Imperfection Sensitivity of Large Cylindrical Shells Under Vacuum Considering Different Geometric Ratios

Abstract

AbstractThe prediction of the buckling resistance of shells is subject to uncertainty since it depends significantly on the initial geometric imperfections caused by the fabrication process. However, the load case of vacuum or uniform external pressure has not yet been extensively studied. Stress design approaches implement a reduction factor alpha that accounts for the effect of imperfections. This factor is assumed to be a general lower bound but does not account for different geometric ratios. However, it is to be expected that different imperfection sensitivities prevail for different cylinder lengths or length to thickness ratios. To better understand this aspect, a comprehensive numerical study of buckling resistances of imperfect cylindrical shells is conducted, which covers a range of different length, radius and thickness ratios with focus on thicker and shorter cylinders. Within this study, three different geometric imperfection forms are investigated: linear bifurcation eigenmodes, and ovalisation and weld depressions, which represent typical imperfections of manufacturing processes. Further, a formulation for longitudinal weld depressions is introduced, since this direction of the imperfection is more deleterious than axisymmetric circumferential weld depressions. The results of this comprehensive study contribute to understanding the effect of different imperfection forms and amplitudes on different cylinder dimensions.