Hi Lok / Collar Selection

[jcfritz]

I'm working on an assembly that joins an anodized/primed aluminum part to carbon fiber composite as well as joining two carbon fiber composite parts and manufacturing prefers using hi-loks. The application does not require a tension fastener.

For the aluminum - carbon part, I need to install the collar on the aluminum side. I'd like to avoid using a stainless collar given their issues with galling and the torque required to break the collar. I'm taking the appropriate steps to prevent galvanic corrosion between the aluminum and carbon composite (e.g., fiberglass ply, fay surface seal) but would like to use an aluminum collar on a titanium hi lok pin. Is the aluminum pigmented hi-kote plus an anodized/dyed aluminum collar acceptable from a galvanic perspective?

The same question applies for carbon - carbon joints. Not looking to crush the composite parts so an aluminum shear collar is preferred here as well.

 

[SWComposites]

No. I have run tests with Al collars on Ti pins, with poor results. The aluminum collars will strip off the Ti pins well before reaching the fastener tension capability, and likely well before reaching the sheet capability (bearing failure modes).

Unless you have specific representative test data for the particular joint materials/configurations/loading/etc. that shows adequate static and fatigue strength, use Ti or Steel collars on Ti pins.

 

[WKTaylor]

jcf...

It appears that You have much to learn on this subject... from hole drilling... effects of stack-up and dissimilar materials, bearing/tension/crush, etc... all aspects of fastening and sealing... and electrical bonding-grounding-lightning, EMP-EMI, HIRF... etc... OH yes... and is this also for 'dry structure or an integral fuel tank or pressurized/controlled environment???

A taste of the related...

AGARD CP-427 Behavior and Analysis of Mechanically Fastened Joints in Composite Structures.

AFWAL-TR-81-3041 V1, V2, V3 Effects of Variances and Manufacturing Tolerances on the Design Strength and Life of Mechanically Fastened Composites

DOT/FAA/CT-86/8 Determination of Electrical Properties of Grounding, Bonding and Fastening Techniques for Composite Materials

A few evolving fasteners designed for composites...

Monogram Aerospace blind fasteners Composi-Lok

https://trsaero.com/monogramaerospace/support/product-part-numbers-technical-drawings/

HUCKCOMP® Lockbolt

https://www.howmet.com/products/aerospace/huckcomp-lockbolt/

LISI SLEEVE TAPER HI-LITE™ System

https://www.lisi-aerospace.com/en/product/sleeve-taper-hi-lite-system/

LISI HST/HSTL

https://www.lisi-aerospace.com/en/search/Composite/

Shur-Lok Sandwich Structure Design Manual

https://www.shur-lok.com/search-results.html

Its late, goodnight

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[Sparweb]

Titanium
Consider this option:
HL11VAZ5 Aluminium Coated Titanium Hi-Lok, 5/32nd Inch Diameter CSK Solid Ti-6Al-4V
I'm with SWComposites on the collar - an aluminum collar won't help you.
Maybe HL198 will work (I haven't thoroughly checked, that's your job).

 

[jcfritz]

WKTaylor,

Agree that I have lots to learn on this subject. As far as more details on the joint, there are no electrical continuity needs, the joint is dry structure/non-pressurized, the composite is a laminate and the aluminum is a 7050-T7451 fitting (anodized and primed). I am fine with using hi-lites for this application and also installing wet with primer/sealant.

Have a plan to test bearing and pull through on these specific joints with actual hardware.

But for galvanic concerns, I am looking for experiential knowledge related to installing an anodized aluminum collar on a titanium pin that is installed through one or multiple carbon fiber composite details.

Sparweb and SWComposites:

I don't doubt your experience, I just worry about the high torque required to break the stainless collar. I've found multiple posts on this site that detail issues with installing these (including in composites). Are any of these issues you have encountered or is that limited to a couple of posts on this forum.

 

[SWComposites]

why a stainless HiLok collar? hundreds of thousands of Ti collars have been used on HiLoks in composite structure without issue. probably SS collars also though I don't recall specifically if we used them on 777 or 787.

i've seen too many Al collars strip off a Ti HiLok pin to ever agree to using them. I don't want to risk the collar being the weak link in the joint.

if you insist on using an Al collar you should wet install the fasteners (not just fay seal) for corrosion protection.

 

[jaceb]

you may use KFN305 nuts instead collars - it should meet your expectations

 

[WKTaylor]

Be very cautious... a large/broad head and broad-flanged collar are necessary to spread compression thru-load to the composite surface... AND avoid torque-turning the collar on bare composite surfaces... a thin aluminum or CRES or Ti washer is necessary.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[WKTaylor]

jc... SparW...

In contact with carbon-fiber-epoxy composites, Titanium BARE-anodized... or CRES/HRA alloy(s) passivated... fasteners/Hi-Loks are galvanically compatible with the carbon fiber. SFL [solid film lube] coatings are mostly compatible... but be careful. However, cadmium/zinc/zinc-nickel/etc plated... or aluminum pigment-coated... fasteners/Hi-Loks in contact with carbon fiber are galvanically VERY incompatible. 'Wet -sealant' installation of fastener helps by adding isolation... but holes in composites can be 'leaky'.

NOTE1. Match drilling composites and aluminum can be verrry-verrry-twicky. Drilling bits and processes for aluminum alloys... work poorly for composites... and vise-versa. Take a peek at SAE AIR5367 Machining of Composite Materials, Components and Structures

Catch 22. Fasteners are the typical electrical grounding/bonding path between details and the greater Assembly.

Catch 22. Also, be cautious about thermal compatibility. Aluminum will expand/contract at predicted rates... while the CF composite will have about 1/10 that same rate of thermal expansion/contraction. This can create a significant strain difference between assemblies.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[SWComposites]

WKT-
re NOTE1. Match drilling composites and aluminum can be verrry-verrry-twicky. > Match drilling CFRP / Titanium stack ups is way more verrry-verrry-twicky; pulling Ti chips thru the CFRP tends to damage it, sometimes badly.

 

[WKTaylor]

SWC concur.

jc... the latest rev 'D' of MIL-STD-889(D) - GALVANIC COMPATIBILITY OF ELECTRICALLY CONDUCTIVE MATERIALS [new title... 'was' Dissimilar Materials']... been expanded/enhanced... A LOT... worth a 'read'.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[Sparweb]

Afraid to fall down the rabbit hole, I based my suggestion on an OEM's fastener selections, regerring to a drawing of a comparable joint, in order to find a quick answer.
This exposes me to the risk of copying another's errors.

 

[MadisonCameron]

The issue of galvanic corrosion when joining aluminum and carbon composite is really important
For the aluminium-carbon part, using anodized or painted aluminum in combination with pigmented hi-lok aluminum should be acceptable from a galvanic corrosion point of view, provided you take the necessary steps to isolate the metal surfaces from each other.
The same applies to carbon compounds.
It is important to ensure that you prepare the surfaces correctly and apply the correct protective coatings to prevent corrosion and other problems.

 

[WKTaylor]

SW... MC...

Aluminum-Pigmented Ti Hi-Lok Pins are not ideal for CRP + Aluminum.

Ti-Anodized or Ti-Anodized + SFL are less dissimilar.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov