Hi Brad,
I am performing 2D quasistatic simulations using the rate and state friction model. In these simulations I am applying normal tensile traction at the fault to model pore pressure effect on the fault strength.
My problem is the following:

I would like to model a case with very low effective stress. In this situation, I noticed that, due to fault slip and domain deformation, normal stress at the fault decreases causing the fault to open (effective stress >= 0) at some locations.

The nonlinear solver then does not converge anymore, which I suspect is related to the frictionless interface.
I have verified that the nonlinear and linear solvers converges in few iterations whenever 1) normal tractions are not applied at the fault 2) or when the effective stress is large enough to prevent it to be larger than zero.
I know you may need a working version of the problem to provide detailed feedback, which I can prepare if needed. In the mean time, would you be able to comment a little on what is the expect behavior of the nonlinear solver when the fault is in tension (effective stress >= 0) ?
Thank you,
Josimar