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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
bicycle with an infinite fatigue life, it would weigh far more than any bicycle 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 pathway 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
bike, lubricate your bike, protect
your bike 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.
• SIGNIFICANT SCRATCHES, GOUGES, DENTS OR SCOR-
ING CREATE STARTING POINTS FOR CRACKS. Think about
the cut surface as a focal point for stress (in fact engineers
call such areas “stress risers,” areas where the stress is
increased). Perhaps you have seen glass cut? Recall how the
glass was scored and then broke on the scored line.
SIMPLE RULE 4 : Do not scratch,
gouge or score any surface. If you
do, pay frequent attention to this
area or replace the part.
• SOME CRACKS (particularly larger ones) MAY MAKE
CREAKING NOISE AS YOU RIDE. Think about such a noise as
a serious warning signal. Note that a well-maintained bicycle
will be very quiet and free of creaks and squeaks.
SIMPLE RULE 5 : Investigate and
find the source of any noise. It
may not a be a crack, but what-
ever is causing the noise should
be fixed promptly.
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