Two of the most prolific composites in modern manufacturing are carbon fiber and Kevlar. Although the two materials share some similarities, they are vastly different. As such, they also have quite different uses. Rock West Composites, a Salt Lake City company that sells both, says that carbon fiber and Kevlar are used by a wide variety of industries ranging from sporting goods to aerospace manufacturing.
If you are like most people, you’ve heard of carbon fiber golf clubs and tennis rackets. You are probably also familiar with Kevlar body armor for police and military use. But there’s probably a lot you don’t know as well. The point of this post is to make you more familiar with some of the basics of these two materials.
Carbon Fiber Basics
When we talk about something like a carbon fiber tennis racket, we are actually using the term incorrectly. The racket material is a carbon fiber reinforced plastic. The carbon fiber is just one component of the plastic. Its life began as unorganized carbon molecules.
Creating carbon fiber require starting with carbon molecules and bonding them together to form crystals. The crystals are then forced to align vertically, thereby forming fibers so small as to be measured in micrometers. The smaller fibers are spun to create longer strands; the strands are bundled together to create tow. Think of tow like yarn or thread. It can be woven into fabrics and used to make things like carbon fiber tennis rackets.
Kevlar Basics
Kevlar is a synthetic fiber made in a lab setting. We owe its existence to an accidental discovery in a DuPont lab in the 1960s. At the time, DuPont was working on a way to make car tires lighter by replacing steel belts with lighter, stronger materials.
One of DuPont’s scientists, Stephanie Kwolek, was working with a polymer that produced a thick, viscous waste product in solution. Kwolek and her peers had been throwing it away. But she eventually surmised that the waste material’s properties might make it a good candidate for a synthetic fiber, so she had it tested.
It turns out Kwolek was correct. That waste product is what we now call Kevlar. Like carbon fibers, Kevlar crystals are spun together to create small fibers which are bonded to make tow. The tow is woven into fabric or sold as thread.
Carbon Fiber and Kevlar Properties
Most practical uses of carbon fiber and Kevlar involve mixing the materials with some sort of epoxy resin to create a reinforced plastic. See the point about the carbon fiber tennis racket above if you don’t understand. Otherwise, let’s talk about the properties the two materials exhibit.
In terms of tensile strength – measured as the amount of force a material can withstand before failing – carbon fiber and Kevlar are very similar. Where they differ is in their strength-to-weight ratios. Density is the key thing to remember here.
If you were to take equal volumes of carbon fiber and Kevlar and compare them side-by-side, you would notice the carbon fiber is more dense. It is also heavier. Both are lighter and less dense than glass fiber, which is why fiberglass is not as popular as it used to be for manufacturing.
Another difference between the two is observed in compression strength. Both glass and carbon fiber exhibit decent compression strength where Kevlar does not. As such, carbon fiber is a better choice when you need multi-directional strength and rigidity.
As you can see, carbon fiber and Kevlar are different. Carbon fiber is the better choice for some applications, while Kevlar is better for others.