Error: Failed to compute elastoplastic strain variables

Problem Description

Why do I get the error Failed to compute elastoplastic strain variables when using plasticity/concrete/soil plasticity?

Solution

This happens because the elastoplastic element cannot evaluate a plastic step if the current stress state is outside of the yield surface. There are three typical situations where you may encounter this problem:

In the first load step

The elastoplastic element fails to evaluate the consistency conditions (due to either loads, displacements, initial stress/strains), and it fails to compute the first elastic-predictor step. That is, your initial state, e.g. assumed in-situ stresses in a geomechanical problem are outside the yield surface.

During postprocessing

When results are requested at other positions than the Gauss points, the elastoplastic element actually performs a stress computation. If the gradients of the elastoplastic strains are a large within an element this computation may fail. If this happens, use the Gauss point variables such as solid.sGpx instead of general variables like solid.sx.

While solving

The error might also be triggered by sharp transitions in loads or material parameters (for example if the material is temperature-dependent) when these depend on time or auxiliary sweep parameters. If so, make sure that the parameter or time step is fine enough to resolve the transition, either by using a shorter step or making the transition smoother. It can also help to change the Predictor to Constant in the Parametric solver settings.

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