group_materi_elasti_volumetric_young_values index $\epsilon\_0 ~ \sigma\_0 ~ \epsilon\_1 ~ \sigma_1 ~ \ldots$

This is a special record to model the volumetric stress part of a nonlinear material, given the experimental results of a volumetric compression test (compression in one direction, fixed size in other two directions).

The table $\epsilon\_0 ~ \sigma\_0 ~ \epsilon\_1 ~ \sigma_1 ~ \ldots$ specifies the strain-stress results for the volumetric compression test. Together with the poisson ratio as specified in group_materi_elasti_volumetric_poisson, an isotropic law in a nonlinear Young's modulus and a constant poisson ratio is fitted to this experiment. The Young modulues in fact is taken as the polynomial expansion $E_0 + E_1 \epsilon + E_2 \epsilon^2 + \ldots + E_{n-1} \epsilon^{n-1}$ where $n$ denotes the order of the polynomial expansion (as given in group_materi_elasti_volumetric_young_order).

The poisson ratio should be taken very high, say 0.4999999 or so, to ensure that the resulting law only models volumetric stresses. Then afterwards a normal young-poisson isotropic law (group_materi_elasti_young and group_materi_elasti_poisson) can be added to get an extra deviatoric part.