Carbon Nmr Shifts

Carbon Fiber An Important Bicycle Component

Thought of as an exotic space-shuttle composite just 10 years ago, carbon fiber is now utilized in almost every bike part, from frames and elements to helmets and shoe soles. Carbon fibers are made from carbon, the ever-present element that forms coal, graphite and diamond and is an element of every organic chemical and every life form on earth. Carbon is the fourth commonest part in the universe and the
Second most common element in the human body.

Polyacrylonitrile ( PAN ) fiber, also the source material for acrylic fiber, is formed into carbon fiber by heating it to extreme temperatures, burning away basically everything aside from carbon. The resulting 5-8 micron ( millionths of a meter ) thick fibers are a tenth the thickness of a human hair and made from carbon atoms strongly bonded together in microscopic crystals aligned parallel to the fibers axis. Powerful and stiff, the fibers have a rigidity index of thirty three million pounds per square inch ( MSI ) and a coarse surface. Expensive processing can strip off this outer surface to show a thinner, smoother
Intermediate Modulus ( IM ) fiber that packs tighter with other fibers for higher rigidity per unit area. A higher priced processing can create High Modulus ( HM ) carbon fibers, which boasts a Youngs modulus rigidity of 42 MSI to 55 MSI or more.

Common-modulus fibers are bundled together into yarn and woven into fabric. A number followed by the letter K designates how many thousands of fibers are in a strand of the yarn ( as in 3K, for 3,000 fibers per strand ). Woven fabric frequently comprises the top layer for cultured purposes, but most carbon fibers in a bike part instead come in flat sheets of tightly packed parallel fibers pre-impregnated with epoxy resin stuck to backing paper. Exactly cut pieces ( plies ) are stacked, or laid up, atop one another at opposing angles ( sometimes 45 degrees ), to fight forces from different directions. Unlike metals, carbon fiber plies in the laminate structure can be oriented to create a composite structure that can be stiff in one specific direction and more
Flexible in another. Indeed, plies must be laid up at angles, because carbon fiber, like thread, is strong if you pull on it but far weaker if you push lengthwise on it or bend it sideways. Nevertheless in a carbon fiber tire bead, you do not need strength in tension alone, so orienting fibers at angles and gluing them along with resin permits the plies to work together, opposing forces from all directions. Subjecting the laminate to high pressure and heat in a mold pushes out air and excess resin.

Well-engineered carbon composite parts have high rigidity and strength, low density and high fatigue life but low elongation they cannot stretch or bend much before they break. Disasters come from not properly engineering the directions and sorts of fibers to handle the loads.

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