Proper material for driveshaft spline adapter

[E3CADCAM]

My first question on the forum... hope I'm posting in the right place.

I'm looking for recommendations on material for a spline adapter. This part is 1.3" in height, 2"dia with roughly a 4" dia flange .5 thick. There are three M12x1.75 taps around a 3" BC on the flange. This part will couple the spline end of a driveshaft to the flywheel for a dyno application. Most of the other driveline components have been mild steel, carb'ed and case hardened. This part has been spec'd for 4140 and I'm a little concerned.

Any suggestions are greatly appreciated.

 

[EdStainless]

What is the strength/hardness of its matting part?
Which do you want to fail first?

Spline on ID or OD?

My policy was to make the part that is easiest to make and replace fail first.

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Plymouth Tube

 

[redpicker]

What are your strength requriements? A 4" diameter bar can be purchased heat treated to about 100,000 minimum yield without any problem, but if you need higher strength than that, 4140 could become too brittle.

Why not use 4340? If this is a one-off part, the cost of the material shoudn't be of concern, and it should be readily available.

rp