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This is Fig. 2 from the paper, "Optimization of an axially compressed ring and stringer stiffened cylindrical shell with a general buckling modal imperfection", by David Bushnell, AIAA 48th Structures, Structural Dynamics, and Materials Conference, Paper no. AIAA-2007-2216, 2007.
This slide shows the outer fiber effective stress (psi) at axial load, Nx= -3000 x 1.00516 lb/in. These results are from Case 4 in Table 4: no Koiter, yes change imperfection, ICONSV=1 . (See Slides 16-18 in the "Buckling Comments" slide show for an explantion of this jargon.)
Shown here is the nonlinear equilibrium state from STAGS at the load factor, PA= 1.00516. The imperfect shell has two initial buckling modal imperfection shapes:
1. a general buckling modal imperfection shown in Fig. 1a of the paper with amplitude, Wimp1=+0.0625 inch, and
2. a local buckling modal imperfection shown in Fig. 61 of the paper with amplitude, Wimp2= -0.0005 inch.
Prebuckling bending of the imperfect shell causes redistribution of stresses among the shell skin and the stiffener segments.
Also, prebuckling bending gives rise to “flattened” regions with an “effective” circumferential radius of curvature that is greater than the nominal curvature of the perfect shell and that therefore causes early general buckling. (See the right-most expanded insert).
This is a STAGS "compound" model analogous to that displayed in the previous slide. In a "compound" model the stringers are modeled as little flexible shell units over part of the circumference of the cylindrical shell and smeared out over the remainder of the circumference.
For viewing figures and tables referred to here but not shown here, please download the 2007 PANDA2 paper from this website. Also, see the PANDA2 slide shows.
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