1. Rapid Toolers: Jordan Medeiros Stephanie Silberstein Hannah Yun
Investigation of the Mechanical Properties of a Single-Cell Tetrakaidecahedron using 3-Dimensional Printing (3DPTM)
Rapid Toolers:
Jordan Medeiros
Stephanie Silberstein
Hannah Yun
3.042 Final Design Presentation
May 12, 2005

2. Overview Motivation Materials Selection & 3D Printing Process
The Tetrakaidehedron
Crystallography
Designing Unit in SolidWorks
Finite Element Analysis (ANSYS)
Mechanical Testing
Conclusions
Further Research

3. Motivation: What and why?
Structure -
Possible Applications -
Structure – What it is, Why its special (space filling, nearly isotropic, etc)
Applications – Orthopedic (Possible manipulation of anisotropy ),Thermal Applications (Engine example), Lightweight applications (Aeronautics)
Motivation & Goals
A tetrakaidecahedron is a 14-sided polyhedron with 6 squares and 8 hexagons. The tetrakaidecahedron, also known as a "Kelvin Foam", is a space-filling polyhedron with a perfectly ordered, spatially periodic, open-cell structure. Prior research has proposed that the multi-cell structure is “nearly isotropic,” making it a potential candidate for applications in aero/astro structures, mechanical devices, or medical treatments (ie, bone replacement materials). Our group is utilizing 3D CAD software to model, and subsequently 3D print, single-cell tetrakaidecahedra to investigate its mechanical properties, including elastic modulus, yield stress, and failure stress. Is the single-cell structure really isotropic? Can we determine whether this structure can be used for the aforementioned applications?

4. Materials Selection Powder Base Impregnation Material Plaster – b ased
Cellulose/starch based
We decided to use a plaster based powder and its corresponding binder, due to its properties of high strength and low elasticity
We impregnated the material with cyanoacrylate, a moisture-cured material

5. Materials Selection Cyanoacrylate (C5H5NO2)
“Z Bond 101” – Moisture Cured
Flexural Strength: 17.2 MPa* (2,495 psi)
E ~ 2.7 GPa* (391,600 psi)
Not like epoxy – doesn’t have to be cured, we can drip it right on
Space-filling model of a small segment of a Super Glue polymer molecule. Notes: Super Glue starts out as methyl a-cyanoacrylate dissolved in an organic solvent. This substance is very unstable, and when it is exposed to even trace quantities of mild nucleophiles it polymerizes (the reactant molecules covalently bond to one another, generating huge product molecules). This process forms a tough flexible solid called polycyanoacrylate, which bonds together a wide variety of different materials.
* Jim Bredt, Z-Corp

6. Overall Printing Process
Start with a 3D CAD Solidworks model, send it to the printer.
Let it dry for an hour, then depowder
Dry at 100°F for 1 hour
Drip cyanoacrylate on shape, let dry
SolidWorks files of our models were exported to Z-Corp’s 3D printing software.
Tetrakaidecahedra were printed in different orientations relative to printing direction, based on the crystallography of the structure. Three different orientations of structures were printed: square face up, hexagon face up, and hexagon edge up.
Printed structures were depowered, and subsequently dried at 100 ˚F for 60 min.
After drying, the structures were impregnated with cyanoacrylate and left to dry overnight at room temperature.

7. Crystallography
These diagrams illustrate the symmetry of the tetrakaidecahedron structure. The tetrakaidecahedron belongs to the highest ordered cubic point group, shown to the left.

8. Building the Model

9. Finite Element Analysis
Tension vs. Compression
Von Mises  directional stress/strain and planar shear

12. Which Happens First? Reminder:
Yellow represents fracture strength for compression
Light Blue represents fracture strength for tension

13. Tetrakaidehedra Testing
Printing & compression in three directions:

14. Tetrakaidehedra Testing

15. Characterization of Materials Properties
ASTM D695-02a (Compressive)
ASTM D (Tensile)
Show samples, pass around?

16. Characterization of Materials Properties
Note: company info: E ~ 391,000 psi
tetra. max σ ~ 250 to 800 psi

17. Conclusions Conclusions
The tetrakaidecahedron unit struts fail in tension
Layer-by-layer processing introduces a level of anisotropy into the material.
Much of our data for our compressive and tensile standards is inconsistent, possibly a result of:
The concentration and depth of cyanoacrylate impregnation into the samples being non-constant
Warping of the samples during the printing process
Conclusions
The tetrakaidecahedron unit struts fail in tension. This agrees with both the virtual testing in ANSYS and the yield strength of the material in tensile tests. This is typical of a granular structure, which is usually much stronger in compression than in tension.
The elastic modulus of the tetrakaidecaheron structure in different orientations, though relatively similar, shows a disparity most likely due to the fact that layer-by-layer processing introduces a level of anisotropy into the material. Because of the complex system of struts, it is difficult to predict and counter the effects of the anisotropy. Furthermore, there may be additional anisotropy inherent in the structure due to the fact that our simplified structure consists of joints composed by two 90° and two 120° angles while the idealized structure consists of joints composed of four struts meeting at 109.5°.
Much of our data for our compressive and tensile standards is inconsistent, possibly a result of:
The concentration and depth of cyanoacrylate impregnation into the samples being non-constant

18. Further Research Possibilities
Changing variables
Further mechanical testing
Analysis on three-dimensional (multi-cell) array of tetrakaidecahedra
Due to our limited time and resources, we were not able to do all the things that would perhaps strengthen our argument. Future research may include: testing the shapes using a thinner strut size, testing the shapes using a smaller structure, using a different material for the printing, further mechanical testing, testing a three-dimensional array of tetrakaidecahedra.
Strut thickness, different materials for printing, smaller structure (one cell)?

19. Thank You! Prof. Chiang, Prof. Roylance, Mr. Toby Bashaw
Dr. Joe Parse, Dr. Yin-Lin Xie
Prof. Lorna Gibson
Prof. Bernhardt Wuensch

20. Questions?