I made a little more progress over the past couple weeks. The top inside edges of the beams have foam fillets which will eventually provide a good gluing surface for the foam and carbon top plate. To make the fillets, I glued three layers of regular density foam to make a sheet 1.125" thick. I actually bought a sheet of 1" foam when I started this project, oh so long ago, unfortunately it is sitting in the boat house in the land of enchantment. In any case, I then sliced the laminated foam sheet into strips with one side beveled at 45-deg. on the table saw. The strips were then carefully formed to the top mold to match the curve of the beam. A layer of glass tape was then laminated to the diagonal edge of the fillet, and extends beyond the fillet edge about 1.25". A layer of peel-ply was added to ensure good adhesion when glued to the beam sides and top. This is the new peel-ply I purchased when I stocked up for the beam fabrication project. It is higher quality than the stuff back home, a little heavier, and it cuts much better (fewer cob webs form along the cut edge). I found this peel-ply is a little easier to handle and place without distorting, too.
So here are a couple shots of the two fillets setting up on the top deck mold. Looks like I am building a model of an olympic ski jump facility! The hardest part of this task was forming the big curve and securing the foam without breaking it. Because of the triangular cross-section, the foam tends to twist when bent to fit the curve. So I went over the curved section of foam with the heat gun to make it more malleable, and preformed it while warm. Then I held the strip in place with screws from beneath every 4-inches, or so, making sure to twist the foam square with the mold. It worked well, with no mishaps. I guess Murphy was taking a nap that day. In any case, the two fillets for the first beam are now cured and holding their shape, as intended. I will glue and laminate them into the beam structure soon. Then I will have to repeat the process three more times, once for each beam.
Before I install the fillets, I applied the first layer of carbon fiber to the beam interior. This roll of carbon has been hanging around the shop since day one, so it is nice to finally make use of it. It is also a lot more expensive than glass (about 5x by weight), and also a lot stronger (about 3x stiffer) and lighter. I am keeping all scraps for later use where I need smaller strips. Since it is unidirectional, I can lay narrow strips next to one another to make a wider lamination without any loss of performance. To laminate the carbon, I put the epoxy on the foam first and then laid the carbon in the wet epoxy. Then I used a squeegee to force the epoxy up through the carbon fibers. This worked very well with minimal foaming due to bubble formation. I was a little worried about working with carbon because I had read that it is harder to fully wet, but this was very easy and neat. Being careful not to apply too much pressure on the fibers, I was able to keep the carbon nicely aligned and positioned around the strut recess.
You can see the results of my handiwork in the photos. I also applied a layer of the quality peel-ply so I can get a maximum bond with the next layers of glass and carbon. Those layers won't go on until the fillets are installed, after this epoxy cures, so the peel-ply is a must. And since you probably can't see the peel-ply in these photos, I must have done a good job wetting it out. This one layer of carbon and peel-ply required 300 mL of epoxy mix. I should calculate how much epoxy is needed for an optimum lamination. This layer was fully wet, but in no way over saturated, and I had to work to pull the epoxy into the peel-ply, so I think it is pretty good. The only hard part about working with carbon was marking it, since I can hardly see my Sharpie marks on the carbon black fibers.
Well, that's it for now. Next task is the fillet installation, then lots of laminating on the inside with both glass and some more carbon.
