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Author: Subject: Carbon fibre wishbones
flak monkey

posted on 17/1/05 at 09:45 PM Reply With Quote
Carbon fibre wishbones

Not really a Locost question I know, but has anyone got any info on the design of these? I have been looking and cant find a thing, I do know they exist though. I'm just doing some concept design work and pretty much any info would be useful.

Thanks in advance,
David





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Liam

posted on 17/1/05 at 10:30 PM Reply With Quote
Yeah - and if anyone could shed any light on how on earth they (or any apparently seamless hollow carbon fibre structure with a good exterior finish for that matter, such as a bike frame) are made, i'd absolutely love to know.

Cheers

Liam

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flak monkey

posted on 17/1/05 at 10:53 PM Reply With Quote
Bike frames are made on mandrels afaik. The tubes are made separately then joined. There was a group project here on this a few years ago. The good finish comes from the production process i think. The cloth is soaked with resin, wrapped in varying directions (to get the required strength) then put in a vacuum bag, then into the autoclave at a rediculous pressure/temperature to cure the structure. The good finish simply comes from the resin being squeezed from the structure and against the smooth vacuum bag.

Well thats how i understand it, of course i could be wrong.

But still, how about them wishbones? Design rules for carbon fibre structures? Anything would be good... All i got so far is a sketch and a density. I know that many high stress carbon fibre structures have an aluminium honeycomb embedded in them. Do wishbones need this (i assume they do)?

Cheers,
David





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britishtrident

posted on 17/1/05 at 11:04 PM Reply With Quote
quote:
Originally posted by flak monkey
Not really a Locost question I know, but has anyone got any info on the design of these? I have been looking and cant find a thing, I do know they exist though. I'm just doing some concept design work and pretty much any info would be useful.

Thanks in advance,
David


Your are unlikely to find much published on the subject racing teams guard that kind of design info pretty closely. However as composite structures go they must be relatively simple as the fibre orientation will be mainly unidirectional because the parts of the component are in theory only loaded in compression or tension , but as with any designing using an anisotropic material devil will be in the detail.

Having seen picutres of fractured wishbones the material used in F1 wishbones apears to be mainly CF not Kevlar.

Assuming you have grounding in the behaviour laminated composites (the Tsai-Hill design criteria) I would start looking "The Journal of Composite Materials" .

[Edited on 17/1/05 by britishtrident]

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paulbeyer

posted on 17/1/05 at 11:19 PM Reply With Quote
send Darren of GTS a U2U. He does work for certain F1 teams and has experience in working with CF.





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dmottaway

posted on 18/1/05 at 12:34 AM Reply With Quote
check out

http://www.mci.i12.com/carbon/

doesn't answer the important structural questions, but does give SOME answers.

interesting site, anyway.

dave

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Avoneer

posted on 18/1/05 at 12:51 AM Reply With Quote
There was a guy on eBay selling ex F1 bones and other bits of the cars. A rear bone went for 30 odd squids - good collectors item and a piece of remarkable engineering.
Pat...





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dozracing

posted on 18/1/05 at 06:46 AM Reply With Quote
Hi all,

Not sure exactly what it is you want to know about them. Ask me specific questions and i'll tell you.

Material is carbon fibre, usually a mixture of M46J uni-directional fibre and cloth. McLaren use M55J fibres in some of theirs.

They used to be made in two halves and bonded together, with bonded on titanium end fittings, with flexures on the inboard end. Now a lot of teams are using carbon flexures at the front and making them in one hit using matched tooling and special consolidation techniques.

One way to make them in one piece is to machine a foam core (usually rohacell) which expands slightly in the autoclave as the carbon cures which consolidates thes fibres against the mould.

They are usually steel moulds these days, when they were all two piece bones then we used carbon moulds.

Can't remember exactly what the layup was, but i would guess the wall thickness was less than 3mm.

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ned

posted on 18/1/05 at 09:49 AM Reply With Quote
sorry, but i just had to mention that you've both posted on the same subject and not had a disagreement!

Ned.





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britishtrident

posted on 18/1/05 at 11:31 AM Reply With Quote
Trouble with CF is it is just so brittle, kevlar is much more forgiving but can't match CF for material properties.

