The Effects of Favorable and Unfavorable Geometric Perturbations on the Response of Pressure-Loaded Hemispherical Shells

Abstract

Hemispherical shells subjected to external pressure loading are known to be sensitive to geometric imperfections. Dimple imperfections and their effects on the buckling and postbuckling response of spherical and hemispherical shells under externally applied pressure loads have been widely studied. The studies have shown that dimple imperfections are unfavorable, and their presence leads to a drastic lowering of buckling pressure, the severity being dependent on the radius-to-wall thickness ratio of the shell. Motivated by a plenary lecture presented by Hutchinson, we have conducted equilibrium analysis through finite element computations of externally pressurized hemispherical shells to understand if we can intentionally design shells with initial geometric perturbations that are favorable to resisting external pressure. We have studied dimple imperfections that can either increase or decrease the local curvature. We show that outward pointing dimples outperform inward-pointing dimples in such a structure and hence can be viewed as being favorable with regards to shell buckling under external pressure. With advances in precision manufacturing, the results presented here serve as a guide to designing shells with intentional perturbations to the initial shell geometry that can lead to favorable outcomes.