Understanding Composites (Carbon Fiber) - Cannondale Chase Series Owner's Manual

2. UndeRstandinG
ComPosites (CaRBon fiBeR)
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/cm3 (grams per cubic
centimeter), titanium 4.5 grams/cm3, aluminum
.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 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-wieght 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,
Cannondale still urges you to 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 may be 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, fallen
cyclist or other object. First, read the Important
warnings at the beginning of PART II Section A.
Bicycles Cannot Protect You in this manual.
At any speed above a fast walk,
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 and fork 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 . Understanding Metals in this section. 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.
Cannondale carbon frames are designed for
normal riding loads with a factor of safety. These
carbon frames will not survive some crash or
impact loads which may result in complete failure.
See "Composite Frame, Fork, And Component
Inspection" on next page.
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your body