Adhesive replacing rivets or bolts

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

pfarber

Well-Known Member
Joined
Feb 21, 2019
Messages
800
Location
Pennsylvania
Several issues. First is that bonding composites to aluminum alloys has been a nice idea that does not work for very long. The composite-aluminum bonds tend to fail over time for several reasons I delineated in an earlier post. If you go ahead with bonding, you should included backup mechanical fasteners. If you are building with mechanical fasteners, why put in the weight and effort for bonding? Once the thing is mechanically connected together, well, composites are not great for mechanical connection - bearing strengths of composites are low and so you end up needing to locally thicken and/or add bushings to make them durable. For lightness, composite designs avoid hardpoints.

Now if you say "my turtledeck is not structural" I have to ask you what you are attaching it to. The fuselage tub will bend in response to loads from the vertical and horizontal tails, and the tub will change dimensions when temperatures change. The turtle deck either has to be much softer than the tub under these loads so that it moves with the tub, or it has to float on the tub.

Moving with the tub means mechanical strength at all of the connections and locally "improved" load carrying to stand the preloads (from mechanical connections) and live loads in use.

Floating the turtledeck means that lifting loads (moving air outside, stationary air inside, the turtledeck is inflated by these) are still carried, but that bending, twisting, or thermal expansion loads are largely avoided. Now the surfaces are moving relative to each other. These surfaces can either have a renewable bearing surface or they will wear on each other. This is also the case with most attempts to bond aluminum to composites - they come loose and now you have either the floating or the firmly attached case... Take your pick.

As I pointed out earlier, if you can get a durable bond, great. The field experience, however, is poor with this option.

If I were faced with this, I suspect that I would just make the turtledeck out of the same stuff I made the tub out of...

Billski
The FAA is going to issue an AD for the Grumman AA series after an in flight incident and random inspection showed delamination on the horizontal stab.

Gonna post it to the BD forum and watch all the fanboys cry.
 

wktaylor

Well-Known Member
Joined
Sep 5, 2003
Messages
333
Location
Midwest USA
Phosphoric acid anodic [PAA] coatings on aluminum + adhesive bonding primer + [compatible] adhesive [film or paste] + uniform pressure + NDI [X-ray, US, tap] + corrosion protective edge-potting/coatings + wet assembly with sealant = high reliability adhesive bonded structure. This high reliability processing was developed in the 1970s by DAC/MAC under the Primary Adhesive Bonded Structures Technology [PABST] program. Thru the decades there have been process and materials improvements to this basic processing... but the concept has remained steady/solid.

Last I heard, Boeing developed a silane-chemistry based process [Sol-Gel or Boe-Gel] that is now in the structural repair manuals [SRMs] of most 7XX jets for adhesive bonding surface preparation for aluminum. This process requires cleaning the aluminum, abrasive-sanding the aluminum to a specified degree [with a no-residue sanding media], quickly applying the water-like Sol-Gel compound... which intimately bonds to the exposed aluminum atoms... and also has a high affinity with epoxies... then applying the epoxy adhesive bonding primer and then proceeding with the repair [yes, this is a repair process]. Boeing claims this system has a high degree of simplicity [for the field], high bond-strength/toughness, environmental durability and is ~95% as a PAA surface prep... and is compatible with PAA processed parts [PAA is a chemical-only production-speed process for parts preparation].

BTW guys, RE the Martian flyer.

The mass of the flyer is ~1.8-Kg = ~3.96# on Earth or ~1.49# on Mars.

I have no doubt that where the graphite is bonded to metal, the metal is a high-strength TITANIUM alloy which is very inert-to and thermally compatible with graphite. DON'T expect the detail-design to be published... the Chinese would love to avoid that costlty R&D.

Also thermal swings on Mars are not so-so-bad... the maximum and minimum service temperatures on Mars are a balmy (+)80F daytime to dri-ice-deep cold (-)100F night-time. My [1950s] jet's design service temperature range was +160F to -65F [bare-polished aluminum]... which has-been NOW more-realistically-revised-to (+)190F 'Saudi-desert' day-time with dark camouflage paint [terrible]... down to (-)100F 'arctic winter-night' [at 40K', frightening for humans].

I imaging that Mars-dust will eventually ground the flyer... either coating/degrading the solar panels... or abrading/degrading/unbalancing the blades... or both. Of course this assumes the batteries/electronics/antennas don't fail first... or it doesn't get blown-over/tumbled by a dust-devil/wind-gusts... or a lands/flips on grossly unsuitable terrain... etc, etc, etc.
 