One of the big problems withcarbon composites is detecting when the fibres that carry the loads have damaged --- ok in the use once then throw\away culture of F1.

However intertesting work has been done on real world composite suspension parts, a few years back LDV were testing composite van springs and found them practical but the investment in existing plant mean't it wasn't viable for production. Since then things have moved on see http://www.mgbmga.com/tech/mgb4a.htm

A lot has also be done on composite replacements for coil springs.

[Edited on 18/1/05 by britishtrident]

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krlthms

posted on 18/1/05 at 07:52 PM Reply With Quote
quote:
Originally posted by Syd Bridge
quote:
Originally posted by ned
sorry, but i just had to mention that you've both posted on the same subject and not had a disagreement!
Ned.


If I know different, there is no way I would put it on an open forum like this. Not when I make my living at it! Let each believe what he wants.

Cheers,
Syd.


This disturbes me. If you have knowledge that you want to keep to yourself, the least you can do is not brag about it.

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Rorty

posted on 19/1/05 at 04:32 AM Reply With Quote
On a bike forum that I frequent, there's been a hell of an uproar recently about carbon fibre and in particular, carbon wheels.
All sorts of crap has been flying around, but the pictures of a crash resulting from a carbon wheel failure were pretty damning. Unfortunately, most of the "good" pics have been removed, but a following rider stated the rear wheel of the bike in front of him "exploded".
Failed carbon wheel.
The maker of the wheels, BST, is a big name in the wheel industry (and knows how to charge).
When the experts can't get it right, I'd be inclined to forget the idea of carbon Locost wishbones...unless you have a suitable budget for lots of destructive testing.





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britishtrident

posted on 19/1/05 at 08:12 AM Reply With Quote
quote:
Originally posted by Rorty
On a bike forum that I frequent, there's been a hell of an uproar recently about carbon fibre and in particular, carbon wheels.
All sorts of crap has been flying around, but the pictures of a crash resulting from a carbon wheel failure were pretty damning. Unfortunately, most of the "good" pics have been removed, but a following rider stated the rear wheel of the bike in front of him "exploded".
Failed carbon wheel.
The maker of the wheels, BST, is a big name in the wheel industry (and knows how to charge).
When the experts can't get it right, I'd be inclined to forget the idea of carbon Locost wishbones...unless you have a suitable budget for lots of destructive testing.


The military spent a lot of money on research grants on projects investigating the failure of carbon fibre composites caused by apparently very minor surface damage such as a small object like a screw driver being dropped on to an aircraft wing panel or stone chips thrown up from the undercarriage which could d cause a panel to break up in flight.

In that type of occurance most of damage is on the reverse hidden side with only a tiny nick visible on the surface that was impacted but the damage spread out in a cone from the impact point so that the crazed area on ther hidden side was much larger. It was found that covering the surface laminas with a tougher more elastic layer --- Kevlar or E glass did a lot to protect the CF from damage.



[Edited on 19/1/05 by britishtrident]

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Liam

posted on 19/1/05 at 01:49 PM Reply With Quote
quote:
Originally posted by britishtrident
It was found that covering the surface laminas with a tougher more elastic layer --- Kevlar or E glass did a lot to protect the CF from damage.


Makes sense. Wouldn't go down too well with the posers who'd actually buy carbon wheels though would it!! They'd want people to damn well know they have carbon wheels!

Have seen these before. Always did seem odd to me to use a brittle material for wheels.

Liam

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dozracing

posted on 19/1/05 at 04:53 PM Reply With Quote
Its quite true what is said about the failure of carbon fibre.

The experiences of F1 teams though is that failures don't exist in a race very often (i can't remember the last wishbone failure). They aren't long races, but we used to test them every 1000 kms, and back in the prost days i can remember wishbones being fine after 5 races.

Its common in F1 to use UD fibres on the outside to protech from damage, but, like Trident days the damage is beneath the surface and often this technique hides damage that a cloth finish might have shown up.

We used to cover them in helicopter tape, and the experience is that they very rarely failed. It is however a different expereince to driving on the road.

I think personally i would be prepared to drive with them on the road, but, i don't know whether i would sell them in this day and age. I think there are more risky elements you can build into your car and commonly are, but, commercially it may be sailing a little too close to the wind for most peoples comfort.

