Page 81 - ESAM-1-2

Engineering Science in
Additive Manufacturing Porous structure performance improvement

layered pore distribution in gradient materials, the material strut diameter can rapidly increase the volume fraction,
collapses layer by layer during the collapse process instead and the porosity of the structure will decrease to achieve
of immediately fracturing along the direction of maximum the desired mechanical properties. The influence of the
shear force at approximately 45° from top to bottom. In optimized radius on the volume fraction is presented in
addition, during the collapse process, densification stacking the stiffness and strength of the material structure, both of
occurs, resulting in a higher area under the stress–strain which are significantly enhanced. 26
curve for gradient materials compared to uniform density; When a material is subjected to perpendicular strength,
this characteristic provides better energy absorption for it may undergo deformation, which can be classified into
gradient materials. 23-25 two types: “bending” and “buckling.” Bending occurs due
In additive manufacturing, products made by SLM to the strain behavior induced in the material by strength
typically exhibit a very rough surface, often with many applied perpendicular to its principal axis, whereas
incompletely melted powders adhering to the surface. From buckling refers to a sudden change in the shape of the
a microscopic perspective, when subjected to an external material when axial strength reaches a critical level. 31-33
force, stress concentrates at the tip of cracks. Cracks with This study focuses on the relationship between material
smaller curvature radius and deeper notches experience strength and Young’s modulus by exploring the effects of
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a rapid increase in strength, causing them to withstand buckling and bending deformations of struts. Zhao et al.
greater strength than other locations. Consequently, they conducted with Cubic, G7, and Rhombic dodecahedron.
are more likely to exceed the yield strength and plastic The results indicate that the Cubic structure mostly
deformation that happened earlier. This phenomenon fractures due to compressive strength, mainly compressed
initiates the propagation of cracks from pre-existing flaws, by perpendicular buckling struts. On the other hand, for
resulting in material fracture, accompanied by a decrease the G7 and Rhombic dodecahedron structures, strength
in both strength and ductility. Stress concentration can be is mainly compressed by bending struts under tension
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expressed as follows (Equation II): and compression. Through the design of strut shapes,
increasing the number of buckling struts can increase the
d ultimate fatigue strength of the material. Conversely, an
σ max = σ ×( 1 2+ ρ ) (II) increase in bending struts prompts the material to develop
fatigue cracks. The growth of fatigue cracks within the
where σ is the stress at the notch, σ is the applied struts significantly affects the material, accelerating its
max
stress, ρ is the curvature radius of the notch, and d is the fracture.
distance from the notch tip to the surface.
The gyroid structure is based on a TPMS. Due to its
Another study adopts the lattice structures with smooth surface, the gyroid structure exhibits high ductility
smooth surfaces based on the mathematical approach of and has been the subject of numerous studies indicating its
triply periodic minimal surface (TPMS). TPMS is a class high energy absorption capabilities. 35,36 According to the
of minimal surfaces that exhibit periodicity in three- above conception, the structure with rounded corners can
dimensional space and possess zero mean curvature at reduce the stress concentration at the node, and the vertical
every point on the surface. Common types of TPMS strut, which is parallel to the compression direction, can be
structures include the gyroid, diamond, and Schwarz- separated by bending and buckling vector, enhancing the
Primitive surfaces, which can be mathematically defined buckling vector could enhance the strength and ductility
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through equations or parametric modeling. With the of the structure. Both of them can enhance the capability
advancement of additive manufacturing technologies, of energy absorption. However, the gyroid structure is
the complex geometries of TPMS structures can now be already smooth enough and without any vertical struts,
fabricated using 3D printing. TPMS structures demonstrate which means that it is difficult to improve the performance
excellent mechanical properties and fluid permeability. 28,29 of the gyroid structure through the design optimization
Optimizing the nodes of the struts causes changes in described above. Hence, in this study, we would like
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strength distribution, which significantly impacts the to explore the performance improvement capability of
deformation behavior of the structure. This optimization tetrahedron structure and compare it with the control
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can result in the structure standing more strength group of gyroid structures, whose mechanical properties
distribution, thereby increasing its strength. The volume are reportedly better than that of tetrahedron structure.
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fraction is a crucial parameter controlling the mechanical Moreover, only the relationship between structures
properties of porous materials, and it can be determined with rounded corners and varying structural angles was
by the strut diameter, optimized radius, and lattice size. explored in previous studies. Thus, this study only revealed
When the unit size is set as a constant, increasing the the different angles between the struts, and research on the

Volume 1 Issue 2 (2025) 3 doi: 10.36922/ESAM025170009