Last edited:

Victor Bravo

Well-Known Member
HBA Supporter
Joined
Jul 30, 2014
Messages
9,233
Location
KWHP, Los Angeles CA, USA
So, wktaylor, in your experience is there a reasonably straightforward use for the new Boeing method or some other similar method... on a small amateur garage-built airplane structural application?

We've all heard and repeated the stories about the failed or troublesome early attempts at structural bonding on homebuilts... the Monnett Monerai/Moni, the Schreder HP-14, etc.

To your knowledge, is there a commercially available product or bonding system for 2024 or 6061 aluminum (whether the Boe-gel or something else) that you WOULD trust for a garage-level homebuilder?
 

dog

Well-Known Member
Joined
Dec 29, 2019
Messages
575
="wktaylor, post: 600585, member: 643"]
Phosphoric acid anodic [PAA] coatings on aluminum + adhesive bonding primer + [compatible] adhesive [film or paste] + uniform pressure + NDI [X-ray, US, tap] + corrosion protective edge-potting/coatings + wet assembly with sealant = high reliability adhesive bonded structure. This high reliability processing was developed in the 1970s bmediay DAC/MAC under the Primary Adhesive Bonded Structures Technology [PABST] program. Thru the decades there have been process and materials improvements to this basic processing... but the concept has remained steady/solid.

Two words stand out,uniform pressure.
That to me means building forms that hold
your parts while pressure is applied while the adhesive sets.
A consideration not mentioned yet is that many
adhesives "grab" ferociously ,with no possibility
of adjusting the placement of lamina.
The pamplet from Fokker shows pieces bieng
placed by hand,though I expect that the people
doing it were not just grabbed off the street.
The learning curve for this appears to be fairly
short on the theoretical side and realy steep and long on the actual doing side.
The big motivator is in my eyes that the difference between building one complex adhesivly bonded structure and 10 is minimal.
And for anyone thinking about adding PV pannels to a wing adhesive bonding is going to
be by far the best option,and when factoring in
that the best PV pannels are built on very thin
stainless steel its an atractive idea to use them
as part of the structure on to of the wings and fueselage.[/QUOTE]
 

karmarepair

Well-Known Member
HBA Supporter
Joined
Jan 13, 2011
Messages
440
Location
United States
So, wktaylor, in your experience is there a reasonably straightforward use for the new Boeing method or some other similar method... on a small amateur garage-built airplane structural application?

We've all heard and repeated the stories about the failed or troublesome early attempts at structural bonding on homebuilts... the Monnett Monerai/Moni, the Schreder HP-14, etc.

To your knowledge, is there a commercially available product or bonding system for 2024 or 6061 aluminum (whether the Boe-gel or something else) that you WOULD trust for a garage-level homebuilder?
3M™ Aerospace AC-130-2 Clear BMS5-162 Type I, Form 2S Spec Surface Pre-Treatment
Skygeek has it in various quantities. I wrote a repair procedure using it and a specific (High Toughness) Scotchweld epoxy for a structural repair 100 feet above the waterline on an aluminum mast on a government asset. The Structural Technical Warrant Holder of the time said "That ought to work, but I'm not putting my PE stamp on your procedure."

In the end, we were not able to use it anyway; the job was in Hawaii and I could not get the prep materials shipped in time to meet the deployment schedule. SO I tripled the already generous bonding area of the doubler plate, and we used the highest grade epoxy we could get on the islands, a product for masonry bonding with a handy static mixer, buffed the crap out of everything with rough Scotchbrite, and prayed. Some kid in a bosun chair did the repair, and I never saw it.

It held for next decade, till we transferred that asset to a Foreign Government and took off the TACAN antenna. I have NO DOUBT it would have eventually failed from corrosion of the substrate at the bond line.

=============================

Would I trust this the BMS5-162 for a garage-level homebuilder? MAYBE. For one thing, the Pre-Treatment is EXPENSIVE. You STILL need a "clean break" surface to start with. But there is enough literature on it's use that I'm fairly positive it would be both structural and durable IF done properly.

Some ideas I've wanted to try -
  • use the MUCH cheaper PreKote (used for paint) as an adhesion promoter.
  • Try the acrylics used for bonding in automotive applications
  • Try moisture cured urethanes like 3M 5200 or the equivalent Sika products
  • Build some lap shear panels and borrow BoKu's "BreakATron"
 

karmarepair

Well-Known Member
HBA Supporter
Joined
Jan 13, 2011
Messages
440
Location
United States
Sounds a bit like what Bede does on the latest BD-4 wing?? Just a simpler procedure and a different goo (...sorry, glue!)?

