Diagram shows a shaft A B with aluminum segment marked 1 of length 1,500 millimeters inside which is a brass shaft marked 2 of length 1,000 millimeters. Both the shafts are centered on the central axis x. The shaft is supported at A and C. A flange B is in between the shafts 1 and 2 on which a torque T is applied. An internal torque T subscript 1 is applied on the post towards A and an internal torque T subscript 2 is applied on the post towards C.

Draw a FBD around flange B.

Assume positive internal torques T1 and T2 in shafts (1) and (2).

The equilibrium equation obtained from this FBD is:

MX=-T1+T2+T=0        T1-T2=T