IMPLEMENTATION AND PRACTICAL APPLICATION OF NON-EQUIVALENT BIAXIAL MEASUREMENTS FOR HYPERELASTIC MATERIALS

In the case of hyperelastic material models, it is not possible to reliably fit the parameters of the constitutive model to general load cases from a single set of uniaxial measurements. In order to obtain a more accurate model, different measurements are used, but these are very complex and difficult to perform in most cases. The most commonly used measurement datasets for fitting are data from uniaxial and biaxial tensile tests and constrained uniaxial loading (planar tension), but due to the complexity of the measurement implementation, fitting is often done with less data. It can be seen that the stress-strain relationship obtained for the uniaxial and equibiaxial test cases envelops the case of planar tension from two sides, the application of which helps to define a better material model. Treloar’s dataset also describes three different cases of experiments, in which the results of these tensile experiments were analysed. However, if we perform biaxial measurements and can control the displacements along the two axes independently, we may be able to generate a new dataset that is neither uniaxial nor equibiaxial measurement data, this dataset describes an intermediate state. This way, we are also able to make other types of measurements in the same measurement setup, which can lead to a more accurate result when fitting a material model.