A Study of the Effect of Imperfections on Buckling Capability in Thin Cylindrical Shells Under Axial Loading Lauren Kougias

Objective To study the effect of ovalization of a thin cylindrical shell on load carrying capability under an axial compressive load Evaluate buckling capabilities for several values of e

FEA Modeling and Part Dimensions Thin cylindrical shell modeled using shell elements AMS 4829 (Ti 6-4) properties used at 70°F Cylinder Dimensions R = 40” L = 80” t = 0.15”

Buckling Capability: Theoretical Solution Theoretical solution for perfect (e = 0”) cylinder: 1,455,952 lb E = Young’s Modulus v = Poisson’s Ratio t = wall thickness R = radius Solution based on experimental data: 420,736 lb kc = buckling coefficient

Methodology Used eigenvalue buckling solution to perform mesh density study to find appropriate element size for analysis for perfect cylinder (e = 0). Eigenvalue buckling solution used to create imperfections in model for nonlinear buckling. Nonlinear buckling analysis performed using Riks modified method for perfect cylinder (e = 0). Riks method is a solution method in Abaqus that models postbuckling behavior of a structure. Nonlinear buckling analysis performed for several ovalized cylinders (e = 0%-100% of shell thickness)

Eigenvalue Buckling Solution Eigenvalue buckling mode four best represents ovalized shape Mesh density study resulted in element size of 2” to yield an accurate solution.

Nonlinear Buckling Results, e = 50%

Summary of Nonlinear Buckling Results Theoretical Solution

Load vs. Displacement Curves Typical behavior of a structure undergoing collapse (on left). Behavior of structure with e = 50% closely matches predicated curve.

Conclusion Adding imperfections in the form of ovalization significantly reduced the load carrying capability of the structure. Further studies that take other types of imperfections into account must be addressed Only addresses isotropic materials and the results should not be assumed to be the same for a composite structure