Transient swelling of cylindrical hydrogels under coupled extension-torsion: Analytical and 3D FEM solutions

To design more accurate soft sensors and actuators, there is a significant requirement for the application of complicated deformation conditions. Coupled extension-torsion is a type of deformation which may be utilized in the property characterization of materials with complex behavior such as soft hydrogels. Hydrogels with coupled diffusion and large deformation behavior have intricate kinetics which should be studied in detail. In this work, a robust semi-analytical procedure is proposed to capture the transient behavior of cylindrical hydrogels in combined loading of extension and torsion in different conditions. Moreover, the whole problem with the same conditions is simulated in COMSOL-Multiphysics as a verification framework of the proposed semi-analytical procedure, where comparing the results shows a good agreement. The results demonstrate that the transient behavior of the cylindrical hydrogel under coupled extension-torsion is significantly dependent on the rate of the deformation and material properties. Besides, since the hydrogel undergoes a highly nonlinear swelling in this deformation regime, the simulations predict a complicated reaction force and moment. Visualizing the effect of different parameters engaged in the material shows the robust behavior of the proposed semi-analytical procedure, which can be employed in constitutive models’ calibration as well as in the design and optimization of hydrogels structures.