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  • Writer's pictureNed Patton

Yes - Bicycles are Made from String and Glue

I want to talk a little bit about the evolution of the composites business, and how far it has come from some fairly simple beginnings to what’s achievable today. The best example that I have found is the evolution of the road bicycle – specifically the bicycles that folks like Lance Armstrong and Greg Lemond ride to victory in the Tour de France.

This bike was the fourth carbon fiber bike that Greg Lemond rode to victory in France. The first one was in 1986, but it looked very much like the 1989 version because the bicycle industry was just starting to make the move from aluminum frames which were somewhat lighter than their steel cousins, to replacing some of the metal parts with carbon/epoxy. If you look fairly closely at the pic on the left, the top tube, seat tube, and forward triangle tube are all made from a carbon fiber/epoxy tube with metal ends where they connect to the rest of the frame. What I found out in researching this is that all four of the rear triangle tubes are also carbon fiber/epoxy with glued on metal ends. What may have been different about this bike is that the front forks were also carbon fiber/epoxy. But in essence, this is a straight replacement of a metal part with a composite part. And the weight savings are not to be sneezed at – they were substantial enough that it gave Greg that edge that he needed to win the Tour de France multiple times.

The pic to the right is the most advanced carbon fiber bike frame on the market today – the Look 795 Aero RS. This bike was designed from the ground up as a composite frame. The only metal parts are the bushings for the crank axle and the front forks. Everything else is carbon fiber/epoxy made from a pre-impregnated carbon fiber/epoxy sheet product called prepreg. This stuff comes either with all of the fibers lined up in one direction – unidirectional prepreg, or with carbon fiber fabric with uncured epoxy impregnated into it. And not just any old carbon fiber/epoxy prepreg either. Look uses high strength carbon fiber in the areas that need strength and high modulus carbon fiber in areas that need more stiffness. And some of the prepreg is fabric and some is unidirectional. The fabric is used where the stresses are two or three dimensional versus those areas where the stresses are more in one direction. And, there are over 400 individual precision cut pieces of carbon fiber/epoxy prepreg that make up the frame of this bike. No wonder just the frame itself is over $5000.

The Look bike frame, even though each piece of prepreg is hand laid into a mold, is also a testament to automation and precision in carbon fiber prepreg manufacture. Computer Numerically Controlled profiler machines are used to cut the prepreg exactly where it needs to be cut so there is little to no waste, and the technicians who cut the individual smaller pieces are so well trained and so precise that every bike frame that comes off the assembly line is very nearly exactly like the last one.

There is a great YouTube that shows this whole process of making the Look carbon fiber bike frame - I hope you get a chance to watch it.

Next post I’m going to introduce something I’ve been thinking about for a while. Elon Musk has said in a couple of interviews something fairly profound about learning. He gives this advice:

One bit of advice: it is important to view knowledge as sort of a semantic tree — make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to.

The advice that Elon is providing here can help with learning complex topics, especially topics as complex as composites. And that's what this blog is about, start with the trunk of the semantic tree of learning about composites, and over time build up the knowledge so that those that follow this blog gain an understanding of what composites are, how they are put together, and why they are one of the most important developments in engineered materials.


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