Compressive properties and deformation mechanism of selective laser melting of Ti6Al4V porous femoral implants based on topological optimization

Although the design and mechanical properties of the porous structure have been widely explored, the porous structure and the unit cell with excellent mechanical properties matching the demands of femur should be further investigated. In this research, a porous structure based on face-centered cubic unit cell was constructed to match the femur's natural state and vertical direction at an angle of 7° via structural topology optimization. Three types of Ti6Al4V porous structures with different pore sizes were produced by selective laser melting (SLM). The influence of porosity on the compressive properties and deformation mechanisms was analyzed by experiments and simulations. In the compression process of three porous structures with different porosities, there are four obvious stages: the early elastic stage, the abrupt drop stage following stress increase, the Area III, and the ultimate densification stage. However, the four stages of porous structure vary in porosity. When the porosity is 81.5 %, the stress fluctuates in the region where the abrupt drop stage following stress increase. With increasing porosity, Young's modulus and yield strength decrease. Only the porous structure with a pore diameter of 0.7 mm and porosity of 67.5 % has a Young's modulus and yield strength meeting the requirements of bones, and is the best bone replacement. Bending is the unit cell's main deformation mechanism based on Maxwell equation analysis. Both the Johnson-Cook constitutive model and the experimental data demonstrate the shear deformation of porous structures. In comparison to the compressive performance of unit cells designed using traditional methods, the topology optimization's unit cells exhibit higher relative Young's modulus.