37
bike.” This really means “composite bike.”
Carbon ber composites are typically a strong, light ber 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 ber
composite at 1.45 grams/cm3.
The composites with the best strength-to-weight ratios are made of carbon
ber in a matrix of epoxy plastic. The epoxy matrix bonds the carbon bers
together, transfers load to other bers, and provides a smooth outer surface.
The carbon bers 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 bers can be placed in specic orientations to optimize
the structure for particular loads. The choice of where to place the carbon
bers gives engineers a powerful tool to create strong, light bicycles. Engineers
may also orient bers to suit other goals such as comfort and vibration
damping.
Carbon ber composites are very corrosion resistant, much more so than
most metals.
Think about carbon ber or berglass boats.
Carbon ber materials have a very high strength-to-weight ratio.
What Are The Limits Of Composites?
Well designed “composite” or carbon ber bicycles and components have
long fatigue lives, usually better than their metal equivalents.
While fatigue life is an advantage of carbon ber, you must still regularly
inspect your carbon ber frame, fork, or components.
Carbon ber 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 ber or carbon ber
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
signicant 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:
To Next Page
Loading...
