mesh problem
mesh problem
(OP)
I am modeling a uni-axial compression test for a rock sample using concrete damage plasticity approach, i found when the element size is 0.1 the model diverges while when the element size is 0.15, there is no divergence problem and the model reaches equilibrium.
the size of the mode is 2 in x 2 in
anybody has an explantion for that.
the size of the mode is 2 in x 2 in
anybody has an explantion for that.





RE: mesh problem
i expect the model diverges when the element size is bigger.
Thanks
RE: mesh problem
RE: mesh problem
RE: mesh problem
RE: mesh problem
RE: mesh problem
Thanks for your advice.
RE: mesh problem
in tools -> job diagnostics you can see where exactly the problem is in your simulation i.e. what element(s) is giving trouble.
RE: mesh problem
RE: mesh problem
The model is just uni-axial compression test for rock sample, i used static general approach.
you can see that the element size for this model is 0.25. when i try to make element size smaller (0.1) the model diverges, i do not know why. please try to help me.
Thanks
RE: mesh problem
RE: mesh problem
I sent you the CAE file, you can see that when the element size is 0.25 the model converges, while if you change it to 0.2 for instance, it will diverge.
could you please help me, i need to understand why this happens and i need to use finer mesh in my model.
Thanks.
RE: mesh problem
I would not dismiss it as being a mesh problem, are you sure your material data is correct?
Try solving the compression using boundary conditions (vs the contact you do now) first.
RE: mesh problem
I took you advice and solved the model without the contact. i applied the load directly to the model, it works and and the mesh problem disappeared. That means that the contact was the main cause for the problem.
However i need to apply with contact.
So you helped me to know that the contact between the rigid platen and the coal sample is the main cause of the problem.
what should i do next?
Thanks.
RE: mesh problem
RE: mesh problem
When i run the model with friction-less contact, in Abaqus viewer, i do not see the rock sample, i think since this friction-less model, the rock sample slides out of the rigid platens. so what i did is just remove the rigid platens and apply the load directly to the rock sample, i believe this is equivalent to the friction-less model. I did not find any problem with the model, no warning message, no error.
When i run the model again with contact, the rigid platen moves 0.02 inch & element size = 0.1 and the coefficient of friction = 0.1. I got many warning messages and the model diverges. this is an example of the warning messages:
The plasticity/creep/connector friction algorithm did not converge at 2 points
The plasticity/creep/connector friction algorithm did not converge at 1 points
The plasticity/creep/connector friction algorithm did not converge at 56 points
The plasticity/creep/connector friction algorithm did not converge at 21 points
While when i keep the load as it is an changing the element size from 0.1 to 0.2, the model converges.
Please note that, if i want to increase the load (increase the displacement of the rigid platen from 0.02 to 0.03 in), i have to increase the element size again.
I wish you understand my problem.
Thanks for helping me.
RE: mesh problem
RE: mesh problem
You mean i have to fix on of the nodes of the deformable rock sample, right? You know i am testing this rock sample between two rigid platens, one of them is fixed and the other one can move only in the vertical direction to apply the load.
So you want me to fix one node for the rock sample?
thanks
RE: mesh problem