Ti bonded frame construction

[Mark Kelly]

I assume you've seen the article on the bonded Ti frame on Cycling Tips.

What I found interesting is that the bond areas are so small, but a back of the envelope calculation shows that the ratio of bondline surface area to (probable) wall thickness is roughly the same as the ratio of the yield strength of 3Al2.5V Ti to the shear strength of a good quality epoxy, so all is well.

We learn something.

[crumpton]

the practical yield strength of the 3Al2.5V Ti in that application would be relative to the tube wall and dia.. what is it? the best you are gonna get in sheer with the best epoxies is under 4kpsi

while the quick calculations say the surface might pass, i'd be striving for a 3x safety margin for the unseen. like the losses due to less than laboratory quality bonding procedure and fitup.

I assume you've seen the article on the bonded Ti frame on Cycling Tips.

What I found interesting is that the bond areas are so small, but a back of the envelope calculation shows that the ratio of bondline surface area to (probable) wall thickness is roughly the same as the ratio of the yield strength of 3Al2.5V Ti to the shear strength of a good quality epoxy, so all is well.

We learn something.

[Mark Kelly]

the practical yield strength of the 3Al2.5V Ti in that application would be relative to the tube wall and dia.. what is it?

I assumed 0.9mm WT. The lug "shelves" appear to be about 15mm long. Tube diameter appears on both sides of the equation so it drops out:

15mm x 30 MPa x Π x diameter ~= 0.9mm x 500 MPa x Π x diameter*

On a practical note: I am fully with you on the safety margin for bonding, my bond areas are 3 - 4 times this size.






* I am fully aware that WT x Π x diameter is only an approximation of the tubing cross sectional area but it's close enough for these purposes.