Hoo Boy Allen,
You really opened a can of worms. I bet they argue you should use Grade
8 nuts and lock nuts too.
Bolts and bolting are often very misunderstood, even by the engineers
who are charged with selecting them. I've learned everything I know
about bolting from the Germans. They don't allow conventional wisdom to
color their judgment, they actually go prove the science. I've confirmed
some of the science with my own analysis.
As simply as I can put it. Grade 8 bolts, while extremely strong, and
not very ductile. They do not tolerate bending and shear loading very
well. Grade 8 should be used in through bolt situations where you can
insure proper preload (torque,) flat mating surfaces and little or no
shear load.
If you have less than ideal bolting situations: tapped holes, flexible
components to be bolted, high shear loads then grade 5 is probably a
better choice. This is because they are far more tolerant to abuse due
to a phenomena called localized yielding.
This is the subject of many volumes of writing, and I've greatly
simplified the situation. No bolt will withstand high numbers of cyclic
loads, over torque or corrosion for very long. I'd be happy to discuss
any particular situation or application.
All that being said, I'm amazed at how some high strength suspension
bolts are mounted. My guess is that their saving grace is that they are
significantly oversized thus lowering overall stress levels.
Jon Rush
LBC286@aol.com wrote:
>
> OK, here goes the bolt strength thread (no pun intended) again.
>
> On another list there is a heated discussion about using all grade 8 bolts on
> restoring a car. Can anyone give me a simple explanation as to why it may or
> may not be a good idea to replace grade 5 with grade 8?
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