Well I think the real stresses come from yawing and wind pushing against the blades not the rotation itself.

Both of these forces concentrate at the root. wind pressure forces are probably obvious. The yaw forces may be a bit harder to understand. Just like any spinning object there are gyroscopic forces that resist moving out of the current plane of rotation and I believe it concentrates in the root / hub area. So now you have at least 3 forces on that area  the force trying to fold them back along the shaft, the force trying to jerk them off so they can fly away and the forces trying to twist them off at the hub. Modeling these is beyond my ability but it sure seems like it is a lot of forces trying to fatigue those blades twisting pushing and pulling in a never ending combination.

I have no experience with the physics involved but given a few years I am fairly sure it could beat any material to death. Just tossing that into the mix.

Good luck with them.

Cheers.

TomW

Without fools, you could not look intelligent. There is no knowledge without questions.