A hyper-viscoelastic constitutive model is developed to
investigate the material properties of uniaxially compressed
cylindrical liver tissue under torsional shear loading. It
utilizes a single parameter Neo-Hookean material model to
characterize the quasi-static hyperelastic behavior of liver
tissue under large deformations and a twelve-parameter
viscoelastic model to characterize its rate and strain-
history-dependent behavior. Hence, the total stress response
of the liver tissue under combined loading of compression
and torsion is expressed as σ t ¼ σ e þ σ v , where σ e and σ v are
the hyperelastic and viscoelastic Cauchy stress tensors