Drive shaft failed during service 2

[goodbadgood]

Hi

One of our drive shaft is failed during service at the area where splines are located. the material is nickel alloy. The fracture surface is oriented at 45 degrees. the chemical and mechanical properties are perfect. some ratchet marks were also observed at spline root while at one location at spline root crack was also observed. Deformation marks were also observed at the spline where fracture has occured by looking at the fracture orientation can we say that the fracture is torsional overlaod failure with fatigue crack initiation? i have uploaded the side view of the shaft. Kindly provide your feedback.

 

[goodbadgood]

See attached picture

 

[desertfox]

Hi

Well to see whether its a fatigue failure we need to see the fracture surface at 90 degrees the the picture you have posted but yes it looks like torsional fatigue from your description and the 45 degree fracture line shows it failed along the principle stress planes.
This site might help:-

http://www.maintenancetechnology.com/2012/07/failure-analysis-of-machine-shafts/

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[RolMec]

Hello,
assuming a very good fatigue strength of the material itself, I'd like to point to something that shows up in your picture:

The fracture imo initiated at a place where the counterpart (hub?) is not only able to move as such but to achieve a chafing or rubbing pattern. The root cause of the failure (crack initiation) seems to be wear, and the fatigue (if present) and final overload (of a reduced sectional area) are derived effects.
So, apart from a pic of the fracture surface, could you pls. show how the counterpart looks like? Furthermore, a check for spline-to-spline match and effectivity of the (if any) hub fixation would be of interest.
Regards


Roland Heilmann
Lpz FRG

 

[tbuelna]

From the picture provided it appears there was local edge loading at the mating tooth tips/roots due to misalignment. Does not appear to be a fatigue problem since there is no damage on the adjacent tooth surfaces. There is fretting and local plastic deformation of the tooth tips/roots at the fracture location, but the other tooth surfaces have no evidence of any wear.

 

[goodbadgood]

thanks guys for your valuable insight in this thread.

 

[mfgenggear]

Yes agree upon the above advice given. an Inspection and record of both splines are in order. against the specification blue print requirements. lead , involute error, and pitch diameter runout. could have contributed to premature failure. and the type of misalignment would also be helpful.