Torque Test On Extension - Torque Load Depending of the Length??? 1

[vieurals]

Hello,

I made some torque test to failure to some extension. These extension are made of 4037 steel and heat treated.
At a 47-51 HRc, these extensions brake at a good load level. But I have a problem with the failure mode:
- the 1.5" long breaks ductile,
- the 3" long breaks ductile,
- the 6" long breaks semi-ductile,
- the 10" long breaks brittel.
WHY? Is the lenght of the extension a factor of a part breaking ductile or brittel? If yes, why?
Note: The extension I am testing have a special shape on the male square. They have all (1.5", 3", 6" and 10") the same shape with a low section at the end of the shank, before starting the male square. But this section is the exact same for all sizes.
Thanks for any help.

 

[BillPSU]

My guess would be that with the longer parts the angle of twist was higher and the failure cause was shear not bending while the shorter parts failing in bending.

 

[EdStainless]

Is the torsional movement to failure the same for all? Say in degrees of wrap/inch of length? How about recording load/wrap?
I'll bet not. The longer ones are not staying straight as they are torqued and they are failing in a different loading mode.

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Corrosion never sleeps, but it can be managed.

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