Sealed rivet joint 2

[JPAdlok]

I'm studying the fatigue behaviour of sealed rivet joint. I’m using Aluminium 7xxx, polysulfide sealant and Hi-Lok rivets. Maybe somebody can explain what is the surface treatment prior to seal the rivet joint?
What is the fatigue behaviour of sealed rivet joint?

 

[MikeHalloran]

So, to you, "study" means "ask someone else".

How would you know if a respondent was pulling your leg?



Mike Halloran
Pembroke Pines, FL, USA

 

[40818]

Ahh, Hi-Lok rivets, would these be made from unobtainium??

Generally speaking, the 7XXX series have similar properties (when being compared to other materials), though you would need to be specific on the actual material used.
The fatigue behaviour of the sealed joint is hugely dependent on its loading type, joint perameters and a mass of other variables. Not least of which is the fit of the rivet, fastener,or even the mysterious Hi-Lok rivet.
If your looking into the benefits of sealing joints to get better fatigue life, then i would think your barking up the wrong tree. Joints arn't sealed for this purpose.

 

[rb1957]

"sealled" ... why ? is this part of the pressure cabin, or a fuel tank ?

 

[JPAdlok]

The specimens tested are double butt joints assembled with sealant on mating surfaces (sealant is a corrosion inhibitive). The Hi-Loks are with aluminium collars installed with clearance . Fatigue test (with sinusoidal loads, R=0.1) shown a terrible behaviour of sealed specimens. The sealant layer acted like a lubricant. Curing condition or surface treatments, can influence the behaviour of sealant.
what is the surface treatment prior to seal the rivet joint?

 

[rb1957]

yahoo fond this ...

http://www.vansairforce.net/articles/tank_sealant.pdf

 

[WKTaylor]

JPAdlok...

1. The question You present is too general. As suggested by these other guys [above], we need more definition as to what Your sealing is attempting to accomplish.

1.1 What level of sealing are You looking for?

Absolute fuel/oil/fluid-seal.
Emergency fuel-seal such as a fuel-cell cavity seal [for temporary exposure to fuel vapor & Liquid].
Environmental seal [isolate disimilar metals and prevent corrosion between menbers].
Cabin Pressurization Seal.
Water or water-alcohol seal
Battery/acid seal

1.2 What environmental exposure ["wet" and "dry"]??

Exposure to: air-blast, jet fuel [JP, Jet-A], gasoline, gasohol, alcohol, oil, hydraulic fluid, acids [battery, urine, coffee, etc], fuel-additives, fire-barrier, lightning/static-electricity, electrical bonding [high current], battle damage, crash-damage, etc
Temperature range: -65F, -45F, +180F, +200F, +250F, +300F, +1200F, etc...

1.3 What construction/design philosophy?

Thin-gage sheet metal, metal honeycomb, composites [general aviation]
Mix of thin-gage and heavy-gage sheet metal, metal honeycomb, composites [commercial transport]
Mix of thin-gage and heavy-gage sheet metal, metal honeycomb, composites [fighter/attack/aerobatic]
All aluminum, or a material mix [aluminum, steel, titanium, etc +composites]
Aluminum, Ti-Cb and/or CRES solid rivets.
Aluminum, Ti, steel and/or CRES blind-rivets/blind-bolts, Hi-Loks, Bolts/screws, nuts/collars
Etc

1.4 What integral tank and corrosion protection design data/handbooks and fabrication standards/specifications are You using?

None
Your best-guess
Company developed
Industry developed

2. In general…

2.1 Define what your environment/loads/stresses will be.

2.2 Define the coating and assembly standards You will build production parts/assemblies to meet.

2.3 Design test components to match Your design needs and coating/assembly standards.

2.4 Test realistically.

3. FYI.

3.1 Improperly designed integrally-sealed and assembled structure can have extremely poor performance in static-strength, fatigue and environmental resistance. Poor sealant squeeze-out from joints [rivets or threaded fasteners] and loose fitting fasteners [after sealant cure] destroys joint performance [fatigue and shear strength]... and the sealant deteriorates [shears/cracks] due to relatively large strains, allowing fluid penetration.

3.2 Properly designed integrally-sealed and assembled structure can have very good long-term performance in strength/fatigue/environmental resistance. Absolute maximum sealant squeeze-out from joints [rivets or threaded fasteners] and tight fit in holes makes a HUGE increase in performance [~90% of bare metal joint]. Due to overall tightness sealant deterioration is greatly reduced.

3.3 Properly applied coatings [fuel resistant primer and sealant adhesion promoters] enhance sealing and long-term leak/environmental resistance of joints.

3.4 Tightly riveted Joints in a cabin-air pressure seal, with high quality corrosion protective finishes, may or MAY NOT actually need sealant to perform adequately.

3.5 If You are struggling with “how-to” check-out the following basic references.

Note: I work for a large company… we have a long history of designing sealed structure… and excellent design and assembly standards, that provide deep design knowledge and processes… but there are still gaps that leave us guessing on older acft due to evolution of sealing techniques [lessons learned].

SAE AIR4069A Sealing of Integral Fuel Tanks

AFWAL-TR-87-3078 Acft Integral Fuel Tank Design Handbook

http://www.vansairforce.net/articles/tank_sealant.pdf

[ref RB1957]






Regards, Wil Taylor