Solved T1830 Add eigenstrain calculations for Ovronnaz

Attention: an applied strain F₁=F with zero Eigen strain E₁ = 0
does not equal a zero applied strain F₂=0 with an Eigen strain E₂=
¹/₂(FᵀF-I). Both cases have the same material stress (Second
Piola-Kirchhoff), but not the same nominal stress (First Piola-Kirchhoff)