Cracked Cast Iron Shaft - Opinon Needed

[MountainCat1M]

Sorry I cross posted this...but this seems like the better board.

http://home.thezone.net/~bpriddle/shaft.jpg

http://home.thezone.net/~bpriddle/shaft_closeup.jpg

This is a cast iron drive shaft on my new snowmobile. It is 1 inch thick. It cracked for no reason that I can see. But it has a weird centre core, that is actually off-centre. Can anyone explain or be able to determine by looking at it if this could have been a faulty shaft? The area circled in
the close-up pic also sticks out alittle.

Thanks for any help

 

[Metalguy]

Looks to me like most of the hex-points were where multiple fatigue cracks began, then linked-up. After the normal slow crack initiation phase, they speeded way up. Is the direction of rotation of the photographed end (photo no. 1) CCW? This assumes that the photographed side is the driving end of the shaft. The rotation looks like it would have been CW if that's the driven end.

That ~central area that looks different than the outer parts of the hex area is all that was driving your sled when it snapped.

What is the large round unrusted area that surrounds the fracture?

 

[Salvatio]

hm... looks like a cup-cone type of fracture (ductile facture?) in the centre, where it;s the last thing to split into 2.

MountainCat1M,
did you ran over some hard rocks or something like that? It looks like there's a large scratch through the wheel (rim?) which is in contact with the hex shaft. Could this impact be the cause of the failure, where the crack(s) started? If the shaft is ductile enough, the snowmobile may still travel some distance, until the c.s.a reduced so that it finally fails.

 

[metman]

metalguy,
Thanks for correcting me on my reversal of ductile/brittle zones. The improved photo's clarify and negate the transition temperature/brittle theory asw noted below. Also the cup cone comment is very relevant and the central final failure area appears somewhat fibrous all pointing to dutile failure. Additionally the periferal failure area appears to have some beach marks and the shininess of this area indicates rubbing action of the mating surfaces during fatigue. Also the unusual pattern on the shoulder of transition from hex to larger round section suggests rough machining (or?) marks which could be gross stress risers contributing to fatigue drack initiation.

Excellent photo's MountainCat. Thanks for the feedback.

Jesus is THE life,
Leonard