Attaching Rod Ends to Carbon Fiber

[petrocks16]

We are a team trying to make a transition from steel A-arms to ones made of carbon fiber. We are trying to make a threaded insert to go inside the end of a carbon fiber tube to which a rod end can screw. We are trying to attach the insert to the carbon fiber by using glue/epoxy.

We are using scotch weld DP-460 that is rated at 4500psi shear strength. We have made a few test specimen and we performed a tension test on it in an instron machine. It is failing at about 650 pounds of force in tension when it is calculated to fail at a much higher force.

Does anyone have an advice they can offer on how to bond a metal (aluminum or steel) insert to carbon fiber? It's something we really want to do, but after 3 different test specimen failing at an embarrassingly low force I need a little guidance.

-steve

[EHog]

use steel.

[Hector]

There is an embarrassing number of threads on this very topic. Use the search function.

[Pico]

I would first ask:

1. Why do you really want to make carbon a arms? Is there a need for it or just wanna have it kinda thing?
2. What sort of % weight savings are you getting?

[MegaDeath]

Experiment with different types of glue, different tolerances between the carbon and aluminum insert, and different surface preparation on the tube and insert.

We did this heavy research on this two years ago, and we found a combination that failed a 5/16" rod end at 4,800lbs of tension and the insert did not budge from the tube.

RESEARCH, RESEARCH, RESEARCH!!!

[Demon Of Speed]

First off use the search function, there are a few topics on this already.

Proper surface preparation. Sand off most of the epoxy on the CFRP tube and clean with acetone.

The distance between the CFRP tube and the insert is critical. I know of a certain professional race team that uses micro glass beads in the glue/epoxy to make sure the correct distance is maintain.

[nick roberts]

Do a quick analysis of your failure.

If your pulling the insert out free of adhesive you probably have an insert surface prep issue.

If you have bits of adhesive on both the insert and ID of the tube you have bad adhesive or your bond line is too thick.

If your pulling the insert out full of adhesive and the tube is clean you probably have a tube surface prep issue.

If you are tearing out fibers from the tube with the insert you have crappy tubes.

My research has shown aim for a bond line of .010". Steel and Al bond the same assuming proper surface prep and cleaning. Cleaning is key to a good bond.

-nick
University of Kansas

[Lorenzo Pessa]

Originally posted by Demon Of Speed:
First off use the search function, there are a few topics on this already.

Proper surface preparation. Sand off most of the epoxy on the CFRP tube and clean with acetone.

The distance between the CFRP tube and the insert is critical. I know of a certain professional race team that uses micro glass beads in the glue/epoxy to make sure the correct distance is maintain.

A chemical expert from Loctite warn us against use of acetone in cleaning bonding surface. It leaves residuals.
She suggest to use specifical products (ok, this is business) or trichloroethylene.
First of all clean the surface, then sand, clean again.

[murpia]

Originally posted by Demon Of Speed:
The distance between the CFRP tube and the insert is critical. I know of a certain professional race team that uses micro glass beads in the glue/epoxy to make sure the correct distance is maintain.
Seems like this would work best with a taper at the insert / tube end. Just push in tight and the bond thickness is guaranteed +/- the tolerance of your tapers.

Do you know if this is the case?

Otherwise if the clearance between insert and tube is annular (and wrong) the beads won't help much.

Regards, Ian

[Demon Of Speed]

Originally posted by murpia:

Seems like this would work best with a taper at the insert / tube end. Just push in tight and the bond thickness is guaranteed +/- the tolerance of your tapers.

Otherwise if the clearance between insert and tube is annular (and wrong) the beads won't help much.


See Picture.
http://www.supercars.net/pitlane/pics/180059/3363497d.jpg

Besides the beads they do use jigs. I know it is possible to maintain the correct thickness for bond adhesive using only properly design jigs.

[KeWLKaT]

The use of glass beas will have an impact on the shear resistance of your bondline. I advise against the use of fillers, as even in standard laminates they automatically dimiish ILSS.

[JasperC]

We always use glass beads when we use an epoxy-based adhesive. You can't really go without them, if you ask me. The thickness of the bond is of vital importance for its strength. The minimal gap for your adhesive should be listed in its data sheet.

Furthermore, as Lorenzo said, clean-sand-clean both surfaces.

Make sure the bond is stronger than the actual tube and make sure you can repeat this a few times before trusting to put your bonded tubes on the car.

Regards,
Jasper Coosemans
DUT Racing Team 2008-2010

[Homemade WRX]

Originally posted by nick roberts:
Do a quick analysis of your failure.

If your pulling the insert out free of adhesive you probably have an insert surface prep issue.

If you have bits of adhesive on both the insert and ID of the tube you have bad adhesive or your bond line is too thick.

If your pulling the insert out full of adhesive and the tube is clean you probably have a tube surface prep issue.

If you are tearing out fibers from the tube with the insert you have crappy tubes.

My research has shown aim for a bond line of .010". Steel and Al bond the same assuming proper surface prep and cleaning. Cleaning is key to a good bond.

-nick
University of Kansas

I love the test analysis tips. Pretty much the same thing we did at work when analyzing our failed joints on a magnesium and carbon joint.

If I recall correctly we were using Resin Lab out of Germantown, WI.

[thewoundedsoldier]

I cant speak specifically to CF / aluminum bonding, but we are running steel control arms with aluminum inserts and we ran two tests showing that Loctite compound #680 failed within 5% of it's stress rating (2800 psi).