Kind regards,

Darren

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ceebmoj

posted on 19/1/05 at 09:16 PM Reply With Quote
hi

we desin the component in cad and spesifi the loads the workststion then works out using Finite elemint analisis the hard points (macheaned metalbits witch are mounted in to the structure) and then produces a cutting plann for the bits of CF,Kevlar, and other stuff. the comp genorated components ar usaly tweaked

the cutting plan is sent to the laser cutting machean witch cutts out each of the peaces of matt.

a 3D printer is used to build up some bits (witch help provide a core and complicated internal CF structure)

the bits are then placed in a set order in to a metal modle also produced by the CAD soft ware along with the wiering loom. top goes on the mold.

place in auto clave gass mark 6 cook presurise vacume and shake it about a bit.

blake

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krlthms

posted on 19/1/05 at 09:31 PM Reply With Quote
C'mon guys
You are starting to sound like old women! Is this the post Chrismas bules, or dark induced depression? Rorty, it must be sunny down under, so waht is your excuse? I mean, where is all the swash buckling, mis spelling, gung ho -that I have grown to know and love in this forum- gone? We are not starting to take ourselves too seriously, are we? If so, I will have to post pics of nekked ladies, or something.
I am sitting here in Chicago, temperature bloody cold (single digit Fahrenheit), in a windowless basement, having lunch, with only you guys keeping me company, so:

Reminder, it is the 21st century. I just came back from the centrifuge room, where we use rotors made out of (you guessed it) CARBON FIBERS. Why do we use them, because nothing else has the same quality. I am gonna give you an idea of the forces involved, up to HALF A MILLION G, sustained for 24 to 36 hrs. We stopped using titanium because the rotors had limited life span, and failed more often than we liked.
Here is a website for the specs of such rotors: http://www.medibix.com/runsearch.jsp?category_id=14360&productsort=manufacturer&view=sku&product_id=417861

OK, so my first point is that CF is a miracle material, and it is amazing that we have such ready access to it. But of course (we all know this), things tend to break when you least expect them, and with maximum damage, if they are not made properly or used within their design limits.
Another example of how good CF is is that the new Boeing 7E7, has the entire fuselage made up of CF (one of the sites below should lead you to the story, or google 7E7 and CF), so there is no escaping CF.

Point number two:
CF is no easier or harder to work with than any other matrix. It has its piculiarities, like any thing else, and these are the ones I know:
1. It conducts electricity, so if it is in contact with a metal it would setup a junction voltage and cause corrosion. There are two solutions to this. First, is to use a bridging layer of glass fiber to connect the CF to your metal. Second, use titanium, because it happens that a junction between CF and Ti generates no voltage! Isn't Nature/God/Darwin cool; they are telling us to use these two exotic materials together.
The second property of CF is that it is brittle, and it is most strong in the tension plane. The brittleness is usually taken care of with having an outer layer of Kevlar, as pointed out in another post. The issue with directionality of strength is taken care of by paying attention to the direction of the weave when laying up the CF matt.
The third property of CF is not really due to the CF itself, but the adhesives used in making the parts, namely, the parts are stronger and lighter if cured in high pressure and temperature, in an autoclave. An autoclave is a fancy name for a pressure coocker. Note that CF is still fabulous to use WITHOUT curing in extreme conditions, but if you wanna try going a step further, then you can generate your own "extreme conditions". In the links listed below you will find out how to do this on a small scale.

POINT#3:
Have we not had (very recently) descussions galore about the desirability of having the front suspension engineered as a weak point, so that it absorbs shock and collapses in a fron collision. Well, if so, why not use a weaker material to make the suspension in the first place? Only kidding, so please don't bite my head off. Seriously, though, isn't the whole ethos of Locost to push the envelope in design and engineering.

Which brings me to my final point:
CF has been used very sucessfully, for some time, by builders below us and above us. Thus, there are many experimental, homebuilt aircraft, that are built mostly of composites, inculding CF. Similarly, virtually all endurance or speed bikes are bulit of CF.
So, to find out about CF you need to go to either aircraft builder websittes, or to bikers. A good start would be the human powered vihecle crowd (and you thought locosters are mad, wait til you see what this lot is up to).

