Buckling Knockdown Factors of Composite Cylinders under Both Compression and Internal Pressure

Do-Young Kim,Chang-Hoon Sim,Keejoo Lee,Joon-Tae Yoo,Young-Ha Yoon,Jae-Sang Park

doi:10.3390/aerospace8110346

Do-Young Kim, Chang-Hoon Sim

Open Access

https://doi.org/10.3390/aerospace8110346

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Abstract

The internal pressure of a thin-walled cylindrical structure under axial compression may improve the buckling stability by relieving loads and reducing initial imperfections. In this study, the effect of internal pressure on the buckling knockdown factor is investigated for axially compressed thin-walled composite cylinders with different shell thickness ratios and slenderness ratios. Various shell thickness ratios and slenderness ratios are considered when the buckling knockdown factor is derived for the thin-walled composite cylinders under both axial compression and internal pressure. Nonlinear post-buckling analyses are conducted using the nonlinear finite element analysis program, ABAQUS. The single perturbation load approach is used to represent the geometric initial imperfection of thin-walled composite cylinders. For cases with the axial compressive force only, the buckling knockdown factor decreases as the shell thickness ratio increases or as the slenderness ratio increases. When the internal pressure is considered simultaneously with the axial compressive force, the buckling knockdown factor decreases as the slenderness ratio increases but increases as the shell thickness ratio increases. The buckling knockdown factors considering the internal pressure and axial compressions are higher by 2.67% to 38.98% compared with the knockdown factors considering the axial compressive force only. The results show the significant effect of the internal pressure, particularly for thinner composite cylinders, and that the buckling knockdown factors may be enhanced for all the shell thickness ratios and slenderness ratios considered in this study when the internal pressure is applied to the cylinder.

Highlights

Composite cylindrical shells with excellent specific strength and stiffness have been widely applied to the launch vehicle’s thin-walled structures
The buckling knockdown factor is defined as the ratio of global buckling loads with and without the initial imperfection of a shell structure, and it is used as the buckling design criterion for thin-walled shell structures
The buckling knockdown factors of thin-walled composite cylinders under both axial compressive force and internal pressure were numerically derived in this study

Summary

Introduction

Composite cylindrical shells with excellent specific strength and stiffness have been widely applied to the launch vehicle’s thin-walled structures. This is to accommodate the higher requirements of lightweight design for space launch vehicles in the new space era [1] such that launch costs can be reduced and payload increased. These structures are designed to withstand various loads, they are prone to buckling under axial compression. NASA established the lower bound of knockdown factors (Figure 1, [2])

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