Additively-manufactured functionally graded Ti-6Al-4V lattice structures with high strength under static and dynamic loading: Experiments

Functionally graded Ti-6Al-4V lattice structures with a step-wise gradient and a continuous gradient were designed and fabricated by selective laser melting (SLM) method respectively. Compression experiments were conducted by electronic universal machine and Split Hopkinson Pressure Bar (SHPB) system to determine the mechanical performance of the material for strain rates up to 1000/s. The potential influence of different loading directions on the material characteristics was explored. All the loading processes were recorded to capture the deformation mechanism of different specimens, and the strain distribution was analyzed using digital imaging correlation (DIC) method. The results indicate that the functionally graded Ti-6Al-4V lattice structures exhibit excellent mechanical properties, which appear to have a promising prospect for energy absorption applications. The strain rate effect is revealed to be resulted from the intrinsic strain rate sensitivity of the bulk material. Finite element (FE) analysis was conducted based on the 3D beam element to simulate the dynamic response of the graded lattice structures, which could be adopted for the prediction of the material strength and the initial collapse mode. Both the experimental and numerical results demonstrate that the designed gradient modes and loading directions exhibit no effect on the mechanical response of graded Ti-6Al-4V lattice structures within the tested strain rates.