“…The general single-variable functions that depend on a principal stretch , appearing in , facilitate the construction of a specific form of strain energy function from experimental data. We note that, recently, separable single-variable strain energy functions have been used to model both elastic and non-elastic solids [ 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. We note in passing that, it is shown in Shariff [ 14 ], the constitutive Equation ( 19 ) has successfully predicted the mechanical behaviour of soft tissues.…”