Compressive properties of Ti6Al4V Functionally Graded Lattice Structures via topology optimization design and selective laser melting fabrication

Abstract

Owing to their comparable mechanical properties, high cell growth and nutrient transport space, lattice structures show great potential applications in replacing and repairing massive bone defects. In this work, topology optimization method was used to design cellular structures with different relative densities (RD = 0.10–0.30). Subsequently, a series of Uniform Lattice Structures (ULSs) and Functionally Graded Lattice Structures (FGLSs) with different RD gradient directions (two types: G1 type specimens with a RD gradient perpendicular to the compressing direction, while G2 type specimens with a RD gradient along the compressing direction) were fabricated via selective laser melting (SLM) technology with Ti6Al4V alloy powder. Here, ULSs as a reference were applied to investigate the mechanical properties, failure mechanism, energy absorption abilities and properties prediction of ULSs. The designed lattice structures owned comparable mechanical properties with natural bone. The mechanical properties (E = 3.13–4.73 GPa, σy = 96.90–180.05 MPa, σpl = 75.12–98.97 MPa) of G1 type specimens were sightly higher values comparing with those of ULSs, whereas mechanical properties (E = 1.42–3.75 GPa, σy = 15.93–66.21 MPa, σpl = 60.26–92.02 MPa) of G2 type specimens were a notablely lower value than those of ULSs. G2 type specimens exhibited a similar failure mechanism of layer-by-layer with ULSs, while G1 type specimens presented a mixed failure mechanism including shear-dominated and bending-dominated mode. Additionally, mechanical properties prediction methods were systematically analyzed and corresponding mathematical models were established successfully for tailoring properties of FGLSs. This work provides a comprehensive understanding that how to design and manufacture well-performance FGLSs and is significant for porous orthopedic implants applications.