crankshaft failure

It looks to be a combination of torsional/bending fatigue. I say this because of the 45 deg. failure and the progressional wavey features.

What is the operation of this pump? Is it off/on a lot?

How accurately was the alignment to the motor done?

Your third and fourth picture are pretty fuzzy - would it be possible to get better close-ups, and also to get a close-up of directly looking down the axis of the shaft?

Here are a couple articles that may be of interest to you -

http://www.asminternational.org/pdf/spotlights/jfap0502p011.pdf

http://ammtiac.alionscience.com/pdf/deskref.pdf

I shall send you as a private message my e-mail so that you can send me the pictures so that I can look a t details better.

At 1st view is started in a high stress area so that either a material defect or a manufacturing mark could be the reason.

The dark staining along the "rift valley" that crosses the fracture transversely (most clearly visible in out of focus photos 3 and 4) would indicate to me a preexisting imperfection from which the fatigue failure developed.

That staining did not happen in a short moment, And it is not at all on the balance of the fracture surfaces. Under a microscope will probably show evidence of scale and or decarb, showing it to have existed as an opening or crack prior to last heat treat.

But using the data that we have, why is there a curvilinear pathway of stained material across an internal transverse section of this failed part?

Answer that and you answer all.

Workmanship. Thats the root cause.

Yes, of course it ultimately failed in fatigue and in torsion, thats how it was employed. but the cause of that failure will likely be shown in the explanation for that staining.

To get better macro photos with ones digital camera, make sure that the lense is racked al the way back to its widest angel, tehn put it on macro. Macro doesn't focus when the lense elements are racked out to telephoto.

my 2 cents

milo