Failed Splined Shaft, Interesting Fracture Zone
Failed Splined Shaft, Interesting Fracture Zone
(OP)
Here's an interesting failure of a small splined shaft that I'm currently investigating.
The Engineer's (hired by the OEM) final report simply stated that the incorrect material and heat treatment had been used.
The end-user has asked for a more detailed report along with recommendations.
There's a lot happening on that fracture surface.




The Engineer's (hired by the OEM) final report simply stated that the incorrect material and heat treatment had been used.
The end-user has asked for a more detailed report along with recommendations.
There's a lot happening on that fracture surface.









RE: Failed Splined Shaft, Interesting Fracture Zone
RE: Failed Splined Shaft, Interesting Fracture Zone
What I find really interesting are the radial cracks running inwards, starting at the top lands of the teeth, the last images shows this.
I would have expected those cracks to start in the corners of the root profiles.
RE: Failed Splined Shaft, Interesting Fracture Zone
RE: Failed Splined Shaft, Interesting Fracture Zone
Material is 4140.
There are multiple failure modes occurring. Quite a few areas are showing signs of fatigue.
Unfortunately the uploading of images here isn't working out too well as the image quality is being significantly reduced
RE: Failed Splined Shaft, Interesting Fracture Zone
You might find this article of use http://www.maintenancetechnology.com/2012/07/failu...
I think it's a rotating bend failure with its multiple radial cracks but we could do with more information about the spline in terms of service loads and the length of time it's been in operation.
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
RE: Failed Splined Shaft, Interesting Fracture Zone
http://www.binsfeld.com/userfiles/filemanager/226/
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
RE: Failed Splined Shaft, Interesting Fracture Zone
RE: Failed Splined Shaft, Interesting Fracture Zone
I find it interesting that around the crack a slight corrosion is present.
possible suggesting a heat treat crack make have been present.
causing the ultimate failure as suggested by others.
I notice to, there is very little wear on the spline tooth flanks.
so no evidence of over load or wear fatigue. just my thoughts.
I know from my experience, 4140 if not harden and tempered correctly
will easily crack.
it would be interesting to do a met lab on a new finished part.
Mfgenggear
RE: Failed Splined Shaft, Interesting Fracture Zone
Application? Pure torsion? Any bending? Load reversals? Torsional vibration? Also which section of the shaft length is subjected to the torque - does the failure coincide with the end of a female splined member?
je suis charlie
RE: Failed Splined Shaft, Interesting Fracture Zone
The purpose of the post wasn't a "how did this happen" type of enquiry.
The intent was to simply show those interested in the topic, an example showing (as corypad has correctly pointed out) the fracture zone of a reversed torsional fatigue failure.
RE: Failed Splined Shaft, Interesting Fracture Zone
Just to expand a little on that rotational fatigue, if you look at the second link I posted which also shows a similar failure on figure 4, it goes on to say that the angle of the fracture face relative to the axis of the shaft indicates whether there was a dominant bending force or tensile force involved.
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
RE: Failed Splined Shaft, Interesting Fracture Zone
Given the shaft cross section, relative spline tooth size, material properties, and condition of the spline tooth flanks, I don't see how the shaft could have failed in torsional fatigue (from either unidirectional or fully reversing load cycles). Even a combined torsional/bending LCF failure at the location shown would have produced some distress in the adjacent spline tooth flank surfaces.
RE: Failed Splined Shaft, Interesting Fracture Zone
Beachmarks in the last image suggest torsional fatigue originating at the outer edge.
If the crack at "A" (a low stress area) was produced during heat treatment (which I doubt), it may have reduced the torsional strength of the shaft, enabling the fatigue failure, but I don't think the failure progressed from there.
je suis charlie
RE: Failed Splined Shaft, Interesting Fracture Zone
RE: Failed Splined Shaft, Interesting Fracture Zone
The pictures is certainly becoming much clearer.
The groove on the LH side is as a result of events that occurred post failure.
RE: Failed Splined Shaft, Interesting Fracture Zone
je suis charlie
RE: Failed Splined Shaft, Interesting Fracture Zone
RE: Failed Splined Shaft, Interesting Fracture Zone
RE: Failed Splined Shaft, Interesting Fracture Zone
Would it be possible to get more details of the associated components and how they were constrained?