Carbon fiber A-Arms

[ucar]

Hello,

Our team pretends to use prefabricated carbon fibre tubes with aluminum inserts to make the suspension wishbones, tie-rods etc.

We already know the way to "stick" the inserts to the tubes, partially thanks to this forum. Nevertheless, we still have the problem of choosing the tubes.

The question is: How can we get the characteristics of the tubes? Is there any seller that gives this information about his tubes?

Thank you

[ucar]

Hello,

Our team pretends to use prefabricated carbon fibre tubes with aluminum inserts to make the suspension wishbones, tie-rods etc.

We already know the way to "stick" the inserts to the tubes, partially thanks to this forum. Nevertheless, we still have the problem of choosing the tubes.

The question is: How can we get the characteristics of the tubes? Is there any seller that gives this information about his tubes?

Thank you

[Demon Of Speed]

If you can't figure this out yourself, DON'T do it.

You can find the general properties of CFRP, then using the tube size you can decide on what tube size you should use.

[ucar]

I don't understand what do you mean with "general properties of CFRP".

As we all know CFRP is an anisotropic material, so the properties of the tubes depend on the way the manufacturer made the tubes (or at least the angle of the fibers).

I KNOW how to work with carbon fiber. What I DON'T KNOW is where or how to obtain the data relative to PREFABRICATED CF LAMINATED TUBES, which are used by many teams in their cars.

[Charlie]

Even if you find a supplier with specifications, I would not be comfortable using any CF tube product without performing my own destructive testing. You really need to do this to check your aluminum insert bond strength anyway.

See what suppliers are available, get samples, and test. That's the proper way.

[ucar]

OK, that is what I thought.

About destructive testing, I am particularly worried about shear stresses and bending behavior. What kind of test do you recommend apart from the usual traction/compresion test?

[Jan_Dressler]

Whatever tests you are doing, take the heat generated by brakes etc. into account.
We tested our A-arms in many ways last year, no problem at all - and still there were some nasty surprises when we tested the car on track, and the brakes got hot for the first times...

[Lorenzo Pessa]

In 2010 we mount for the first year carbon fiber A-Arms as you describe it.

We had some data from carbon tube manufacturer (a fishing rod firm) then we tested at traction.
We found that our weakness was the bonding.

I think you need to make your own testing. Other infos are useless.

[Radii]

Since the A-Arm is a compression/tension member (theoretically) you should size the tube with buckling in mind as the failure mode. As Demon of Speed mentioned, you can take a general figure for both the Modulus and the strength numbers, use a healthy FoS and appropriate boundary conditions to find the right sized tube (solve for I).

As Charlie mentioned, destructive testing is also a must even after you choose your tube size. Most likely the bond between your insert and tube will be the weakest link and fail. Make sure you look into surface preparation of the aluminum ("pickling") for maximum adhesion.

As a side note from our own use of carbon tube A Arms, besides running a static test I would also run a fast load/unload cycle on your tubes as well. We found that at high strain rates, the tubes were actually very compliant even when passing load conditions. The high displacements caused us to step up at least one tube size to lower compliance in our suspension.