Thrust Bulkhead Construction

The thrust bulkhead was made from carbon fiber and fiberglass. Mick Kelly donated the carbon fiber and provided much needed input on its method of construction. It contains 12 layers of carbon fiber and 4 layers of fiberglass. The layers include: 4 CF, 2 glass, 4 CF, 2 glass, 4 CF, with each layer turned 90 degrees from the last.

 

The epoxy used was Pro Set 135/237. The manufacturer's data sheet says to cure at RT for 15 hours, and post cure (heat) for 8 hours. I consulted than and jumping straight to the post cure was acceptable. (Why I asked them about this will become apparent later.

 

The layers were built up on an aluminum platen. A sheet of Mylar (donated by Mick Kelly) was first placed on the platen. Each cloth was place on top of each other, with epoxy carefully added in between. A final layer of Mylar was added, and another platen was placed on top.

 

The platen assembly was then placed in my MTS load frame. An oven was placed around the assembly. I then began programming the load frame to apply pressure on the platen. The distance between the two platens was monitored to within 0.0001". As I applied the load, the platens would come together and squeeze the excess epoxy out. As I applied more load, the platens got closer to each other, and more epoxy came out. I continued to apply load until the platens didn't move much at all. The layers started out at about 3/8" thick, and ended up at 0.1245" thick.

 

A few ideas were given to me on the amount of load needed to make the perfect resin to fiber ratio. The consensus was that 50 to 100 psi would be my target. Having a roughly 6 ¼" disk of carbon fiber between the platens, meant that I had about 30 square inches of surface area to compress. The load I ended up with on the platens was 2,040 lbs. This means that I applied 68 psi to the carbon fiber. (Sounds like the sweet spot to me!) Once I found the load I wanted, the MTS load frame kept this exact load on the assembly while it cured. I then programmed the oven to maintain 140°F for 15 hours. This was done so that I could do the entire cure cycle overnight.

 

Once removed from the platens, the bulkhead was ground to 6" diameter. This came out very solid and stiff. Tapping on it gives a glass-like sound.

 

Layers with epoxy on the bottom platen

 

Top platen in place, before loading

 

View of platen assembly inside furnace, with small load applied

 

View of furnace with load applied, and temperature ramping up

 

View of finished bulkhead after rough-size grinding