Re: Threaded Fastener Torque in 6061-T6 Aluminum

In article <Xns97429D8052E7ccoughranucsdedu@xxxxxxxxxxxxx>, Charly
Coughran <ccoughran@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> mbarclay@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (michaelbarclay) wrote
> in news:1136476045_387@xxxxxxxxxxxxxxxxxxxxxxxxx:
>
> > All the information that I can find on recommended threaded fastener
> > torques and corresponding clamp loads are based on the proof load of
> > the screw, not the material that it is screwed into.
> > Where can I find information on the recommended torque of a fastener
> > being screwed into a 6061-T6 Al plate? Also the coresponding pull
> > out load (i.e. at what load do the threads strip in the aluminum)?
> >
>
> That is because in most normal circumstances the bolt will fail rather
> than the nut. Remember that the root diameter of the nut is larger
> than the root diameter of the bolt. This means that the stress is
> less in the nut.

Also, the nut is in compression, unlike the bolt that is in tension.

> A simplifed formula for tension (i.e. axial) loading
> in a female thread is:
>
> Pu= (pi Dm Fs L)/3
>
> where:
> Pu = ultimate load
> pi = pi
> Dm = mean diameter
> Fs = shear strength of tapped material
> L = length of good thread
> 3 = emperical derating factor
>
> If you play with these numbers, you will discover that if you have 1
> bolt diameter of good thread, you are usually in good shape if you are
> tapping into reasonable metals.

The usual recommendations that I have seen specify that the nut
material (or insert material) should be more ductile than the bolt.
This allows the nut's threads to plastically deform under compression
which actually puts more of the threads in bearing, spreading the
load better across the nut.

--
Harry Andreas
Engineering raconteur
.

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