Carbon fiber products billed as lightweight and super duper strong. Build cars & fly rods out of the stuff. But during manufacturing process it looks like fiberglass. Lay the fabric on a mold, paint it with a resin, wait, enjoy strong lightweight product.
Given the fabric is flippyfloppy to begin with, why does credit for the strength not go to the goo that gets painted on?
Fiberglass is glass strands embedded in a plastic matrix. Carbon fiber is woven carbon fiber embedded in a plastic matrix. As such, fiberglass, carbon fiber, and plastic have nearly the same look, hand feel, and weight. Nothing is painted on; rather, the carbon fiber/glass is embedded inside the plastic. Most consumer applications of carbon fiber (like knives and watches) provide only marginal improvements over pure plastic and are essentially decorative.
Strength and hardness are distinct.
Kevlar is quite strong but floppy too.
Diamond is harder than steel but steel is stronger than diamond.
By putting the fabric in the goo, it becomes able to withstand a lot more than it otherwise would.
And toughness is different from both strength and hardness.
http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-toughness/basic.html
http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/
For some reason, I’m having fun with these. In the interactive charts, roll pointer over areas to see members of the class
Thanks for responses so far. Patience please. I do get the difference between hardness and strength and durability.
I guess my question is–take a bicycle frame made of this stuff. it weighs a fraction of a steel frame and yet is rigid enough to do the same job. So riders enjoy. But does the carbon fiber give anything that, say, flannel couldn’t do? If so, what? Surely the CF is more than simply a lattice for the goo?
uhhh… well, for one, the materials are compatible, whereas flannel is like spongy cotton, I’m pretty sure it’s be like trying to imbibe a towel with wax and then expecting it to stay stable and rigid and solid.
I’m pretty sure one of the things is that carbon fiber has a high tensile strength.
Oh, and, obviously, overall the material is strong enough to replace metal parts for certain applications, like bicycles. It’s not nearly as strong as metal, but it’s STRONG ENOUGH to act as a body/structure, and saves massively on weight.
From Wikipedia
“The properties of carbon fibers, such as high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion, make them very popular in aerospace, civil engineering, military, and motorsports, along with other competition sports. However, they are relatively expensive when compared to similar fibers, such as glass fibers or plastic fibers.”
There are many different levels of carbon fiber quality; low quality has more goo, higher quality has less, really high quality uses even higher strength carbon nanotubes these days.
This may be a bit of a tangent, but for bikes, CF has directional stiffness properties that metal does not allowing a frame to be laterally stiff and radially compliant - basically giving comfort and road shock absorption without losing efficiency or power.
No carbon fiber bike will last as long as a steel or titanium bike though, AFAIk.
Have you ever broken a piece of thread by pulling on it? That’s tensile strength and that’s the “strength” of carbon fibers. You can easily break a cotton thread but trying the same thing with a carbon fiber thread of the same diameter will require a lot more force to break it. In fact, more force than if the “thread” was a steel wire.
As for carbon fiber composites, like fishing rods, yes, part of the strength is from the resin matrix, but the individual threads of carbon fiber are still very resistant to tension forces and since you have fibers running in different directions, that strength translates to the whole piece. In fact, for may high-end components, the orientation of the various layers and types of fabric is tightly controlled for best results.
There is in fact a product with the properties you describe. It is known as micarta, and consists of cloth or paper embedded in plastic, just like fiberglass or carbon fiber reinforced polymer. Usually, a heavy and thick cloth like canvas duck (imagine a sandbag) or heavy linen is used. This results in slightly improved toughness and strength, with no change in hardness (since the exterior is still plastic). The visual appeal of the product is also improved, which is important since the primary use of micarta is luxury knife handles. It is possible to make micarta with flannel, and some people have in fact done so. In this case, the only real benefit is visual, with very little change in any meaningful attribute of the finished product.
In short, carbon fiber does do a job that flannel can’t. You could probably make a functional bike out of fiberglass (since you can make a bike out of unreinforced plastic), but carbon fiber resin matrix is definitely better.
Is there a difference in construction techniques for high performance applications?
I mean, when making a bicycle frame or a wing or a driver, is there a specific effort to align carbon fibers with the maximal stress?
For bicycles there is. It is important to have the grain going in such a way the the bicycle does not move side to side in the rear (among other things) - when bikes do this too much riders describe it as being like a wet noodle.
Yes to both. The highest quality composites are made from “pre-preg” which is a process whereby the fabric is dipped in resin and then run between wiper bars that leave a very specific amount of resin coating the fabric and then the fabric is “staged” by running it through a drying process that drives off the volatiles and then is rolled up with a plastic separator sheet. The resultant fabric is perfectly coated (unlike if it was done by hand) as performance is determined, in large part, by the quality of the resin/fabric matrix. Using pre-preg gives way more control than saturating the fabric by hand, but it’s also way more expensive.
Once the fabric goes to manufacturing, the pieces are laid into a mold (with careful alignment and compression of layers) and then usually the whole thing is vacuum bagged and cured in an autoclave under a specific pressure and temperature. It’s way more complicated than hand laminating a surfboard, for example.
Most carbon fiber components are built on a core material of lightweight and high compression strength materials. Two layers of carbon fiber material glued to opposing faces of a 1 inch think sheet of Styrofoam create a sandwich which is far stronger in most directions than those two layers one atop the other. Carbon fiber has very little compressive strength and great tensile strength. In order to deal with real world loads which don’t conveniently align with your carbon fibers you have to use many different alignments of the fiber and/or use a core to apply the force at an angle which tries to bend the fibers against a core material. Honeycomb core materials can be strong and extremely light weight to make large lightweight components.
You will see good examples of this in archery bows. Epoxy impregnated fiber glass and carbon fiber are used to make the flexible limbs on bows. Carbon fiber limbs are thinner yet stronger than fiberglass. They are also slightly less elastic and a little too rigid in compression.
Are there different weave patterns for different applications?
As others have said, absolutely. The key benefit in aerospace applications is that we can tailor strength directionally. Being able to make shapes that are only as strong as they need to be for loads in each direction is a huge area for optimization of structure.
As explained by posters above, most aerospace applications use a combination of pre-preg cloth and pre-preg tape carefully laid according to design to add strength along a particular axis.
One thing you won’t see in carbon fiber applications is the equivalent of the “chop gun” used in fiberglass fabrication of things like boat hulls.
Yes. Not for specific applications, but for different general purposes. Unidirectional cloth is used for the greatest strength in a single direction. Bidirectional cloth has varying weave patterns, some are a ‘looser’ weave that allows the cloth to conform to irregularly shaped surfaces at the expensive of some stiffness and strength in particular directions. There are also complex weaves where several layers of cloth are tied together with interstitching. For the greatest strength and lightest weight smaller pieces of unidirectional and bidirectional cloth are laid up in specific directions on a particular part.
For those who are interested, there was a “How It’s Made: Dream Cars” episode that showed the construction of a carbon fiber vehicle (a Lamborghini, IIRC) including the vacuum and autoclave process.