Effect of the direction of the gradient on the mechanical properties and energy absorption of additive manufactured Ti-6Al-4 V functionally graded lattice structures

Abstract

Functionally graded (FG) lattice structures are gaining increased attention in engineering applications due to their excellent mechanical properties and high energy absorption. This study aims to investigate the effect of the direction of the gradient on mechanical properties and energy absorption of FG sheet-based (FGS) lattice structures. The design approach of FGS lattice structures with different directions of volume fraction gradient was established. The FGS samples with the gradient from perpendicular to parallel to loading directions (θ = 0º−90º) were fabricated by laser powder bed fusion technology with Ti-6Al-4 V powder. The mechanical properties, deformation behaviors, and energy absorption of the FGS samples were systematically investigated. Results show that the deformation behavior of FGS samples changed from local shear to layer-by-layer fracture with the increase of θ, gradually improving the load-bearing capability during the compression process. The fluctuation of the strain-stress curve for FGS lattice structures can be reduced by decreasing the θ. Tunable mechanical properties and energy absorption were achieved by changing the θ. The FGS sample with θ = 0º had the highest elastic-plastic properties, while the FGS sample with θ = 90º absorbed the largest amount of energy before densification. The failure of the FGS lattice structure was influenced by the combination of brittle fracture with smooth plane morphological features and ductile fracture with dimples. Moreover, the deformation behaviors and strain-stress curves of FGS samples were successfully predicted using the finite element method with Johnson-Cook plastic and damage models. Finally, energy absorption plots were provided to select of FGS lattice structures for specific energy-absorbing requirements. This work provides an efficient method to control the mechanical properties and energy absorption of FGS lattice structures for engineering applications.