Originally Posted by
maartendc
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.
I see no reason to push people away from CF frames and forks that are properly constructed but people aren't buying an 18 lb carbon fiber bike. Carbon nanotubes still have to be held together with resin. I think that it could give a longer lifespan to CF in a best case scenario but most of this isn't engineering - it is manufacturers guessing at things. Remember that these things are mostly made in China and they have more than enough work for the best engineers in fields other than bicycle design.
I did contact some CF engineers and they did convince me that you CAN built a safe and light CF bike. But all it takes is the slightest problem with the layup and it can break at that point. And the construction technique for building these things inside of molds with inflatable inner liners sure doesn't seem that foolproof to me.
Perhaps graphene offers more strength to light bikes but I really haven't been able to find any real information on it except the raving from dopes that don't know anything about it. But I think that layering graphene by molecular attachments would be pretty damned expensive. A sheet of graphene is only one molecule thick so you would have to layer these sheets with cross linking the molecular structure. The problem and advantage of this is that there would be pretty much two molecule thick sheets separated by cross bonding of carbon molecules here and there. This would separate the sheets with open space but I imagine that could give more strength than the two sheets laid one upon the other and covered in resin to hold the assembly together.
One of the things I haven't been able to discover is how large they have been able to make the sheets since this would be important to mechanical construction techniques.