The BOSOR5 computer program for the nonlinear buckling analysis of axisymmetric shells is used to obtain pressures corresponding to non-axisymmetric buckling of several ellipsoidal vessel heads tested by Alix and Roche at the Centre d?Etudes Nucleaires de Saclay in France. All of the heads buckled in the plastic range. Incipient buckling is predicted to occur at pressures about 20 percent lower than the pressures at which the first visible buckles appeared in the test specimens. This result is consistent with previously obtained predictions for torispherical heads tested by Patel and Gill. It is conjectured that the formation of visible buckles in the test specimens is a post-buckling process-that the initial post-buckling behavior immediately following bifurcation from the fundamental axisymmetric state is stable, with incipient buckles steadily growing in amplitude with increasing pressure above the bifurcation point until one or more of them suddenly becomes visible and the pressure drops. The analysis is based on meridional discretization and includes moderately large prebuckling deflections and elastic-plastic material behavior. Incipient buckling pressures are calculated from an eigenvalue analysis yielding buckling modal displacements that vary sinusoidally around the circumference of the head. The prebuckling state of the shell is obtained from an incremental and iterative procedure contained in a double iteration loop for each load increment: an inner loop for solution of the nonlinear geometric problem with material properties held constant and an outer loop for update of the material properties. A sub incremental method is used for accurate determination of plastic flow within each load increment.
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| Number of Pages : | 34 |
| Published : | 1981 |
