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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
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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/cm3 (grams per cubic centimeter), titanium 4.5 grams/cm3, aluminum 2.75 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-weight 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, you must still 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 maybe 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, other cyclist or other object. at any speed above a fast walk, your body 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,
fork and other components is irrelevant to what happens to your body.
What should you expect from your carbon frame? it depends on many complex factors. But 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
Section 2. A, Understanding metals
in this appendix. 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.
Inspection of Composite Frame, Fork, and Components
Cracks:
inspect for cracks, broken, or splintered areas. any crack is serious. do not ride any bicycle or component that has a crack of any size.
Delamination:
delamination is serious damage. Composites are made from layers of fabric. delamination means that the layers of fabric are no longer
bonded together.
Do not ride any bicycle or component that has any delamination.
these are some delamination clues:
1. a cloudy or white area. this kind of area looks different from the ordinary undamaged areas. undamaged areas will look
glassy, shiny, or “deep,” as if one was looking into a clear liquid. delaminated areas will look opaque and cloudy.
2. Bulging or deformed shape. if delamination occurs, the surface shape may change. the surface may have a bump, a bulge,
soft spot, or not be smooth and fair.
