Abaqus Convergence Problem in Press Unloading Step

[EthanSun]

Hi everyone,
I'm working to apply a load and unload process to a ring part along with a core part in the center.

There are two discrete rigid cylinder, one under and one above, and are not showed to make it more clear.

I made two steps, one is load and another is unload. In the load step I set a -0.5 displacement of the rigid body in z direction and in the unload step 0. The problem is, the job exited with error due to convergence problem at the beginn of unload step. So in the result I can only see the load process. It need to be pointed out that the model works fine with some material in Abaqus and the failure only happens when I apply the User Material.

Up to now I trid the following solution but none of them worked:
1. change the element type(I'm using C3D10M now)
2. use amplitude tabular to make load and unload process in one step
3. change the parameter in the step (which is most commonly used)
4. refine the mesh

I have trid a lot of times but cannot find a solution, so I turn to you for help. Any suggestion would be appreciated!

Thank you in advance for the time

 

[DrBwts]

If its only happening with your UMAT then that suggests to me that your UMAT is only well defined during compression.

 

[EthanSun]

Hi DrBwts

Thank yoo for the answer. The UMAT has been used in other similar job and worked well. So will it fail still in certain situation?