[6pack] Non LBC, Metallurgy related Question

[Navarrette, Vance]

 	Titanium has many wonderful properties, but it is not, generally speaking,
stronger than steel.

	It is AS STRONG AS steel, and weighs 40% less. It also has a much higher
melting point than either aluminum or steel, which is why it is used on the
SR71. Titanium has excellent corrosion resistance compared to steel.

	Some drawbacks to titanium:
	It has a much lower modulus of elasticity than steel. This means it stretches
a great deal more than steel at the same PSI load.
	Titanium has poorer fatigue resistance than steel. It will crack much sooner
when it is cyclically loaded at or near its yield strength. Cyclic loading
strength is typically HALF that of carbon steel for equivalent life.
	Titanium is exceedingly difficult to machine, whereas steel can be machined,
then heat treated greatly reducing processing costs. Special tooling is
required to machine Titanium, such as when cutting threads on studs.
	It will weaken dramatically when contaminated with even small amounts of some
materials such as Cadmium or Chlorine. Normally this means that you must have
two sets of tools, one for titanium and one for everything else. Your tools
pick up trace amounts of cadmium from ordinary bolts, and this will be
transferred to titanium. If the titanium then is used at high temperatures, it
will fail in spectacular fashion (e.g. heads falling off of bolts for no
apparent reason).

	My guess is that the studs failed due to fatigue (i.e. cyclic loading
failure) so the bulletin said replace them with steel. Cheaper, stronger,
longer lasting. Only drawback is weight in this application.

    Vance Navarrette
    Cogito Ergo Zoom
    I think, therefore I go fast

-----Original Message-----
From: 6pack-bounces at autox.team.net [mailto:6pack-bounces at autox.team.net] On
Behalf Of Bruce Simms
Sent: Monday, November 23, 2009 12:56 PM
To: 6pack at autox.team.net
Subject: [6pack] Non LBC, Metallurgy related Question

Last March, 17 offshore oil workers & crew were killed when their Sikorsky
chopper fell hard into the Atlantic off Newfoundland.

The titanium studs that
held the gearbox oil filter in place failed, leading to a massive loss of oil
pressure.   Subsequent service bulletin for these machines had them change
out
the titanium studs out for steel ones.   I thought titanium is stronger then
steel?

Hey, inquiring minds wanta know.

Thanks,

Bruce Simms