convergence problem in Abaqus standard
convergence problem in Abaqus standard
(OP)
I am running a model for uni-axial compression test for a rock sample, the load is applied through displacement control, where the a rigid platen is forced to move a predefined distance. I used static general step in abaqus. i am facing a convergence problem when a strain softening of the rock sample is adopted.
I am wondering how can i overcome that problem in abaqus standard.
I know that abaqus explicit has more capability to overcome convergence problem. so my question is: how can i use abaqus explicit dynamic to solve a static problem.
Again the model is similar to Uniaxial compression test, the problem comes strain softening of the material.
please help me.
I am wondering how can i overcome that problem in abaqus standard.
I know that abaqus explicit has more capability to overcome convergence problem. so my question is: how can i use abaqus explicit dynamic to solve a static problem.
Again the model is similar to Uniaxial compression test, the problem comes strain softening of the material.
please help me.





RE: convergence problem in Abaqus standard
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RE: convergence problem in Abaqus standard
I wish you could help me IceBreakerSour.
Thanks
RE: convergence problem in Abaqus standard
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RE: convergence problem in Abaqus standard
In .Sta file, 0.224 of the job has been completed. These are the error messages that i found in the .Msg file:-
***WARNING: THE SYSTEM MATRIX HAS 116 NEGATIVE EIGENVALUES.
***WARNING: THE PLASTICITY/CREEP/CONNECTOR FRICTION ALGORITHM DID NOT CONVERGE
AT 96 POINTS
***WARNING: THE SYSTEM MATRIX HAS 8 NEGATIVE EIGENVALUES.
EXPLANATIONS ARE SUGGESTED AFTER THE FIRST OCCURRENCE OF THIS MESSAGE.
8 SEVERE DISCONTINUITIES OCCURRED DURING THIS ITERATION.
8 POINTS CHANGED FROM SLIPPING TO STICKING
***WARNING: THE SYSTEM MATRIX HAS 10 NEGATIVE EIGENVALUES.
EXPLANATIONS ARE SUGGESTED AFTER THE FIRST OCCURRENCE OF THIS MESSAGE.
8 SEVERE DISCONTINUITIES OCCURRED DURING THIS ITERATION.
8 POINTS CHANGED FROM SLIPPING TO STICKING
this message repeated many times.
Again my model is just Uniaxial compression of rock sample, the rock sample is a deformable material, the platens used to apply the load are discrete rigid bodies. There is an interface between the rock sample and the rigid platens. When i solved that model assuming that the mechanical behavior of the material is elastic-perfect plastic, i did not have an problem, while when i changed the material behavior to strain softening which the actual behavior, the model diverges after 0.224 of the job.
I used solution control to overcome the divergence, i changed the residual control factor from 0.005 to 0.01, also i changed the solution correction control from 0.01 to 0.05 and i used analysis = discontinuous.
I am looking forward to your advice.
Thanks
RE: convergence problem in Abaqus standard
Are you new to this forum? If so, please read these FAQ:
http://www.eng-tips.com/faqs.cfm?fid=376
http://www.eng-tips.com/faqs.cfm?fid=1083
RE: convergence problem in Abaqus standard
I used the Riks method, but unfortunately the model did not converge, only 0.29 of the job has been done, and i got that error message.
Too many attempts have made for this increment.
in the Riks method, i used the following information.
Initial arc length = 1
minimum arc legth = 1E-20
max arc length = .1
Again, this model is just a uni-axial compression test for rock sample. the properties of the rock sample are as follow:
E & Newo
300000 0.2
stress & Plastic strain
2000 0
2300 0.005
1500 0.007
900 0.01
200 0.013
As you see there is a strain softening, and that is the main cause for divergence.
RE: convergence problem in Abaqus standard
Are you new to this forum? If so, please read these FAQ:
http://www.eng-tips.com/faqs.cfm?fid=376
http://www.eng-tips.com/faqs.cfm?fid=1083
RE: convergence problem in Abaqus standard