Classic Axle Failure

I think we have all read about or studied stress risers with respect to failure. As I was gathering up scrap for a trip to the steel yard a few weeks back, I cleaned up the remnant of of the Spicer short side axle that was still stuck in the side gear of the D25. Absolutely classic failure with the fracture lines starting at the bottom of nearly every spline.


Only a slight amount of rotational fracturing evident right in the center which probably occurred after it initiated shearing at the splines. Unfortunately, the remaining portion of the short shaft tore up the inner seal pocket so the rest of the housing went to the scrap yard too. I had initially entertained the thought of putting it back together as a temporary fix. That tore up surface was probably good as it resulted in the building of a D44 replacement.

 

Amazing. The cracks descend into the shaft until the diameter of the shaft is too small to withstand the torque. I wonder how much twist was needed to make those cracks. To me, this clearly shows why more splines is better. Since the stress focused at the bottom corner of each spline, the more locations that stress is distributed over, the more force the splines will withstand before breaking. The size (cross sectional area) of each spline does not matter so much as the number of splines.

 

Partially true Tim, the more splines is not always better but most times yes. The shape of the spline has more to do with its failure than anything, sharp corners are a no no on anything stressed, its why involute splines are more common now, no sharp corners and they can take about 3x the load, if the above splines would have had a .030 -.040 radius in the corners they would not have fractured near as easy, the sharp corner is where all the stress started regardless of what the shaft looks like.

 

Another example, on a bigger scale. I just found the busted piece of 1 1/2" 23 spline Dana 70 shaft from my old dump truck.

 

It's kinda pretty in its own way.

 

It's like a metallic chrysanthemum ...forged by Vulcan. Or something.

Thanks for sharing, OP. Always nice to see metal carnage.