Test MethodCharacterization of hyperelastic rubber-like materials by biaxial and uniaxial stretching tests based on optical methods

Rubber-like materials exhibit a particular stress-strain behaviour known as hyperelasticity. Several models are available in the literature for these materials, based on the definition of a particular expression of the specific potential deformation energy. Among these, Mooney-Rivlin and Ogden models are the most used. In both cases, at least uniaxial and biaxial stretching tests are required to fit the model and extract material parameters. In this work, an experimental rig was set up to carry out equi-biaxial tests: the classic bulge test method has been coupled with optical devices allowing measurement in real time of the stress and elongation levels of the specimen. Uniaxial stretching tests were performed by means of a standard tensile machine and a video extensometer. Quasi-static experimental results were used to calibrate hyperelastic models. Finally, a planar tension test was carried out to validate the material models fitted from uniaxial and equi-biaxial data. FEM simulations of the test procedures give a useful comparison between numerical and experimental data.