Kona bicycle Owner's Manual page 41

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/cm3 (grams per cubic centimeter), titanium 4.5
grams/cm3, aluminum 2.75 grams/cm3. Contrast these
numbers with carbon fiber composite at 1.45 grams/cm3.
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 direc-
tions (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. Car-
bon 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, which is why we tell
you that crash worthiness cannot be a design criteria.
With that important note, 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, & Components
Cracks: Inspect for cracks, broken, or splintered areas.
Any crack is serious. Do not ride any bicycle or compo-
nent that has a crack of any size.
Delamination: Delamination is serious damage. Compos-
ites 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 delam-
ination. These are some delamination clues:
• 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.
• 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.
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