<VV> axle breakage

[levair at aol.com]

The axle broke at the junction of the flange holding the wheel studs 
and the stub axle; no bearings or splines involved.  The wheel  stayed 
on the car due to having disc brakes.  The wide wheel is back space 
centered on the flange.
    The plan is to prepare another hub by adding metal in the attachment 
radius by Tig welding.
Maybe it will last another 45 years if I stay earth bound.

Warren


Subject: Re: <VV> [indyscca] Autocross report
And as expected, I had to eat humble pie today at Terre haute.

My car broke the stub axle splines where it drives the rear wheel hub.
I didn't even get one run in it.
However, thanks to lots of friends and their cars, I did not miss a
run.

Now, did it break because of the added torque of 2+ added(30%) psi, the
huge jump( and landing two) weeks ago at 16 th Street, or 45 years of
age of the part, or all three?? I have run V8s through the same type
axle hubs without failure. .
Warren



===========================================


Was the failure at the end of the splines, or part way into the hub?



The fracture surface contains clues , unless the faces were in contact 
for a few frantic revolutions after complete fracture, and beat each 
other up.


DJ Wulpi was an engineer for the International Harvester Corporation. 
He shared a batch of his failure analysis experiences in books and 
articles over the years.
Some pictures based on Wulpi's work are all over the Web.
http://www.asminternational.org/pdf/spotlights/jfap0502p011.pdf
http://www.metallurgist.com/html/ShaftFailure2.htm


Regardless, I'd guess it is a fatigue failure of some kind.
It Could be "Low cycle" fatigue where some plastic or permanent 
deformation occurs during each loading event and relatively few hole 
shots are required for failure.
Or, it could be "high cycle" fatigue where the load only causes 
"elastic" deformation, and takes millions of cycles for a final failure


Repetitive loads causing stress well below "ultimate strength" or for 
high cycle fatigue, even "yield strength," over time, create a tiny 
crack, or cracks, that grow some with each additional stress cycle.
Frequent enough magnaflux inspection would reveal initiation of cracks 
well in advance of failure.


The 1965 Chassis shop manual Section 4, Fig 66 suggests The portion of 
an LM "drive spindle" inboard of the wheel bearings handles mostly 
torque, and little or no bending. A basic radius is shown at the 
transition of the splines. Probably plenty good enough for the intended 
service.


The steps to cure or postpone "low cycle" and "high cycle" fatigue are 
similar.
First reduce stress concentration thru improved geometry . No sense 
sending in the star quarterback wearing mittens and flip-flops.
Second, improve material properties to raise the "endurance" limit 
above the highest stress the part will see. Could be a higher strength 
material, a nitride treatment, or the almost magic Shot-peening of the 
original part.


I'd prepare Magnafluxed spindles by removing material to create a 
profile more like the area adjacent to the spline on this this -
http://www.pirate4x4.com/tech/billavista/PR-35Spline/DCP_6548.JPG
What's important is a Big smooth radius, and a minor diameter less than 
the spline root diameter to reduce the vicious stress concentration at 
the ugly transition at beginning of the splines .
In Shop Manual Fig 66 it looks like some material could be removed at 
the end of the spindles spline and still provide centering diameter 
adjacent to the bearing,


Then , follow up with shot peening with cast steel shot to an intensity 
shown on page 20 of this MIL spec
http://www.godfreywing.com/pdf/AMS-S-13165.pdf

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