Toy

????? enlighten me.

NickSimcheck

UH? *chuckles* What would you like to be enlightend on?

Toy

What are the pros and cons of each? While searching for an aftermarket hood, i found that R-Magic makes one in kevlar instead of carbon fiber so i just wanted to know if there are benefits to using kevlar over CF.

KevinK2

kevlar, yellow fiber, is tougher, less likely to crack with impact. carbon fiber is stiffer, hood can be made lighter.

DomFD3S

While I am not an expert, this is what I know.

Carbon Fiber (dry) is nothing w/o resin. When carbon fiber and the resin is applied, it is subsequently dried. After this, the result is a plate or sheet of stiff carbon fiber. This is assuming that you're solely only using pure carbon fiber.

Kevlar is used in making bullet proof vests. What is different is that instead of using all carbon fiber in the layup process, they may decide to use either sheets of kevlar, a mix of carbon fiber and kevlar strands, etc.

Both carbon fiber (pure) and carbon kevlar utilize the same basic procedures. However, they have different properties.

Here are two websites on the subject:

www.carb.com
www.uscomposites.com

LLADNAR

actually most "carbon fiber" is actually carbon kevlar,,carbon fibers themselves are all black,,and most carbon fiber is cross meshed with a grey or yellowish material(kevlar) which gives it its classic look.

Bigus Dickus

Carbon has a higher elastic modulus than Kevlar, making it stiffer for a given weight or geometry.

Kevlar is actually both lighter and stronger than carbon fiber, but since stiffness, not strength, typically dictates design in hoods, body panel, and structural components, carbon is usually the composite of choice.

There are many different weaves of each type of material, and different weights as well. There are also several carbon/kevlar hybrids, but I'd hardly call those the majority of weaves.

Carbon/kevlar hybrids, from my experience, are more for looks than anything else. Usually the application is better suited for one material or another.

PaulC

I work in the air craft industry, granted its in the IT field now. However I do have several years in the engeneering dept doing inspections. Also I have several years of Air Force experience as well. not being ignorant on the uses of both of these materials in the production of air craft pieces and having seen the result of many many hours of use. Pure kevlar or pure carbon fiber panels seldom work well. The F22 Raptor and F35 JSF both use a mix of Kevlar and Carbon fiber for stiffness and impact resistance. Granted most of us are not going to be shot at like a jet fighter will be. But the same principal holds true for us as well. For that occational fender bender we all will experience.

The best products will be a mix of the two.

Also every one else here seems to be well informed and giving good information from what I know on the subject.

CrackHeadMel

iTrader: (2)

all i know is a few years ago i was buildign a go-cart, my dad works where they make kevlar and cf everying, i could get Tones of scrap if i wanted, well, here s my point, i had a seat made for my cart that was 1/4 inch think sealed kevlar, then, a week later after the resin dryed, it took 5 Titanium ($85 each) to drill the 2 hols i needed to mount it, if i had the chance, id make EVERYING out of kevlar, one time we made kite string cus a friend had a large *** kite that always snapped its line, it was i think 32 thread, pretty small, worked great as kite line, also was strong enough to tow his 90ish Capris Station wagon up a hill, kevlar is nutty stuff,

Bigus Dickus

Yes, Kevlar is hell on scissors, saws, drills, mills, and everything else, but that doesn't make it a wonder material for structural purposes. It is great though where abrasion resistance is a good thing.

The matrix can fail, leaving you a limp noodle structure even if the fabric is perfectly intact. Sometimes this is a very desireable property, which is why many fracture prone components have Kevlar or hybrid "burst" layers as a crack arrester.

Carbon doesn't tend to act the same way because the carbon filaments are themselves fairly stiff and brittle (cloth still feels flexible, just not the same as Kevlar). Carbon fractures rather quickly when it fails.

user 84205

OK i dont know much about the F-22 or F-35.

BUT, currently im an inspector and a composite tech for the military. I have the pros and cons for ya.

Carbon fiber, looks better, also about the bullet thing, carbon fiber isnt made to stop a bullet, its made so the bullet will go straight threw, and the surface will still retain 99% of its strength, or some high percent (I would have to check the book) Als carbon Fiber is actually really easy to work with then KEVLAR, if any one here has worked with KEVLAR you know that I mean. You can sand the finished project, but its very difficult due to "threading" as its called. Its too hard to explain, but needless to say its a pain in the ***.. Carbon fiber you can sand all day(with a repirator). As in weight, they are actually pretty much the same. Raw the KEVLAR feels heavier but the finished project feels the same.

ALL I would recommend mixing them. If you look at the fibers close, you will see the patterns/matrix isnt the same. So basically even after they have gone threw a clave, vaccum bag or whatever you method maybe, there will still be TINY pockets... Thats why if you want to make a bullet proof vest you do one lay-up, if you make a carparts or whatever you would use a different one, and so on and so forth. Same with carbon fiber, it all just depending on how strong you want it..

