Table I.

Examples of polyconvex functions to be used in constructing W. All the terms reported here ensure a stress-free reference configuration. The fourth function adapts the idea presented in Gasser et al. [39]; the symbol 〈·〉 represents the Macaulay brackets 〈·〉=0.5((·) + |(·)|).

Response type	Φi(C(u))	Notes
Isotropic	${(\frac{I_1^b}{I_3^{b/3}}-3^b)}^a$	a ≥ 1, b ≥ 1
	${(\frac{I_2^{3b/2}}{I_3^b}-3^{3b/2})}^a$	a ≥ 1, b ≥ 1
Anisotropic	${\langle I_4^b-1\rangle }^a$	a ≥ 1, b ≥ 1
	${\langle b\frac{I_1}{I_3^{1/3}}+(3-3b)I_4-3\rangle }^a$	a ≥ 1, b ∈ [0, 1]
	〈(I1I4 – I5)b – 2b〉a	a ≥ 1, b ≥ 1