Adhesive replacing rivets or bolts

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cvairwerks

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May 12, 2010
Messages
263
Location
North Texas
I work for one of the big 2 aerospace companies here in the US. We never bond anything to aluminum with a conversion coating in place. It's always removed, the bond made and after it's fully cured, any exposed area the coatings were removed from, the coatings are restored. We use a variety of adhesives and all require careful adherence to storage, application and curing criteria. In all of the different aircraft that I've worked on there, I don't know of a single structural joint that is adhesive only.....
 

dog

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Joined
Dec 29, 2019
Messages
445
The unfortunate conjunction of liability assosiated with patents and or propriatry processes makes the idea of publishing a specific claim defined in enginering terms
a non starter for a "bond" as marketed to
the world.
Hence the companys producing adhesives
advertising there engineering services and then
for the rest of us giving broad hints and the examples of bike,automotive,and others on the
net.
Anyone after specific repeatable properties is
well advised to start with what the most ambitios amatures are doing and get numbers.
And trust that everyone everywhere is after the same thing,lighter,stronger,more durable ,better looking,and as affordable as possible.
 

reo12

Member
Joined
Jan 15, 2021
Messages
21
I'd love to see someone figure out what it takes to stop aluminum from oxidizing from the edge of the adhesive and spreading - releasing the adhesive bond as it progresses.
I guess I've been around long enough to have seen failures of bonded aluminum structures. Thankfully none are aircraft.
Back in the 70's we scrapped some military electronics cabinets that were anodized a gold color and bonded with what appeared to be a yellowish/beige epoxy. We cut some down into 4 legged tables to use around the shop. They were funky - ugly tables and prone to simply fall apart at the most in-opportune time. It came to where only one was left. I had it sitting unused outside the shop for some 10 years. I went to move it and it fell apart in my hands. The hard adhesive had debonded from the aluminum.
I have no less than 4 Winnebago LeSharo motorhomes. The roof is made of 2 longitudinal sheets of finished aluminum overlapped and bonded with molten Garolite plastic. Every one of them has debonded.
Both methods of bonding produced what appeared to be successful joints only to fail over time. Unfortunately with aluminum the oxide layer on a part can be so thin as to not be visible. It can break the bond of an adhesive without distorting the joint or producing any outwardly visible indication of a failed joint. Scary to think of not being able to see that a joint has failed on a flying machine.
 

Blackhawk

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Apr 18, 2008
Messages
240
Location
AUSTRALIA
The BD-4 uses bonding of the wing skins and they look as if they only buff the area to be bonded; it would be interesting to find out if any have failedBD4 2011-09-23_11-29-42-X3.jpg
 

TLAR

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Joined
Sep 29, 2020
Messages
291
Bonding some kind of material to Aluminum, oh what a topic.
The moderator saying no way, and has for years. He is a knowledgeable guy, with a big degree.
Other people myself included, say yes. Aircraft industry professionals are conservative and say no.
The answer has a lot to do with the forces that the bond will experience.
This topic has been beat to death here on HBA.
When subjected to peel it’s gonna need a mechanical fastener to prevent the peel from ever getting started in the first place.
3M no thanks
If you want to glue some stuff together
look at Lord adhesives.
Be sure and not get any on your finger
 

dog

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Joined
Dec 29, 2019
Messages
445
Or from actual engineering analysis and testing for bomb tossers that go well over Mach, and experience from doing it since 1952.
The Mars Flyer has successfully operated
useing carbon to metal bonds under the most extreme conditions ever attempted.
Carbon to aluminum and other metal bonds are
becoming ubiquitous in demanding aplications
where no other fastening is used ,or can be.
One huge aplication is the bonding of wind turbine blades to the metal hub attach points
with nothing but adhesive.

Please publish your assertations of
"actual engineering analysis" of aluminum carbon bonds ,from 1952,what did they try
useing?welding?contact cement?,firm admonition?,bubble gum?
 

Kyle Boatright

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Nov 11, 2012
Messages
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Location
Marietta, GA
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.
The cabin top is mechanically attached to the aluminum airframe by close to a hundred pop rivets and something like 30 nuts and bolts. Any adhesive used (proseal) is to prevent water intrusion through the seams. People fair the aluminum/composite joint with various composite materials, but those are not structural bonds.

Edit: Looks like RV7Charlie already posted an update correcting the post I quoted.
 

wsimpso1

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Oct 18, 2003
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Saline Michigan
The Mars Flyer has successfully operated
useing carbon to metal bonds
The Mars Flyer example has no validity for us here. This craft had no atmospheric oxygen nor water during its trip to Mars. Once on Mars, the atmosphere is comprised of a couple percent N2 and Ar, the rest CO2, tiny traces of H2O, and virtually no O2. That is a pretty inactive environment for metals, and won't oxidize aluminum, so our corrosion driven bond failures can not happen there. I think we can assume the parts were adequately protected prior to launch.

