Diagram shows an aluminum shaft A B marked 1 and a brass shaft B C marked 2 with a flange in between at B. Both the shafts are centered on the central axis x. The shaft is supported at A and C. A torque T is applied at B. The radial and longitudinal lines are shown on the shaft. The deformation of the shaft is shown with a counterclockwise segment at B of angle phi subscript B, angle of twist. A caption to the bottom left of the shaft 1 reads: phi subscript 1 = phi subscript B. A caption to the bottom left of the shaft 2 reads: phi subscript 2 = negative phi subscript B.

The relationship between internal torque T in a shaft and its angle of twist ϕ is given by:

ϕ=TLJG

Therefore, the torque-twist relationships for shafts (1) and (2) can be expressed as:

ϕ1=T1L1J1G1    andϕ2=T2L2J2G2