| At least that's how I learned it :-) But I'm not a metallurgist (don't even
| play one on 'net :-). Perhaps someone has more info??
Back when I was in junior high school, my parents were building a new house.
I collected the wire scraps the electrician left behind. Among them was
about 2 feet of what I now know to be Al USE cable. I tore it all apart
and extracted all the individual aluminum wires. That's when I discovered
they were no good for soldering.
But one thing I did try was twisting them. I had a few inches of one of
the aluminum strands and bent about an inch on each end 90 degrees to make
it easy to twist. I was curious how much I'd have to twist the aluminum
to make it break. I expected to see the whole length between the bends
gradually twist all at once. But that didn't happen. Instead, the twist
took place at some point, usually, but not always, closer to one end.
As I continued twisting, the was a boundary between straight wire and
twisted wire, and then another boundary back to straight wire. The part
where it was twisted then grew along the length, usually, but not always,
just in one direction. There was a definite pitch to the twist that was
constant. Eventually I would have the entire distance between the two
bends twisted. At that point it was much harder to twist, but quickly
broke somewhere when I forced it. On about the 3rd or 4th try at this
I decided reverse the twist. I noticed that this produced a reverse
twist zone of wire that propogated back over the forward twist as I
continued reverse twisting it. Eventually I had reversed the whole wire.
In one case I made the wire twist forward then reverse then repeating
many times and it didn't break. In another case I managed to get the
wire to have several alternating (between twist direction) zones along
the length, each about 3mm long. I also measured a very slight drop
in distance between the bends after twisting as compared to a straight
wire. There did appear to be some kind of compession taking place.
I could never get a wire to untwist back to straight.
Eventually I ran out of little aluminum wires.
I suspect this may be related to aluminum's ability to flow. Maybe it
just isn't as dense in this form as a wire as it otherwise could be.
Maybe I should look for a phase state diagram for aluminum and see just
what allotropes it might have under various pressures in the solid state.
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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