Comparing the buckling strength of spherical shells with dimpled versus bumpy defects

TL;DR

This study compares how inward dimpled and outward bumpy defects affect the buckling strength of spherical shells, revealing that bumpy defects lead to higher buckling resistance and different post-buckling behaviors, based on finite-element simulations.

Contribution

It provides the first systematic comparison of dimpled versus bumpy defect geometries on spherical shell buckling strength using validated finite-element models.

Findings

Bumpy defects result in higher knockdown factors than dimpled defects.

The relationship between defect parameters and buckling strength differs between defect types.

Distinct post-buckling behaviors are observed for the two defect geometries.

Abstract

We investigate the effect of defect geometry in dictating the sensitivity of the critical buckling conditions of spherical shells under external pressure loading. Specifically, we perform a comparative study between shells containing dimpled (inward) versus bumpy (outward) Gaussian defects. The former has become the standard shape in many recent shell-buckling studies, whereas the latter has remained mostly unexplored. We employ finite-element simulations, which were validated previously against experiments, to compute the knockdown factors for the two cases while systematically exploring the parameter space of the defect geometry. For the same magnitudes of the amplitude and angular width of the defect, we find that shells containing bumpy defects consistently exhibit significantly higher knockdown factors than shells with the more classic dimpled defects. Furthermore, the relationship of the knockdown as a function of the amplitude and width of the defect is qualitatively different between the two cases, which also exhibit distinct post-buckling behavior. A speculative interpretation of the results is provided based on the qualitative differences in the mean-curvature profiles of the two cases.