Max Torque for Steel Torsion Bar - Calculate Now

[2slowtogofast]

A cylindrical torsion bar made of steel (E = 209 GPa) with diameter of 20mm. The allowable shear stress for this material is 200 MPa what is the max torque that can be safely applied to this bar.

$$\tau$$ = Tr / J

$$\tau$$ = shear stress
T = torque
r = radius
J= second polar moment of area

I was thinking of using this formula but I would not have used E = 209GPa in my solution is this wrong? If so could somebody point me in the right direction.

 

[PhanthomJay]

You are correct, you don't need E; the max torque is a function of the max stress and the geometry of the section. It is not related to the elasticity modulus. You would need the shear modulus G if you wanted to calculate the amount of rotation, not the stress.

 

[2slowtogofast]

thanks