Why is fatigue an issue?
The space elevator is 100,000 km long
Construction climbers go the whole way
A 20 inch diameter wheel must rotate almost 63 million times to get to the end of the ribbon—smaller wheel, more revs
The climber gets traction by squeezing its wheels against the ribbon
The lower the coefficient of friction between the wheels and ribbon, the harder the climber must squeeze, forces and stresses are higher