The role of imperfection geometry in the buckling of thin spherical shells

The elastic buckling of thin spherical shells under external pressure is sudden and catastrophic, often driven by geometric imperfections several orders of magnitude smaller than the shell radius. Recent work has demonstrated that under uniform external pressure, the reduction of the critical buckling load caused by a localized imperfection can be precisely predicted using a priori knowledge of the defect geometry, opening the door for further work towards understanding the complex and fascinating imperfection sensitivity which pervades their mechanics. Merging desktop stereo-lithography 3D printing with recently developed techniques for introducing symmetric, dimple-like defects into the shell’s mid-surface, we utilize a combination of precision experiments and results from classical shell theory to investigate the effects of defect amplitude, angular width, and localized thickness variation in the reduction of the buckling strength of spherical shells under uniform external pressure. Then, to explore the role of defect shape, we present a technique to create asymmetric defects which allows for systematic variation of the amplitude and degree of asymmetry of the imperfection. Utilizing a point-loading probing scheme, we characterize the stability landscape and evaluate the variation of the buckling strength over a range of pressurization levels and applied probe forces.