As I and others have stated, successfully gluing aluminum means increased FOS (costing you increased weights), you may lose robustness with decreased reliability that comes with it, and you have largely unknown fatigue and life properties. If your design works and lives and is light enough, more power to you.

Go in forewarned, then have a test program that combines atmospheric contaminates, thermal cycling, and fatigue loading, and let us know how it comes out. This daunting prove-out makes me want to go with the known...

Billski
 

cvairwerks

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Joined
May 12, 2010
Messages
263
Location
North Texas
Huge design and operational philosophy difference between Ingenuity and a manned platform. Ingenuity was designed and built with a life of less than 1 hour....Flight time for it is measured in seconds, not hours. Ingenuity is a whopping 4 pound vehicle vs the stuff I work on that ranges from 13 to 185 tons. Our operational lifetimes are measured in the thousands of hours, with structural integrity being proved out to as much as triple the operational life.

If you want the relevant engineering documentation, you'll need the appropriate clearances, ITAR licenses and a demonstrated need to know. Even though I have worked on them, I never had the need to know, as I was not a design, fatigue or reliability guy, just a builder/fixer/breaker of the product.
 

dog

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Joined
Dec 29, 2019
Messages
445
The Mars Flyer example has no validity for us here. This craft had no atmospheric oxygen nor water during its trip to Mars. Once on Mars, the atmosphere is comprised of a couple percent N2 and Ar, the rest CO2, tiny traces of H2O, and virtually no O2. That is a pretty inactive environment for metals, and won't oxidize aluminum, so our corrosion driven bond failures can not happen there. I think we can assume the parts were adequately protected prior to launch.

As I and others have stated, successfully gluing aluminum means increased FOS (costing you increased weights), you may lose robustness with decreased reliability that comes with it, and you have largely unknown fatigue and life properties. If your design works and lives and is light enough, more power to you.

Go in forewarned, then have a test program that combines atmospheric contaminates, thermal cycling, and fatigue loading, and let us know how it comes out. This daunting prove-out makes me want to go with the known...

Billski
Mars Flyer has had to withstand bieng built on
earth,with all ambiant conditions,extream g loading on liftoff and braking,vacume,ultra cold
temps and day night thermo cycling on mars
at a very low pressure.
Conclusion ,sticky stuff worked.
Drive shafts of carbon aluminum handle thermo cycling and road conditions while bieng
torsionaly loaded and reverse loaded,just fine.
Bicycles that people are trusting there lives on
in trafic, made from carbon bonded to aluminum,hold up.
Wind turbine blades,the list goes on.
The numbers to quantify all of these in engineering terms are obviosly out there,just not publicly availible as yet.
 

wktaylor

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Joined
Sep 5, 2003
Messages
318
Location
Midwest USA
Structural adhesive bonding is a scientific art that requires sophisticated training to accomplish with high confidence... if You want the structure 'fastener free'.

Let me tell You a WKTaylor long-short story. A costly batch of film adhesive for F-15 aluminum honeycomb repair was approaching the end of its freezer-life. Shop chief didn't want to 'scrap-it' so he called me to discuss options: Lap shear test results over 4000-PSI at Room-Temp was the mandatory minimum strength: (+)4000-PSI OK!... (-)4000=PSI.. SCRAP. I was called to review test results, which were all over-the-map from 4050 down to 2400-PSI. NO-GOOD: SCRAP! Shop chief was not happy. About a week later he called and asked for a 're-do of the testing'... Why?... 'trust him'. The second go-around the lap-shear testing results were totally different: 4100 down to 3880 PSI... whaaaaat happened? Everything was exactly the same... EXCEPT... the SECOND technician who made the test coupons had extensive adhesive bond training and experience... the first technician to do the job was essentially under qualified and the shop was loosing overall confidence in the MAN due to sloppy workmanship. I qualified the adhesive for another 3-month usage-extension… and I gave the second technician a gold-star confidence rating.. he became my go-to-guy for all issues related to high reliability and durability structural adhesive bonding… I learned a LOT from him.

I cannot emphasize the benefit of knowledge, training, processes and materials for high reliability and durability adhesive bonding.

I want to caution anyone bonding carbon fiber-cloth to aluminum... isolation using one or more layers of dense glass cloth... between the aluminum and the carbon fiber is important... but equally important is ensuring the aluminum has corrosion protection [a separate topic entirely, later] and the glass cloth MUST be completely resin-sealed against moisture intrusion... glass-fibers will microscopically 'wick' moisture along microcracks/porosity in the resin and along the fibers to the metal: VERY BAD!!

