BUCKLING AND INITIAL POSTBUCKLING OF OVAL CYLINDRICAL SHELLS UNDER COMBINED AXIAL COMPRESSION AND BENDING

Buckling and initial postbuckling of an oval cylindrical shell under pure bending and under combined uniform axial compression and bending is investigated. The first- and second-order stability equations are developed from the Donnell-type equations that are shown to be appropriate. The solution of these two sets of equations determines, respectively, the buckling characteristics and a “sensitivity parameter.” The buckling loads are found to be in good agreement with the engineering approximation based on the assumption that buckling occurs when the local axial stress equals that corresponding to the classical buckling stress of a locally equivalent circular cylindrical shell under uniform axial compression. Results also show that an oval cylinder can be stronger or weaker than the equivalent circular cylinder, depending on the orientation of the couples. However, in any case the oval shell is always found to be sensitive to imperfections; the greater the load-carrying capacity, the greater the sensitivity. Furthermore, in contrast to the behavior of the circular and weak oval cylinders, buckling of the strong oval cylinder need not initiate at the position of maximum compressive stress.