I ride with several 10+ y.o. ti frames which are fine, and one on which a downtube weld failed with bad results. That rider is now back on his even older custom steel bike. Almost all of us now ride carbon, no failures even in crashes.

No, there's pretty much no proof of anything w/r to bike frames, though the above frame testing link is very interesting. That said, the carbon/epoxy matrix used in bike frames has technically by far the greatest fatigue resistance. See: http://calfeedesign.com/tech-papers/...l-white-paper/

Left out of most discussions are wood/epoxy frames, which offer all the fatigue resistance of and stiffness carbon fiber without the fragility. Wood is the original composite material. For instance: https://www.bicycling.com/bikes-gear...d-bike-review/ There are trees swaying in the forest which are thousands of years old.