Actually I have one more point to make:
It is basically a disclaimer in two parts. The above is written with a certain tongue in cheek, so apologies in advance to any person offened by the content (on the other hand: lighten up). Second, I am not building anything; I am following Kurt (of Kmini fame) to take at least a year and research and plan before applying saw to metal. In the reasrch process I have learned enormously from the amazing collective genius (and maddness) of this forum (this means: thank you graber, rorty, kurt, BT, and all, not least Syd).
My final final point is that I have a centrifuge running, so I better get back to work.

Here are some sites to be getting on with:
http://www.germancarfans.com/photos.cfm/photoid/3030603.001/page/2/size/regular/mercedes/1.html

http://www.recumbents.com/wisil/bythefoot/bythefoot.htm

http://members6.clubphoto.com/mars548268/715654/guest.phtml

http://www.sheldonbrown.com/rinard/howibuil.htm

http://www.boeing.com/news/releases/2005/q1/nr_050111g.html

Cheers and sorry about the lack of edit.
KT



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Rorty

posted on 19/1/05 at 09:56 PM Reply With Quote
Don't get me wrong, I'm all for carbon fibre, but it's still a relatively new material and there is a lot of industry ambiguity. Also, I can't afford to play with it myself, nor afford an expert to expand his learning.
I'm not a Luddite, I was just suggesting the use of carbon for Locost wishbones may not be the easiest or most prudent choice.
As an aside, a friend bought some carbon "race" parts from a well known manufacturer for his GSXR 1000. They weighed more than the glass parts he'd used the previous season! Obviously wet laid and pretty, but what a croc! Buyer beware in the accessory industry.
What are you doing in your bunker? Is Dubbya annoying the Soreheads again?





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krlthms

posted on 19/1/05 at 11:27 PM Reply With Quote
quote:
Originally posted by Rorty
Don't get me wrong, I'm all for carbon fibre, but it's still a relatively new material and there is a lot of industry ambiguity. Also, I can't afford to play with it myself, nor afford an expert to expand his learning.
I'm not a Luddite, I was just suggesting the use of carbon for Locost wishbones may not be the easiest or most prudent choice.
As an aside, a friend bought some carbon "race" parts from a well known manufacturer for his GSXR 1000. They weighed more than the glass parts he'd used the previous season! Obviously wet laid and pretty, but what a croc! Buyer beware in the accessory industry.
What are you doing in your bunker? Is Dubbya annoying the Soreheads again?


Rorty,
you have a U2U.
What would be incrdibly sexy would be this : Make front suspension so that the lower bones are made from metal and operate a remote shock/spring thingy with a rocker stick you know. Then, here comes the sexy bit, build an upper bone from CF that is solid and has an inverted wing profile, so that as the car gets faster, the downforce on the front wheels gets larger. What is wrong with this idea, since nobody seems to have tried it?
One more thing I forgot to add in my previous mail is that titanium and CF have the same thermal expansion rates. God/ Nature/ Darwin? Eienstein, or whoever is in charge, really wants Cf to be used with Ti.
Back to the dungeon now.
As for affordability. Rorty, I keep seeing offcuts on sale at Ebay, so I imagine doing things with CF on the farting-about scale should not be to $$$
Have a look at the sites of recumbent bike lot; they are really mad. Riding around at 50 mph in a cotraption the strength of a match stick!
Back to the dungeon!
Cheers
KT

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Rorty

posted on 19/1/05 at 11:52 PM Reply With Quote
quote:
Originally posted by krlthms
I keep seeing offcuts on sale at Ebay, so I imagine doing things with CF on the farting-about scale should not be to $$$


I suppose there's nothing wrong with hand laying CF, but when you get into autoclaves, the cost rises.
Aren't different resins required for non prepeg/autoclave use?
I've worked with "old fashioned" glass fibre plenty of times, but haven't touched CF, so my knowledge of it is nil. I would like to experiment with it though.





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krlthms

posted on 20/1/05 at 12:12 AM Reply With Quote
quote:
Originally posted by Rorty
quote:
Originally posted by krlthms
I keep seeing offcuts on sale at Ebay, so I imagine doing things with CF on the farting-about scale should not be to $$$


I suppose there's nothing wrong with hand laying CF, but when you get into autoclaves, the cost rises.
Aren't different resins required for non prepeg/autoclave use?
I've worked with "old fashioned" glass fibre plenty of times, but haven't touched CF, so my knowledge of it is nil. I would like to experiment with it though.


