When a machine member is subjected to torsion, the torsional shear stress set up in the member is

The torsional shear stress in a circular shaft varies linearly from the centre to the outer surface of the shaft.

According to the torsion equation:

τ = (T × r) / J

Where:
τ = Torsional shear stress
T = Applied torque
r = Radial distance from the centre
J = Polar moment of inertia

Since the stress is directly proportional to the radial distance (τ ∝ r):

• At the centroidal axis (r = 0): Shear stress is zero.
• At the outer surface (r = R): Shear stress is maximum.

Therefore, the correct statement is that the torsional shear stress is zero at the centroidal axis and maximum at the outer surface of the member.