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Over the summer, I researched at the Dynamic Structures Lab at Stony Brook University. The lab investigates novel shape-morphing structures.
One area of interest of the lab is meta-materials - materials engineered to provide special properties.
The figure on the right shows an auxetic metamaterial - a material that exhibits a negative Poisson's ratio.
Rotating squares allow expansion in all directions under tension
My project was to find a way to create an auxetic fabric. Here's the result:
Folded State
Unfolded Meta-Fabric
Another Folded State
This is an origami-inspired, auxetic fabric system. It achieves its auxetic properties by folding out of plane, allowing for compression in both directions simultaneously. It also has the added benefit of multi-stability: The fabric prefers to remain completely folded or completely unfolded unless loads are applied.
The metamaterial is produced by 3-D printing a special tile pattern onto pre-stretched fabric. The tiles guide the fabric after releasing the tension, allowing it to fold instead of shrinking.
Shown on the right is the setup for printing: I stretched the fabric up to 50% of its original size and clamped it to the build plate using binder clips.Â
The stretch of the fabric was checked with a rectangle drawn on the fabric, stretched to a 17 by 19cm rectangle on the plate.
An Ultimaker 2+ was used to print PLA onto the stretched fabric. It took a lot of trial and error to get consistent, reproducible prints onto the fabric.
Leveling the bed is difficult, as the Ultimaker opts to use the two forward-most corners and back-center of build plate. However, the fabric at those locations is thicker than in the center, which leads to poor calibration.
With the right printer height, tiles can be printed that are rigid enough not to warp when the fabric is released from stretch, allowing for the best possible sample.
If all goes well, the tiles are well-adhered to the fabric, strong enough to resist bending, and will survive when the tension in the fabric is released.
For the best results, I printed two layers of PLA for each tile, which allows for rigid tiles even if the first layer is messed up. Z-Retract is also used to ensure the fabric is not dragged while the nozzle moves.
After removing the fabric from the printer, we can cut out the sample and observe its behavior!
The tile pattern is based on the Miura Ori - an origami fold that exhibits auxetic properties. It was developed by Koryo Miura for use in deployable space structures.
At first, I tried printing the pattern itself on the fabric, but that didn't cause any folding action. Instead, the fabric just shrunk around the tiles.
To reduce shrinking, I tried connecting the tiles with plastic beams. While these lines prevented shrinking, the lines prevented folding and limited the overall deformation of the fabric.
Having teeth instead of beams allows us to have folds while restricting shrinking near the tile.
Through the lab, I was able to perform tensile tests to characterize the elasticity of the fabric. An Instron machine was used to find force-displacement curves, and this data will be used for modeling the system
Our next steps are to test different parameters (number of teeth, space between tiles, etc.), figure out a better fabrication method, and develop numerical simulations of the fabric to further the concept.
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