The Rule of Carbon

Editors Note:  Following the recent article on Carbon Fiber Wheels (Cycling Dynamics, 04/18/2013), here is a more in-depth look at this wonder material.

Composites are pretty cool things.  In the most basic definition, a composite is when two or more materials are combined together to make a new, unique, and stronger material.  Therefore, something as simple as concrete, or as complex as carbon fiber, are both classified as composites.  In between are a world of materials such as fiber glass and plastics, however, the subject of our study will be carbon fiber.

Carbon composites can be formed into just about anything one desires, from prosthetics, to wheelchairs, to cars, to satellites, to whole airplanes (yes, they do), plus bicycles and their associated components.  Carbon structures are light, strong, can withstand ridiculous temperature variations, positive and negative atmospheres, are moisture impervious, non-conductive, low maintenance, and have a relatively long life.  A wonder material?  You bet.  However, like all things in this life, carbon does have its limitations.  Carbon composite structures do not take certain stress loads very well, especially blunt impacts.    

 Raw Carbon Fiber Weave

So just what is Carbon Fiber?  In its most basic form, it is strands (or threads) of carbon which are then weaved into a cloth.  Depending on the intended use, the cloth is woven into different weight weaves, and it is here that the finished product gains its grade, strength and expense.  On its own, it is strong in tension (though easy to cut laterally), and it is very flexible.  Think of a blanket, and you get the idea of the properties of carbon cloth.  Add a resin, and in most cases, some heat and pressure, and the whole picture changes dramatically (as can the shapes). 

   

Carbon Monocoque Lola

And now for a very important distinction - The carbon fiber in your bicycle is not the same as the carbon fiber in a race car, nor is it the same carbon fiber used in a Boeing 787 commercial airliner.  The blanket term carbon fiber needs to be used very carefully, as it encompasses all similar composites (such as Carbon Graphite), much as the word steel encompasses all alloys, thereof.  And, while carbon is amazing stuff to work with, what has some of us bothered in the aerospace industry are sub-surface delaminations which cannot be detected until a catastrophic failure of a structure occurs.  And, these are not false concerns, folks. 

Failed Airbus Vertical Fin Carbon Fiber Attachment Lugs

Think back to September 2001, and the American Airlines Airbus A300 in New York which shed its vertical stabilizer in-flight.  Regardless of what “Officials” said about the First Officer’s “Stomping” of a rudder pedal (rudder hard-over); the real cause was delamination of the load bearing fin attachment points, which were all carbon composite.  A host of other manufacturers use a Titanium/Carbon combination to insure lightness, strength, longevity, and most of all, serviceability.  A Federal Aviation Administration (FAA) certified repair station I used to work at kept a 1948 Cessna 140 as a parts-fetcher/lunch wagon/play toy.  I could rudder hard-over on it all day and the tail/rudder would not fail.  Then again, it is made completely out of aluminum.

Lugged Carbon Fiber Bicycle Frame

So, what does this have to do with bicycles?  Well, the grade of composites used is pretty good stuff, but it is designed for a ground based vehicle, thus supreme strength and redundancy of load paths are not built in (in my opinion).  They work well, do the job, and in many cases look awesome, but stress loads are not their unique forte. 

Now, the stress loads I refer to are primarily compression, tension, and torsional, plus extreme bending loads.  As a bicycle frame, the carbon will work fine.  Ride the bike out of its design load and it will fail.  This is where the quality of the carbon comes into play, and unless the company you bought it from tells you so, you have no idea where the raw materials came from, its grade rating, who formed and cooked it, plus, who assembled the final product (plus the risk of contamination). 

I personally ride an aluminum frame, but that is due more to cost consideration then a fear of carbon.  Carbon composites are damn cool things, and you can do a whole lot of things with them.   My next bike probably will be carbon fiber.  I use the word probably, being Titanium and Stainless Steel look almost too cool to pass up, and I really like their durability. 

Arai LTD, Carbon Fiber Corsair V Helmet

Bottom line, carbon fiber bike frames, wheels and components can achieve some pretty cool performance parameters these days.  However, just keep an eye on your carbon bike for any visible damage, and by all means, avoid extreme loading conditions like Volkswagen sized pot holes, plus collisions with vehicles and immovable objects (like your Mother-in-Law).  It is a very good material to work with, however, it is not THE material to solve all of the industrial applications for the Ages.

With this in mind, a decent carbon component, if properly cared for, should last almost a life time.  But, today’s carbon composites will definitely be outshined by tomorrow’s carbon composites, and that is what I am truly waiting for.