BOSOR5计算机程序用于轴对称壳体的非线性屈曲分析，用于获得由Alix和Roche在d？中心测试的几个椭球形容器封头的非轴对称屈曲所对应的压力？法国萨克莱核练习曲。所有的头都扣在塑料范围内。初始屈曲预计发生在比试样中第一次出现可见屈曲时的压力低约20%的压力下。这一结果与Patel和Gill之前对复曲面球形封头的预测一致。据推测，试样中可见屈曲的形成是一个柱状结构- 屈曲过程，即从基本轴对称状态分岔后立即出现的初始后屈曲行为是稳定的，初始屈曲的振幅随着分岔点以上压力的增加而稳定增长，直到其中一个或多个突然可见，压力下降。分析基于子午离散化，包括较大的预屈曲挠度和弹塑性材料行为。通过特征值分析计算初始屈曲压力，从而产生沿头部周长呈正弦变化的屈曲模态位移。壳体的预屈曲状态通过包含在每个荷载增量的双迭代循环中的增量和迭代程序获得: 内循环用于求解材料性质保持不变的非线性几何问题，外循环用于更新材料性质。次增量法用于精确确定每个载荷增量内的塑性流动。

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.