Pure bending is a condition of stress where a bending moment

Bending Moment

A bending moment exists in a structural element when a moment is applied to the element so that the element bends. Moments and torques are measured as a force multiplied by a distance so they have as unit newton-metres , or pound-foot or foot-pound...

 is applied to a beam without the simultaneous application of axial, shear

Shear stress

A shear stress, denoted \tau\, , is defined as the component of stress coplanar with a material cross section. Shear stress arises from the force vector component parallel to the cross section...

, or torsional forces

Deformation (mechanics)

Deformation in continuum mechanics is the transformation of a body from a reference configuration to a current configuration. A configuration is a set containing the positions of all particles of the body...

.
Pure bending is the flexure (bending

Bending

In engineering mechanics, bending characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element. The structural element is assumed to be such that at least one of its dimensions is a small fraction, typically...

) of a beam under a constant bending moment (M) therefore pure bending only occurs when the shear force (V) is equal to zero since dM/dx= V.

KINEMATICS OF PURE BENDING

1.In pure bending the axial lines bend to form cirumfrential lines and transverse lines become straight and radial lines.

2.The axial lines which does not bend called neutral axis.