Material point failure 1

[sgdon]

Dear memebers,

can anyone explain the reason why a material point would failed to converge in an increment step for a numerical analysis. I am using Abaqus/Explicit.

Thanks.
sgdon

 

[EdR]

Sgdon:

Not familiar with Abacus' quirks but some general possibilities are:

1. Material property (model) improperly defined
2. Max. load reached and material continues to yield and structure to deflect in this area.
3. Time step too large

Hope this helps...

Ed.R.

 

[sgdon]

Hi EdR, thanks for your reply.

The material model is definitely correct. For the 2nd point, can i assume that the continued yielding or deflect of the material has caused the element grossly distorted, resulting in material point failure? For the 3rd pointer, can you explain the rationale why a big time step can cause material point failure?

I apologise for not descibing the problem more completely, the failed elements are involved in a contact situation. Can this be a possible cause as well? If yes, how?

Thank you so much.

sgdon

 

[EdR]

Generally you should see a gross distortion if the 2-nd point is true however depending on the model "gross" may not be as big as you might expect....

Large load increments in nonlinear problems can induce a situation where convergence of the model will not occur...e.g a diverging oscillation in the solution will occur...this tendency may be exagerated in dynamic problems, particularly where contact is involved, the thing to look for is "large" accelerations that continue to change sign and grow....specifically when dealing with contact problems you may also encounter the situation where one element generates large contact forces and the adjacent elements separate...this situation leads to the same kind of divergent solution described above...

Hope this helps....

Ed.R.