Hello,

I am using Abaqus 2022. I have an issue with a simple straight beam loaded by in-plane moment and an out-of-plane force at right end. With nonlinear deformation turned OFF there are no problems but when nonlinear deformations are turned ON I am running into convergence problems.

The model is as follows:

1. Beam of length 60 is discretized into 240 B31 elements.
2. E = 1.0E7 and G=3.76E6 (linear elastic).
3. Cross-section is circular with radius 0.2.
4. Left end is clamped (all DoFs).
5. Mz = 120 is applied at first step and incremented by 60 from step 2 through step 22.
6. Fz = 0.5 is applied at first step and incremented by 0.25 from step 2 through step 22.

I tried different modifications like:

1. Turned OFF nonlinear deformations – analysis runs to completion but is just a scaled solution of simple linear beam analytical solution.
2. Retained nonlinear deformations but turned OFF Fz force - analysis runs to completion but deformation is completely in-plane.
3. Changed beam type from B31 to B33 – analysis fails at end of step 2.
4. Increased mesh density - analysis fails at end of step 3.
5. Applied Fz at 1st step and held constant through rest of the steps - analysis fails at end of step 3.
6. Decreased Fz by orders of magnitude to 1.0e-6 in first step and held constant through rest of the steps - analysis fails at end of step 6.

Does anyone have suggestions or explanation to understand what is going on? I would have expected the model to converge.

Thanks,

Vikram