Jamis Bicycle Owner's Manual - page 30
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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 the layers of fabric are
no longer bonded together. Do not ride any bicycle or component that has any delamination. These are some delamination clues:
1. A cloudy or white area. This kind of area looks different from the ordinary undamaged areas. Undamaged areas will look glassy, shiny, or
“deep,” as if one was looking into a clear liquid. Delaminated areas will look opaque and cloudy.
2. Bulging or deformed shape. If delamination occurs, the surface shape may change. The surface may have a bump, a bulge, soft spot, or not
be smooth and fair.
3. A difference in sound when tapping the surface. If you gently tap the surface of an undamaged composite you will hear a consistent sound,
usually a hard, sharp sound. If you then tap a delaminated area, you will hear a different sound, usually duller, less sharp.
Unusual Noises: Either a crack or delamination can cause creaking noises while riding. Think about such a noise as a serious warning signal. A
well maintained bicycle will be very quiet and free of creaks and squeaks. Investigate and find the source of any noise. It may not be a crack or
delamination, but whatever is causing the noise must be fixed before riding.
WARNING: Do not ride a bicycle or component with any delamination or crack. Riding a delaminated or cracked frame, fork or
other component could lead to complete failure, with risk of serious injury or death.
B. Understanding composites
All riders must understand a fundamental reality of composites. Composite materials constructed of carbon fibers are strong and light, but
when crashed or overloaded, carbon fibers do not bend, they break.
What Are Composites?
The term “composites” refers to the fact that a part or parts are made up of different components or materials. You’ve heard the term “carbon
fiber bike.” This really means “composite bike.”
Carbon fiber composites are typically a strong, light fiber in a matrix of plastic, molded to form a shape. Carbon composites are light relative
to metals. Steel weighs 7.8 grams/cm
3
(grams per cubic centimeter), titanium 4.5 grams/cm
3
, aluminum 2.75 grams/cm
3
. Contrast these
numbers with carbon fiber composite at 1.45 grams/cm
3
.
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.