Jeremy Senne

Don, Great question. The answer depends a bit on some of the hairy details but I'll give it a quick shot. It wasn't clear if your layup technique is hand wet layup (dry fabric that you are manually wetting out with resin) or hand layup of prepreg (material that is already impregnated by resin and generally requires freezer storage). The answer is the maximum vacuum that you can pull for both but for slightly different reasons: If you're hand layup of prepreg, the amount of resin is already set as a part of the prepreg process (unless it's very high resin content in which case you may still squeeze some out at high vacuum). In this case you really just want to squeeze as hard as possible with vacuum. If you're hand wet layup, the amount of vacuum that you pull will actually help determine your final fiber volume (amount of fiber vs resin) as the more vacuum you pull the more resin you will squeeze out of the sides of the laminate. This is a trick that infusion guys use to tune their fiber volume on big parts. In your case, though, if you're looking for minimum weight you'd want to squeeze out as much resin as possible by pulling maximum vacuum you can achieve. Regarding properties, your maximum LOAD in-plane won't appreciably change with fiber volume as the fiber will control that. Your maximum STRENGTH (which is normalized to thickness) will increase as you squeeze out more resin and achieve a higher fiber volume content. The same can be said about your STIFFNESS (load vs. deflection) which won't change, but your MODULUS (load vs deflection normalized to thickness) would increase as you squeeze out more resin. Note for wet layup there's one additional complication to watch. If you have bubbles trapped in your wet layup resin they can grow under vacuum if they can't escape the laminate during cure, which can create higher void content than if you used autoclave pressure (which would collapse the bubbles), hence the autoclave being the gold standard for curing. Three tricks to help here: 1) After you mix your resin pull vacuum on it. It'll look like boiling water because all the bubbles will expand and froth but then it will be air-free. You can use a cheap vacuum chamber like this one: https://www.vevor.com/vacuum-pump-c_11109/vevor-5-gallon-vacuum-chamber-upgraded-tempered-glass-lid-vacuum-degassing-chamber-304-stainless-steel-chamber-for-stabilizing-wood-resin-degassing-silicone-degassing-and-plaster-degassing-p_010758564652?adp=gmc&utm_source=google&utm_medium=cpc&utm_id=15698890952&utm_term=&gad_source=1&gclid=Cj0KCQjwqpSwBhClARIsADlZ_TkMesI7iv86wsA6SLjUNuKEcRscf7o-uFqL3vsngUogx3WG_S07dT4aAvuGEALw_wcB 2) Ensure that the breather in your bag has a path all the way to the vacuum hose. Some folks will erroneously only cover their part with release film then breather, but not put a breather path to the vacuum hose. This results in the hose pinching off the vacuum bag to your tool and keeping your part from actually seeing full vacuum. 3) Pull vacuum during the entire cure as it will help provide a path for any bubbles still trapped to get pulled out of the laminate. Hope this helps, Jeremy

Yeah the one that everyone takes for granted or ignores is cure shrinkage. You can mitigate the tooling CTE mismatch all day long, minimize thermal gradient during cure, and even minimize fiber/matrix CTE mismatch. Cure shrinkage will persist. I think I saw a graph once that it accounts for ~30-50% of the springback.

There's also a few trade schools that offer a range of programs. Not sure where you reside but in CA I've come across these guys at a few show: https://www.thefabschool.com/programs/advanced-composites-technologies/ I did a quick google search for "Composites Trade Schools" and found a few options in a few states.

Yeah it was an off-the-shelf stormtrooper suit. A wet layup fiberglass splash mold was made off of that set, then the carbon fiber set was made from the splash mold.

It was probably 3 weeks of nights and weekend efforts to wet layup and trim all the parts.

Some guys I used to work with did this back in the day: https://carbonfibergear.com/blogs/carbonfiber/star-wars-fans-carbon-fiber-enthusiasts-carbon-fiber-stormtroopers

One more update to John's answer. The layup definitely contributes significantly to the overall aggregate modulus of the tube, but if you were expecting an all unidirectional tube to have the same modulus as the fiber you'll probably be disappointed to find its 40-50% low. The other factor to consider is fiber volume compared to matrix volume, where the matrix is the resin the fiber is set in (usually epoxy or cyanate ester). This boils down to a rule of mixture combination of the fiber contribution to modulus and the resin contribution to modulus at the volumetric level where the two usually add up to 100%. The easy calculation is E_Total = Vf*E_fiber + Vm*E_matrix, where E_Total = Combined modulus, Vf = Fiber Volume, Vm = Matrix Volume, E_fiber = Fiber modulus, and E_matrix = Matrix modulus. Most composite laminas (and laminates) are in the range of 40% to 60% fiber volume, which the higher performance structures closer to 60% fiber volume. Since the fiber modulus is usually 10x or more the modulus of the matrix, you'll see the modulus of laminate at about 60% of the fiber modulus. If you're thinking that becomes a huge knockdown when you do a multi-angle layup like [0/45/90/-45/-45/90/45/0] and then also go with 60% fiber volume you're right. Usually this has you around 30-40% of the fiber modulus.

General comment on this. If you or your team are experienced in vacuum bagging with typical release film/breather/vacuum bag/sealant tape materials you will probably need to be in the 10+ quantity range before you see a benefit. It is worth noting that this is also very ply count dependent. If your ply count is low, this really only helps you with final bag. If your ply count is high (30+) and you have a lot of debulk steps this can significantly cut down on the disposable material use and time to bag. Most places that I've worked have had some sort of quick debulk setup for flat plates as this shows a ROI quickly.

It's worth noting that you should also use some sort of epoxy or other adhesive as a fillet bond along the corner joints to keep the structure together. If you really want to go all-out you could bond angle clips between the adjacent faces for the strongest structure of that construct. That's how a lot of satellite structures are built.