Adhesive replacing rivets or bolts

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dog

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Factory processes and materials under better control than we can manage in home shops.
Billski

My point is that the materials and procedures to successfully bond aluminum and carbon are available now, and being done by private individuals in compliance with any applicable law or regulation. As to individuals, there skills and prior experience ,their shops, and budgets, now ,always and forever is unknowable.

Results count and people are getting them.

If a particular type of bonded joint has a particular failure mode, what?, every kind of bonded joint is exactly the same, get the procedure right or it fails at an inconvenient time and place. The wobbly discussions here about which glue to use in wood construction are far more likely to get someone in trouble.
 
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Dan Thomas

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Factory processes and materials under better control than we can manage in home shops.
Yeah, and a drive shaft is small and doesn't have a long bond line.

Glue a strip of CF to an aluminum rib or something similarly stiff, then set it out in the snow at -30°F. Then put it out in the summer sun at 100°F. It will debond. Mechanical stresses caused by differences in the coefficients of linear thermal expansion.
 
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BoKu

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Glue a strip of CF to an aluminum rib or something similarly stiff, then set it out in the snow at -30°F. Then put it out in the summer sun at 100°F. It will debond.
Yeah, no. I've effectively done that. If you do the bonding right, the stresses are reacted by the joint and what you get are just internal stresses as stuff equilibrates. If adhesive bonds came apart every time they were exposed to stresses, we wouldn't be calling those compounds adhesives.
 

Rhino

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Yeah, no. I've effectively done that. If you do the bonding right, the stresses are reacted by the joint and what you get are just internal stresses as stuff equilibrates. If adhesive bonds came apart every time they were exposed to stresses, we wouldn't be calling those compounds adhesives.
But there are many adhesives that don't hold up to those stresses, and we still call them adhesives. There is no perfect adhesive for any application.
 

rv7charlie

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If you want an example of successful composite bonding to aluminum, look to the RV10's cabin top. But that still doesn't address the home garage *design* issues. The -10 was designed by qualified engineers for homebuild processes. I'd trust the 10's design; I wouldn't trust mine.
 

terke

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You may wish to have a look at 3M 5200. I know there are several canopies flying around the sky at 250mph+ that are held in place by that stuff. A canopy manufacturer suggested that adhesive to me 10 years ago.
 

wsimpso1

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You may wish to have a look at 3M 5200. I know there are several canopies flying around the sky at 250mph+ that are held in place by that stuff. A canopy manufacturer suggested that adhesive to me 10 years ago.
Hmm 3M 5200 is a sealant that may work for sealing Plexiglas to aluminum, but this thread is about structurally attaching aluminum. 3M's own site does not even mention 5200 for this purpose. How about something that does structurally attach aluminum to other things, like the OP was suggesting?

Billski
 

TLAR

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So the stress are reacted by the bond in the joint, Hmmmm, nope. The part will fail eventually due to too much stress, internal combined with external. The part will need replacement much earlier than a better designed part that takes into account the undeniable thermal coefficient differences.
 

rv7charlie

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If you want an example of successful composite bonding to aluminum, look to the RV10's cabin top. But that still doesn't address the home garage *design* issues. The -10 was designed by qualified engineers for homebuild processes. I'd trust the 10's design; I wouldn't trust mine.
Too late for me to edit the earlier post; perhaps an admin can do it for me. I was mistaken about Vans bonding the cabin top to aluminum; it's riveted like the rest of the a/c. The adhesive I was thinking about is used to bond the windows into the 'glass cabin top.

Apologies for the confusion
 

dog

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Please cite a few that are reccomended for bonding aluminum.
A very casual search reveals a large and competitive variety of bonding systems for any and all materials, and there are numerous bonding systems for carbon to X.
This is homebuilt experimental aviation where latex paint,and hardware store glue are discussed and used openly.
As detailed here the procedures for bonding wood are beyond some people,and yet others work comfortably with airospace grade materials and discuss those procedures casualy.
There are plenty of people bonding carbon to X at home,testing the bonds and detailing there results,automotive and bicycle use in primary
structures,have not dug for aircraft use ,but there are pictures bieng posted here of such things,recently a motor mount. And a quick read yields the ancient standard,that a good bond is stronger than the material,now in carbon and X.

Its what? 50 years of retail availibility of carbon?
 
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Victor Bravo

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I have been informed (by a person who has plenty of technical background to be credible) that there are in fact certain "conversion coatings" (similar to but NOT exactly the same as Alodine) that make aluminum far far more bondable and yield a much longer service life to the bond. Some kind of acid bath, then some kind of chemical conversion dip, then a solvent or water rinse. When done properly, you are apparently able to get approx. 75% bond strength on aluminum with epoxy.

This sounds to me like it would be halfway between something a homebuilder can do (we use Alodine easily enough) and something that has to be done in an aerospace MFG environment.

