# Why do not the limit stresses when using a nonlinear material match the calculated stresses?

When calculating nonlinear material models (especially for plastic material models), the calculation is always performed in relation to the original constant internal forces. Therefore, the smoothing of FE elements should be set to "Constant" (see Figure 01).

Furthermore, the stresses are related to the principal stresses $\ sigma_1$ or $\ sigma_2$.

Even taking these conditions into account, deviations from the defined limit stress may occur. They usually result from the defined solidification modulus. This fact is explained in detail in the technical article, which you can access under Links below.