Real Shells Exhibit a Universal Localized Buckling Mode with Marginal Imperfection Dependence, Part II: Experimental Results*

An understanding of the nuanced relationship between the failure properties of real shells and their defects remains elusive.  We have developed an experimental system that allows for direct, non-destructive, characterization of a commercial soda can's geometric defect structure (w₀) as well as its radial deformations (w) under axial loads (F_a).  We predict the initial buckling location of our imperfect shells, later confirmed with high-speed videography, using numerical solutions to the equilibrium von Kármán-Donnell equations.  Poking at the predicted location enables non-destructive accurate measurements of the critical axial load (F_c) to within 1%.  By imaging below F_c, we directly observe and characterize our shell's buckling eigenmode in the experimental system.  Shells exhibit a localized buckling mode, consistent with simulations, whose shape is marginally dependent on the underlying defect structure of the shell.  Together, these results change our fundamental understanding of the role of localization and imperfections in the failure of thin shells.