Buckling assessment of axially loaded cylindrical shells with random imperfections

The buckling strength of axially loaded cylindrical shells is greatly affected by geometric imperfections. Due to the difference between test results and classical theory solution, current codes of practice require the application of knockdown factors to the classical buckling load. Another approach is to conduct a rigorous analysis incorporating geometric and material imperfections. However, the shape of imperfections that result in the minimum buckling load is questionable. In this work, the effect of random geometric imperfections on the buckling strength of axially loaded cylinders was investigated using the finite element method. Geometric imperfections were modeled by a series of cosine functions with various deterministic and random variables. The imperfection profile was fully characterized by the power spectral density function of the random process which was established by assuming a decaying cosine autocorrelation function. A large number of artificial cylinder samples was generated and grouped into five groups according to the geometric imperfection configuration. Elastic and inelastic buckling analyses results were compared to published test results and to the results obtained using the ASME Code Case N-284. Statistical analysis of the finite element results was accomplished using the Analysis of Variance technique to determine the worst imperfection configuration. On the basis of the statistical study, axisymmetric imperfections were found to be the worst imperfections for axially loaded cylinders. These results were used to establish an equivalent axisymmetric imperfection that can be easily implemented in the analysis of axially loaded cylinders