Stress monitoring of PET beverage bottles by Digital Photoelasticity

Polyethylene Terephthalate (PET) is used in many packaging applications. PET is especially important in the carbonated soft drink industry, where the pressure of carbonation and the imposed and residual stresses in the bottle bases can sometimes lead to cracking, and failures. In the process of bottle blowing, residual stresses are created and remain in the bottle base as a result of the uniaxial and biaxial stretching in these regions. It is advantageous to measure these residual stresses and the mode of stretching, which may be related to the failure characteristics of the bottle bases. Photoelasticity can be used to examine these residual stresses in the sidewalls and bases of bottles. This work reports on a residual stress measurement tool for the bottle blowing industry.