Crankshaft Failure Mode Analysis

[pbiebach]

I have a broken crankshaft where I am trying to determine the cause of failure.

here are some pics of the cracked surface.
http://i54.tinypic.com/2exvfc9.jpg
http://i52.tinypic.com/10z9zzc.jpg
what is known:
1) the crank shaft was under very light load at time of failure

What do you guys think?

[brewnog]

Fatigue. Crack propogation originating from the oil drilling shown.

[pbiebach]

Thanks for the reply, could you explain how you are able to tell this?

[brewnog]

1) Beach marks clearly visible showing nucleation site is likely somewhere around the fracture face on the drilling.

2) 90% of the time they fail like that.