Page 74 - MSAM-3-3

Materials Science in Additive Manufacturing Gradient porous material design criteria

φ = cosY cos X cos Z - sin Z sin X sin Y = C (2) layer was 71% and the height of this layer was 3 unit cells,
D
To design the gradient porosity materials, MS Lattice and the aspect ratio of each layer was 1. The 60 – 70 – 80%
and SolidWorks were used for the CAD models of porous (3/2/1) indicates that the sample was divided into three
samples. The Schon-Gyroid sheet and Schwarz-Diamond layers, and the porosity and layer height were, respectively,
60% and 3 unit cells (aspect ratio 1) for the first layer, 70%
sheet lattice structures were introduced to generate the and 2 unit cells (aspect ratio 2/3) for the second layer, and
porous structure of the porosity materials. The unit cell 80% and 1 unit cell (aspect ratio 1/3) for the third layer.
size is set to 5×5×5 mm . To build up the mechanical
3
property database for further calculation, uniform 3. Results and discussion
porosity materials were prepared with porosities of 50%,
60%, 70%, 80%, and 90%, which cover the most studied 3.1. Correlation between sample design and
porosity range, as shown in Figure 1. For the design criteria deformation-induced densification phenomenon
exploration and the development of empirical energy The energy absorption of materials is usually calculated
absorption prediction rule for deformation-induced by determining the integral area under stress-strain (SS)
densification of gradient porosity materials, the gradient curves. Hence, higher maximum stress or strain leads to
porosity materials with different porous structures, increased energy absorption. However, maintaining high
porosity, and porosity change were prepared, as shown in strength and high ductility simultaneously is challenging.
Figures 2 and 3. To evaluate the tendency of deformation- For example, increased dislocation density of metal
induced densification phenomenon, the gradient porosity materials leads to higher strength but lower ductility.
materials were designed with two porosity changes However, introducing the gradient porosity into porous
approaching an average porosity of 50 – 90%, such as 70 – materials leads to increased ductility while maintaining
71% (3/3), 70 – 72.5% (3/3), and 70 – 75% (3/3), as shown strength, which means it is a promising way to improve
in Figure 2. Meanwhile, to develop the empirical rule for energy absorption capacity.
estimating energy absorption, the effects on the porosity Moreover, TPMS structures show a high energy
changes and the aspect ratio variations of each layer of absorption capacity among the various porous structures.
the porous materials should be evaluated simultaneously. During the deformation, TPMS porous materials tend to
Hence, the gradient porosity materials with three porosity be densified during compression, leading to high ductility
variations were designed, such as 60 – 70 – 80% (2/2/2), and high energy absorption. Figure 4 shows a typical
60 – 70 – 80% (3/2/1), and 70 – 80 – 90% (2/2/2), as shown SS curve of a uniform porosity TPMS material. During
in Figure 3. The 70 – 71% (3/3) means that this sample was the deformation, the uniform porosity TPMS material
designed as a gradient porosity material with two layers; undergoes three different deformation stages. The first
the porosity of the first layer was 70% and the height of stage involves elastic and plastic deformation until the first
this layer was 3 unit cells, and the porosity of the second fracture/load drop occurs. The higher the toughness at

A B

Figure 1. (A and B) The 3D model and printed samples of the Schon-Gyroid and Schwarz-Diamond uniform porosity materials with porosities of 50%,
60%, 70%, 80%, and 90%

Volume 3 Issue 3 (2024) 3 doi: 10.36922/msam.4234