# A Computational Geometry Generation Method for Creating 3D Printed Composites and Porous Structures
## 4 Conclusions  
The study describes and implements a computational method for generating porous materials and composites for additive manufacturing techniques. The method allows for potentially using available materials to create hybrid metamaterials with tailored properties. For the purposes of this study, three geometries were generated and each was split into two segments. Materials were applied either in one segment for porous structures, or in both segments for composites. PLA, TPU, and Nylon were used to generate four types of specimens i.e., porous PLA, porous TPU, PLA and TPU composite, and PLA and Nylon composite. Twelve specimens were produced in total, and tested under quasi static compression.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Material** & **Density (kg\(\cdot\)m\({}^{-3}\))** & **Stress (MPa) at 0.1 Strain** & **Stress (MPa) at 0.2 Strain** \\ \hline \multirow{3}{*}{PLA-Nylon composite} & 949.47 & 23.25 & 31.39 \\  & 905.79 & 20.87 & 29.74 \\  & 900.27 & 22.32 & 32.54 \\ \hline \multirow{3}{*}{PLA-TPU composite} & 974.15 & 12.79 & 18.03 \\  & 866.64 & 10.27 & 15.21 \\  & 1.01 \(\times\) 10\({}^{3}\) & 14.28 & 20.55 \\ \hline \multirow{3}{*}{Porous TPU} & 586.55 & 0.59 & 1.031 \\  & 574.09 & 0.54 & 0.97 \\  & 557.39 & 0.55 & 0.94 \\ \hline \multirow{3}{*}{Porous PLA} & 515.52 & 4.7 & 6 \\  & 507.44 & 4.6 & 6.7 \\ \cline{1-1}  & 492.80 & 4.55 & 5.98 \\ \hline \end{tabular}
\end{table}
Table 2: Specim densities and nominal stress response at 0.1 and 0.2 nominal strain.  
Two types of porosity were included in the porous materials i.e., porosity introduced by the Voronoi cells and partial infill within the solid parts. Similarly, the composite structures also included partial infill for both materials. Material combinations that could otherwise be difficult to achieve using traditional methods were geometrically intertwined to produce different properties. The use of Voronoi cells results in complex geometries with a potentially large interface surface area that allows for the materials in composites to intertwine in a stable manner. Additionally, stochastic porous structures that can resemble organic configurations may be suitable for cell scaffold applications [9].  
The method provides a number of variables that can be potentially manipulated to define the macroscopic material properties. The number, size and positional distribution of the Voronoi cells, the infill percentage during 3D printing, and the combination of materials could provide a range of resulting properties. Material combinations can also have synergistic effects e.g., in damage and vibration management [31].  
Further study is required to fully characterize the resulting materials, and determine the range in achievable properties and limitations of the method. Additionally the effect of surface roughness and interface friction in composites could be studied. The number of material combinations is limited by the capability of the additive manufacturing equipment, however the method could also potentially be used with other types of materials (e.g., metals, ceramics, bio printing gels), additive manufacturing methods and size scales. This could potentially find applications including heat exchange, permeability, acoustics, or be used with conductive materials as part of smart material systems. These would be the topics of future work.  
This research received no external funding.  
Not applicable.  
The raw/processed data required to reproduce these findings can be shared upon request and within reasonable time. These cannot be shared at this time due to time limitations.  
The authors declare no conflict of interest.