State Of Stress in Combined Bending and Torsion:

In previous Section, we have let the effect of Bending Moment, a moment that tends to bend the axis of the beam, in terms of stresses generated by it. Other kind of moment that tends to rotate the member around its axis is called as twisting moment or torque it generate shear stresses in the member. This phenomenon is called as Torsion. Study of stresses & 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 generated at a point situated at a radial distance 'r' from the axis of the shaft is specified by

                                                    t = Tr  /J                    

Here, J is the polar moment of inertia of the cross-section of the bar.

While a member of circular section is subjected to bending moment and torques both, the maximum stresses because of both load cases are generated only in extreme fibres and hence, situated the critical section is not a problem.