Abstract
<title>Abstract</title> <p>This work investigates the mechanical response of an incompressible hyperelastic cylinder subjected to pure torsion and combined tension–torsion loading. The constitutive behavior is described using the Pucci–Saccomandi model, which combines the Gent finite extensibility potential with a logarithmic term depending on the second invariant of the Cauchy–Green tensor. The formulation is developed in terms of principal stretches, allowing the derivation of general expressions for the stress components as well as the resultant quantities, namely the axial force and the torque. The results reveal a pronounced strain-stiffening behavior under torsion, together with a strong coupling between axial stretch and twist. In particular, the model predicts the possibility of a reversal of the Poynting effect depending on the choice of material parameters. These findings highlight the ability of the proposed framework to capture complex nonlinear interactions in elastomeric materials under multiaxial loading. The present study provides a consistent theoretical basis for the experimental identification of constitutive parameters from combined loading tests and offers useful insights for the modeling and design of elastomeric structures subjected to coupled deformation modes.</p>