Abstract: Material nonlinear problems that involve loading conditions that produce stresses outside the quasi-proportional limit (e.g., sequential loading and unloading with reverse plasticity) can now be solved in StressCheck® using the incremental theory of plasticity (ITP). The implementation of the ITP is rate (time) independent and considers the von Mises yield criterion and the associated J2 flow rule with isotropic/kinematic (mixed) hardening for 3D, plane strain, plane stress, and axisymmetric analysis.