I am thinking that vacuum bag + home made oven would do the trick. I imagine that the trick of wrapping tape around the CF object and introduincing pin holes is also similar.
As for resins; I am not sure how much of the differences are due to the underlying chemistry and how much is just sales hype, but I imagine if you stay with one system (which is precisely what the manufactureres want you to so) you should be OK.
Incedently, if you look at the site of the guy who made a time trials bike out of CF in his garage, you will see somewhere that he gets a mail, several years back, from a high school student from OZ (maybe the same age of our Adam) saying how he also made a CF bike at home. Fast forward, if you google the Ozzy guy's name, you will see now that he is a famous triathlete / bike maker.

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britishtrident

posted on 20/1/05 at 12:13 PM Reply With Quote
A lot of the the pit falls with CF are with long strand fibres, short strand composites are easier to engineer but can never have the ultimate tensile strength of long strand.
A lot of the reason CF hasn't made a big impact in the car world outside F1 is that unlike aerospace where it is relatively easy to get a handle on the size and direction of the forces involved it is not so with the loads from a cars suspension -- all those nasty kerbs and potholes.



[Edited on 20/1/05 by britishtrident]

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Rorty

posted on 20/1/05 at 12:34 PM Reply With Quote
quote:
Originally posted by krlthms
I am thinking that vacuum bag + home made oven would do the trick. I imagine that the trick of wrapping tape around the CF object and introduincing pin holes is also similar.


I hear what you're saying and I'd normally be the first to jerry-rig some jigs or contraptions to have a go at making something.
However, with the methodology still in relative infancy and product longevity very much under a cloud, I would be inclined to bank my money for the time being and build the suspension out of tried and tested steel tube.
Tomorrow's another day.





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krlthms

posted on 20/1/05 at 04:22 PM Reply With Quote
Syd,
It is hard not to treat your comment with the contempt it deserves. However, I will, this time, reply to you because I am worried that someone who doesn’t know your history in this forum might take what you say about CF and locosts seriously.

Maybe I am a Yank, maybe I am not, but at least the talk I have put in the previous messages has CONTENT. You, on the other hand, just tell everyone how great you are with 30 years this, and 30 years that, and how impossible and tricky everything is.
It is your attitude that is offensive: "I know how it is done, but I don't want to tell you".
Well you don't get away with it every time. So, now, having been shown for the fraud you are, you start rather condescendingly talking about cost and stuff. The information that you want to keep to yourself (assuming you knew it in the first place) is all out there in public domain, and if you follow it, I am sure you could build complicated and durable structures, for sports cars, out of CF, affordably.
To make my point further, let me quote to you the comments in one of the sites I listed (http://www.recumbents.com/wisil/bythefoot/bythefoot.htm) verbatim:

"Car racers want to keep secrets to themselves," Beauchamp said. "Recumbent racers are more than willing to help each other out. They're happy to tell you what they did to make themselves go faster."

Sounds familiar?

One more thing, I am not an armchair expert, I am a student. I listen to others and learn from their knowledge and experience, provided they are willing to share it.

I don't know if you are old or not, but you are certainly grumpy. All I can say to you, in my best Yankee imitation accent is: Mr Bridge, you can take all the CF knowledge that claim to have….. and shove it.
KT

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krlthms

posted on 20/1/05 at 04:30 PM Reply With Quote
quote:
Originally posted by britishtrident
A lot of the the pit falls with CF are with long strand fibres, short strand composites are easier to engineer but can never have the ultimate tensile strength of long strand.
A lot of the reason CF hasn't made a big impact in the car world outside F1 is that unlike aerospace where it is relatively easy to get a handle on the size and direction of the forces involved it is not so with the loads from a cars suspension -- all those nasty kerbs and potholes.



[Edited on 20/1/05 by britishtrident]


BT,
Good point, but the frame of a recumbent bike made of CF, and weighing a few pounds, carrying a 200 lb man, at up to 70 mph, probably experiences forces of the same order of magnitude?
KT

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