A visco-hyperelastic model for hydrogels with different water content and its finite element implementation

The visco-hyperelastic properties of hydrogels, which are greatly influenced by water content, play a crucial role in the potential applications in cutting-edge fields. Therefore, quantifying the effect of water content on the visco-hyperelastic behavior of hydrogels is necessary. In this work, we have proposed a visco-hyperelastic constitutive model which considers the water content for large deformation of hydrogels by introducing internal variables that can characterize the viscous dissipation. In the model, the evolution equation of the internal variable is established to achieve the coupling of viscoelastic and hyperelastic responses. To further understand the influence of water content on the visco-hyperelastic behavior of hydrogels, we modified the power-law relationship between water content and initial modulus through experiments. The accuracy of our visco-hyperelastic model is validated by uniaxial tension and relaxation experiments on hydrogels with varying water content. To facilitate the application of the constitutive model, we implement the constitutive model into ABAQUS user subroutine UMAT through constructing linear interpolation function. The results of the finite element analysis further confirm the capability of proposed model to describe the viscoelastic response of hydrogels under complex loading conditions.