Shear and Torsion

Shear: A force (or stress) which tends to slide the material on one side of a surface relative to the material on the other side of the surface in directions parallel to the surface is termed a shear force (or shear stress).

Torsion: A moment that is applied about the longitudinal axis of a member is called a torque which tends to twist the member about this axis and is said to cause torsion of the member.

For a circular shaft or a closed circular section member subjected to torsion:

• Plane circular cross sections remain plane and the cross sections at the ends of the member remain flat.
• The length and the radius of the member remain unchanged.
• Plane circular cross sections remain perpendicular to the longitudinal axis.

For a non-circular section member or an open section member subjected to torsion:

• Plane cross sections of the member do not remain plane and the cross sections distort in a manner which is called warping. In other words, the fibers in the longitudinal direction deform unequally.