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Old 05-24-2012, 05:07 AM   #61
kpt4321
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Quote:
Originally Posted by Twin-shocker View Post
there is no reason why they shouldnt be strong, light, and cost less to produce that metal racks.
Show me ANY component on ANY motorized vehicle which is made of carbon fiber and is CHEAPER than the metal alternative. The proof is in the pudding, buddy.

The ONLY time carbon fiber is used is when there is a big enough benefit to pay off the high cost. For example, body panels on high-end sports cars, monocoque chassic on race cars, structural/body pieces on next-generation airliners.

There is a reason that cheap cars and basically all motorcycles are still metal, and only race cars/bikes use carbon parts. It's expensive.

If is was cheaper, stronger, lighter than metals, as you are proposing, can you please explain to us why there isn't a single example of this on a production motorcycle?

I'd also love to see evidence of your experience with carbon/composite parts.

I do like your production plan though:
1. Use a plastic tote as the shape for the top (I don't quite follow how a rack looks like a plastic tote, but ok...)
2. ...
3. Profit!

(Somehow, you have managed to completely skip over how you're going to create the whole rest of the structure. But you've got a plastic toe shape for the top, so you're good!)

Now I remember why I block your posts...

In the end, you're just a guy running your mouth who constantly fails to provide any evidence for your claims.
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Old 05-24-2012, 06:06 AM   #62
Twin-shocker
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I cant really see why so many people are so obsessed with carbon fibre? In the case of something like a luggage rack, using this in wet lay form wouldnt be much stronger than GRP, and would mean unit costs 5-6 times greater than using more appropriate materials.

If you wanted to use pre-preg carbon and item was properly designed, then it would be far stronger than the bike frame it mounted to. In this case though a fit for purpose part could be easily made on a DIY basis, using the materials and production techniques outlined in a previous post of mine.

Something like Diolen cloth is far more suited than carbon for making mouldings such as a luggage rack, and this in combination with CSM, foam core, and epoxy or VE resin system, will be a great deal less costly.

In regard to race car parts there is an obvious need for parts which are both lighter and stronger than metallic alternatives, and carbon is becoming increasingly common even in low tech race series such as NASCAR for instance.

However unless altering cosmetic appearance is the primary aim, there is little need for pre-preg carbon parts on road going machinery, but many seem to have little understanding of this, and seem think carbon is the only possible material to use.................
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Old 05-24-2012, 06:47 AM   #63
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In regard to race car parts there is an obvious need for parts which are both lighter and stronger than metallic alternatives, and carbon is becoming increasingly common even in low tech race series such as NASCAR for instance.


NASCAR runs some low tech technology/components due to their rules structure. However, if you think that it is a low-tech series overall, you're sorely mistaken. The design of the cars is extremely high tech, and there is a TON of money in it.

(For reference, I greatly dislike NASCAR, but facts are facts).

This just makes my point. The only places that are seriously utilizing composite technologies are industries/markets with EXTREMELY high levels of cost/funding.

The idea that it is cheaper than a metal structure is comical.

Quote:
However unless altering cosmetic appearance is the primary aim, there is little need for pre-preg carbon parts on road going machinery, but many seem to have little understanding of this, and seem think carbon is the only possible material to use.................
So, you think the only reason Boeing and Airbus are using carbon prepreg is for aesthetics?

Nobody ever said carbon was the only option. I'm still waiting for your proof that ANY fiber/epoxy composite is, as you claimed, cheaper, lighter, and stronger than a steel structure.

As usual, you make a bunch of claims but have no data to support them.
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Old 05-24-2012, 02:00 PM   #64
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Originally Posted by kpt4321 View Post
Composites are a good (and sexy!) choice for a project like the one you showed, where you can lay it up on an existing continuous surface and just glue it on when you're done. It just is there to add a layer of protection, but it doesn't need to have significant standalone structural properties.
Reason to choose composites for the project as shown was twofold:
- Freedom to shape it like the tank
- The very good resistance of aramid to sliding over asphalt/rocks/whatever.

The carbon is only there for aesthetics. Easiest way to nicely finish the product. I could as well have used another layer of glass and paint that. After all, it is the propterties of the aramid I was after and I am not the kind of guy that becomes all warm and fuzzy from 'real carbon fiber'.

