[GeoMechanicsApplication] Add output item SHEAR_CAPACITY

[avdg81]

Aim

As a developer (or user), I would like to be able to assess the shear capacity of a soil body (assuming I'm adopting a Mohr-Coulomb material model). To this end, I would like to have a SHEAR_CAPACITY output item at integration point level.

Acceptance criteria

Given a Kratos model part that has been assigned a Mohr-Coulomb material model;
When the user requests the output item SHEAR_CAPACITY;
Then for each integration point in the given model part the shear capacity is calculated and written to an output file for further postprocessing.

Given a Kratos model part that doesn't have a Mohr-Coulomb material model assigned;
When the user requests the output item SHEAR_CAPACITY;
Then a warning is raised that the SHEAR_CAPACITY cannot be calculated, since the assigned material model doesn't support it.

Implementation details

• Make sure that you define, create, and register a new application variable named SHEAR_CAPACITY:
  • geo_mechanics_application_variables.h: define it.
  • geo_mechanics_application_variables.cpp: create it.
  • geo_mechanics_application.cpp: register it.
• Make sure that a bug in the calculation of Lode's angle has been fixed.
• Extend the CalculateOnIntegrationPoints(const Variable<double>&, ...) member functions of all relevant element classes (UPwSmallStrainElement, SmallStrainUPwDiffOrderElement, ...) such that they can calculate the shear capacity.
• For the calculation of the shear capacity, reuse the utility function StressStrainUtilities::CalculateMohrCoulombShearCapacity. It requires the cohesion $c$ and the friction angle $\phi$, as well as the current stress vector for each integration point (e.g. taken from data member mStressVector).