Axle failure, thoughts 9

[4130 metalworks]

Hi, I'd like to get the groups thoughts on why this axle shaft failed and how to best go about testing the rest of them. The shaft is heat treated 4140, from machining the splines the hardness seems to be the outer 2-3mm.
Unfortunately I don't have much information from the manufacturer to go with

The vehicle is reasonably heavy but low powered and was travelling at speed when this happened

Thanks in advance for any help

 

[enginesrus]

And what did a hardness test say?

 

[ShataCastings]

1. Check whether the hardness is in correct range.

2. Take a torsional rigidity text in a simulated aseembly condition (if test cost is not in consideration), compare result with theoretical value.

 

[MechyMarco]

6k!? What is the test scope? 1k to slice and do a simple case depth survey of a couple slices should be more than enough. Do one far away from fracture surface and one right beside.

Friction could have heated it up to austenitizing temp and then you end up with brittle surface to fracture and start cracking.

Looks like fatigue on bigger OD fracture donut with rapid fast fracture failure of centre circle.

Replace with 4330V 150ksi min yield and Gas FNC. Should be invincible compared to this. Cost increase of material is not much. Gas FNC is cheap.