Fig. 3.

Circumferential–experimental (■), circumferential–strain energy (□), axial–experimental (●), axial–strain energy (○). Cauchy stress versus stretch ratio for the 1 to 1 (Left) and 2 to 1 (Right) change in biaxial stretch testing protocols. The stresses based on the strain energy function along with the experimentally measured stresses are plotted against the corresponding primary stretches (axial and circumferential).