Table 2.

The parameters in the strain energy function for each of the constitutive phases in the tissue. The data are fitted to the constitutive models in Holzapfel and Gasser (2000).

Strain energy function	Holzapfel and Gasser (2000)	Present model
Matrix W(0)	μ(I1 − 3)/2	μ(I1 − 3)/2 − μ ln I3 + (κ/2 − μ/3) (I3 − 1)2
Collagen fibers $W_{\mathit{fiber}}^{(r)}$	$\frac{k_1}{2k_2}\{exp[k_2{(I_4-1)}^2]-1+exp[k_2{(I_4^{\prime }-1)}^2]-1\}$	$E_1{(\lambda -{\lambda }_0^{(r)})}^2/2+E_2{(\lambda -{\lambda }_0^{(r)})}^3/3$
Parameters	μ = 0.300kPa	μ = 0.375kPa, κ ≫ μ
	k1 = 0.562kPa	E1 = 5.0 kPa
	k2 = 0.7112	E2 = 45.0kPa