State of Stress In Combined Bending and Torsion:

Here, we have considered the effect of Bending Moment, a moment that tends to bend the axis of the beam, in terms of stresses generates through it. Another type of moment that tends to rotate the member about its axis is known as twisting moment or torque it produces shear stresses within the member. This phenomenon is known as Torsion. Study of stresses and strains because of torsion is extremely difficult except for members with circular (solid or hollow) cross-section. If a torque of magnitude T is applied on a circular bar, the shear stress generates at a point located at a radial distance 'r' from the axis of the shaft is given by

 τ = Tr /J

here in the equation, J is the polar moment of inertia of the cross-section of the bar.

While a member of circular section is subjected to both bending moment and torque, the maximum stresses because of both load cases are produced just in extreme fibres and thus, locating the critical section is not a problem.