Effects of Structural Perturbations on Strain Growth in Containment Vessels

Strain growth is a phenomenon observed in the elastic response of containment vessels subjected to internal blast loading. The local dynamic response of a containment vessel may become larger in a later stage than its response in the initial breathing mode response stage. It has been reported in our previous study that bending modes may be excited after several cycles of breathing mode vibration, due to the dynamic instability in cylindrical and spherical shells without structural perturbations. The nonlinear modal coupling between the breathing mode and the excited bending mode is one of the causes for the strain growth observed in containment vessels. In this study, we demonstrate that, due to the existence of structural perturbations, various vibration modes may be excited in containment vessels in earlier response stage before the occurrence of nonlinear modal coupling. The linear superposition of the breathing mode and the vibration modes excited by structural perturbations may cause larger response than the pure breathing mode response, which is a different strain growth mechanism from the nonlinear modal coupling. In the later response stage when the nonlinear modal coupling happens, not only the breathing mode, but also the vibration modes excited by structural perturbations will interact nonlinearly with the bending modes excited by dynamic unstable vibration. Dynamic nonlinear finite element program, LS-DYNA, is employed to understand the effects of structural perturbations on strain growth in containment vessels subjected to internal blast loading.