confusing issue.

[Simon012]

Hello
I was calibrating a simple model (Uniaxial compression test). the model is just one element C3D8r. the model is elastic-perfect plastic. Please see the attached input file.

i run the model two times. one time i used displacement control to apply load on the model, the second time i used a distributed load on the top surface of the model.

When i used displacement control (-0.1), the model converge, while when i used distributed load control (1000 psi), the model did not converge. please note that the deformation resulting from the displacement control (-0.1) is higher than that from the load (1000 psi)!! and the applied load is little bit higher than the yield point. note that the yield stress is 900 psi

What confused me more are:
1- the model converges when i use displacement control (-0.1 in) to load the model.
2- the model "does Not" converge when i used load (1000 psi).
3- when i apply "both" the load and displacement on the top surface of the model,i.e, (1000 psi & -0.1 in) the model converges.

Can anyone explain that to me.
Thanks

 

[Simon012]

Any body has any comment?

 

[IceBreakerSours]

This is an age-old problem. Load control causes instability whereas displacement control does not. There is plenty of information available on the internet about this. If you must use load control, there is another option known as the Riks method. It simply uses displacement control to match the loads.

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