Characterization of PVA hydrogels’ hyperelastic properties by uniaxial tension and cavity expansion tests

Abstract

The mechanical behavior of rubber-like materials is dominantly non-linear elastic. Their mechanical response is measured by numerous conventional techniques including the universal loading machines (tension and compression) and indentation. Recently, an unconventional technique based on cavitation rheology has been implemented to measure the mechanics of these materials. The loading mechanism of this technique is different from the axial force–displacement mechanism observed in the other techniques thus the aim of this study is to investigate the difference between the cavity expansion technique and one of the conventional techniques, uniaxial stretching, to understand the difference in material responses under each loading mechanism. PVA hydrogel was used as a representative to hyperelastic materials. The gels were loaded by both techniques, and hyperelastic models (Yeoh, Ogden, and Arruda–Boyce) were used to model their behavior. Finite Element (FE) simulations were performed to reproduce the experimental data. It was observed that the tension stresses generated during the cavity expansion test were similar to those generated in the uniaxial tension to a strain level of 45%, afterward, the cavity tension stresses increased exponentially exceeding those generated in the uniaxial tension. When the von Mises stresses, from both tests, were compared against the major tension stress data, it was observed that the cavity test imposed tension stresses that were twice of those generated during the uniaxial tensile test. In addition, the hoop stresses were significantly larger than the applied pressure. These observations indicate to the equi-biaxial nature of the cavity expansion test.