I was curious as to how fiber composites are fastened to other materials and which methods work and don’t.
For instance It’s pretty obvious that you can glue fiber composites to other materials with epoxy.
Likewise can you thread fiber composites? Could you drill holes through them and clamp them together with nuts and bolts? etc etc etc
What methods have you guys tried and what works and what doesn’t?
there are a number of ways to fasten composite panels to other composite structures or metal structures.
rivets, epoxy bonding adhesive, using raw composite cloth and laminating the two parts together, riv-nuts, screws nuts bolts, etc. Only thing you shouldn’t do is put cf in direct contact with metal… it needs a barrier between the two like fiberglass cloth or enough epoxy bonding glue that the cf and metal don’t contact each other directly.
You can thread directly into composites however it’s better if you can recoil them. I would not use a depth that is less than 2D, plus test the loads that they can take before putting under critical loads.
Bolting through is fine but use a good sized washer, and it’s cored put in a hard point or a tube to prevent the core crushing.
There is a good spec sheet on repairing composites for aircraft that talks in depth about fastening composites, but I have lost it somewhere in my computer, sorry.
Stainless and titanium fasteners can be used in direct contact with carbon.
Lemme ask the opposite question then. What fastening processes are weak or I should totally avoid. One that comes to mind is nailing composites together.
yeah don’t ever use nails.
This subject can get very very complex. But basically glue with sanding and solvent wipe prep, or bolts through.
you can use “nails”, it is called Z-pinning. However, it’s done in dry fiber form with an ultrasonic hammer.
Normally, epoxy, and bolts are normally. Avoid any metal joints that are in direct contact with carbon fiber. Carbon and the metal will form a battery of sorts in presence of humidity, and start to corrode. A way to avoid that is wrap the holes in a glass layer, or coat the bolts with primer. If you are dealing with glass fiber, any bolt will do.
There are pros and cons for each. If the 2 parts are bolted together, it will be weak in shear, and sometimes in compression, especially after impact. That hole will start crack formation and fail starting at the hole. Epoxy can vibrate apart if torsional loads are applied, and the epoxy is more brittle than the composite. However, it is easy, and can sometimes be stronger than a bolt (read: single point loading, vs entire surface bonding). If you want to attach a stiffener to a panel, epoxy should be the way to go as long as you won’t expect major loading.
If using epoxy, you have to prep the surface correctly. You can’t just glue 2 shiny pieces together. Each surface has to he roughened, and cleaned correctly (Acetone WILL leave residue), and the bonding epoxy must be cured correctly. Peelply is a good way to easily achieve good bonding surface. Leave the peelply on the are where you want to bond until you actually have the epoxy ready to glue the parts on.
As Moke mentioned, you can also insert hardpoints in your composite (click-bond is one company), where you make your part WITH a metal fastener inside, be it a bolt or hole. They are prepped to bond well inside your part. Then you can just bolt your 2 parts together nice and easy!
In the end, it depends on what you want to do, what stresses will be placed on the part, how much stress, and part size/assembly limitations.
Could you further clarify Z pinning?
I found this article that briefly describes the process but I’m still slightly confused
http://www.icf11.com/proceeding/EXTENDED/4466.pdf
From what I understand this manufacturer takes prepreg and through some process ultrasonically nails it together with metal clips before layup?
yup, exactly that. most of the time I think are pins of carbon fiber (like, 1000 fiber thermoplastic rod)
AThere has been lots of research, but it never was the best way to do it. i think it cuts fibers in the laminate.
nails… lol. perhaps a heavy duty staple gun? lol.