The composites with the best strength-to-weight ratios are made of carbon fiber in a matrix of epoxy plastic. The epoxy
matrix bonds the carbon fibers together, transfers load to other fibers, and provides a smooth outer surface. The carbon fibers are
the “skeleton” that carries the load.
Why Are Composites Used?
Unlike metals, which have uniform properties in all directions (engineers call this isotropic), carbon fibers can be placed in
specific orientations to optimize the structure for particular loads. The choice of where to place the carbon fibers gives engineers
a powerful tool to create strong, light bicycles. Engineers may also orient fibers to suit other goals such as comfort and vibration
damping.
Carbon fiber composites are very corrosion resistant, much more so than most metals.
Think about carbon fiber or fiberglass boats. Carbon fiber materials have a very high strength-to-weight ratio.
What Are The Limits Of Composites?
Well designed “composite” or carbon fiber bicycles and components have long fatigue lives, usually better than their metal
equivalents.
While fatigue life is an advantage of carbon fiber, you must still regularly inspect your carbon fiber frame, fork, or
components.
Carbon fiber composites are not ductile. Once a carbon structure is overloaded, it will not bend; it will break. At and near
the break, there will be rough, sharp edges and maybe delamination of carbon fiber or carbon fiber fabric layers. There will be no
bending, buckling, or stretching.
If You Hit Something Or Have A Crash, What Can You Expect From Your Carbon Fiber Bike?
Let’s say you hit a curb, ditch, rock, car, other cyclist or other object. At any speed above a fast walk, your body will continue
to move forward, the momentum carrying you over the front of the bike. You cannot and will not stay on the bike and what
happens to the frame, fork and other components is irrelevant to what happens to your body.
What should you expect from your carbon frame? It depends on many complex factors. But we can tell you that if the impact
is hard enough, the fork or frame may be completely broken. Note the significant difference in behavior between carbon and
metal. See Section 2. A, Understanding metals in this Appendix. Even if the carbon frame was twice as strong as a metal frame,
once the carbon frame is overloaded it will not bend, it will break completely.
Inspection of Composite Frame, Fork, and Components Cracks:
Inspect for cracks, broken, or splintered areas. Any crack is serious. Do not ride any bicycle or component that has a crack of
any size. Delamination: Delamination is serious damage. Composites are made from layers of fabric. Delamination means that
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