Identification of anisotropic properties of polymer sheets from heterogeneous biaxial tests

Abstract

The stretch blowing process for PET bottle induces the anisotropic mechanical properties due to the different elongation of macromolecular chains. For example, the Young's modulus can be multiplied by almost two in the longitudinal direction and more than 3 times in the hoop direction of the plastic bottle. However, the process is complex and the elastic properties present dispersions which depend on the process condition. Therefore, it is necessary that the 5 parameters from the orthotropic elastic properties can be all obtained during a single realization. The symmetry of the elasticity tensor reduces to 4 characteristics to be determined. To achieve this identification process, firstly, the displacement field is measured using image correlation and biaxial tests are carried out on a machine developed in our laboratory. Then, the virtual field method on a specific cruciform specimen with a hole is managed to identify the orthotropic elastic properties. The optimal position of the hole is also studied. Finally, the identified orthotropic constitutive parameters from this method are compared to the results obtained by classical methods.

Keywords

• Virtual field method
• Orthotropic elastic properties
• Heterogeneous biaxial test