Quote:
Trying to lay up a rack is a lot harder. It needs to be strong/stiff in several axes, which means you've got to fabricate some sort of beams (angles are easiest, i-beams most effective, tubes perhaps most convenient).
That would be some kind of tube. Easy to wrap tightly using fabric in 'tape-form', easy to control fiber direction. It would also allow me to create the rack from a lightweight material such as PVC tubing and when finished: wet fabric with epoxy, wrap it tightly, and finish.

Or polycarbonate tubing. Already pretty strong stuff, almost unbreakable (your visor is made out of it), easy to make a good, strong weld on, and epoxy bonds well to it.

Quote:
It needs to mount to existing surfaces, which generally means you need to bond in some inserts to bolt through.
Of course; add metal to the plastic rack before wrapping. Easy to fabricate.

Quote:
It needs to be impact-resistant, which is generally not its strong suit
Carbon has problems, but I am more interested in aramid and woven glass (to improve bonding). Aramid fibers don't break so easily. Especially when laid up on polycarbonate so the epoxy won't crack so quickly I don't see why it would perform bad in the impact resistance department.

One problem I do see: metal deforms permanently before breaking, composites do not deform before breaking....

Quote:
(note that few motorcycles have body panels made from fiberglass, especially off-road ones).
Law of numbers. What is a good method to construct one piece is probably not good for mass production. It is much easier and far cheaper to mold those panels from ABS or polypropylene...

Same with steel for racks: it is available, cheap, and almost anybody knows how to work with mild steel. Makes it a perfect choice for someone wanting to make a business from building racks. Especially because nobody except me cares about the weight of such a rack.

Quote:
None of this is impossible, but it's far from easy, and it's questionable whether the savings of a couple of pounds are worth the large amount of extra effort and the additional risk.
Oh, just call me nuts. I am always willing to try something different as long as I have fun doing so. 9 of of 10 times it tuns out that there was a reason the rest of the world does it like they do, but sometimes...

It would at least gain me a lot of experience with what composites can and cannot do.
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Old 05-24-2012, 02:58 PM   #65
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There is no need whatever to use costly aramid materials for this project..........Diolen cloth and CSM is fine (Diolen fibres are used for making seat belts, so are very strong indeed). Layup over foam or aluminum honeycomb core material, with stringers going from side to side, and laminate side members with incorporated mounting points to the ends of the stringers.

For cosmetic appearance use a layer of carbon lookalike Eglass cloth in silver under a clear UV resistant epoxy gel coat, and it will look very nice indeed. If you can find a part from something else, which seems as though it would do the job of side members, then use these parts to make a couple of single use moulds from silicone, which can be backed up with car body filler to provide stiffness.
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Old 05-24-2012, 03:09 PM   #66
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Quote:
Originally Posted by kpt4321 View Post


NASCAR runs some low tech technology/components due to their rules structure. However, if you think that it is a low-tech series overall, you're sorely mistaken. The design of the cars is extremely high tech, and there is a TON of money in it.

(For reference, I greatly dislike NASCAR, but facts are facts).

This just makes my point. The only places that are seriously utilizing composite technologies are industries/markets with EXTREMELY high levels of cost/funding.

The idea that it is cheaper than a metal structure is comical.



So, you think the only reason Boeing and Airbus are using carbon prepreg is for aesthetics?

Nobody ever said carbon was the only option. I'm still waiting for your proof that ANY fiber/epoxy composite is, as you claimed, cheaper, lighter, and stronger than a steel structure.

As usual, you make a bunch of claims but have no data to support them.

A good example of a light/strong,inexpensive part are the composite pods used to house life rafts on
board ships. These obviously need to be very light, extremely strong, and cost effective to produce.

The fact that they can be dropped from 45M onto a solid concrete surface, and the life raft within remains intact, seems to suggest they work pretty effectively!

