Fig. 4.

Circumferential–experimental (■), circumferential–strain energy (□), axial–experimental (●), axial–strain energy (○). Cauchy stress versus stretch ratio for the 0:1 (Left) and 1:0 (Right) biaxial stretch testing protocols. Material parameter coefficients used were derived from the 1:1 and 2:1 biaxial stretch protocols for the sample group. To aid in the strain energy fitting visualization, two vertical axes scales were employed, where curves on the right of the plot area correspond to the axis on the right. Units for all vertical axes are MPa.