Experimental and numerical investigations into collapse behavior of hemispherical shells under drop hammer impact

Dynamic response for a series of cylindrical shells filled with water were discussed previously, which indicated that the limit buckling load of the cylindrical shells was greatly improved by the presence of water. To obtain a good protective structure, a double layered liquid-filled hemispherical shell structure is designed. Three kinds of structures (single layered empty hemispherical shell, double layered empty hemispherical shells, and single layered liquid-filled hemispherical shell) are compared with the double layered liquid-filled hemispherical shells. The collapse behavior of four kinds of hemispherical shell structures and their deformation modes under drop hammer impact are presented to investigate the effects of inner water on the response of the liquid-filled hemispherical shells. Test results show that the effects of inner water mainly include "distributing loadings" and "ironing effect". Double layered liquid-filled hemispherical shells have the highest bearing capacity among all four kinds of structures. Three-dimensional numerical simulations of all the tested specimens were carried out using ANSYS and LS-DYNA. Under same impact condition, the effective protection space of empty hemispherical shells is very small due to its larger vertex displacement. In terms of generalized specific energy absorption (eta) of structures with same vertex displacement, liquid-filled hemispherical shells are better than empty shells. For liquid-filled shells, eta of double layered shells is smaller than single layered shell, but single layered shell has no inner space. Parameter analysis indicates that only the outer thickness has a significant effect on the impact force. Increasing the outer thickness and ensuring a reasonable distance between the inner and outer shell can improve the crashworthiness of double layered liquid-filled shells and protect the internal objects.