HOPE ALL THAT HELPS, SORRY IT WAS SO LONG
Jason

user 84205

OK i dont know much about the F-22 or F-35. But i do know about F-18, F-14, EA6B, E-2, C-2, and Helos

BUT, currently im an inspector and a composite tech for the military. I have the pros and cons for ya.

Carbon fiber, looks better, also about the bullet thing, carbon fiber isnt made to stop a bullet, its made so the bullet will go straight threw, and the surface will still retain 99% of its strength, or some high percent (I would have to check the book) Als carbon Fiber is actually really easy to work with then KEVLAR, if any one here has worked with KEVLAR you know that I mean. You can sand the finished project, but its very difficult due to "threading" as its called. Its too hard to explain, but needless to say its a pain in the ***.. Carbon fiber you can sand all day(with a repirator). As in weight, they are actually pretty much the same. Raw the KEVLAR feels heavier but the finished project feels the same.

ALL I would recommend mixing them. If you look at the fibers close, you will see the patterns/matrix isnt the same. So basically even after they have gone threw a clave, vaccum bag or whatever you method maybe, there will still be TINY pockets... Thats why if you want to make a bullet proof vest you do one lay-up, if you make a carparts or whatever you would use a different one, and so on and so forth. Same with carbon fiber, it all just depending on how strong you want it..

HOPE ALL THAT HELPS, SORRY IT WAS SO LONG
Jason

user 84205

oops sorry about the double post too...

PaulC

I know about the F22 and F35 due to the fact I work out at Lockheed Martin now. And I used to work with Northrop Grumman making replacement panels for hte B2.

A combination of kevlar and CF is what the engineers determined best so I for one (not being an engineer) will follow thier advice. Especially since they got to spend millions testing and playing with the stuff to find the best combo

Bigus Dickus

All I was trying to point out was that "best" or "best combination" can be different for different applications. For the F-22, I'm sure they found the perfect CF/Kev weave.

Sometimes all you need is stiffness, not strength, toughness, or durability. Rear wings often fit this categoy... the forces are not so huge as to cause structural failure, but any deflection distorts the wing into a less than perfect aerodynamic shape. For this application, straight carbon is often the best choice.

Sometimes all you need is strength in tension, not stiffness. Perhaps it's a composite pullrod for suspension or something similar. Straight Kevlar might be a better choice.

Hybrid weaves are nice, but from my experience you can usually get the optimum composite charcteristics by alternating different weaves of different materials (i.e., kev, carbon, carbon, kev... you get the idea). Each ply can be tailored for tow orientation, can be whatever weight cloth is appropriate, or could even be uni if needed. Hybrids are usually just the easiest way to get a good combination of properties, but not necessarily the optimum.

BTW, I've personally constructed a carbon fiber gearbox, carbon fiber/tubular alloy steel semi-monocoque chassis, and am currently designing composite structures for military applications.

I love carbon! Such an easy material to work with for DIY projects.

user 84205

Well off the subject or the THREAD, I got some new carbon fiber in today, and it has a few small lines of what looks like Kevlar. Now its not a constant weave, its more like if you cut a 10 inch piece there is about a total of 1 inch of this kevlar. Is that the weave style your talking about? Or are you talking about a layer or carbon, then a layer of kevlar so on and so on?

ALSO BIGUS, I do all that your talking about too, at the bottom there for the military. ONLY what kind of gearboxes are you talking about? Not helos right?

sinfestboy

if you get kevlar, you'll be safe when people shoot at you

look, its snoop doggs kevlar hummer on 28's!

RETed

I doubt that's Kevlar...
It's most likely an intermediate thread to keep the CF strands in place due to the weave pattern.


-Ted

user 84205

RETED,
Ya I was curious, we never had gotten it like that before. I didnt really mess with it that much. If I dont
have to touch it I dont..

Bigus Dickus

canman... that does sound like stitching. Sometimes they do use Kevlar thread for that though (usually, actually as far as I can remember). Is it yellow? Of course there are Kevlar's died different colors, but natural yellow is the most common for stitching. Sometimes crows feet or harness satin weaves use this stitching, but not usually.

Oh, and that gearbox was a small automotive two speed box... held some custom straight cut gears for a low power application.

user 84205

ya its just the natural yellow color.

Thats cool about the gear box though.. I was just
curious of they would try to make a Composite one to replace the shitty Magnesium ones they have now, for helos..

Node

iTrader: (1)

Bigus Dickus and canman, it sure would be great isf you could post some pictures of your custom stuff you've done (unless of course you're not allowed)
and a CF Tranny case, hmmm

Bigus Dickus

This is the best I can do for now... none of the pics I have are digital, and I don't have a scanner handy.



This is a large gantry 5-axis CNC mill doing the rough cut on the mold used to make the case. It's an Arboga mill... something like 16 feet travel in the x direction, thirtee feet or so y, and a few feet z.

PaulC

I wasnt trying to start a debate...... I was just alittle buzzed from after lunch the other day.

Node

iTrader: (1)

good lord thats a lotta CNC power
I remember doing that stuff in school, the CNC lathe was kinda sucky, the mill and router where cool as hell, the mill was tiny the router was kinda big though.