Universal Features of Buckling Initiation in Thin Shells

Where, when, and how does a thin shell fail? Geometric imperfections are thought to play an essential part in the buckling of a thin shell, but how they interact to control the onset of failure remains unclear. We experimentally probe the initiation of shell buckling using coke cans as a model system. A large dimple is imparted onto the can's surface and is laterally probed with a poker to predict the can's axial capacity. By filming the can's surface with high-speed videography, the nucleation of buckling from axial loading is directly observed, revealing that larger dimples tend to set the initial buckling location. However, the influence of the can's background geometric imperfections can still occasionally dominate, causing nucleation to occur far from the dimple. In this situation, probing at the dimple leads to an overprediction of the axial capacity. Furthermore, when buckling does initiate at the dimple, a surprising universal feature emerges; even though different cans show a range of axial capacity, all cans whose buckling initiates at the prescribed dimple exhibit a similar critical deflection at the dimple. Together, these results hint that a better understanding of the initial buckling location may allow for better predictions of the onset of failure.