Steel Vs Titanium Fasteners - Preload / Clamping Force

[jack20]

Hi,

I am trying to determine the difference between a steel and titanium fastener of the same diameter and length when torque tightening to a standard value.

Obviously the steel fastener is stiffer than the titanium and I believe this means the titanium fastener is likely to have a higher preload and a be under more tension than the steel? I need a quick simple way to demonstrate this can somebody help point me in the right direction?

Thanks in advance

 

[SwinnyGG]

Your logic assumes that X amount of torque induces Y amount of elongation, no matter what the bolt material is. This is not the case.

A bolt is a spring, plain and simple. Hooke's law does apply. But the energy stored by the elongation of the two different bolts cannot occur at the same elongation unless the two springs have the same rate, which they do not.

Go back to the spring analogy- we know that if we consider the titanium and steel bolts as springs, that these two springs have different rates- the rate of the titanium 'spring' is about half the rate of the steel 'spring'.

If I hang these two springs from a hook, and hand a 5lb (or 500 or 5,000 or 5,000,000lb) load from the end of each of them, they will stretch different amounts; the titanium spring will stretch about twice as much. The stored energy is the same in both springs (which is the applied torque), and the force applied to the beam (which is the bolt preload) they hang from is the same- the only difference is elongation, because of the differing spring rates.

 

[rb1957]

ok ... I was thinking more in terms of angle of twist (and sloppily using "torque" to describe it).

if you apply an angle of twist to a nut, you'll get the same extension, hence 1/2 the load. But (I guess) you only applied 1/2 the torque to get the same angle of twist (if 1/2 strain energy out, then 1/2 energy in).

another day in paradise, or is paradise one day closer ?

 

[SwinnyGG]

Ahh.

Yes- if you're using the same angle of twist for the two bolts, you absolutely will get 1/2 the load from the titanium bolt, by imparting roughly 1/2 the strain energy.

The rest of the analogy trickles down. Might want to be careful about using those terms interchangeably in the future..

 

[rb1957]

thx, but I've already tripped on that sword ...

another day in paradise, or is paradise one day closer ?