Originally Posted by
Mark Kelly
Don't know where you got that figure but I don't think it's right. From the figures I can find, 6Al4V Ti (as used by Stronglight) is actually stronger than 4130 CrMo. For Ti: 6Al4V Yield strength 880 MPa, shear strength 550 MPa in annealed condition. For CrMo: 4130 Yield strength 500 - 700 MPa, shear strength 300 - 400 MPa, values dependent on heat treatment. The poor reputation of Ti BB spindles comes form the early Campy examples which were made (badly) from the wrong alloy. IIRC they were CP and the machining left a stress riser right in the weakest spot.
Where Ti falls down is that it is much more flexible, having roughly half the modulus.
You are not factoring in that you must compare parts (ti vs cro-mo) that displace the exactly the same dimensions, volume and thickness etc. Then plug in your analysis and ti will fall down in the shear strength dept vs high-end cromo.