Strain Field Measurement on 3D Surfaces: Application to Petaloid Base of PET Bottles under Pressure

Abstract

Validation of stretched blown bottles of polyethylene terephthalate (PET) by using numerical simulation is an important industrial goal. This necessitates the identification of the PET material characteristics. Because the biaxial elongation of macromolecules induces great modifications of the mechanical properties of the material, it is difficult to manage an accurate simulation: properties are not well known in the base or neck region of the bottles.

The aim of the work presented here is to provide an identification tool for the orthotropic elastic properties in the 3D regions of PET bottles of carbonated soft drinks. More specifically, we focus on the behavior of the petaloid bases when bottles are submitted to internal pressure like during burst or ESC (environmental stress cracking) tests. A stereo correlation tool has been developed in order to build digital 3D surface; comparing the initial surface with the same surface when the bottle is under pressure, it is possible to evaluate the membrane strains at each point of the petaloid surface. Two bases, one with large valleys (LV) between the five feet and one with small valleys (SV) which highlight very different behavior at the ESC test, are compared with this tool. Coupled with a finite element simulation managed on the same bases, these results allow the identification of the induced mechanical properties. The LV case presents specific characteristics that are discussed in the last section of the paper.