Carbon for the Rest of Us

So Far, this Carbon Seatpost on Buddy Hasn't Turned into Splinters

FOREWORD - THE CHALLENGE

CITIZEN RIDER, in his post here, presented a challenge that I cannot resist. You see, he expressed frustration at a bicycle subject that I deal with professionally, but which never before occurred to me to post about on a bike transportation blog. Carbon. You see, it's often amused me to see what cyclists and their publications, such as Buycycling Magazine, say about carbon bike components. Still, I never really thought to say much about the nonsense I hear every day. I've limited my inputs to occasional comments on blogs, such as here.

You see, as some of you know, I'm an engineer. More significantly, as far fewer know, I have over 30 years of carbon composite experience in flight vehicle structures. These range from flaky homebuilt aircraft up to things that lead me to take offense when people talk about "rocket scientists." It's somewhere upward of 300 composite assemblies over the years.

The world of carbon composites is vast and complex. Some of it is fundamental to making weapons of war, so I'll stay away from things that will cause me to be thrown into prison for violating the "International Trafficking in Arms Regulations." Don't look here if you want me to spill the beans on how to build the world's most advanced fighter jet, or how to sabotage carbon helicopter blades. Put simply, carbon is just another material. Like many, if you abuse it, it can kill you. Aircraft manufacturers have failed with the material (of COURSE my example is Airbus) Carbon is more than just a fashion statement, though it is clearly THAT as well.

If you want to use carbon composites as MORE than a fashion statement, there's a lot of stuff you need to know, and I'll plan on doing a series of articles that, strung together, constitute at least a short story on the subject for regular people - and bike mechanics.

First off, I'll treat a few of the items brought up in CITIZEN RIDER'S excellent challenge. This will preceed the organized treatment:

CR COMMENTS AND OBSERVATIONS
#1 - All those inspection items are not going to do you any good at all, though squid magnotometers at least sound really cool. In aircraft, beyond a visual inspection to see really extreme stuff, it is really only ultrasonic or xray inspection that is used. I think most bike shops and people are not in a position to do xray inspections. Even ultrasonic inspections are not as wonderful as most think. Ultrasonic equipment suitable for a bike shop can be had for $200-$4000 via ebay. The upper end seems more than I'd want to pay. The lower end is a thickness measurer. Maybe just not good enough. For a dedicated bike mechanic, there are other common sense solutions, however.

#2 - It is not wise to abhor carbon fiber, nor to develop a fondness for it. As I said, it's another material, with its proper place. OTOH, here and here, it is just a style statement. I do not plan to talk about composites as design style statements in this series.

#3 - Tapping. Perhaps I'll regret accusing someone who thought tapping on composites was fine as living in the dark ages and practicing witchcraft. Tests have shown that tap testing, despite the impressions of those doing it, are unreliable AT BEST and positively worthless in most cases. Still, I reluctantly admit I do it myself often.OTOH, you CAN do MUCH better.

#4 - Ham, get those thoughts out of your mind - and THIS is why this preface post was made NOW. "Or, do I change is every 4/5 years - 20,000 miles?" HAVE NO DOUBT WHATSOEVER - WHEN CARBON GETS DAMAGED, AND THE LOAD IS TOO HIGH, IT'LL GO THE VERY NEXT TIME THAT LOAD IS TOO HIGH. IT COULD BE TODAY. IT COULD BE NEVER, BUT TIME HAS NOTHING TO DO WITH IT. It's NOT like a crack in aluminum or steel that will grow. It'll either work, or it'll fly apart. NO WARNING. If you have ANY doubts, go read THIS (luckily, the rider only broke his collarbone) or ANY OF THESE. The common thread is time is not something you can use to predict a failure. It'll either be OK, or it'll be gone. Imagine, if you will, what would happen if a front fork suddenly flew apart while you were riding at 20mph towards a corner in heavy traffic. NOT PRETTY.

#5 - Composites are not just sexy black replacements for metal components. Carbon composites are brittle. They are more like plywood or reinforced concrete. Get those thoughts about cracks and bent components completely out of your mind. That is not what these materials do. They either work, or they break. There's not a lot in between. As a cyclist, you want to make sure the ones you use work.