<VV> axle breakage

[levair at aol.com]

I appears that the fatigue started around the factory hole for 
clearance for a socket to reach the bearing retaining nuts.
    It's only fair to say that this hub has been raced on for 20 some 
years and abused with huge sticky tires and high cornering loads.   No 
fear of failures for daily drivers.


Warren

-----Original Message-----
From: djtcz at comcast.net
To: virtualvairs at corvair.org
Sent: Mon, Oct 18, 2010 9:02 am
Subject: Re: <VV> axle breakage

----- Original Message -----

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


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



sounds pretty likely like bending loads from cornering causing fatigue. 
Do you have the pieces? They would be helpful to identify if the 
crack(s) originated from a rough, as forged surface, or a corner or 
other feature left from machining. Either way, improved geometry 
(grinding a smooth contour) and shotpeening could net a significant 
fatigue/endurance improvement.


The best TIG welding ever done by man is a casting with relatively 
uncontrolled alloying and heat treatment, full of residual stresses and 
lacking the improved grain size and grain flow and other benefits of 
the original forged material.



" The fatigue resistance of a welded joint is inferior to that of base 
material. In low carbon steel the fatigue limit is approximately 50% 
for butt joints and 15- 25% for lap
joints. This phenomenon deals mainly with the combined effect of stress 
concentration and particularly residual stresses: The higher the 
mechanical properties - the higher
the level of harmful tensile residual stresses ."
http://www.shipstructure.org/pdf/93symp13.pdf


"It was observed that the bending fatigue strength decreases after the 
TIG (Tungsten Inert Gas) welding process application on AISI 4130 
steel, with subsequent decrease due to re-welding sequence as well. "
http://www.scientific.net/MSF.636-637.1451


The " AWS rates the endurance limit of some welded joints as low as 
7ksi, regardless of the strength of the base metal or the filler 
metal."
http://ficientdesign.com/2010/03/weld-failure-design-considerations/




Is this the same area of failure experienced by others?


Dan T



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