Gary- pete: Titanium/steel materials data

Posted by steveg on February 20, 1997 at 20:39:01

This message is here for gary & pete cuz I got a bad E-mail address and this was a deliverable due from me.. I may be ooc for several days so I used this board to get info out.. sorry to impose.. steveg
we at work researched the mess we spoke about last night.
I was wrong on the thermal guess.. Here's what we got
The "alpha" for steel is 6.07X10-6, titanium is 4.9x10-6
This means that steel expands more than titanium when heated .. this
means the nut gets tighter when heated because the stud expands more
than the nut. this is the "good" for those two materials in this
application.
The bad for this application... Titanium is much more elastic than
steel.. On a stress/strain curve plastic deformation will occur in
steel at a load ~~37% lower than titaanium. Steeel tensile max runs
to 70,000 psi, titanium about 110,000 - 115,000 psi. To put it more
simply... you need to torque the titanium nut much more than a steel
nut in order to get the same locking force you'de have on a steel
nut.. If you have materials do a test to failure. Torque a
titaniun nut till something breaks.. then re-torque the engine nuts
@ about 75- 80% of that load... ie. if your mock-up breaks
at 200FT/Lbs torqeue the engine to 150-175 ft/lbs.. when torqued to
loads for steel the nut isn't grippiing like steel because it is
just stretching at that lower load.
Hope this helps .. everyone at work enjoyed the diversion...
steve

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