“…For a hyperelastic material, the nonnegative scalar potential W exists, such that W (X, I) = 0, where I is the second rank unit tensor, and (X, F) = ∂ W (X, F)/∂F T for all tensors F and almost all points X ∈ Ω. For an isotropic material, the potential is a function of principal invariants of a strain measure, for example the left Cauchy-Green tensor B = F · F T [8,9], the Hencky logarithmic tensor H = ln √ B [10,11] or principal values of the left stretch tensor = B 1/2 . All descriptions are equivalent.…”