Structural Mechanics - Strain

[KarasTomas]

Discussion related to pull request #49 following the issue #33.

Current version of strain functionality works with strain tensor:

$$ \boldsymbol{\varepsilon} = \begin{pmatrix} \varepsilon_{11} & \varepsilon_{12} & \varepsilon_{13} \\ \varepsilon_{21} & \varepsilon_{22} & \varepsilon_{23} \\ \varepsilon_{31} & \varepsilon_{32} & \varepsilon_{33} \end{pmatrix}, $$

in a voigt vector notation:

$$ \boldsymbol{\varepsilon} = \begin{pmatrix} \varepsilon_{11} \\ \varepsilon_{22} \\ \varepsilon_{33} \\ \varepsilon_{23} \\ \varepsilon_{13} \\ \varepsilon_{12} \end{pmatrix}. $$

The question is whether this is sufficient for a fatigue analysis.
Or should the version with shear strains, $$\gamma_{12}, \gamma_{23}, \gamma_{13}$$, be implemented as well? Should True vs Engineering strain also be considered?

Few follow up points:

• Should we implement calculations for simple strain cases (uniaxial, no shear, etc.) to reduce computation time?
• Is the current version of Von Mises (component-based) sufficient and correct?
• What other signing methods should be implemented for Von Mises?