[AR] Re: fatigue life (was Re: Re: SpaceX F9 Launch/Update...)
- From: David Weinshenker <daze39@xxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Mon, 28 Dec 2015 14:35:24 -0800
On 12/28/2015 02:18 PM, Henry Spencer wrote:
The
tough part would be the very dynamic things, like acoustic and vibration
loads.
Yeah, I can think of ways to -expose- "dynamic" fatigue
sensitivity - e.g,, instrument the amplitude as well as
the force of the exciter interface to the "system-under-
vibration-test", and sweep the excitation frequency looking
for features in the impedance that suggest resonances at
certain frequencies - then lean on those frequencies
watching especially for shifts in the impedance suggesting
that some degradation (cracking, work-hardening, etc.) is
occurring.
With a nasty enough mentality and a powerful enough vibration source
you should be able to make something crack -somewhere-; the question
then becomes the correlation between this observation and the expected
operating stresses. (I suppose one could adopt the philosophy of fixing
the fatigue resonances wherever they appear, whether or not they would
be excited by "expected" flight loads.)
-dave w
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