Breakwater-CLEAN surfaces are essential in application of finishes and adhesive bonding. Handle parts clean/fresh/chemical-free cotton gloves or boiled cheesecloth.. and use plain/clean/unwaxed Kraft paper for a clean working surface an temporary storage of cleaned parts. Dirty/sweaty/oily air will interfere with adhesive quality... clean...clean... clean.

Also I MUST emphasize a few other important points. Kevlar is notorious for moisture absorption... more-so than even fiberglass... and it has stretch for energy absorption... not high enough stiffness.

All fabrics in any laminate must have a chemical 'sizing' applied to the fibers that is compatible with the adhesive resin-type in-use. This is applied during manufacturing and has to be verified.

Wet-resin lay-ups on dry fabric have certain advantages/disadvantages... as do resin pre-impregnated [pre-preg] materials.

Metal-to-metal adhesive-bondline thickness MUST be controlled ~0.005-to-0.008. Thinner the bondline is brittle. Thicker the bondline tends to be less-stiff and prone to voids.

'Peel' between sheets is a major factor in metal-to-metal failures... as is moisture penetration/creep along porous bondlines.

Where practical long-edges should be smooth/rounded, or tapered-thin... and corners generously radiused or chamfered... again peel considerations.

MIL-HDBK-337... is old... but has lots of useful info. Adhesives and finishes have changed/improved... techniques and supporting materials and tools and processes have been consistent/important for years.

More later, if anyone is really interested... wife is grumbling... dog needs a walk.
 

dog

Well-Known Member
Joined
Dec 29, 2019
Messages
445
I have seen a clean room built in an ancient
warehouse,cheap strapping,staples,heavy vapor barrier ,consruction tape.Add some filters and fans.
Personaly the idea of working at +- .001" is
relaxing,and seeing the results that are only
possible from achiveing those tollerances is
very gratifying.
Any further info on adhesive bonding in aircraft
is apreciated.
 

aterry1067

Member
Joined
Dec 18, 2020
Messages
5
Location
Phoenix Valley
Huge design and operational philosophy difference between Ingenuity and a manned platform. Ingenuity was designed and built with a life of less than 1 hour....Flight time for it is measured in seconds, not hours. Ingenuity is a whopping 4 pound vehicle vs the stuff I work on that ranges from 13 to 185 tons. Our operational lifetimes are measured in the thousands of hours, with structural integrity being proved out to as much as triple the operational life.

If you want the relevant engineering documentation, you'll need the appropriate clearances, ITAR licenses and a demonstrated need to know. Even though I have worked on them, I never had the need to know, as I was not a design, fatigue or reliability guy, just a builder/fixer/breaker of the product.

I bet I work on some of those same airplanes in the field that you built in the factory. Nearly all of our adhesive failures have been the result of poor surface prep, regardless of what materials were being bonded. There are documented procedures in place, and the abrade, solvent wipe, abrade, solvent wipe method works OK, when it is done properly. But I have witnessed many young maintainers, after abrading or wiping, will almost always wipe the abraded area with their fingers or they will blow hot, moist air on it from their lungs. Either way, surface prep is destroyed by contamination, and we suggest they start over and explain why. However, we can't be there for every nutplate or bracket, so inevitably, parts become disbonded....and we get to do it all over again.
 

reo12

Member
Joined
Jan 15, 2021
Messages
21
The Mars Flyer has successfully operated
useing carbon to metal bonds under the most extreme conditions ever attempted.
Carbon to aluminum and other metal bonds are
becoming ubiquitous in demanding aplications
where no other fastening is used ,or can be.
One huge aplication is the bonding of wind turbine blades to the metal hub attach points
with nothing but adhesive.

Please publish your assertations of
"actual engineering analysis" of aluminum carbon bonds ,from 1952,what did they try
useing?welding?contact cement?,firm admonition?,bubble gum?
The "mars flyer" is called Ingenuity. Ingenuity was purpose built to be a short lifespan machine used in a low moisture - low oxygen environment for minutes over the course of days. That is it. Not years. Just days.
 

dog

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Joined
Dec 29, 2019
Messages
445
Mars Flyer just seems right somehow. And using it as an example of a flying machine was to dispel the notion that carbon bonds by nature are not reliable under extreme temperature cycling.

Quite clearly, successful carbon metal bonding is possible over conditions that exceed those found on this planet.

All this is relevant to the near future of homebuilt aviation.

The vast majority of kids are being exposed to flying things (in there hands) that are made from carbon (or look to young minds like carbon) and are electrically powered. Three D printing is growing up with those same kids. Balsa is getting exotic, aircraft grade spruce is best not talked about, and shop class in school is a pale remnant, the products of trade schools come out with no hands on experience.

The dreamers that have drive and ambition are going to dream in carbon. Ensuring that general aviation does not die in the generation gap is important.
 
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