Ok I will add to above and see if I can get it
The high contact forces between the splined shaft and the coupling caused an (a) extreme tension
cycle(s) on the shaft when trying to displace in or out of the coupling(over a slight bump, lean, etc..). This high tension combined with all the small cracks that were propagating due to fatigue in bending and rotation, caused the material to prematurely "neck",dereasing the effective x-sectional area and causing it to fail as depicted. This shaft was designed for rotation to transfer torque, bending to support the car, and tension from when the shaft displaces in and out and the contact forces between the splines under rotation work against it. Maybe the tension from contact forces was not modeled right during design or adequate assumptions weren't made(doesnt work since the other side is ok), or lube ran low (sounds good to me) causing too much contact force which increases tension while the spline plunges in and out of the coupling, or...assumptions go on forever.
I thought it might be due to a trigger happy pit crew spinning the nut on too tight, but after a Q&D calc.I came up with an outrageous amount of torque needed to cause a tension failure by itself assuming a 2 in. dia, and if it was going to fail due to overtightening it would have failed in the threads not the spline.
The splined end is all distorted from when the the shaft broke and pulled out of the coupling at a high RPM.
That's all I can think of this late without a picture of the assembly...especially considering it's spring break for me and I am not supposed to think about this type of stuff this week.
Are you telling us everything? Did this part fail in regular race conditons or is there more to this failure, like a spin out?
A question for you Dave,
What kind of a correlation can you give between HRC and Brinell? I do not own a materials handbook so I think in terms of Brinell since I can quantify properties from it instead of it being it's own scale like HRC.
Kris
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