Hi, I'm Elizabeth (Maylin) Rawson, the 2023-2024 Aeroshell lead. I made this article based on my own experience as lead conducting and managing the composite manufacturing of Daybreak (2022-2024). This document is primarily for aeroshell management to understand how to choose and acquire materials in preparation for a layup. This is also helpful for aeroshell members who want to understand more about the materials that we use.

To future aeroshell leads: try to ensure you get as many donations as possible. Composites are very expensive; I spent roughly $17000 in 2023-2024 (very few donations). Please work with your operations lead in advance to acquire materials.

My favorite places to buy materials, especially fabrics, are Composite Envisions and Fiberglast. As of the time I'm writing this I know that we have a 20% discount code from Fiberglast. However, I actually prefer Composite Envisions because you can buy basically everything you need there which means that you can order in bulk. Additionally, their clearance section is better. If you buy from their 2nd quality fabrics, their fibers can get really cheap and rival Fiberglast.

Fibers

Fiber type

Fiber	Uses	Pros	Cons
Carbon fiber	Used for the exterior of the car	Lightweight	Conductive → does not allow radio waves to travel through it Communicate with data acquisition on where they're placing the radio to make sure that you don't have carbon fiber surrounding it
Fiberglass	Typically used for making molds	Flexible Cheaper than other fibers Non-conductive → allows radio waves to travel through it	Heavy
Kevlar	Required in the canopy by regulations	Fireproof Shatterproof	Difficult to cut: you need a $30 diamond dremel bit

Tow: A bundle of fiber that is identified by the number of carbon filaments they contain. Each "k" stands for a thousand fibers.

Tow
1k
3k
6k
12k

Weave: the way the fibers are bundled together

Fabric stability: ability for a fabric to maintain its weave angle and fiber orientation
- The higher stability a fabric has, the lower the formability
Crimp: the curvature of a fabric in a single weave
- A very tight weave will make the crimp (curve) become more tight.

Weave	Definition	Uses	Pros	Cons
Plain weave	This is one of the most common types of weaves for carbon fiber. A tow strand in plain weave passes over 1 tow and under 1 tow.	Flat panels (includes sandwich composites) Bulkheads Tubes	High fabric stability	Poor with curved geometry/complex contours Harsh crimp in the tows due to the short distance between interlaces. The harsh crimp can create stress concentrations which can weaken the part over time.
Plain weave (spread tow)	Like your regular plainweave, but the filaments are spread into a wider tow.	Flat panels (includes sandwich composites) Bulkheads Tubes	Less harsh crimp in comparison to regular plain weave	Poor with curved geometry/complex contours More expensive than regular plain weave
Twill weave (2x2)	This is one of the most common types of weaves for carbon fiber. If you follow a tow strand in a twill weave it passes over a set number of tows and then under the same number of tows. Since this is 2x2 twill weave, it passes over 2 tows and under 2 tows. There is a longer distance between tow interlaces which means fewer crimps.	Curved geometry Typically bottom shell, canopy	Flexible Can conform to complex contours Fewer crimps compared to plain weave thus less potential stress concentrations.	Less fabric stability than plain weave
Twill weave (3x3, 4x4, etc)	Twill weave with less formability than standard 2x2 twill weave. The weave is less tight than 2x2 twill. We have historically rarely/never used this, but if you need to make a composite with many complex, tight curves then you may want to consider this. There is an even longer distance between tow interlaces which means fewer crimps than regular twill weave	Curved geometry Typically bottom shell, canopy		More expensive than regular twill weave Less fabric stability than 2x2 twill weave

Density

Fabric orientation

Fabric Orientation

Picture

Definition

Uses

Pros

Cons

0-90

Molds

Uses significantly less material
Cheaper
Easier to cut and prep

Weaker along the 45 degrees diagonal

45-90

(Quasi-isotropic)

Sturdier composites
Aeroshell

Stronger along the 45 degrees diagonal

Harder to cut and prep
Uses significantly more material
More expensive

After you have determined all of your fabric qualities, you need to calculate how much fiber you are going to use. The best way to do this is to go into the CAD file of the aeroshell and then create rectangular sketches that are the size of the fiber rolls that you plan to buy.
1. Make sure you have 3-5 inches of overlap for each layer of fiber.
Find the area of these rectangular sketches
Know how much ply you want in your composite, and then multiply the area by the number of ply.
Then, add 50% to the final amount you get.
1. You will always need more than you think. People will never cut fiber optimally or lay down fiber optimally. When I ordered material, I had a 30% buffer and it was not enough.

Resin

Pot life determines how long you have to work with the resin in a pot/bucket before it starts to cure. Most laminating resins that cure at room temperatures have a really low pot life.
- Higher pot life gives more leniency.

Mold Smoothers

Joint compound: https://www.homedepot.com/p/USG-3-5-gal-Soquete-Ready-Mixed-Joint-Compound-380066/202329615
- We use this and it sucks and makes mold release horrible. Please find an alternative mold sealant that is not joint compound
Spackle
Bondo: This is used on composite to patch gaps

Vacuum Materials

Vacuum bag
- Stretchy vacuum bag such as Stretchlon 200 is basically a necessity for any layup that isn't relatively thin.
  - https://www.fibreglast.com/product/stretchlon-200-bagging-film-1678

Breather:
- Breather is separated by density. Which one you choose is not that important as long as its roll width is wide enough for the composite you want to make. I chose based on price.
Peel Ply
- Allows for easier release of vacuum bag from part and gives a better finish
Tacky tape
- We use any kind of yellow tacky tape. Yellow tacky tape performs well in hotter temperatures and it is higher quality.
- Avoid gray tacky tape. It can be used for test composites or smaller composites but I would strongly advise against using these for anything that's important
- Make sure to cover your tacky tape with a wide masking tape so that epoxy and fabric scrap doesn't get onto and ruin the tacky tape. Remove the tape right before bagging

Disposables/Other Tools Needed

Gloves
1. We usually went through about 5-6 boxes of gloves at a large layup
Paint Brushes
1. We used between 10 and 15 paintbrushes depending on the layup length and the epoxy used
Acetone
1. At least 1 can of acetone is needed for layups to clean out tools (and hands)
Fiberglass Rollers
1. 5 or so would be nice to have as these are used to properly press down fabrics to the mold
2. Make sure to clean these properly
3. It is also nice to have a corner roller on hand
Squeegees
1. At least 5 are needed to help spread and saturate the fabrics properly
Mixing buckets
1. Have at least 3 or so buckets on hand for mixing epoxies
Mixing Sticks
1. Have 10 or so mixing sticks (you can split a regular pain mixing stick into 4 pcs and that works for the most part) on hand as these will usually have to be changed every few batches of epoxy
Kevlar Scissors
1. Have at least 3 on hand as these are needed to trim your fabrics as well as cut patching strips during the layup
  1. Make sure to clean these regularly

References:
https://www.elevatedmaterials.com/carbon-fiber-weaves-what-they-are-and-why-to-use-them/

Related articles

Page:

2022-2024 Composites Layup Process
Page:

Brief Overview of Composite Materials
Page:

Resin Infusion 101
Page:

Laser Cutting
Page:

Aeroshell Wet Layups for Dummies

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