Layup Experiments

[Joedang]

There are a few unresolved/open questions surrounding the layup process. Individually, each is pretty simple, but they all require a cure cycle. The new oven may make this easier, if we're allowed to walk away from it.

These are not just idle questions. Answering them could really inform the MFG of the airframe. Doing them all would take a really long time, but if I get volunteers we can perform multiple tests in a single cure cycle. (This also happens to be a good opportunity to introduce people to the layup/cure process.) Ideally, each person could answer one or two questions.

• When laying up many layers of prepreg, do the layers slide around during curing? What's the porosity like?
  We ended up using 10 layers of prepreg for the fin brackets. The layers don't really slide around at all. Layered that thick, they dribble out a lot of epoxy. The ratio of dry to wet cells looks about the same as with the non-surfaced modules. We didn't cut them open, but I would guess the porosity is low, since they expel a lot of epoxy.
• Can the prepreg be supplemented with a 2-part epoxy?
  Heck yes it can.
• The new shrink tape doesn't really release from parts like the old shrink tape (supposedly it was the same product...). Are there any better methods for releasing the shrink tape other than using release film?
  It might be possible to coat it in a thin layer of pastewax as it's being rolled on, but that doesn't seem worth the effort. It would be better to just call the Dunstone and figure it out.
• If you replace the Venturi pump with a mechanical pump, does that significantly increase compaction? (The hardest part of this is acquiring and setting up the pump.)
• How well would it work to layup CF into/onto a sharp corner if you cut sheets to butt up against the edge and just use many layers?
  Not very well. If you need to do that, the best option is to use twill weave and a filler/gel-coat.
• How dimensionally stable is 3D printed PET when vacuum bagged and cured?
• Can an SLA print be used at support/fillet material?
  Probably, if it's a room-temp epoxy. PLA definitely works for room-temp epoxy.
• Can 3D printed PVA be used as a medium for "lost-X" (in this case lost PVA) molding/casting?
  PLA does not really work, since its melting temperature is above the working temperature of F-2000 epoxy. If you try to melt away the PLA, the epoxy starts smoking!
• Can you layup a strain gauge into a module?
• Can you run a wire conduit through the seam of a nomex core?