Poisson's ratio
At finite strains, the relationship between the transverse and axial strains formula_55 and formula_56 is typically not well described by the Poisson's ratio. In fact, the Poisson's ratio is often considered a function of the applied strain in the large strain regime. In such instances, the Poisson's ratio is replaced by the Poisson function, for which there are several competing definitions. Defining the transverse stretch formula_57 and axial stretch formula_58, where the transverse stretch is a function of the axial stretch (i.e., formula_59) the most common are the Hencky, Biot, Green, and Almansi functions