Making Carbon Fiber Tougher – With Steel

Carbon fiber is a pretty tough material all by itself. Combine it with an epoxy resin and you can create a carbon fiber reinforced plastic (CFRP) tough enough to make airplane fuselage panels and wings from. But like any other material, carbon fiber still offers plenty of room for improvement.

Improve is just what Slovakian bike builder Kellys did when they partnered with another company to create a new composite material that is as light as standard carbon fiber but twice as tough. How did they do it? By combining the carbon fibers with stainless steel.

Combining carbon fiber and steel might seem like a juxtaposition, but it’s not. The secret is in how and where the stainless steel is utilized. Kellys has come up with a way to create an entirely new e-bike frame that is lightweight, incredibly durable, and impact resistant.

How Standard Carbon Fiber Frames Are Made

Rock West Composites, a Salt Lake City company that specializes in carbon fiber and other composite materials, explains the standard carbon fiber bike frames are constructed with pre-fabricated tubing. The tubing can be made through a number of different processes including filament winding, spinning, and even manual layups. Filament winding is the fastest and most cost-effective method.

Carbon fiber tubes are then cut to size, trimmed and finished, and assembled to create a bike frame. The fibers embedded in the tubes are aligned in a specific way to give the frame structural support at key locations. Additional support can be achieved by adding extra layers of carbon fiber material.

Combining Carbon Fiber with Steel

With a basic understanding of how carbon fiber bike frames are built, how might you integrate stainless steel to make them tougher and more impact resistant? Kellys haven’t insert stainless steel plates or installed steel braces to join carbon fiber tubes together. Rather, they have returned to the basics of CFRPs.

Engineers understood that structural integrity within a carbon fiber part is the domain of the actual fibers within. If they could make those fibers stronger, they could improve the product. That is exactly what they did. They added stainless steel fibers to the mix.

The stainless steel fibers are not applied uniformly across the entire bike frame. Rather, they are only added at strategic locations where extra strength is necessary. The steel fibers, in conjunction with the already tough carbon fibers, increase both durability and impact resistance without significantly increasing weight.

Fibers As Reinforcements

What Kellys is doing with their new bike frames is based on the time-tested principle of composite reinforcement. In fact, the whole process of fabricating with carbon fiber is built on the same principle. It is remarkably similar to how contractors reinforce concrete with rebar.

As tough as concrete is, it is also fairly porous and brittle. A concrete bridge abutment with no reinforcement would not be able to stand up to even moderate impact from a passing ship. But reinforce the concrete with rebar and it is a whole new ballgame. Rebar provides extra strength that overcomes the brittle nature of concrete.

What consumers normally refer to as carbon fiber is actually a CFRP. In other words, it is a plastic reinforced with carbon fibers in much the same way concrete is reinforced with rebar. All Kellys has done is take the reinforcement principle to a new level by adding stainless steel fibers in key locations on their bike frame.

Time will tell if the frame lives up to its billing. There is no reason to believe it will not, especially if you understand how well small carbon fibers can reinforce a plastic material.