Designs and mechanical responses of 3D-printed Ti6Al4V porous structures based on triply periodic minimal surfaces with different iso-values

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With the increasing applications of additive manufacturing in orthopaedic implants and numerous designs of porous structures available, there is a strong need and opportunity to optimize the structure designs for improved bone integration. Here we created a unique group of sheet structures based on triply periodic minimal surface (TPMS) by varying the iso-value and systematically examined how iso-value influences the mechanical performance of sheet diamond TPMS structures compared to the Octet truss structure. Four iso-values (C) 0, 0.25, 0.5, and 0.75 were designed for sheet Diamond (OSD) TPMS with varying porosity, and Ti6Al4V powder bed fusion was used to produce the porous structures. Compressive tests revealed that iso-value C significantly affected mechanical performance, and interestingly, the impact was porosity-dependent. At high relative density (>0.25), OSD0 (C = 0) displayed the highest elastic modulus and yield strength, whereas at low relative density (<0.25), OSD0.5 showed the highest among all OSD structures. Regarding failure mechanisms, OSD0, OSD0.25, and OSD0.75 showed a mixed domination of stretching and bending, while OSD0.5 was predominantly stretching-dominated. Finite Element Analysis (FEA) found that local yielding initiated at cell nodes upon loading, followed by surface bending and the formation of single or multiple shear bands near the cell nodes. This work demonstrated the feasibility of improving the mechanical performance of porous TPMS structures by simple adjustments in their governing trigonometric functions, serving as a starting point to customize porous structures for specific applications.