It is now common for the main frame to be made of metal and the fork of carbon fiber..
The relative ductility of metals and the lack of ductility of carbon fiber means that in a
crash scenario you can expect some bending or bucking in the metal but none in the
carbon. Below some load the carbon fork may be intact even though the frame is
damaged. Above some load the carbon fork will be completely broken.
The basics of metal fatigue
Common sense tells us that nothing that is used lasts forever. The more you use
something, and the harder you use it, and the worse the conditions you use it in, the
shorter its life.
Fatigue is the term used to describe accumulated damage to a part caused by repeated
loading. To cause fatigue damage, the load the part receives must be great enough. A
crude, often-used example is bending a paper clip back and forth (repeated loading) until
it breaks. This simple definition will help you understand that fatigue has nothing to do
with time or age. A Trike in a garage does not fatigue. Fatigue happens only through use.
So what kind of “damage” are we talking about? On a microscopic level, a crack forms in a
highly stressed area. As the load is repeatedly applied, the crack grows. At some point the
crack becomes visible to the naked eye. Eventually it becomes so large that the part is too
weak to carry the load that it could carry without the crack. At that point there can be a
complete and immediate failure of the part.
One can design a part that is so strong that fatigue life is nearly infinite. This requires a
lot of material and a lot of weight. Any structure that must be light and strong will have
a finite fatigue life. Aircraft, race cars, motorcycles all have parts with finite fatigue
lives. If you wanted a Trike with an infinite fatigue life, it would weigh far more than
any Trike sold today. So we all make a tradeoff: the wonderful, lightweight
performance we want requires that we inspect the structure.
What to look for
• ONCE A CRACKS STARTS IT CAN GROW AND GROW FAST.
Think about the crack as forming a path- way to failure. This
means that any crack is potentially dangerous and will only
become more dangerous.
SIMPLE RULE 1 : If you find
crack, replace the part.
• CORROSSION SPEEDS DAMAGE. Cracks grow more quickly
when they are in a corrosive environment. Think about the
corrosive solution as further weakening and extending the
crack.
SIMPLE RULE 2 : Clean
your trike, lubricate your trike,
protect your trike from salt,
remove any salt as soon as you
can.
• STAINS AND DISCOLORATION CAN OCCUR NEAR A CRACK.
Such staining may be a warning sign that a crack exists.
SIMPLE RULE 3 : Inspect and
investigate any staining to see if it
is associated with a crack.
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Summary of Contents for Commuter 2.3
Page 30: ...Connect Mainframe ...
Page 31: ...Handle Bar Connection ...