So although this discussion is about bonding dis-similar materials, the actual bonding to the aluminum half of the assembly is reasonably possible. The chemical conversion coating may or may not have some effect (good or bad) on the galavanic corrosion aspect, I have no idea about that.
 

rv7charlie

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There are 2 part adhesives that are used to bond truck & trailer aluminum skin to underlying 'rib' structure, that are usable in a 'commercial' (ie: body repair shop) environment. To me, that at least implies that the processes don't have to be lab-grade and should be relatively easy for a homebuilder to learn and control. For decades the BD-4 has used some variant of 'proseal' (fuel tank sealant) to bond ribs to aluminum spar (originally, fiberglass ribs; currently, aluminum honeycomb), and to bond the current aluminum skin to the aluminum honeycomb ribs. Biggest issue for the older fiberglass 'panelribs' (combo of rib & one bay worth of fiberglass skin) was that the fiberglass itself would eventually start weeping fuel, in the bays that were used as fuel tanks. Interestingly, the Grumman a/c that were designed by Bede and built in controlled, FAA-certified environments, *have* had issues with skin debonding.

To me, the bigger issue is the general idea of changing an engineered, proven process (aluminum riveted to aluminum) for a critical structural area, without an acknowledgement from an aero engineer that it is 'safe'. If I were simply adding a 'turtledeck' to a complete truss structure (steel tube or the BD4 aluminum angle truss), I'd see it as similar to gluing the canopy onto the aluminum frame on my RV7 with tipup canopy. There are some pretty extreme air loads on a bubble canopy, but it isn't part of the structure of the a/c.
 

wsimpso1

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Will somebody please cite a system marketed for bonding aluminum in a home shop or auto/truck repair shop type of customer.

I have no doubt that the oxide layer can be removed and then a conversion coating applied in a high cleanliness low oxygen environment, then bonded, then all edges sealed to prevent corrosive intrusion - I have worked with suppliers who do this well, most of the time. They all seemed to have quality problems molding or bonding to these surfaces at some point.

I even do not doubt that if we have high enough FOS, we can have something resembling a long enough lived assembly using low technology approaches, like ProSeal - in exchange for assembly simplicity, that high FOS means you take a weight hit. Since Weight is the Enemy of almost everything in airplane performance and capability, I would sure hope that most of us have gone beyond Jim Bede's awful compromises there.

In the meanwhile we have folks telling us that the products are out there, but nobody has told us (yet) what product to buy that does it or what report or product instructions direct us in its use. Even then, I want to see a report showing it surviving a salt air test to a suitable lifetime.

Billski
 
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rv7charlie

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Several years ago, I watched a friend who owns a successful body shop (and has added an aircraft paint shop) do an aluminum bonding operation with one of the commercial products. Unfortunately, I can't pull the brand/part number from memory. If I can catch up with him, I'll ask him what they're currently using.

I did find a link in my saved bookmarks to this company. I *might* have saved it when I saw my friend using structural adhesive, but I truly don't remember for certain. I picked one product, MP55310, more or less at random, and downloaded the TDS. No 1st hand knowledge of the company or its products. To be clear, I added the words 'aluminum bonding' to the file name for my own uses in file searches, but you can read the TDS for yourself.

Charlie
 

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wsimpso1

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H.B. Fuller and 3M both cite MMA (methacrylic) adhesives for bonding to metals. H.B. Fuller even says it works on untreated aluminum. Hmmm. They also say "outstanding bond strength" and "very durable".

What is "outstanding"? Tensile strength of the adhesive 4350-5800 psi, which is about one-ninth of 2024-T3 aluminum. Shear strength on aluminum is 3700 psi, which is about one-sixth of 2024-T3. While that sounds kind of small, think about using a circle of it three times the diameter of a squeezed rivet you might use instead and it will have about the same basic strength. Use a generous FOS on rivets and bonded joints, and the strength when new looks like it might be OK.

What is "very durable"? This is where the unknowns get at us and is exactly our concerns for bonding aluminum... And no data from fatigue or corrosion-fatigue is shared. We have no idea how many cycles it will take at some known stress/humidity/temperature. Maybe you can sweet talk a supplier out of such test data - good luck! Better use big FOS if using it to bond and be able to inspect the joints with an eye toward removal from service if it starts to act up.

Do you really want to put in enough inspection panels so you can look at every rib and have that much exposure to maybe having to make new major structure?

Billski
 

BBerson

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Avid/Kitfox have wood rib ends bonded to aluminum tube spars with 3M 2216. Very low stress because the ribs are in compression held by the diagonal bracing so it works. Once assembled chewing gum might hold it. The adhesive is rubbery and that is purposeful to prevent peel and water in the crack as would happen with brittle adhesive on aluminum.
 
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