Composite wishbones

[noname]

I allready know the basics, lighter, stronger, possible indefinate lifespan if used within the manufacturing tolerances but i was looking for actual facts and data to back up what i hypothesise to be correct.

Information about cost as well would be good. I've read that carbon materials can be relativly cheap now and manufacturing cost can be lower than making metal components but have any teams ever offically published a cost ratio between the two.

I have not got trough the links provided earlier so sorry if I am repeating things you already knew.

Joining composite parts, as well as composite-metal connections (you have metallic joints on both ends of the wishbone), is not so simple. Partially due the fact composites do not like "localized" forces.

Maybe it's not a big deal in case of wishbones (my experience with them is limited to the fact I knew how they look like), I am talking from the aviation perspective. As an example - one of "Dreamliner" prototypes was grounded few weeks ago due issues with joints and fasteners connecting wings and fuselage.

[scarbs]

Swordfish,
PM me I might have some info for you...

Scarbs

[Jersey Tom]

Information about cost as well would be good. I've read that carbon materials can be relativly cheap now and manufacturing cost can be lower than making metal components but have any teams ever offically published a cost ratio between the two.

No, because there's no such thing. Everything is on a part-by-part basis. Also kinda depends on what you mean by cheap. CFRP itself usually isn't too expensive... if you have your own CNC shop then you aren't spending much cash in making tools and molds. However, there is the big up front cost to have a CNC! Same with autoclaves, etc.

Unfortunately a lot of this is lost at the university level when there's no such thing as billable engineering hours, overhead, machine depreciation, etc.

Fabricating control arms from welded steel is very cost effective, and steel components can be surprisingly light weight and incredibly strong. Carbon does give you totally control on part geometry and has high specific strength when compared to S-glass, steel, etc.

[bajanf1]

If you are going to build composite wishbones and dont have facilities to test them you may want to consider trying to build very light steel wishbones. I worked with composite wishbones for formula student and as noname mentioned before the bonding is not simple. We found this out the hard way when one of our bonds broke. We did some more research on general CF-aluminum bonding and were lucky to get some advice from the guys at TU Delft who use CF wishbones. All joints were done again and then we tested the hell out of them. Eventually we got no failures but unfortunately this was after the competition. There is a lesson here about timely research swordfish.

[marcush.]

If you are going to build composite wishbones and dont have facilities to test them you may want to consider trying to build very light steel wishbones. I worked with composite wishbones for formula student and as noname mentioned before the bonding is not simple. We found this out the hard way when one of our bonds broke. We did some more research on general CF-aluminum bonding and were lucky to get some advice from the guys at TU Delft who use CF wishbones. All joints were done again and then we tested the hell out of them. Eventually we got no failures but unfortunately this was after the competition. There is a lesson here about timely research swordfish.

in truth theres not much mystery about bonding cf really .You have to use the proper
process and have a handle on all relevant parameters .To attempt something like that
in a not controlled invironment not having done your homework will result in the joints biting you .Aluminium CF bonds are of course not the best idea to start with simply because of the very different expansion over temperature.
So my word is not only the possibility to test them ,but to build them properly is the key step you must be very sure off ,not forgetting to be sure you know all the
forces in the game till you put them aside when the job is done....
but then to step up your game with CF fabricating is a not only designwise a huge
mountain to climb ...as a matter of fact you need many molds,and expertise to build those , clean room ,vaccum ,oven for tempering and someone who is experienced in laminating to do a proper job so everything is not just a cf is fancy exercise....
To me a fabricated steel wishbone does make a lot more sense but thats only my 2 cents.

[Jersey Tom]

in truth theres not much mystery about bonding cf really .You have to use the proper process and have a handle on all relevant parameters .

Easier said than done.

To me a fabricated steel wishbone does make a lot more sense but thats only my 2 cents.

Why not? Cheap, easy, simple, and can be done light weight.

[marcush.]

having been involved in both CF fabrication as a modelmaker and have done a lot of TIG Welding fabrication also wishbones in 15CDV6 and 25CroMo4 ,I would always choose the Steel option ,Tom .
You just don´t get yourself into more trouble than you can handle when messing around on racetracks.
Of course a state of the art CF-titanium inserted wonder of a wishbone is something to admire ....but realistically if all lmp cars use steel this should ring some bells...

generally speaking you have to prepare the metal surface very thoroughly by blasting and etching and the trick is to prevent the surface to oxidise before applying the bonding resin .But then the first thing you need to have is a blasting chamber with inert gas filling ....Hello NASA anyone?
The cf side is quite easy though: clean clean clean and a strip of tearoffcloth on all bonding areas when laying up the parts.

It can be done ...but to step up to do something like that is really beyond most of us and looking at USGPs Video they will not bother with something like this..

[Jersey Tom]

Ahh read that wrong. At first I thought you had said "doesnt make more sense." My bad.

[WhiteBlue]

Titanium seems like the proper material for wishbones. Will work many races instead of a having to pass a structural test each race.

[czt]

but realistically if all lmp cars use steel this should ring some bells...

I though LMP's only used steel wishbones as that is what is specced in the regs?

[Jersey Tom]

Titanium seems like the proper material for wishbones. Will work many races instead of a having to pass a structural test each race.

How do you figure?

[marcush.]

Actually the design loads will not be the problem ,but the niggling peaks at elevateed temps will ....
so structural testing between races ...how far can you go without compromising integrity of the part? My view is to do batches of the parts and asign a percentage of those to destructive testing ,in fact replicating the forces seen in the car .
Unfortunatelly those forces are only available after the event so one has to rely on last years data for the test input... again you need a factor of safety to add ....
seriously I don´t want to be responsible for things like carbon wishbones in F1.

[WhiteBlue]

Titanium seems like the proper material for wishbones. Will work many races instead of a having to pass a structural test each race.

How do you figure?

Titanium has the metallic properties which would make it endure multiple races without material fatigue and the cracks that are a problem in carbon fiber. It is more ductile than carbon fiber but has a much lower specific weight than steel. Ten years ago all F1 teams used Titanium unless I'm very mistaken.

The problem with carbon fiber suspension parts is the exposure to impacts. They are very brittle and so any debris that hits a suspension member can cause a damage that you don't see except by fluxing it.

Carbon fiber has the lower mass and thus the higher performance but it is not worth the cost IMO if all teams agree.

On the other side you do have a safety aspect. Metallic suspension parts can be dangerous in accidents as Senna's death and Timo Glock's accident in Suzuka this year showed.

[riff_raff]

WhiteBlue makes an excellent point. The elongation rate of GRE composites is basically zero. This means that they don't fail as "gracefully" as a metal part in an impact situation. A composite part will shatter, while a metal part will crumple.

Another issue with composite wishbones is that a wishbone structure is basically a tension/compression member. Carbon fibers are great in tension, but lousy in compression.

[Mystery Steve]

Another issue with composite wishbones is that a wishbone structure is basically a tension/compression member. Carbon fibers are great in tension, but lousy in compression.

The fibers themselves are lousy in compression, but the matrix is not... the composite shares properties of both.