The cross-sectional geometry regulated Poynting effect in ribbed silicone rubber tubes

With the increasing and refined applications of silicone rubber devices in the biomedical field, it is of great significance to accurately describe and predict the mechanical behavior of them under large deformation. This paper finds that after considering the influence of higher-order shear strain on the normal stress, the Poynting effect in ribbed silicone rubber tubes with certain cross-sectional shapes exhibits a new phenomenon—a non-monotonic trend between axial deformation and twist angle. This paper develops a nonlinear finite element program for simulating large deformations of hyperelastic materials, and studies the Poynting effect in ribbed circular tubes of twisted silicone rubber. The results show that in the ribbed circular tubes with a porosity between 12% and 40% (with the number of ribs ranging from 12 to 26), there appears a normal to reverse conversion of the Poynting effect, that is, the axial extension ratio first decreases and then increases during a monotonic loading process, indicating that the influence of higher-order shear strain on normal stress cannot be ignored when the cross-sectional shape is complex. Especially in ribbed circular tubes with about 20% porosity, a substantial change of axial normal strain from −0.035% to 0.035% can be achieved within a twist angle range of 180°. Based on this, the quantitative influence of higherorder shear strain on normal stress is studied. These research results provide a theoretical basis for accurately controlling the axial expansion and contraction of twisted parts and indicate that a normal to reverse conversion of the Poynting effect can be implemented by designing the cross-sectional shape under certain conditions.