Breaking point of rod under torsion

[saim_]

A steel rod like the one shown in the attached picture is fixed from one side and increasing amount of torsion is applied on the other side. Eventually, the rod breaks. Now it will obviously break from one of the two chamfered locations, where the middle portion of the rod with the smaller diameter increases to turn into the larger diameter ends, due to the stress concentration effect. But from which of the two sides will it break; the fixed end or the movable (rotating) end?

 

[saim_]

?

 

[Claws]

Everything else being equal, the rod doesn't 'know' which end is having torque applied and which is fixed, thus it can break at either end.

 

[cloa513]

http://en.wikipedia.org/wiki/Torsion_(mechanics )
It will break at the turn end because its not infinitely stiff (if infinitely stiff you are correct Claws). The rotated end will have some rotation so greater shear stress.

 

[Studiot]

greater shear stress.

Don't you mean shear strain?

 

[AlephZero]

The rotated end will have some rotation so greater shear stress.

If you explain why you think that statement is true, we might be able to explain why you are wrong.

The behaviour of the rod does not depend on the coordinate system you use to describe it.

For any situation in mechanics where rotations are important, you need to be clear about the difference between large rotations and large strains.