Hi! Chuck
Since you are now testing all the theory that is suggested please test
what is claimed to be the correct procedure........ Torque up to full
load a lock nut first measuring very accurately the elongation of the
bolt. Then apply the main nut and torque it up to the same torque on top
of the lock nut. Check the elongation of the bolt (it should be the
same). Then holding the main nut steady back off the lock nut to the
underside of the main nut, and you should find that the elongation
hasn't changed.
The point to all this is that when you torque up nuts onto bolts the
working tensile strength of the bolt is the objective you are trying to
always replicate. It is easier to get repeat tensile strain on a bolt by
specifying the torque on the nut than to fanny about measuring the
loaded length of all bolts individually.
If you under tighten nuts the bolts will obviously not achieve their
design objective and remain elastic. Correctly loaded bolts within their
design loads will also remain elastic.
However should you over tighten then the bolt will eventually get to
its yield point where it starts to "waist" and it gets progressively
considerably longer without any useful increase in load until it breaks.
Bolts that have entered their yield area are plastic and do not return
to their original length when loosened hence they are scrap.
You will find that the vast proportion of bolts on the Europa are
designed to be in shear not tension hence they are not generally torqued
up.
It's only necessary for such finite tensile requirements on highly
stressed items such as engine compartment and fire wall forward.
Some applications can subject the bolts to over load in service by the
nature of the application. For instance the bolts holding a crane slew
ring together are highly stressed and in a very critical operation apart
---From the elastic considerations the repetitive loading and unloading
causes a metallurgical change in their composition called WORK
HARDENING, at regulated periods these have to be considered "life
expired" scrapped and replaced with new.
So one reason for torquing bolts is to control against over tightening
as well as undertightening since as you will see above you could finish
up with condemned bolts.
Regards
Bob Harrison G-PTAG Europa 337 MKI/Jabiru 3300
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Chuck
Popenoe
Subject: RE: Europa-List: lock nuts
I've been following this thread and haven't been convinced by the
arguments.
So, as an curious experimental scientist, I happen to have in my lab a
Skidmore-Wilhelm tensile test device, capable of measuring the tensile
load
on a bolt quite accurately. I placed a 1/2-13 bolt in the device and
with a
fitting nut, torqued it to 6000 lbf measured tensile force. I then
placed
another 1/2" nut on top and torqued it down as a locknut. The tensile
force
on the bolt did not change--remained at 6000 lbf. Next, I loosened the
locknut and tightened it to snug condition, and while holding the
locknut
fixed, backed off the lower nut to lock the pair. The bolt tensile
preload
decreased to 5000 lbf. I repeated the set of experiments again, with
the
same result. Q.E.D.! This little experiment confirmed my suspicions
that
the locking nut should remain on top. Please tell me if am I doing
something wrong?
Pops
A036 -- on hold at the moment.
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