Buckling Loads of Small Cylindrical Shells under Axial Compressive Loads

摘要

Thin-walled stiffened or unstiffened, metallic or composite shells are widely used structural elements in aeronautical and space applications. These structures are often highly sensitive to initial imperfections and therefore have buckling loads much lower than those computed for perfect structures. Analysis and testing of imperfect shells have been a major research area during the last century. This paper will present the results of the buckling analysis and imperfection sensitivity of small cylindrical shells, and their comparison with experimental results. For the analytical work, a hierarchical multi-fidelity approach is used to solve the buckling problem. An important aspect is inclusion of the effects of plasticity on buckling response of these thin-walled shells. The buckling response of such shells is often an elastic process, and therefore plasticity effects are ignored in the analysis. It will be shown that analyzing the buckling behavior of the shell based only on elastic buckling will not provide an acceptable comparison with experimental result, hence, requiring the inclusion of plasticity effects. It will be demonstrated that, due to both the geometric imperfections and the Poisson expansion of the shell, internal moments are introduced in the shell wall. The influence of these moments is very large; at 38% of the theoretical buckling load the moments already generate stresses that exceed the yield stresses. Local buckling occurs at those locations where the geometric imperfections are the largest, even though the imperfections are less then the wall thickness. Comparison of the finite element results that include the plasticity effects with the experimental tests show a promising match between buckling loads and buckling patterns.