Measuring Hyperelastic Properties of Hydrogels Using Cavity Expansion Method

Abstract

Numerous methods have been proposed to measure the mechanical properties of hyperelastic materials such as hydrogels. Common techniques, such as tension, compression, and indentation test, experience various challenges due to material structure and surface conditions. These challenges affect the measured mechanical properties of the tested material. Therefore, a new technique is proposed to measure the hyperelastic mechanical properties of hydrogels by introducing cavity deformations to the internal solid structure of hydrogels. The data obtained from the cavity test were analyzed mathematically by using three strain energy functions and then were validated numerically through finite element (FE) simulations. Computed Tomography (CT) imaging was implemented to investigate the shape of the cavities, which showed that the proposed technique is capable of applying controlled spherical deformations. The stresses in the cavity test were generated in the radial and hoop directions; therefore, the validation process took into consideration both types of stresses. The numerical simulations considered the two common views about hyperelastic materials: slightly compressible and incompressible. A comparison between experimental results and FE simulations of the cavity test has shown a good agreement in pressure-deformation data.