Originally Posted by
cyclintom
As a construction engineer I would expect you to be more knowledgeable about resins than that. Resin never really cures completely and continues to harden over their lifetime. Progressively slower and slower of course but at the same time the resin grows more and more brittle and is degraded by UV light. This hardening in the older bikes didn't much matter because they were so overbuilt that even the resin hardened almost to glass hardness was stronger than any expected load on these bikes. But the new bikes are not built for strength, they are built for ultimate lightness. Several people have bragged that DuraAce equipped bikes with DuraAce wheels (not the lightest around) are under 12 lbs. My brothers 10 year old Giant TCR-0 weighs 16 lbs. Giant well knew how to build lighter bikes then but didn't. Now you ain't got a bike unless it's well under 16 lbs.
Alright I stand corrected on resins, don't know much about them. Steel, concrete and brick are more my thing
I would assume or expect that bicycle manufacturing engineers conduct testing on the lifespan of CFRP over time, under UV exposure etc., and build in necessary tolerances accordingly.
It is possible that carbon fiber bicycles used to be designed with higher tolerances thus safer. It is also possible that some manufacturers are skirting the limits of what is allowable. On the other hand, it is just as feasible that advances have been made in the resins and layups of carbon fibers, or just in the design of the frames themselves, such as to reduce the weight without compromising strength or durability.
I know BMC for example started implementing carbon nanotubes (little strands of carbon atoms just a couple of nanometers thick), and infused them into the resin. I can imagine this would at least partially mitigate any failure or propagation of cracks throughout the resin for example. So there might be other reasons than just "designing them less safe" that can reduce weight.
I think there is no reason for pushing people away from carbon fiber composite bicycles, and the "evidence" I have seen on the failures is anecdotal at best. Googling pictures of broken carbon fiber bicycles is no scientific evidence of a widespread problem. I just googled "aluminum frame failure" and came up with similar photos on aluminum frames.
I would love to see a proper scientific study done that tests a large number of frames after 1, 5, 10 years into their lifespan, on impact, fatigue, etc. Until I see a study like that proving that carbon fiber is unsafe after a number of years, or a statistic analysis of CFRP failure related injuries, I don't see any reason to spread fear about it.