metal compatible with carbon fiber

I am hand laminating some carbon fiber rowing outriggers.  I want to put a supporting strip of metal on the interior, both for bolts to pass through and for the oarlocks to attach.  I understand that stainless steel will corrode embedded in carbon.  Obviously, the metal will not come into contact with saltwater directly, but I also understand that crevice corrosion can damage it.  These are recreational rowing fixtures, so I might be overthinking this one.  What metal should I choose  for this?  I have some 3/16" stainless steel blanks laying around that would be ideal...

 

Overbored

Anarchist
711
59
So. Cal
You are making carbon riggers to make them light and strong. why add metal, the carbon is plenty strong to support an oarlock without a metal insert. besides that for there to be corrosion there needs to be water in-between the materials if there is water between the materials then they are not bonded together any longer so why bond it in the first place. If you did use a metal the stainless steel will only last for 50 years bonded to carbon. if you want it to last longer use a layer of fiberglass between the two materials.

 
Last edited by a moderator:
All good points.   Stainless steel corrodes with "crevice corrosion" when not exposed.  However, your point underscores my feeling about it as well--how much can it possibllly corrode in this application?  Probably very little.  The second question, is  it necessary--I think it  might not be necessary as well.  The attachment points (metal pins) at the hull and and oarlock itself, are points of constant motion, and thus wear.  Eventually, an oarlock will wear an ellipse at the insert.  But how  long is eventually?  One year, or 200?  Since this is belt and suspender engineering, I would be interested to hear further commentary on the necessity of an insert in either of those points.  

Does bronze or brass corrode with carbon fiber? 

 

slug zitski

Super Anarchist
6,251
1,234
worldwide
I am hand laminating some carbon fiber rowing outriggers.  I want to put a supporting strip of metal on the interior, both for bolts to pass through and for the oarlocks to attach.  I understand that stainless steel will corrode embedded in carbon.  Obviously, the metal will not come into contact with saltwater directly, but I also understand that crevice corrosion can damage it.  These are recreational rowing fixtures, so I might be overthinking this one.  What metal should I choose  for this?  I have some 3/16" stainless steel blanks laying around that would be ideal...
Marine grade stainless and carbon  are common used in structures 

I have never seen any problems 

 

SloopJonB

Super Anarchist
68,723
12,370
Great Wet North
All good points.   Stainless steel corrodes with "crevice corrosion" when not exposed.
When wet  but not exposed to air.

Nevertheless, I have never been a fan of metal inside a laminate - seen way too many problems with it and they are invariably a complete bitch to repair.

 

Russell Brown

Super Anarchist
1,695
1,301
Port Townsend WA
Titanium isn't that hard to source or to work with. Tapping holes is the only really scary part as it's a bit rubbery and can break taps. There are lots of different alloys, some extremely corrosion resistant and some for strength. Grade 5 is common for structural work and use with carbon. I'll bet McMaster would have what you need.

 

slug zitski

Super Anarchist
6,251
1,234
worldwide
The pictured 30 year old carbon mast has a bonded laminated stainless steel boom gooseneck saddle 

I have  never seen any bleeds or corrosion 

679D353C-D74F-482D-87AD-6E036667D22A.png

 

DDW

Super Anarchist
6,561
1,126
You are only going to need a tiny bit of metal to line the holes, there is labor involved in the build, why not do it right and use titanium? Grade 2 would be fine for this (it is stronger than stainless steel and 1/2 the weight), significantly cheaper than grade 5 and a little easier to work. 

 

solosailor

Super Anarchist
4,066
816
San Francisco Bay
I understand that stainless steel will corrode embedded in carbon.
Not really. As mentioned, polished 316 stainless will take forever to corrode even with direct constant contact.  I've got a boom mount pin that goes through 4x carbon thick walls and there is zero corrosion after 12 years.

 

slug zitski

Super Anarchist
6,251
1,234
worldwide
Stainless Steel


There is no evidence of the formation of corrosion for stainless steels coupled to carbon composite. However, it is reported that some types of stainless steels (such as types 410 or 301) are susceptible to localized corrosion (pitting corrosion and crevice corrosion) when they are connected to a carbon composite in aerated 3.5% NaCl (simulated seawater). It is believed that the pitting corrosion will be enhanced by increasing Ac/Aa. (For more information about pitting corrosion, see A Look at High Nitrogen Stainless Steels .)


Titanium


By looking at the standard electrochemical potential of titanium, it seems that this metal is an active metal. However because of the formation of a dense stable and protective oxide layer, titanium is placed among the noble materials and just below graphite or carbon in the galvanic series table. (For a primer, see the article An Introduction to the Galvanic Series: Galvanic Compatibility and Corrosion .)

Therefore, there is no significant gap between titanium and carbon-fiber-reinforced composite to create galvanic corrosion. This means that commercially pure titanium and its alloys are completely resistant to galvanic corrosion when they are coupled with carbon composites.

 

Zonker

Super Anarchist
9,714
5,669
Canada
IF the stainless parts were electropolished (like that stainless gooseneck fitting might have been) then yes you will have just minor rust staining and not much corrosion. OR if they properly isolated the faying surfaces with e-glass. I suspect slug doesn't know.

BUT if you machine/cut/drill or tap a piece of stainless steel without treating the cut edge, the stainless is "active" and is much lower on a galvanic scale. And that is the difference. 

Maybe listen to the guy who has been involved in building AC boats (Russell) or designing them (me) rather than the paid skipper. We both think Ti is the gold standard. If you use stainless steel KEEP AN EYE ON IT. When stainless steel corrodes it can hide for some time with a tiny crack - but be corroded half way through.

 

slug zitski

Super Anarchist
6,251
1,234
worldwide
IF the stainless parts were electropolished (like that stainless gooseneck fitting might have been) then yes you will have just minor rust staining and not much corrosion. OR if they properly isolated the faying surfaces with e-glass. I suspect slug doesn't know.

BUT if you machine/cut/drill or tap a piece of stainless steel without treating the cut edge, the stainless is "active" and is much lower on a galvanic scale. And that is the difference. 

Maybe listen to the guy who has been involved in building AC boats (Russell) or designing them (me) rather than the paid skipper. We both think Ti is the gold standard. If you use stainless steel KEEP AN EYE ON IT. When stainless steel corrodes it can hide for some time with a tiny crack - but be corroded half way through.
Well , that mast pictured was built in Switzerland by Andy Steiner 30 years ago 

it has very many pieces of embedded stainless 

it had stood the test of time 

in addition Andy built the first America’s Cup composite mast , then built carbon masts for the America’s cup and mega yachts for the next few decades 

if you have technical questions I suggest you contact Andy

http://www.carbonsconcept.com

 

Zonker

Super Anarchist
9,714
5,669
Canada
Then I guess Andy knew of the issues of putting carbon fiber in direct contact with stainless steel and isolated the embedded bits with e-glass as I said.

 

Latest posts




Top