Fig. 4.

The stretching energy φ(J) (top) adapted from Goldstein and Leibler (1989) for a temperature T ~ 30^∘C, with related local stress ${\phi }^{\prime }\left(J\right)=\tau \left(J\right)$ (bottom). The areal stretch $J_o=1$ corresponds to the unstressed reference configuration ${\mathcal{B}}_0,$ while Σ_M indicates the Maxwell stress.