In fact, I was considering a shaft with a screwed coupling on the end. The assembly is used to agitate a fluid. I needed to know, if the agitator's rotation sense is inverted, if the coupling would unscrew. This problem has been solved, however, by rotating the shaft always the same sense.
But...
I need to know how much torque is required to unscrew a nut or a screw.
Is there a standard ratio which is working for every case? I mean, I think it is closely related to the tightening torque, so it should always be something like 50% of the tightening torque.
I could calculate that but I'm...
The only valuable information I ever found on shear stress is
Sy(shear) = 0.577 * Sy(tension)
Ref: Mechanical Engineering Design, 4th ed., p. 234
Shigley & Mitchel
McGraw Hill
