Numerical investigation of crashworthiness behaviour of lattice structure filled thin-walled tubes

Thin-walled tubes have been mostly used in passive vehicle safety systems as crash energy absorber. Metal additive manufacturing technologies, which have become very popular in recent years, enable the production of novel filler materials to further improve the crashworthiness performance of thin-walled metal tubes. In this study, two different types of lattice structures (i.e., body-centered cubic, BCC and body-centered cubic with a vertical strut, BCC-Z) were proposed as filling material in thin-walled square-section aluminum 6063-T5 tubes and the energy absorption performance of the hybrid structures were investigated using finite element method under axial and oblique loads. At this point, hybrid structures were formed by placing the lattice structures produced by direct metal laser sintering method using AlSi10Mg metal powder into the thin-walled tubes. Then, hybrid structures were tested under various loading conditions, and the nonlinear dynamic finite element model was validated by taking into account various parameters such as imperfection, damage models, strain rate sensitivity and interactions between the tube and the lattice structure. In addition, in order to enhance the energy absorption performance of hybrid structures under oblique loads, graded lattice structures were proposed and the crashworthiness performances of graded lattice structures and their uniform counterparts are compared at the same weight. At this point, the effect of lattice structure type, lattice member thickness, number of vertical lattice unit cell, tube thickness, draft angle of lattice structures and base diameter of lattice structures on the energy absorption performance of hybrid structures were investigated by taking into account various crashworthiness criteria. This thesis study revealed that the lattice structures as filling material significantly improve the crashworthiness performance of thin-walled tubes due to hybrid interactions that promote progressive deformation between the lattice and the tube under both axial and oblique loads. In addition, the energy absorption performances of the lattice structure filled thin-walled tubes under axial loads can be considerably improved by the appropriate selection of number of lattice cell, diameter of lattice cell and tube thickness. The results revealed that the proposed structures are potential candidates for crashworthiness applications.