Calculating Max Torque and Shaft Twist for Socket Wrench

[confusedkarl]

Homework Statement

The steel shaft of a socket wrench is 18mm diameter and 450mm long. If the allowable shear stree is 70 MN/m^2.

Homework Equations

i) What is the maximum permissible torque T that may be extered with the wrench?
ii) Through what angle (theta) in radians will the shaft twist under the action of the maximum torque?
iii) Through what angle (theta) in degrees will the shaft twist under the action of the maximum torque? G = 80 GN/m^2

The Attempt at a Solution

Im pretty happy how to do the radians to degress conversion but haven't a clue on the forumulae or process I need for i and ii =(

 

[gabbagabbahey]

A good starting place would be to examine the relationship between the torque on the wrench, and the shear stress it imparts.