This is Fig. 1 from the paper, "BOSOR5 - Program for buckling of complex, branched shells of revolution including large deflections, plasticity and creep" by David Bushnell, in STRUCTURAL ANALYSIS SYSTEMS, Vol. 2, A. Niku-Lari, editor, Pergamon Press, pp. 55-67, 1986, called "1986 BOSOR5 user's manual paper" in the next slide.
This slide shows axisymmetric pre-buckling deformations predicted by BOSOR5 for an internally pressurized elastic-plastic ellipsoidal pressure vessel head. Elastic-plastic bifurcation buckling (shown in the next slide) is caused by the relatively narrow band of circumferential compression that occurs in the knuckle region where the profile of the axisymmetrically deformed shell falls inside that of the undeformed shell.
Accurate predictions of incipient (bifurcation) buckling require the inclusion of both nonlinear geometric behavior and nonlinear material behavior in the BOSOR5 simulation.
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