I4CIel solid.CIel11*a01M1^2+2*a01M1*solid.CIel12*a01M2+2*a01M1*solid.CIel13*a01M3+solid.CIel22*a01M2^2+2*a01M3*solid.CIel23*a01M2+solid.CIel33*a01M3^2 Fourth invariant, Media I6CIel solid.CIel11*a02M1^2+2*a02M1*solid.CIel12*a02M2+2*a02M1*solid.CIel13*a02M3+solid.CIel22*a02M2^2+2*a02M3*solid.CIel23*a02M2+solid.CIel33*a02M3^2 Sixth invariant, Media W1 cM/2*(solid.I1CIel-3) Isotropic isochoric strain energy density W4 k1M/(2*k2M)*(exp(k2M*(I4CIel-1)^2)-1)*(I4CIel>1) Anisotropic strain energy density, first fiber family W6 k1M/(2*k2M)*(exp(k2M*(I6CIel-1)^2)-1)*(I6CIel>1) Anisotropic strain energy density, second fiber family Wvol kappa/2*(solid.Jel-1)^2 Volumetric strain energy density