Dynamic buckling of cylindrical stringer stiffened shells

The dynamic buckling of cylindrical stringer stiffened shells was investigated both numerically and experimentally. A new criterion to define the numerical “dynamic” buckling load was developed yielding consistent results. The ADINA finite element code was applied to simulate the static and dynamic buckling loads of the shells. It was shown numerically that when the period of the applied loading (half-wave sine) equals half the lowest natural period of the shell, there is a slight drop in the dynamic load amplification factor (DLF). The DLF is defined, as the ratio of the dynamic buckling to the static buckling of the shell. This factor drops below unity, when the ratio of the given sound speed in solids, c, to the velocity developed axially due to the applied dynamic loading, approaches unity. It means that, for this particular loading period, the dynamic buckling load would be lower than the static one. It was shown numerically that the shape of the loading period, half-wave sine, a shape encountered during the tests, as well as the initial geometric imperfections have a great influence on the dynamic buckling of the shells. The relatively simple test set-up design to cause a shell to buckle dynamically did not fulfill our expectations. Although, the process leading to eventually the dynamic buckling of the shell worked properly, still no test results were obtained to form a sound experimental database for this phenomenon. Based on the numerical predictions, correct guidelines were formulated for better test procedures to be applied in future tests, which will be reported in due time.