Most of us love the look of a beautiful, glossy carbon fiber surface. It almost seems like you’re dealing with a space material or something out of the future. Maybe you’ve even owned a surfboard or a kiteboard that’s made out of it. No one can deny that it’s a game changer over the more common, legacy fiberglass products. It’s important to know if those differences always an improvement, or if there are other things to consider.
In order for us to take a shallow dive into the comparison of carbon fiber vs. its traditionally alternatives, we need to make sure that we allow ourselves to have an open mind. What I mean is that many times, people are set in their ways based on anecdotal experiences or disinformation. This is most prevalent when you ask someone who makes the best truck…Ford, Chevrolet, Dodge, Tesla, Lordstown, etc.
The most important thing for the reader of this article to understand is that this is not a deep dive, rather it’s a surface analysis of the real-world usefulness of using Carbon Fiber or an alternative for a particular application.
It’s very important to get one very basic statement out there that most of us already know. When we talk about building out of Carbon Fiber, Fiberglass or Kevlar, we are talking about creating a product which is constructed out of a composition of epoxy resin and a woven cloth material. When the epoxy resin is cured and the chemical reactions are complete, the result is a rigid and semi-durable material. We will refer to this material as the ‘composite’ in this article. The following will discuss the characteristic differences of the composites based on which woven cloth(s) is/are integrated within the composite. For the purposes of comparison, the type of epoxy resin is to be considered a constant.
This is the category which the majority of people pay attention to when going for Carbon Fiber. It’s sexy, sleek and looks like it’s going a hundred mph while sitting still. You can get different weave thicknesses and shines. Simply put, it’s stunning in the daytime and at night.
Carbon Fiber has a look that is pretty difficult to fake while maintaining the structural characteristics that make is so unique. Something to realize is that it’s ALWAYS black. You may be wondering why I made that statement since we have all seen a myriad of colors of Carbon Fiber materials on the market.
In order to get those colors and tints into the material, the Carbon Fibers are blended with a separate, woven material called Aramid (commonly referred to as Kevlar). Aramid is naturally tan or yellowish, but it can absorb pigments to alter its color during the layup process (when the resin is added to the cloth). When Kevlar is blended with Carbon Fiber, you end up with quite the range of visual options. It’s important to realize that there are some limits to this since Carbon Fiber is black and the Aramid is already yellowish. So, some of the lightest colors are very difficult to obtain.
Traditional Fiberglass, or E-Glass, also absorbs color well during the layup process. It is typically produced in white, which allows a builder to change it to an infinite number of colors and tints. Or, just let it go clear. In fact, if the largest range of artistic options while maintain the weave is your most desired quality, you’ll need to stick with E-Glass.
This is a big one. We are talking about the ability of the various cloths to stick to the epoxy once cured. Aramid is deficient in this regard. Its properties prevent its fibers from bonding to the epoxy as strong as Carbon Fiber or E-Glass. Keep this in mind if you’re choosing a colored Carbon Fiber material which is blended with Aramid.
Aramid absorbs moisture very well, so if there is any kind of damage, or if the fibers are exposed to water, you can expect a higher likelihood of delamination. This is most important to consider in boats or watersports toys.
This goes hand in glove with the previous reference to delamination. When we talk about Aramid, or Kevlar by trade name, we immediately think of bullet proof vests and military armor. So, you might think that in an environment where boats bang up against docks, or in surfboards and kiteboards that hit reefs and rocky beaches, that Aramid would be preferred. Let’s look into that.
This is double-edged. On one hand, Aramid is without a doubt more resistant to blows and scrapes. However, if the composite is damaged in a manner that exposes the fibers to water, then you would expect the product to begin delaminating quicker than Carbon Fiber or E-Glass.
Wouldn’t a bullet-proof boat hull be preferred on a boat that typically puts its bow on the beach? Maybe, Maybe Not. What about a SUP board that gets banged around on as a rental?
Density and Strength to Weight
Comparing density in this case is basically that if it is heavier, it’s denser for the same size piece of a composite.
If you make an item out of each of the 3 we’ve discussed so far, you find out that Kevlar is the lightest, Carbon Fiber next (but pretty close to the same) and E-Glass is heaviest by nearly double.
So, if you figure that E-Glass is twice as heavy and it only takes half the amount of Carbon Fiber or Kevlar to make a piece of the same strength, then you can produce an item for half the weight. That’s strength to weight in a nutshell.
Something to consider is that the orientation of the fibers in the composite play another role in deciding which material is appropriate for your build. This is because different materials vary in tensile strength depending on where the forces are applied. Kevlar is a great example to use to explain this because it is the only one of the 3 that have a significant difference of strength in compression vs. tension. Kevlar is quite high in tensile strength but can be 10 times weaker in compressive strength. Therefore, when force is applied perpendicularly, it has a higher tendency to crack or fail.
Stiffness of a composite is measured as Stress/Strain in the same plane. Strain is the distortion of the material. The important point here is that stiffness may be desirable or undesirable depending on your application. Imagine riding in a race car vs a Mercedes sedan. That’s not exactly how it works, but a more flexible material (lower stiffness) is desirable in certain environments and applications. Dragsters sometimes mount the engine directly to the frame rails without absorbing motor mounts that are found in street cars. There are no springs or shocks on dragsters, but the frame is designed with a certain elasticity to interact with the tires as its suspension.
Failures due to fatigue are possibly something to consider for you. If your build is subject to constant and rhythmic bending and straightening, then you will want to be more cautious when using Carbon Fiber. Of the 3 materials, it is most prone to failure in this category and not in a small way. Kevlar dominates in this arena, but E-Glass composites can be quite resilient depending on how they’re built.
This is often disregarded in the discussion, because all three of the materials we’ve discussed have very good UV resistant qualities. The problem is that in a composite, they are combined with epoxy resin which is particularly terrible when used in high UV environments. Special care should be used when choosing a resin for your build, coupled with a top coating that’s appropriate (ie gelcoat or paint).
Kevlar and E-Glass are non-conductive and therefore consideration does not be given when using one of them in your build. Carbon Fiber is very conductive though. This is quite important to aviation, because of the radio frequency interference issues. This is absolutely imperative to consider. Also, in the marine environment, Carbon Fiber is a large contributor to galvanic corrosion when metal fasteners are used in the material.
In Conclusion, whether you chose Carbon Fiber, Kevlar or E-Glass for your build, particular attention needs to be given to each of these categories so that you can appropriately design around possible deficiencies. One material might be better for a certain part in your build, while it would not be the appropriate part in another.
In aviation, lighter is almost always better, but do you sacrifice wing loading and therefore have a terribly bumpy ride in light turbulence? So, keep it light, but you might have to address the wing design.
In boat building, you need to figure out if a stiff and light hull is ideal. If you’re sailing around a calm lake, then most definitely. But, when you’re in an unforgiving ocean environment, do you really want a stiff hull that doesn’t flex in the changing sea state?
—-Maybe, Maybe Not