Hyperelastic Materials Characterization by Planar Tension Tests and Full-field Strain Measurement

Abstract

Several techniques for full-field strain measurement are nowadays available and reliable, and the topics of research should be to find well suited methods and procedures to use the great amount of data in an appropriate and sharp way. In this terms, one of the best and effective techniques developed in recent years is the Virtual Field Method (VFM). In this paper a Digital Image Correlation technique is applied to acquire strain fields on flat rubber specimens with different aspect ratios. They are loaded with a standard traction machine and the different types of geometry generate heterogeneous tensions distributions (from uniaxial up to more and more biaxial). A recursive numerical procedure is proposed in order to find the best fit material dependent parameters of a particular hyperelastic model. Global load data, deformation data of the surface of the specimen and stress distribution data obtained starting from a guess set of constitutive law parameters are used to calculate the terms and coefficients of the VFM equations. Two independent virtual fields are involved in the procedure to use as many as possible available data. After a recursive process where the global error defined from VFM equations is minimized and combining together data from all specimen geometries, it is possible to obtain a set of material parameters able to reproduce a heterogeneous planar tensional state.