Yes, as noted in my comment on Mark L's comment (third paragraph, first
line of my e-mail), clamp force for the WAFs is irrelevant for exactly
the reason you have noted. Although the comment about "greater length
... than it will see in service" is not exactly what we need to see in
the application where linear loads are being constrained.
My intention was to clarify what we are actually attempting to
accomplish when there is a torque requirement on a fastener so that the
original author of the issue (the concern about stripping the nylon on a
lock nut at low torque loads) had some basis for the lack of a torque
requirement on the fasteners in the WAF. i.e., as you note, the forces
are shear forces, not tension loads, so the only requirement would be
for the assembly to be "tight" enough to prevent lateral movement, but
did not require a specific "torque" to be effective.
Note that in many high performance applications requiring control of
linear motion of the joint, where access to the fastener is possible,
the actual change in bolt / fastener length is the specification: e.g.,
connecting rod bolts (think top fuel motors in drag racing and others)
are considered single use fasteners and are frequently verified for
"clamp force" by measuring the change in length of the bolt. The next
time the engine is disassembled, the bolts are discarded.
In some engineering test environments (usually during the functional
design period), clamp forces are verified in a load cell to confirm that
the material selected performs at the anticipated functional level
required. Where tension loads are in effect, the clamp force must exceed
the anticipated load on the assembly by a suitable percentage to allow
survivability of the device without introducing excessive mass/weight to
the assembly, etc. for those devices where clamp (tension) loads are
critical.
However, in most cases, physical properties of various materials can be
found in industry publications from ASTM, SAE, and other standards
bodies. Machinery's Handbook is a good quick reference to start with.
See
https://www.amazon.com/Machinerys-Handbook-Toolbox-Erik-Oberg/dp/0831130911.
It is kind of pricey, but you can usually find an older version pretty
cheap. I have Volume 24 and usually find what I need. I think I paid 10
bucks for it at a local garage sale a few years back. If you know how to
do a proper search, these days on line can work very well also.
Having said that, to minimize shear events, the bolts in the WAF
assembly should be a tight fit in the holes to minimize movement in
shear which, if lateral slop were present would (theoretically) enhance
or increase lateral forces subjecting the joint to undesirable side
loads on the assembly (or vertically from an observer's viewpoint) which
would potentially result in premature failure of either the fastener or
the spar.
Mark Wegmet
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
On 11/7/2021 8:34 AM, Flesner wrote:
On 11/7/2021 7:49 AM, Mark Wegmet wrote:
Another way of looking at "torque" requirements at the basic
engineering level of fasteners is to consider that it is a conversion
of (unmeasurable) clamping force on a fastener to a (measurable)
rotational force that con.......
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
In my non-engineering understanding of "torque / stretching" a bolt is
to stretch the bolt to a greater length (we're talking thousands of an
inch) than it will see in service so t......
....torque values are irrelevant except as to not crushing the wood.
Is that what you were saying?
Larry Flesner
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