UMAT convergence problem

Hi,

Im simulating the behavior of anisotropic material using a UMAT subroutine. The UMAT works fine when using single element. However, when I use multiple elements (C3D8R), I get convergence problems.

The problem is as follows:
The simulation stops suddenly with error Too many attempts...... The point where the simulation stops depend on the elements size. When I increase the element size (coarser mesh) I get better convergence, but for finer meshes, the simulation isnt completed.

Ive tried to increase the hourglass stiffness, and I found that for higher values, the simulation is completed, but the resulting forces are higher !

Is this problem coming out from the definition of the DDSDDE matrix inside the UMAT, or its a result of using reduced elements (C3D8R)?

Thank you in advance.

Best Regards.

Abaqus Standard has by default an upper limit of 100 increments per step.
Set the parameter INC to the command STEP.

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Good luck

Frank