Causes of cracks in petaloid bottom of carbonated pet bottle

Petaloid design in bottom for carbonated PET bottles is wide spread. Crack problems exist in the bottom of the bottles. Through this paper we investigated the causes of bottom crack. We examined the physical properties of material and tensile yield stress variations according to the stretch ratio of PET. Then we analyzed stretch ratio and strength in the bottom of blown bottles. We also performed crack tests to observe crack phenomena. The distributions of effective stress and maximum principal stress were examined by computer simulation to seek the influence of bottom design on crack. We concluded that the bottom crack occurs because of not only insufficient strength of material due to the insufficient stretch of PET but also coarse design of petaloid bottom. The stretch ratio at bottom in bottle blowing should be higher than strain hardening point of PET to have enhanced mechanical strength. The crack in the bottom of PET bottles occurred through crazing. The maximum principal stress at valleys in the petaloid bottom of bottles was higher than the other area in the bottom and this maximum principal stress strongly affected the crack in the bottom of bottles.