Angle of Twist in Torsion
Angle of Twist in Torsion: Consider a circular shaft subjected to torque. It is assumed that plane sections perpendicular to the axis remain plane even after loading. Isolating an element form such a member
A line segment in the surface of the shaft, AB is initially parallel to the axis of the shaft. Upon application of torque, it occupies a new position AB'. The segment OB now occupy the position OB'.
This equation gives the relative angle of twist between any two sections of a shaft distance dx apart. To find the total angle of twist φ between any two sections 1 and 2, all rotations of all elements between 1 and 2 should be summed up