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OptiPhil 285845 160 Wheel fell off John Deere 4430 either
Wheel fell off John Deere 4430
I saw this tractor next to a highway near Morganfield,
Kentucky.

The tractor was in the corner of a field, so the driver was
probably prodding the independant brakes when the axle
snapped off like a carrot !
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Re: Wheel fell off John Deere 4430
Any metalurgists out there that can explain the failure!
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Re: Wheel fell off John Deere 4430
probably done 20,000hrs & you'd be a bit weak at the knees
by then too
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Re: Wheel fell off John Deere 4430
Aint no metalurgist, but I can tell you why:

It's an old crack that has started at the weakest point on
the axle - the spline (I think it's called...). Anyway - you
see the theres a "round'ish" area around the spline - that's
an old crack that's probably startet months or possibly
longer ago. The reason it's dark is because dirt has gotten
in to it.
Well since the crack is on the outer perimeter of the axle,
it will - when the wheel rotates - change between being up
and down. Because of the load from the tractor, this will
provide a push-and-pull effect stressing the crack. And for
every time it rotates, the crack will be slightly larger,
causing the white, curved lines you see goin out from the
original crack. Theyr called beach marks or beach lines.
Sooner or later the stress on the remaining piece of axle
that is fine, will become too much and ripe the rest of the
axle apart - and thats what you see has happend on the right
side in the picture.
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Re: Wheel fell off John Deere 4430
When a first small crack occurs, peak strains will occur on
the end of the kerf. So it's easier to rip further. Just
think of tearing off a piece of letter paper: if you grab it
and pull, nothing will happen. If you start a small rip, and
do it again, it will tear in half because the strains peak
in the end of the kerf.

The same effect is with sudden diameter changes. At
engineering class, they teach you to design lathework pieces
with no sudden changes in diameter, allways make a radius to
even out the strains in the corner.

BTW, most halfaxles dont break because of doing 20.000 hrs,
most axles that lasted 20.000 hrs will never break in normal
conditions. They do break because of material impurities,
the carving because of blunt lathe chisels, or just
overload.
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