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Abaqus: Using Riks method always has negative LPF Increment.

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siranjoy

Mechanical
Feb 21, 2014
1
Hello everyone

Now I am using abaqus to calculate post-buckling problems of a plate under lateral compression load with two lateral boundaries simply supported and one longitude end simply supported and the other longitude end free. After introducing imperfection in the thickness from eigen mode, I use Riks method to do the iteration. Here I used displacement load in the lateral b.cs. But during iteration, I always see negative LPF Increment after loading to some step, which means unloading from previous step. The worse thing is the cycling between loading and unloading. I can not obtain the fully-loaded state no matter how many increments I use.
I think the model can sustain continuous increasing load. Why the Riks method can never get out of the loop of loading and unloading. I saw some other people got this problem too. Does this relate to bifurcation point? And how can I solve this problem?

Thanks for your kind reply.
O(∩_∩)O
 
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