B0S0R5—program for buckling of elastic-plastic complex shells of revolution including large deflections and creep

Abstract

B0S0R5 can handle segmented and branched shells with discrete ring stiffeners, meridional discontinuities, and multi-material construction. The shell wall can be made up of as many as six layers, each of which is a different nonlinear material. In the prebuckling analysis large-deflection axisymmetric behavior is presumed. Bifurcation buckling loads are computed corresponding to axisymmetric or nonaxisymmetric buckling modes. The strategy for solving the nonlinear prebuckling problem is such that the user obtains reasonably accurate answers even if he uses very large load or time steps. B0S0R5 has been checked by means of numerous runs in which the results have been compared to other analyses and to tests. The prebuckling and plastic bifurcation (eigenvalue) analyses are described, with the most important equations given. These equations are derived from a finite difference energy method. The strategy for solving problems simultaneously involving large deflections, elastic-plastic material behavior, and primary and secondary creep permits the use of rather large time and load steps without undue sacrifice in accuracy. This strategy is based on a subincremental iteration method in which the size of the subincrement is automatically determined such that the change in stress is less than a certain prescribed percentage of the effective stress. The theoretical treatment of discrete ring stiffeners, the material of which is elastic-plastic and can creep according to a primary or secondary creep law, is also given. Discrete rings of arbitrary cross-section are considered to be assemblages of thin rectangular elements. The structure of the B0S0R5 computer program, which runs on the CDC 6600 and on the UNIVAC 1108 and 1110, is described. The paper gives comparisons between test and theory for many configurations, including axially compressed cylinders and internally and externally pressurized shells of various shapes with and without ring stiffeners. The results of sensitivity studies are given in which the effect on predicted critical load of various analytical models of the ring-shell wall intersection area are explored. A method of predicting the effect of welding on buckling load is described, and an example involving a ring-stiffened doubly-curved shell is given. Welding the ring stiffeners to a shell introduces residual stresses and geometrical imperfections, both of which reduce the load-carrying capability.