"The Enlightenment" wrote in message
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"Keith Willshaw" wrote in message
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"The Enlightenment" wrote in message
om...


All hypersonic aircraft, like the SR71 irrespective of material
don't
have fatique problems becuase the heat effectively heat treates
(aneals) any work hardening metal. Titanium, inconel, austenitic
steels all are the same.



Complete and utter cobblers

A statement that is complete hyperbole.


No one that comes from extensive expeience in welding and
fabricating titanium structures.



The normal stress relief temperature for titanium is around 1000 F
and the annealing temperature is closer to 1300 F

source:
Titanium Metals Corporation
Titanium Design and Fabrication Handbook for Industrial Applications

Keith



This web site recommends a 2 hour holding temperature as low as 500C
for stress relief heat treatment.
http://www.deutschetitan.de/eng/profi/kb6.html


Only for commercially pure titanium and that is the absolute bottom end of
the scale for stress relief only.

Your claim was that annealing occurs , the data table you provided
recommends a temperature of 700 Deg C ( for soft annealing of
CP Ti and 730 for commercial alloys. In other words around
1300 deg. F as I stated.

Even stress relief of usable alloys requires a minimum temperature
of 1000 F and that needs to be an EVEN distribution if thermal
stresses are not to be induced


The SR71 achieves a temperature of between 300C and 450C in localised
areas that Janes listed in 1974 while many web sites speak of 1100F as
the Blackbirds skin temperature. This is well withing the heat
treatment range though short of the full annealing I claimed.


Any article that claims SR-71 skin temperatures reach 1100 F is
less than believeable. NASA refer to max sustained temperatures
of around 600F on their aircraft

The article I read regarding this effect seemed quite plausible and of
positive benefit.


Given the differences in temperature between different parts of the
aircraft and the resultant thermal stresses this hardly seems like to
be a positive benefit, then there's the little matter of the scaling and
oxidation that occur at annealing temperatures unless one maintains
an inert atmosphere.

Keith