an example).

 

[squiddi]

I don't use dynamic implicit. I'll try what you suggest as soon as possible, thanks again.
The funniest thing is that if I put 8200N instead of 8000N (or 6800N instead of 7000N) it works!!!
p.s. Not so funny

 

[IceBreakerSours]

Upload your INP.

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[rstupplebeen]

Sounds like you are just getting into a rut in the analysis. Try adjusting the initial increment so that with cutbacks you do not get the exact same steps as before. For example try having the initial increment be 0.011 instead of 1. Nonlinear can be very finicky. I hope this helps.

Rob Stupplebeen

https://sites.google.com/site/robertkstupplebeen/