>>Ed Devinney writes,"
>>The question is what bolt strength to use: Grade 8 may be strongest overall,
>>but in this use do I actually want Grade 5, to allow some stretch rather
>>than having them shear? My mechanical-enginerd friends and I went round on
>>this, but we figured the race-volk would know best. Any takers?
Ed..it is a technical question, not a race question; listen to your mechanical
e-nerd
friends. (When the doctor says you got a heart problem and shouldn't drive in
that race,
would you get the second opinion from the race-volk?) Ask your race friends
how to tune
the suspension or carbs, etc.
The answer (and the why) to your question is as follows: The higher strength
bolts will
provide higher capacity (failure loads), which is one thing you want (I
assume?). If you
want to build in some energy absorbing capability, you need to design it into
the system,
which *probably* is not done by simply using lower strength bolts. I expect
that the
compliance (stretch) provided by the many components which will deform when
your harness
experiences design loading (we hope never) will completely dominate the
behavior of the
system. That is to say that the stretch of the straps plus the deformation (if
any) of the
parts to which it is anchored, plus the deformation of the warm body (yours?)
contained in
the straps will be equivalent to 10-100 times the deformation you could get
from grade 5 or
any other grade of bolt. Note that the elastic deformation of the grade 8
bolts will
actually be greater than that of the grade 5 bolts. The plastic deformation
may not be.
Still, I expect any potential increase in plastic deformation offered by the
lower strength
bolts will be trivial in comparison to the deformations in the other
components. Note that
whether a bolt "shears" or "stretches" (fails in tension?) depends on how it is
loaded, not
on what grade of steel is used.
Finally, the question is probably moot, unless the bolts represent the weak
link in the
system (ie., something else may fail first.) If bolts are the weak link, then
it sure
makes sense to use the higher strength bolts!
Best regards,
Ray
-------------------------------------
Name: Ray W. James
Texas Transportation Institute
Civil Engineering Department, Texas A&M University
E-mail: Ray James <rwj4123@sigma.tamu.edu>
Date: 09/21/94
Time: 09:59:54
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