Hierarchical double-hat beam for axial crashworthiness

Double hat-beams (DB) made of high-strength steel are widely used in automobile body for their excellent impact resistance. To further improve the crashworthiness of DB, the concept of hierarchy is first introduced into the design of DBs to obtain the so-called hierarchical double-hat beams (HDBs). The finite element model of DB is validated by impact tests. It is found that the hierarchical structures exhibit better energy absorption characteristics and deformation stability compared with DB. Among them, the mean crushing force (MCF) values of DBT and STT exceed DB 70.63% and 49.47% separately, and their specific mean crushing force (SMCF) values exceed DB 32.34% and 45.06% respectively. The triangular hierarchical structures perform better than quadrangular and hexagonal models. The effects of substructure size and geometry on the impact resistance of HDBs are further investigated, and the impact resistance of HDBs can be effectively improved by increasing H1 value and adding microstructure to the substructures. The SMCF values of DBT-8, DBT-10, DBQ-8, DBQ-10 and DBT-III are 116.31, 109.61, 45.36, 79.59 and 66.50% higher than that of DB. In addition, these HDBs show novel deformation patterns that resemble the letter “T”, the symbol “+” and the mushroom. In summary, the hierarchy of structure can significantly improve the crashworthiness of DB.