As to NASCAR being high tech, thats really rather silly dont you think? An ex F1 engineer I know was in the US working on special ignition systems for one of the teams, and he was struck by the fact that even though enormous amounts of sponsors money is poured into this sport, that everything it pretty crude and agricultural looking.
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Old 05-25-2012, 01:50 AM   #67
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Originally Posted by Twin-shocker View Post
There is no need whatever to use costly aramid materials for this project..........Diolen cloth and CSM is fine
Aren't you a little confused with building a boat? Regular CSM is used with polyester resin and doesn't work too well with epoxy because epoxy does not contain teh necessary solvents (styrene..) that dissolve the binder between the strands. Searching for online Diolen sources only point me to kayak and boat sites. Regular composite supply shops don't stock it, but i suppose I could get it at the same shop granny buys the fabric for her new dress.

I also don't see why I would prefer CSM over woven glass fabric; CSM is only slightly cheaper but it needs much more resin and results in a far lower fiber content in the laminate, and far worse mechanical properties of the finished laminate. If I was building a boat where I needed a ton of resin and a truckload of fiber, I might consider polyester/CSM.

But for what do I use composites? Make a protector, copy a plastic part, build an enclosure for some electronics, etcetera. All low volume/surface area stuff, so the price difference between epoxy/woven fabric and polyester/CSM if not worth the extra smell and itch of polyester/CSM.

Epoxy, aramid tape/band, woven glass, maybe some carbon fabric and some disposables would cost somewhere between $50 and $75 for the rack. With low-spec materials such as polyester resin, CSM and diolen instead of high-spec aramid/dyneema/epoxy/carbon/bla I could save $20 or so. Percentually a lot cheaper. Absolute amount of money: not worth it. It is the equivalent of 2.2 gallons of fuel, so if I have to go out and visit 3 stores to buy it, I already burnt most of it.

As I said before: the game is different for a one-off hobby project and a professional trying to make a living.

Quote:
..
..
then use these parts to make a couple of single use moulds from silicone, which can be backed up with car body filler to provide stiffness.
If I go with composites I still do not intend to make a mould at all. Just make what I want out of a lightweight material which would be mainly tubing, make inserts out of 5754 aluminium sheet, skin it with fabric+epoxy, and paint it. Since the fabric can be wound tightly around the structure, I expect that a fiber density in the composite of 35-40% is possible this way.

But still, I do value the opinion of ktp4321 on this since he certainly seems to know what he is talking about.

Maybe the 'proof of the pudding' method would be the best to figure out whether it is a suitable material or not. Make one or two tubes out of aramid/glass/epoxy, maybe on different substrates (I still think that thinwalled polycarbonate tube would be a good choice to improve impact strength), and bend/smash them until they break.
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Old 05-25-2012, 05:50 AM   #68
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Had a spare half an hour, so I decided to do a quick test. A bit too quick probably since things did not work out too well.

Aramid, glass (both 160g/m2, don't know how to convert to crippled units), and a piece of impact resistant electrical tubing in which I put a bend.



I used some small aramid leftover pieces from previous projects ( I always keep them since they can be used to reinforce a corner or something on the next project) and only used a bit from the roll. That was problem #1; impossible to nicely wrap small irregular pieces around the pipe.

The glass 'band' was cut too wide. Thought that the twill weave could be forced around the bend, but not so. Due to time limits I decided to continue, but it would have been better to unwrap it, cut it in half, and redo.

To top it off: this suboptimal fabric needed about 30% more resin than calculated. Of course I only made 15-20% extra because I expected to be able to wrap tightly.

Who was it again that said 'I can do quick, cheap and high quality. Pick two'?



Oh well, i would use aramid and glass band for wrapping tubes in a 'real' design anyway, which makes it a lot simpler. And for a no/no go test this tube is still suitable; I am going to destruct it anyway. If that is way too easy, it is a no-go. If that is hard, the real thing would only be better.

Epoxy is a general purpose room temperature curing type, needs 24 hours. To be continued....
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Old 05-25-2012, 09:39 AM   #69
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Powder bound CSM works perfectly with all epoxy resin systems, and if you intend to contact mould your parts, using a combination of this and Diolen cloth will be far easier than kevlar.

Wrapping tubes is not particularity effective for a project such as this, and you will find a rectangular form tapering off at the far end, will be both stronger and easier to make, and should be ideal for load bearing side members.
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Old 05-27-2012, 06:06 AM   #70
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Epoxy had 2 full days to cure. Time for destructive tests. Well, ehm, destructive? Until now I failed to completely destruct the pipe.

