Week 8

Composites

What am I building this week?

This week I built a composite layup using silkworms

The idea is to use silkworms to "3D print" the fibers onto the lay-up surface. Given a flat, two-dimensional surface, silkworms will happily deposit their silk. I was also interested in material properties of a silk composite because silk has some nice material properties. Silk also has some interesting material properties. It's relatively strong strength to weight and each silkworm spins about 1 km of super thin (10-50 micron) silk fiber. The huge length of despoited silk is not aligned but is highly tangled. Perhaps the tangling will create some interesting properties? Let's see!

Making the molds

The silkworms need a surface to deposit their silk. I decided to design a simple wave. The major design consideration was not giving the silkworms to much z. They are constantly searchin for a three-dimensional space (for example, a corner) to spin a cocoon. I designed a simple wave in Rhino and milled a wax surface using the tabletop Shopbot.

I also created some small, raised foam rectangles for samples. I'll use the samples later this week for tensile testing. I design the simple rig for these raised platforms in Kokopelli and milled it out of foam on the tabletop Shopbot.

Milling the foam mold for the silk fiber composite test pieces.

Harvesting the silk

This was the easiest part. I had already been raising silkworms for a few other tests - so I plopped on a bunch of silkworms onto the wax milled surface. If you want to learn more about the silk worm lifecylce and order some, Mulberry Farms is a great vendor.

Silkworms spinning fiber onto the wax layup.

Silkworm close-up. The "mint chocoloate chip" silkworm had eaten food dyed green. The silk was still white.

This is the finished fiber layup.

I only had time to leave the worms on the surface for 2 and a half days. This piece had considerable lower density fiber than the composite samples.

Notice the aligned fibers on the edges.

An interesting next step in this work could be creating a surface with small ridges aligned orthogonally on the surface. The ridges could attract the silkworms and create a denser pattern of aligned fibers

Throughout the last couple weeks, I plopped 20-30 silkworms onto this glass piece to spin. The glass contained a thin layer or silk and I decided to harvest silk from it for my composite samples.

I lasercut the silk into a specific rectangular pattern.

The silk was stuck to the glass. I gently pried it away using tweezers.

All of the silk pieces ready for composite layup. The burlap pieces were created to test against the silk composites.

Doing the layup

Unfortunately, I don't have pictures or video of the entire process (my hands were busy!). I did my best at applying very little resin on each fiber sheet (typically 1-2 drops). I used 5-6 strips of silk for each composite sample.

Vacuum setup

Vacuum in progress

Taking out the composites

Silk block composite

Results

The wave layup

The layup was thin and flexible and retain the geometry of the silk layup.

The edges of the layup were noticeably stronger and stiffer where the silkworms had aligned their fibers

The layup set-up for the silk composite test peices.

Both the wave lay-up and the silk composite ended up being flexible, light and decently strong. I'm not sure how much of the properties are from the resin vs the silk. The next step in this research is to make a small resin-only layup and compare the properties. I'm also planning to test the composites on the CBA instron later this week. My intuition is that the silk composite is going to perform poorly in the stength testing. When visually inspecting the silk fibers, it appears that the fibers may have dissolved (disassociated from their crystalline form into an amorphous form) and aren't forming any type of internal strutures for the composite. But, I will know for sure after testing. Stay tuned for the results!