Bill,

I have seen the issue that Werner wrote about on many programs, that
is, the manufacturing and or test environments can be much more
damaging than the use environment.  This is why one should design (as
well as perform a reliability analysis) for the whole life cycle.
When you perform this life cycle analysis, you can tabulate the damage
for each life cycle segment.  This approach to fatigue analysis was
used very successfully on the Air Force F22 as part of the Avionics
Integrity Program (AVIP for short).

On a recent LEO commercial imaging electronics system that I worked on
I was able to show our customer that the testing environments consumed
over 80% of the total life cycle fatigue damage for some components.
I was only able to do this after requesting that the customer gave me
a detailed "day in the life" thermal profile of the satellite
environment so that I could compare the on orbit fatigue damage to the
test environment damage.  I choose to use an elastic plastic total
strain approach to compare the low cycle (about 20 cycles) fatigue
damage caused by the test environment with the relatively high cycle
(about 40,000 cycles over 7 years) fatigue damage caused by the orbit
environment.

With this data we were then able to negotiate a reasonable number of
test cycles that could "screen out" infant moralities while not
forcing a design that would require expensive materials.

Please reply (personally or to TechNet) with any comments or further
questions.

--
Karl Sweitzer                     voice: 716.47.77546
Eastman Kodak Company             pager: 716.25.33681
800 Lee Road                        fax: 716.47.77293
Rochester, NY 14650-3118         mailto:[log in to unmask]

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