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This is Fig 2 from the 1986 BOSOR5 user's manual paper. This slide shows a typical pressure-deflection curve for an internally pressurized ellipsoidal (or torispherical) pressure vessel head and photograph of a buckled test specimen.
With increasing internal pressure, Individual buckles or pairs of buckles appear in the knuckle region where the pre-buckling circumferential membrane stress is negative as the internal pressure is increased. Provided that fracturing of the shell wall does not occur, the shell can be stable in its far post-buckled state as more and more circumferentially narrow buckles appear.
In metallic specimens buckling usually occurs at internal pressures for which there is significant pre-buckling plastic flow. Both nonlinear geometric and material behavior must be included in the buckling model in order accurately to predict initial buckling and post-buckling behavior.
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