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

2. 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

3. 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”

4. 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

5. 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)

6. 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.

7. Nonlinear Buckling Results, e = 50%

8. Summary of Nonlinear Buckling Results
Theoretical Solution

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

10. 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