Multiscale study of the dynamic behaviour of additively manufactured Ti6Al4V cellular metamaterials

Abstract

Additive manufacturing (AM) enables the creation of complex geometries like lattices with tunable mechanical behaviour. This technique is frequently used in a diverse range of alloy systems, including steels, nickel-based superalloys, titanium and aluminium alloys, among others. These materials, combined with intricate designs, are leading to innovative metamaterials for lightweight, energy-efficient components in impact applications. However, gaps remain in understanding the connection between the lattice architecture, the resulting microstructure and processing defects and the mechanical behaviour under dynamic conditions of these cellular materials. . This study investigates the dynamic behaviour of Ti6Al4V BCC lattice structures manufactured by Laser Powder Bed Fusion (LPBF), using a multiscale approach to examine both individual struts and whole lattice structures under high strain rates. The Split Hopkinson Pressure Bar and Direct Impact Hopkinson Pressure Bar are used for dynamic testing, while design variables such as printing orientation and strut diameter are considered. Additional analyses on surface quality, microstructure, and fractography are conducted to correlate with the mechanical performance. Results show that the mechanical properties of individual struts are both dependent on the diameter and orientation, especially the former. Struts with larger diameters exhibit higher ductility, while mid-size struts (1 mm diameter) present the higher peak flow stress. For the lattice structures, the dynamic plastic/crushing stress, the energy absorption and the failure modes are influenced strongly by strut diameter, with a minor impact from printing orientation. Lattices formed by struts with larger diameters exhibit higher plastic/crushing effective stresses, but the optimal energy absorption efficiency is achieved with smaller diameters due to densification. These findings highlight the importance of considering size and orientation in the design of lattice structures for dynamic applications.