Table 1.

Four forms of the anisotropic strain energy function considered

Model	Model A	Model B	Model C	Model D
	Fiber strain energy
$W_f^{\ast }({\lambda }_t^2)$	$=\frac{\eta }{\gamma }[e^{\gamma ({\lambda }_t^2-1)}-1]$	$=\frac{\eta }{\gamma }[e^{\gamma ({\lambda }_t^2-1)}-1]$	$=\frac{\eta }{2}({\lambda }_t^2-1)$	$=\frac{\eta }{2}({\lambda }_t^2-1)$
	Fiber recruitment
	Abrupt commences at λ > 1	Abrupt commences at λ > 1	Gradual commences at λ = 1	Gradual commences at λ ≥ 1
d1(λa)	= δ[λ–λa1]	= δ[λ–λa1]	$=\{\begin{array}{ll}{\mathrm{\Gamma }}_{\mathit{PDF}}\hfill & {\lambda }_a\ge 1\hfill \\ 0\hfill & {\lambda }_a<1\hfill \end{array}$	$=\{\begin{array}{ll}{\mathrm{\Gamma }}_{\mathit{PDF}}\hfill & {\lambda }_a\ge {\lambda }_{a1}\hfill \\ 0\hfill & {\lambda }_a<{\lambda }_{a1}\hfill \end{array}$
	Fiber orientation
ρ2D(θ)	= πδ[θ]	General	General	General