Optimization design of a novel hybrid hierarchical cellular structure for crashworthiness

Cellular structure has attracted extensive attention due to its lightweight, superior mechanical properties, and excellent energy absorption property. In nature, the animal bone and plant stem both are cellular structures. It is found that these natural cellular structures additionally have a hierarchical characteristic which makes them extremely strong and ultra-light. Inspired by the hierarchical characteristic of the natural cellular structures, a novel hybrid hierarchical cellular structure, named octet-truss-TPMS (HOTT) structure is invented based on both octet-truss lattice and triply periodic minimal surfaces (TPMS) structure in this study. The specimens of the HOTT structures are fabricated using 3D printing technology and are tested by a universal testing machine. To carry out numerical simulation for the crashworthiness of the HOTT structure, the finite element (FE) model of the HOTT structure is established. The FE model is verified because the crushing forces and deformation modes obtained by the FE simulation are consistent with the test results. Based on the FE model, the crashworthiness of four HOTT structures with different configurations is studied. The effect of design parameters (i.e., equivalent density rho E, level set constant C, structural parameter N, and impact loading velocity v) on their crashworthiness are investigated. Moreover, a multi-objective optimization method based on metamodels and the NSGA-II algorithm is employed to optimize the crashworthiness of the HOTT structures. The optimal designs of four different HOTT structures with maximum specific energy absorption (SEA) and minimum peak crushing force (PCF) are ob-tained. Based on the Pareto fronts of the multi-objective optimization, the crashworthiness of four HOTT structures are compared. Furthermore, the crashworthiness of the HOTT structures is compared with that of the non-hierarchical octet-truss structure and the traditional aluminum foam with the same weight. The comparison result shows that the HOTT structure has better crashworthiness than the non-hierarchical octet-truss structure and aluminum foam. Thus, the HOTT structure is an excellent energy absorber and has extremely potential applications in impact engineering.