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This slide is from the paper, "Optimization of perfect and imperfect ring and stringer stiffened cylindrical shells with PANDA2 and evaluation of the optimum designs with STAGS", by David Bushnell and Charles Rankin, AIAA 43rd Structures, Structural Dynamics and Materials Conference, AIAA Paper 2002-1408.
ABSTRACT: Ring and stringer stiffened perfect and imperfect angle-ply cylindrical shells under combined axial compression and in-plane shear are optimized with a program called PANDA2 for the minimum weight design of stiffened panels, and the optimum designs are then evaluated with use of a general-purpose finite element code called STAGS. The good agreement between PANDA2 and STAGS predictions for the nonlinear collapse of imperfect stiffened shells justifies the use of PANDA2 for preliminary design. A new PANDA2 processor called STAGSUNIT automatically generates STAGS input files for cylindrical panels and shells with both stringers and rings that have various open cross sections such as Blades, Zees, Jays, Tees and Is. In STAGSUNIT the edge conditions are formulated so that STAGS models of sub-domains of a long cylindrical shell with many stiffeners can be constructed that do not have artificial prebuckling stress concentrations near the edges that might significantly affect predictions of bifurcation buckling and nonlinear collapse of the sub- domain. Many STAGS models of optimized shells and sub-domains of shells with Blade, Zee, and Tee stiffening are generated and explored, both with respect to linear bifurcation buckling and nonlinear collapse. The behavior of shells with an initial imperfection in the form of a general buckling mode of the imperfect shell is described from a physical point of view. Some difficulties encountered during this project are described.
Displayed here is the nonlinear static collapse predicted by STAGS for an internal-blade-ring and external-blade-stringer stiffened, angle-ply, composite cylindrical shell under combined axial compression Nx = -700 lb/in and in-plane shear Nxy = +40 lb/in. The cylindrical shell was previously optimized by PANDA2.
Fig. 27 Mode of collapse according to STAGS
Fig. 28 Inner and outer fiber axial strain according to STAGS in the most critical finite element as a function of the load factor, PA. (PA = 1.0 is the design load factor to which the stiffened shell was previously optimized by PANDA2.)
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