thjakits
Jim Bede fell in love with Polysulfide back in the 1950's, and used it to wax his mustache, style his hair, and stick airplanes together. It's lower in both strength and modulus than epoxy, but it's tenacious. The peel values on most any material (aluminum, hair, fingernails, skin) are quite good, as is the toughness and elongation. It takes a lot of bond area, which both the original Bede fiberglass and the current honeycomb ribs provide. The YouTube video shows the current Bede gang using an air driven gun to apply what I'm guessing is a two-part compound (Thiokol, ProSeal, or FireSeal - same BASIC stuff as RV fuel tanks use). It looks pretty simple, neat and practical. With wide enough flanges, you could do this with foam or beaten aluminum ribs. That wide flange drives you to a catalyzed product - moisture cure polysulfides or urethanes won't cure all the way across a wide flange. Scuffed "Clean break" is good enough prep for the aluminum.
 

wktaylor

Well-Known Member
Joined
Sep 5, 2003
Messages
333
Location
Midwest USA
The following web-page [on MasterBond website] has a some-what useful introduction to adhesive bonding surface-preparation complexity.
Master Bond infographic on surface preparation techniques for different substrates | MasterBond.com

Abaris Training is useful for learning in-depth engineering and technical aspects... including hands-on... for composites and metal bonding [pricey... but worth the cost if serious about these processes]. Abaris Training

Let me see what other 'good-stuff' I can find on this subject.
 

TLAR

Banned
Joined
Sep 29, 2020
Messages
319
You can just tape two different materials together with high molecular creep tape.
Tape provides the highly prized viscoelastic function needed for joining two different materials.
Foam will need to be carefully sanded to at least 220 grit, carefully vacuumed then washed and dried.
Aluminum, just wipe off the oil with a solvent
 

wktaylor

Well-Known Member
Joined
Sep 5, 2003
Messages
333
Location
Midwest USA
TLAR... my curiosity is killing me...

What is 'high molecular creep tape'? I've never heard that term before.
What applications have used these tapes?
What are typical qualified products, IE: manufacturer's part numbers?
 

TLAR

Banned
Joined
Sep 29, 2020
Messages
319
Mr. Taylor
Please do your due diligence, sir. No disrespect intended.
what has been discussed in this post doesn’t even scratch the surface.
Adhesive tape is a pretty well guarded product.
Differential thermal expansion rate is the limiting factor now, and even that factor can be overcome up to a point.
One point is peel must not be allowed to even start, so a mechanical fastener is in order

For the interested, a short primer on how adhesives work might be in order. Especially for the new adhesive products now available.
I ain’t gonna endorse the brand, as I have not done the testing, but Lord products website provides a wealth of information
 
Last edited:

wktaylor

Well-Known Member
Joined
Sep 5, 2003
Messages
333
Location
Midwest USA
TLAR... interesting engineering challenge.

I contacted both 3M-Industrial Tapes and Lord-Adhesives/Tapes Tech support.

3M does have product line VHB Tape - Specialty Tapes [see attached brochure]. Upper service temps are impressive... although properties fall-off fast... Low service temperatures have glass-transition about -40 to -50F and all of the tapes had very low shear strength and low stiffness compared with most epoxies. Also, there were definite words to avoid prolonged contact with chemicals; which I presume means everything from cleaning solvents to oils to fuels, etc. There was one known application on a jet... attaching wear-strips to flaps. For giggles, I'll still dig deeper when I have time... I love this kinda info.

Lord adhesives and Tapes division understood what I was asking but indicated they did NOT have tape products that were categorized as 'high molecular creep tape'... even when they knew about the 3M VHB tape and its properties. Yes they had very strong/tough tapes... with pressure sensitive and heat-fused adhesives... 1-side and 2-side... but not in this definition.

From the available definitions/TDS... the 3M and Lord 2-sided tapes are primarily for industrial and ground transportation applications.... and others in that performance realm.

I have to admit, re-reading Your statement [post #75]… thus...

what has been discussed in this post doesn’t even scratch the surface.
Adhesive tape is a pretty well guarded product.
Differential thermal expansion rate is the limiting factor now, and even that factor can be overcome up to a point.
One point is peel must not be allowed to even start, so a mechanical fastener is in order

For the interested, a short primer on how adhesives work might be in order. Especially for the new adhesive products now available.
I ain’t gonna endorse the brand, as I have not done the testing, but Lord products website provides a wealth of information


… actually raises the hair on the back of my neck and gives me chills.

No disrespect intended... Strictly my skeptical-emotional response based solely on my experience... but then I know that I don't know everything.
 

Attachments

  • Like
Reactions: dog

TLAR

Banned
Joined
Sep 29, 2020
Messages
319
Mr. Taylor
I can assume you know how adhesives work.
There is no engineering challenge. Only solutions.
Specifically what part of my post gives you chills?
What forces are you trying to overcome with adhesives?
 
Top