Simplified Methodology for Prediction of Critical Buckling Pressure for Smooth-Bore Composite Cylindrical Shells

Abstract

The critical buckling pressure of composite cylindrical shells can be pre dicted using linear eigensolutions or geometrically nonlinear instability calculations. Classical linear eigensolutions generally overpredict the critical collapse pressure by a sig nificant margin. Nonlinear instability calculations tend to provide more accurate results but at a greater cost. A simple accurate method for predicting critical buckling pressures is needed to reduce the time and cost associated with generating preliminary structural designs for composite pressure hulls. In this article, simple closed form equations for the critical buckling pressure of smooth-bore composite cylinders were developed and vali dated. The equations are valid for both solid and sandwich shell configurations. These equations are a modification of the classical Von Mises eigensolution for isotropic cylin drical shells with length to diameter ratio's varying between 0.5 and 8. The modified equa tions take into account reductions in the buckling pressure due to material anisotropy, shear deformation, nonuniform stress distribution through the thickness, and effective shell thickness (sandwich shells only). The buckling equations were validated using hydrostatic pressure test data for two solid shell configurations and three sandwich shell configurations. The predicted values of critical buckling pressure were within 15 % of the experimental values for the solid shells and within 5 % of the experimental values for the sandwich shells. These results demonstrate the viability of using these simple equations for preliminary design of composite pressure hulls.