A point is denoted as plastic failure point if it is currently on the failure envelope (e.g. Mohr-Coulomb envelope). If, due to unloading, the stress state drops below the Mohr-Coulomb envelope the point is no longer a plastic failure point, even though it has undergone irreversible deformations in the past.
This works the same for all types of plastic points: tension cut-off points, hardening points and cap points.
Since PLAXIS 2D 2012, a new option in the Output program is introduced: Plastic Point history. Per type of plastic point, it is now possible to see if in any proceeding calculation step a stress point was ever in this state.