Biaxial deformation of rubber-like solids: comparison of theory and experiment

The strain-energy function of a rubber-like solid may be characterised by stress-deformation data from experimental tests in which two principal stretches of a homogeneously deformed specimen are varied independently. In the context of the continuum theory of finite elastic deformations, a framework is described within which such experimental results can be assessed. It is based on the separability of the strain-energy function according to the Valanis-Landel hypothesis (1967). This hypothesis is supported by experimental data for a variety of rubber-like solids up to quite large biaxial stretches, and for this reason the strain-energy function is best expressed in terms of principal stretches rather than a pair of independent deformation invariants.