Originally Posted by
B. Carfree
As someone who has had several steel bikes fail at the seat tube/bottom bracket junction, including a tandem, as well as a few fail at the top of the seat stays, I'm not sure I buy that. In my failures, there was no visible damage, not even paint cracks, and it's not like simply pedalling down the road (no wrecks) should bend the bike too far, and yet there they were, all broken. Obviously I applied forces that were beyond the capability of the metal to withstand over time.
I would be concerned that an impact like the OP's would hasten such failures. I suppose one of our materials folks will set me straight here, but I wouldn't be quick to dismiss the possibility of the frame failing prematurely because of the wreck.
Big difference here:
Wreck is one big energy impulse.
Riding is MANY energy impulses as you pedal and bounce. Thus metal fatigue becomes an issue. The problem is in the crystal alignment of the material. In it's initial state the crystals are somewhat jumbled but as the material is worked the crystals rearrange becoming aligned. The aligned state is harder but more brittle.