Tern Quick Haul D7i Manuel D'utilisation page 37

Metals are subject to fatigue. With enough cycles of use, at high enough loads, metals will eventually
develop cracks that lead to failure. It is very important that you read the basics of metal fatigue below.
Let's say you hit a curb, ditch, rock, car, another cyclist or other object. At any speed above a fast walk,
your body will continue to move forward, 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. If an impact is hard enough the fork or frame may be bent or buckled.
On a steel bike, the steel fork may be severely bent and the frame undamaged. Aluminum is less ductile
than steel, but you can expect the fork and frame to be bent or buckled. Hit harder and the top tube
may be broken in tension and the down tube buckled. Hit harder and the top tube may be broken, the
down tube buckled and broken, leaving the head tube and fork separated from the main triangle.
When a metal bike crashes, you will usually see some evidence of this ductility in bent, buckled or folded metal.
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 bicycle in a garage does not fatigue. Fatigue happens only through use.
In terms of damage, 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.
What to Look For
A CRACKS STARTS TO GROW
(AND GROW FAST)
CORROSION SPEEDS DAMAGE
SIGNIFICANT SCRATCHES, GOUGES,
DENTS OR SCORING CREATE
STARTING POINTS FOR CRACKS
SOME CRACKS (particularly larger ones)
MAY MAKE CREAKING NOISE AS YOU RIDE
Fatigue Is Not a Perfectly Predictable Science
Fatigue is not a perfectly predictable science, but here are some general factors to help
you and your Dealer determine how often your bicycle should be inspected. The more
you fit the "shorten product life" profile, the more frequent your need to inspect. The more
you fit the "lengthen product life" profile, the less frequent your need to inspect.
Factors that shorten product life:
• Hard, harsh riding style
• "Hits", crashes, jumps, other "shots" to the bike
• High mileage
• Higher body weight
• Stronger, more fit, more aggressive rider
• Corrosive environment (wet, salt air, winter road salt, accumulated sweat)
• Presence of abrasive mud, dirt, sand, soil in riding environment
Factors that lengthen product life:
• Smooth, fluid riding style
• No "hits", crashes, jumps, other "shots" to the bike
• Low mileage
Response
If you find a crack, replace the part.
Clean your bike, lubricate your bike, protect your
bike from salt, remove any salt as soon as you can.
Do not scratch, gouge or score any surface. If you do,
pay frequent attention to this area or replace the part.
Investigate and find the source of any noise.
It may not be a crack, but whatever is causing
the noise should be fixed promptly.
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