Buckling of Isotropic and Composite Cylindrical Shells with Circular Cutouts

Abstract

Predicting the critical buckling load of cylindrical shells with circular cutouts subjected to uniform axial compression is an important part of the structural design in the aerospace industry as buckling significantly reduces the load-carrying capability of the structure. A cutout constitutes a major disruption in the shell geometry, and therefore it should be expected that it has a significant effect on the sustainable buckling load. An analytical solution for estimating the buckling load of isotropic and quasi-isotropic composite cylindrical shells with circular cutouts is developed to assess changes made to the geometry and the material during the preliminary design phase quickly. The Ritz method is employed to minimize the total potential energy of an ideal shell that contains a central opening in order to predict a linear buckling load. Finite element simulations are conducted to verify the accuracy of the analytical solution. In addition, they are used to investigate the evolution of buckling modes, the effects of initial geometric imperfections, as well as the shell failure mode. The nondimensional curvature parameter α can be used to categorize the buckling behavior of cylindrical shells and is a function of the cutout radius, the shell radius, and the shell thickness. A small cutout has virtually no influence on the buckling load compared to a pristine shell and the displacement pattern at buckling is global. The buckling load decreases rapidly for moderately large cutouts where the stability loss is the result of a local buckling mode that immediately leads to global buckling. Cylindrical shells with large cutouts are again relatively insensitive to an increase of the cutout size, but the buckling load is greatly reduced relative to a shell without a cutout. Large openings also feature a stable local buckling mode where substantial lateral prebuckling displacements emerge before the structure buckles globally. While the analytical procedure theoretically should not capture the onset of global buckling independent of local buckling, it follows numerical trends for cutouts of moderate and large size regardless. Therefore, it may be used during preliminary design to estimate the impact of changes made to the shell geometry and material. Local buckling is caused by high compressive stresses next to the cutout and, in some cases, large lateral prebuckling displacements. The detrimental effect of the stress field may be partially relieved in composite cylindrical shells by reducing the amount of axial bending stresses that occur. Hence, the chosen stacking sequence can have a significant influence on the buckling load of shells with moderate and large openings.