Re: Questions about the DH Comet

Date:         25 Sep 97 01:39:43 
From: (Gerard Foley)
Organization: The Greater Columbus FreeNet
References:   1 2 3 4 5 6
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Charles Crosby ( wrote:

: >From a book on De Havilland (sorry, forget the title) the statement was
: made that they were aware of the dangers of the window corners, so they
: tested the design extensively.  However, they subjected it to a static
: over pressure test first, and THEN tested for fatigue at relatively high
: amplitude and reduced cycles.  The theory was that this method of testing
: may have resulted in some stress-relieving plastic deformation at the
: stress concentrations, and that it didn't accurately simulate the high
: cycle, low amplitude stress situation in practice.  I'm not a stress or
: fatigue analyst, but to my mind it sounds like a very realistic and
: practical type of "Oh Shit" situation.

This is not impossible.  It is also possible that the plastic deformation
resulting from a static test could strengthen the materials involved
(by "work-hardening) so that a later fatigue test on the same hull
could be invalid with respect to normal hulls.