Metal fatigue and stiffness
SwiftSolo said:
Titanium has historically been accepted as having relatively poor stiffness. On the other hand, its' flex characteristics change very little after thousands of flex cycles (within its' intended working range).
Not a very accurate analysis.
On the fatigue front, steel and Ti essentially experience no fatigue as long as they are kept within their fatigue limit. Frames made from these metals, properly constructed and barring manufacturing defect, essentially last forever. Ti alloys, per unit mass, are just as stiff as steel or aluminum, and certainly can be formed into tube shapes, thicknesses, and diameters that result in more than stiff enough frames. Those frames are lighter than an equal performing steel frame, and more durable than an equal weight aluminum frame. If a bicycle frame is too flexy, that simply means that the tubes are too thin and/or too small in diameter, not due to the material of construction.
BTW, if a composite structure has lost stiffness, it certainly is on its way to failure due to matrix cracking, fiber breakage, or fiber pullout.
All that said, VERY few riders will ever experience any sort of loss of performance of their frame (unless they experience crash damage), regardless of the material.
