Bedienungsanleitung Burley Bicycle (Seite 24 von 27) (Englisch)

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In most cases a fatigue crack is not a defect. It is a sign that the part has been worn out,

a sign the part has reached the end of its useful life. When your car tires wear down to

the point that the tread bars are contacting the road, those tires are not defective. Those

tires are worn out and the tread bar says “time for replacement.” When a metal part

shows a fatigue crack, it is worn out. The crack says “time for replacement.”

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

• Lower body weight

• Less aggressive rider

• Non-corrosive environment (dry, salt-free air)

• Clean riding environment

WARNING: Do not ride a bicycle or component with any crack, bulge or dent,

even a small one. Riding a cracked frame, fork or component could lead to

complete failure, with risk of serious injury or death.

B. Understanding composites

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/cm

(grams per cubic centimeter), titanium 4.5 grams/cm

, aluminum 2.75

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 bicycle 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 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 SCORING

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

whatever is causing the noise

should be ﬁxed promptly.

Burley Bicycle Seite 24

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