Richard: Thanks for the interesting article. The one problem with the
analysis is that the typical hardware store Grade 8 or Grade 5 don't seem to
have the inspection processes to assure that they really are of the 120ksi
or 150ksi. Assuming the grade 8 bolts really are grade 8, I have no trouble
calculating a big safety factor in my application. However if they are only
marked grade 8 but are of a lesser quality material??
Over in Engr.tips.com I get pummelled for talking about using any bolt not
covered by either AN (grade 5) or MS which can go grade 8. However, with
the counterfeit bolts that have slipped into the US I am not sure that an AN
bolt is an AN bolt.
Another curiosity found in the helicopter and not in his Rock crawler is the
vibration frequency. My helicopter has a 2/rev vibration generated in the
blades a propogates thru the head into the main rotor shaft and beyond.
2/rev corresponds to 61,200 cycles/hour. For a 10million cycle for fatigue
failure, this is only 163hrs. Since fatigue strength is usually a fraction
of tensile strength, the stronger bolts can jack the 10million cycle to
20million and beyond. The grade 8 bolt, and I hope it is a true grade 8
bolt, can give me more of a margin. Of course proper torqueing keeps the
stress from truly cycling and I get a larger margin.
Thanks again for your post as it kicked my little grey cells into gear and
has motivated me more to explore the bolted joints to a greater degree.
Stu
"cavelamb himself" wrote in message
...
Back to bolts...

My point was that an super strong bolt can overtress the attached
structure without any indication that it has happened - until a
fitting breaks or something like that.

This fellow comes to a different conclusion than I usually do.
THe last line "When in doubt make it stout" will appeal to those
who think an airplane can be built so strong that it can not be
broken.

But I trust that you, of all people, will know better than that.

Very informative article on bolts - grad 5 vs grade 8.

http://www.rockcrawler.com/techrepor...ners/index.asp

Richard