Visualizing Stress Distribution in 3D Printed Lattices

The first portion of this article showcases my final project in PDF format. My first prototype is shown below the PDF.

Click here to view the final prototype video.

TristanWSchwabFinalProject

First and Second Prototype

Project Description:

For the initial prototype of this project, I demonstrate the unique complacency of lattice structures designed and optimized through NTopology and manufactured on an Ender3 Pro and Formlabs3 using elastic materials. I showcase my design process, my thought process in building lattices in NTopology, and my process to build an interface to visualize force distribution through a lattice.

Click here to see the prototype demonstration. 

Designing a Lattice:

There are multiple platforms for designing lattices. I selected NTopology, a software used in the industry and readily available on a student license. NTopology is unique for its interface with AM and easy “block” UI, which proved to be very efficient when learning about different lattice structures and adjusting parameters.

Figure 1: Fluorite and Body Centered Cubic Lattice Structures generated in NTopology after importing a CAD Body

Printing Process:

The first CAD bodies that I designed had small voids which I envisioned could house the force sensitive resistors. This idea would have likely worked, but printing on my Ender3 in TPU, an elastic filament, proved that printing any of the lattices with the support structures for the voids was not easily scalable, and unnecessarily overcomplicated the design. Ultimately, those prints did not turn out to be the best, and I decided that generating a simple rectangular prism lattice without voids would be the best solution. 

Unfortunately, the files I sent to the Jacobs Center to print on their FormLabs SLA printer were unusable. I wish I had given more thought to the initial design so that I could use an SLA print for a comparable demonstration, but I submitted my initial design prematurely. This print was made in elastic 50A resin, which may have been a bit too elastic for the purposes of this project.

Figure 2: Example of TPU failed lattice print with voids
Figure 3: Failed SLA print.

It turns out that the best print is the simplest design. This cannot be more true when it comes to printing elastic lattices, which fundamentally behave like springs. I tried a variety of lattice designs, Weire-Phelan, Kelvin Cell, Isotruss, Fluorite, etc… all of these lattices are nearly impossible to manufacture without support structures. I prioritized visualizing the cells themselves, so printing at a low density was a heavy consideration. The best lattice for my purposes was the Body Centered Cubic Design, which does not present overhangs greater than 45 degrees which would necessitate printing supports. 

Circuit Design

To begin my circuit design, I set up one FSR embedded in a lattice which I had on hand. Once I generated the right print, I tried embedding two FSRs accompanied with LEDs. I was having some trouble with getting the LEDs and FSRs to stay connected with the jumper wires, so I decided to solder end tips to all of them and plug them into the female-male jumper wires and wrap them in electrical tape for final presentation. 

Figure 3: Front and back faces of body-centered cubic lattice embedded with LEDs and FSRs.

Final Setup

When I was initially applying a force to the front face of the lattice, it was actually expanding outward as a result of the Poisson’s Effect. It turns out that this effect was so great that the corner FSRs were not picking up a force, since the upper face of the slots I cut out from the lattice were lifting upward. To counteract this, I built a foam board frame to contain the lattice. This made the entire setup a bit more portable and pleasing to look at, though it took away the side view of the lattice and made it more difficult to see the bottom face force response. 

I’ll be honest, this setup looks like a jumble of wires and trying to make the wires clean and orderly was an extremely difficult aspect of this project. After a few tries, I decided to separate the wiring for the left and right sides of the lattice, and this effectively cut my odds of miswiring in half. I also color coded the jumper wires as practice to improve visibility for myself and viewers.

Figure 6: Side view of foam board slots for FSRs and LEDs.
Figure 7: Split wiring from left and right sides.
Figure 8: Arduino board using all analog ports. Voltage source from battery pack.

Figure 4: Of course, the code.
Figure 9: Side view of foam board slots for FSRs and LEDs

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