Nonlinear models can fail to converge for many reasons. In a model with plasticity that is loaded with a force, one reason the solver can fail to converge is that the solution has reached the ultimate load capacity of the structure and there is no static equilibrium at the next increment of force. If you plot the force-displacement curve and the slope is approaching zero, that is evidence that this is the reason for the failure to converge.
The corrective action is to change from a force loaded model to a displacement loaded model. While the solver will fail to converge as the force-displacement curve approaches a zero slope, the displacement loaded model can continue to increment the displacement to the next increment, but the reaction force will decrease.
Please plot the force-displacement curve and show the slope. Note: you have to require the solver to take small time increments by using a large value for minimum substeps to get many points on the force-displacement curve.
Clear the mesh and File Save As to a new file name that you can create a Workbench Project Archive .wbpz file to attach to your reply.