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

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

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?

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

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

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.

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

Building the Model

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

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

Tetrakaidehedra Testing Printing & compression in three directions:

Tetrakaidehedra Testing

Characterization of Materials Properties ASTM D695-02a (Compressive) ASTM D638-03 (Tensile) Show samples, pass around?

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

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

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)?

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

Questions?