<VV> axle breakage

[djtcz at comcast.net]

----- 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