Page 87 - MSAM-2-3

Materials Science in Additive Manufacturing Functional graded and hybrid TPMS lattices

illustrates a larger low-stress area for the graded lattice with The lowest displacement at point 2 was detected for the
a relative density of inner 5% and outer 45% (Figure 4B). graded gyroid with a relative density of inner 5% and outer
As shown in Figure 4C, the central part illustrates a smaller 45%. As a result, the stiffness at the top region increased,
low-stress area for the graded lattice with a relative density indicating that the introduction of graded gyroid lattice
of inner 45% and outer 5% compared with the uniform structure as infillings of implants can protect the bone from
case. In addition, a more uniform stress distribution was damage. Compared to the uniform case, the displacement
obtained on the graded lattice structure with a relative at point 3 for two graded gyroid lattices also increased,
density of inner 45% and outer 5%. The stress on the whereas the displacement at point 4 reduced. As a result,
external surfaces was found to be higher than the stress in the stiffness at the side region decreased, indicating that the
the core region for both the uniform case and the graded introduction of graded gyroid lattice structure as infillings
lattice with a relative density of inner 5% and outer 45%. of implants can effectively relieve the stress shielding effect.
We also found no stress concentration in the transition
region for both the graded cases, pointing to the excellence 4. Case study 2: Solid-network-based hybrid
of the smooth grading with the sigmoid function. Taken TPMS lattices in tuning compliant response
together, the sheet-based gyroid lattices with graded For the hybridization of TMPS lattices, Stratasys J750
relative density can match the flexible mechanical demand (Stratasys Ltd.), which is based on the material jetting
of the bone implant application. technique, was utilized to manufacture all samples.

The displacement histories recorded at four points, Stratasys J750 fabricates objects by solidifying the droplets
which are shown in Figure 2C and D, in the gyroid lattice of photopolymers with ultraviolet light. A previous study
at different compressive strains are shown in Figure 5. For has shown that Stratasys J750 is capable of accurately
two graded gyroid lattices, the displacements at point 2 fabricating samples with sharp features (e.g., cube) at
decreased compared to that of the uniform gyroid lattice. 500 µm level and samples with round features (e.g., cylinder)

A B C

Figure 4. Stress contour of sheet-based gyroid lattices at 5% strain: (A) Uniform lattice with a relative density of 25%, (B) graded lattice with a relative
density of inner 5% and outer 45%, and (C) graded lattice with a relative density of inner 45% and outer 5%.

A B C

Figure 5. Displacement histories of the sheet-based gyroid lattices recorded at four points: (A) Uniform lattice with a relative density of 25%, (B) graded
lattice with a relative density of inner 5% and outer 45%, and (C) graded lattice with a relative density of inner 45% and outer 5%.

Volume 2 Issue 3 (2023) 6 https://doi.org/10.36922/msam.1753