On Fri, 18 Jan 2008 00:23:57 +0000, Christopher Tidy
wrote:

cavelamb himself wrote:
Nick Mueller wrote:

clare at snyder.on.ca wrote:


In double shear a loose grade 8 will snap uner impact. A grade 5 will
flex. It MAY permanently deform,
A loose grade 8 bolt in shear WILL brake on impact.



You forget to consider the forces.
A grade 5 bends under a certain load, where the grade 8 doesn't even bend
with the same load. Wen the grade 5 breaks, the grade 8 just bends.
Again, a bolt that is plastically deformed by design is simply an error.

Facts (metric grades):
grade 5.6 : 500N/mm^2 and 300N/mm^2
grade 8.8 : 800N/mm^2 and 640N/mm^2

A bit simplified:
The grade 5.6 bends at 300N/mm^2 and breaks at 500N/mm^2
The grade 8.8 bends at 640N/mm^2 and breaks at 800N/mm^2
So the grade 8.8 doesn't even bend when the grade 5.6 already failed
completely.


Nick


That's the best argument I've ever seen to NOT use 8's in aircraft
structures.

Is it just me, or does that argument make no sense?

Chris

Well, grade 8 bolts are NOT used in aircraft, for what it's worth. AN
bolts are closer to grade 5.
They DO bend. They don't(theoretically, and hopefully) snap.

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