CHECKPOINT #1 | Carbon

Files

Parts (Laser-cut)

Acrylic plate (top/bottom) 1/4" thick

Acrylic plate (middle) 1/8" thick

Videos (Injection)

5 mm

10mm

20 mm

Looking at the videos, we can observe that there is fiber alignment in the nozzle. However at longer fiber lengths, the carbon clogs up the syringe as shown in the image above for result of the injection.

Orientating FIbers

Syringe Ejection

Past Projects

[Checkpoint #1 - 4/7/17]
Results and Discussion

For our first test, we wanted to know from which lengths did casting happen and which will be the optimal fixed fiber length for Stage 2 of the experiment...

In our first round of experiments we observed and determined some interesting facts to guide our research:

The viscosity of corn syrup makes the well mixed fiber align itself significantly due to the shear in a short distance (in 20 - 30 mm through a nozzle of 2 - 1.5 mm). As such, any fiber length larger than 20 mm clogs the hole and syringe.
Although adding water to the solution creates a better mix, the viscosity loss makes it clog and the fibers are not as aligned; the fibers binds to one another and clogs in the mix.
We need a better mixing method prior to the addition of the syrup and also a better method to mix the carbon fibers in the corn syrup and subsequently, epoxy resin.
To check mixing with other viscosities we may explore other thicker fluids that lie even closer to epoxy resin in terms of viscosities (We may explore boiling corn syrup to further increase its viscosity.)
Beginning of the injection the fluid behaves in a circulate flow, therefore we should create paths (linear array of injection holes) so the fiber flows horizontally rather than spread in circles.
High viscosity helps prevent agglomeration. possible explanation is that any in-homogeneity in the mixture would lead to a local agglomeration. the agglomeration grows when the fluid lacks the shear force (viscosity) to drive the flow of fiber. the fluid would be `squeezed´ out of the agglomeration and the clogging gets worse.
Other than the lack of viscosity, the difference in Van der Waals force between fiber and fiber and the that between fiber and fluid might also be responsible for causing clogging.
There are two easy ways of quantitatively measuring the viscosity of resin, if measuring is necessary.
1. [Rough approximate] Dropping a 1" steel ball bearing into the solution and seeing how long it takes to get through it and this method does not work too well for an-isotropic materials.
2. Creating a jig of a moving plate over a stationary plate with the liquid in between.

RESULT: We discovered that viscosity is crucial in carrying the flow. As such, we need to vary the viscosity of the syrup in the next test (along the approximate viscosity of epoxy) while keeping in mind the syringe hole.

- Result of the injection of different fiber lengths into the molds with increasing fiber length starting from left to right (5 mm, 10 mm, 20 mm). 30 mm was not tested as for the 20 mm test, we noticed clogging, which resulted in air gaps appearing in the sample.

- Carbon samples cut into lengths of (from left to right): 5 mm, 10 mm, 20 mm and 30 mm.

Experiements

What's next?

Knowing that we want to find a syrup for now that matches approximately to the viscosity of epoxy, we found out that the range of resin viscosity is 3,000 - 13,000 cP while the range of syrup viscosity is 2,000 - 30,000 cP. For the next test, we will be testing out different ranges of viscosity of the syrup to simulate the resin viscosity. Then we would test the entanglement behavior of the fibers within that range. We also realized we need to look into the size and position of the injection hole as it could influence fiber alignment and clogging.

As initially, we didn't anticipate that viscosity would prove such a large problem, we decided that our main goal of this research was fiber entanglement and alignment, but if we have enough time, we would do Instron testing to validate any claims of sttrength vs. fiber length given that the alignment is satisfactory. If we do, we have possible Instron testing dates the week of 4/17, knowing that we need to design the mold shape into a dog-bone that is at least 1" wide and 4" long so that the failure point does not lie in the clamps.

In terms of materials, we will start making another mold, buy larger syringes, buy 1/2" - 1" steel ball bearings and keep track of costs due to our student budgets.