Page 83 - MSAM-2-3

Materials Science in Additive Manufacturing Functional graded and hybrid TPMS lattices

theoretical analysis, plate-based lattices, which have the From the work proposed by Ren et al. , the hybridization
[23]
potential to reach the Hashin-Shtrikman upper bounds, have of the I-graph-and-wrapped-package (IWP) and primitive
been proposed as an excellent candidate for high-strength TPMS lattices have shown their extraordinary stiffness
withstanding scenarios . Unlike the truss-based or plate- under bending loading. To further modify the mechanical
[14]
based lattices that are constructed from explicit geometric behavior of TPMS lattices, the hybridization of different
primitives, triply periodic minimal surfaces (TPMS) surface- TPMS lattices has been numerically analyzed and tested,
based lattices, which are generated based on the implicit illustrating their improvement in energy absorption and
[18]
TPMS functions, have attracted the attention of researchers the modification of the deformation characteristics . In
due to their high specific strength and energy absorption the work proposed by Novak et al. , the plateau region
[19]
capabilities . with either hardening behavior or constant response can be
[15]
TPMS can be characterized through the summation of a obtained by the hybridization of gyroid and diamond lattices,
series of sinusoidal functions, resulting in a surface that has which enables their potential applications in crashworthiness
the capacity to minimize its surface area within a predefined protection. The effects introduced by hybridization require
boundary, while simultaneously maintaining a zero mean more in-depth investigation due to the extensive design
possibilities offered by the flexible hybridization approach.
curvature and periodicity in 3D space. TPMS surface-based Nevertheless, the selection of an appropriate hybridization
lattices can be categorized into sheet-based TPMS lattices and
solid-network-based TPMS lattices. With the TPMS, the 3D strategy, aimed at optimizing the structural performance of
space can be separated into two regions, the solid-network-based the system, remains undetermined.
TPMS is generated by infilling the specific region separated In this work, popular TPMS design approaches,
by the surface. Instead of infilling regions, the sheet-based including graded design of sheet-based lattices and
TPMS is generated by thickening the surface. The numerical hybridization of solid-network-based lattices, along with
and experimental analyses of the mechanical performance of their potential applications, were examined. In this paper,
both solid-network-based and sheet-based TPMS have been we present the methods of generating TPMS lattices, the
reported [15-18] . In addition, graded designs in the TPMS-based strategies used to design uniform gyroid, graded gyroid,
lattices have been developed and investigated . Apart from the and hybrid design. Subsequently, we present our works in
[19]
linear grading on the lattices’ thickness, the graded TPMS in two the numerical investigation of the graded gyroid lattices,
and three dimensions has been manufactured and investigated, which are regarded as an application to resolve the stress
showing a great increase in energy absorption ability compared shielding effect. To explore the effectiveness of the selected
to the uniform TPMS lattices . hybridization strategies, several hybrid TPMS lattices were
[18]
designed, fabricated, and tested. In the last section, the
Classical TPMS lattices such as primitive, gyroid,
and diamond with different materials have been widely main findings of this work are summarized.
investigated . Among TPMS structures, the sheet-based 2. Design strategies of hybrid gyroid lattices
[20]
gyroid structure has been proven to own a high strength-to-
mass ratio as well as a low level of stress concentration when As illustrated in the previous work, TPMS can be obtained
compared with other types of lattices [15,21] . In the context of by utilizing different approaches, such as implicit,
orthopedic implant design, it becomes imperative to provide boundary, and parametric functions. In this work, the
adequate physical stimulation to promote bone regeneration, solid-network-based TPMS lattice, which was utilized to
while also ensuring compatibility with the mechanical further generate hybrid lattices, as described in Section 4,
attributes of the adjacent bone tissues. Stress shielding is a was generated by applying the implicit function approach:
phenomenon that occurs when an implant, which is stiffer f (x,y,z) ≤ c (I)
than the neighboring bone, cannot properly transfer forces
to the nearby bone tissue. This can potentially hinder the where c is utilized to determine the isovalue offset from
regenerative process and increase the risk of implant the zero level-set. For the sheet-based TPMS lattice
failure . One potential way to reduce the stress shielding investigated in Section 3, the solid region is calculated as:
[22]
effect is by intentionally making the implant less stiff near f (x,y,z) 2 (II)
2
the area where it connects to the scaffold and tissue. Using ≤ c
functionally graded gyroid lattice designs in this context is a where the thickness of the structure is controlled by
promising way to make this approach more effective.
intervals [-c,c], leading to the generation of the solid phase.
The mechanical performance of TPMS lattices can be The different mechanisms of generating TPMS lattices are
tuned with a combination of different unit cells instead of clearly shown in Figure 1A, where the gyroid unit cell is
only adjusting specific topologies of a single type of unit cell. regarded as an example.

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