How localized imperfections modify the buckling threshold of cylindrical shells

Shells buckle and collapse at load levels below the thresholds predicted by linear stability analysis. The reduction of the load-carrying capacity has been linked to extreme sensitivity to geometric imperfections. Historically, spatially extended periodic imperfections have been analyzed using linear and weakly nonlinear theory. Recent fully nonlinear approaches suggest however the importance of spatially localized imperfections. We thus characterize experimentally and numerically the effect of spatially localized imperfections in an axially loaded cylindrical shell. For different types of imperfections, the buckling thresholds as a function of its size shows similar behaviour. This suggests a universal failure mechanism due to local buckling.