Cut-though. Was quite a job to cut a piece off.
Laminate ended up quite thick, but as said before: fiber density is a lot lower / resin is a lot more than what should be.



I stressed the bend by loading the pipe axially with approximately 150kg. Would not break, bent only a little, sprung back with weight removed.

Tried to break it by clamping the bend in the vise:



I stopped because the vise would probably break earier than the pipe. Again: the jaws of the vise managed to fracture the outer glass layer, but not the aramid.

Impact test. Very scientific method: drop a piece of concrete weighting around 20kgs from a meter on the pipe, edge of the concrete first.



Detail:



Not very well visible on the picture: the outer glass layer cracked, the aramid is still intact.

OK, how would a 28mm OD/2mm wall thickness RVS304 pipe react to the same kind of abuse?



Oops...


Preliminary conclusion of this very unscientific test: aramid/glass is a well suitable construction material for a luggage rack.
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Old 05-27-2012, 02:26 PM   #71
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Originally Posted by DaBit View Post

Preliminary conclusion of this very unscientific test: aramid/glass is a well suitable construction material for a luggage rack.
Cool! What's the weight of your composite tube like compared to the aluminium or steel tubes that are the alternatives?

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Old 05-27-2012, 03:12 PM   #72
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The tube should have weighted around 70 grams based on square meters of fabric, resin need of the fabric and length of PVC used, but due to waaaay too much resin and sloppy laminate the current tube weighs a little over 100 grams (yes, it is THAT bad. Will do better next time).

Would have to measure the outside diameter of the tube to compare with steel and/or aluminium. Guess it is somewhere around 25mm/1" with a length of approximately 40cm / 16".

Quick guesstimate: by going a little thinner on the aramid (as said before: a broken subframe and a totally intact rack makes no sense) and adding a little carbon in the mix for the pieces not subject to direct impacts, an entire rack could be made with a total weight of 850-1100 grams. Below 2.5lbs for you Americans. The same in steel would be around 4kg/9lbs.
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Old 05-28-2012, 12:04 AM   #73
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If you made the part using flattish rather than round section (boomerang shape would be ideal for side members), it would be stronger, easier to make and would look better than a tube. You will also need to use compression or vacuum moulding, as any resin rich composite part will not have uniform strength and failure is likely in weaker areas.
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Old 05-28-2012, 05:22 AM   #74
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I am considering a core of EPS. Not the grainy isolation stuff, but more the 'hamburger box / isolated coffee mug'-like foam. Quite pressure-resistant and very light.

Using vacuum bagging for this project is probably not the best idea; the mounting points would make it quite hard to get the foil pressed to the laminate everywhere without bridging. But there exists something called 'crimp tape'. Wrap around, heat it, and it crimps 20% or so, just like the crimp socks you use when wiring. Sounds good.

About the cross-section of the tubing: where the cases mount I would need something with a good support area and/or a good pressure resistance. Of all geometric forms the cylindrical one is the strongest/stiffest/most pressure resistant for a given amount of material. A rectangular one would provide the most support area for the cases. Dimensions in X and Y directions could be varied (create an oval or rectangle) to increase strength in a certain direction.

But is it that important? Load on the loop carrying the cases is minimal. Let's say we have 30kg of luggage per side (far more than I would ever take with me), and due to the shock bottoming hard (or heavy vibration) acceleration is 5G's. Then that is still only equivalent to 150kg of load which is distributed nicely since the case itself provides rigidity too and is supported on the loop at more than one location.

The real stressed parts of the rack are the mounting points and pieces supporting the loop. A straight rectangular or round form is not optimal for them anyway; Touratech&co use trapezoid-shaped forms there too.

The advantage is that these parts are not likely to be subjected to a direct impact, so I could use a few layers of carbon or carbon/aramid hybrid fabric there to increase load bearing strength.

Oh well, one way or the other it is possible to make a useable rack. Let's sell the TT rack and alu cases to raise funding first
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Old 05-28-2012, 07:05 AM   #75
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PU foam is an inexpensive core material, but a combination of this and aluminuium and polypropylene honeycomb would make for a much more durable moulding, as the alternative cores used in the right places would mean a rack that was pretty much indestructable:http://nida-core.com/english/nidapro...o_sandwich.php
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