• The cross section of a straight beam remains plane when the beam deforms due to bending. This causes
tensile stress on one portion of the cross section and compressive stress on the other portion. In between
these portions, there exists the neutral axis which is subjected to zero stress.
• Due to the deformation, the longitudinal strain varies linearly from zero at the neutral axis to a maximum
at the outer fibers of the beam. Provided the material is homogeneous and linear elastic, then the stress
also varies in a linear fashion over the cross section.
• The neutral axis passes through the centroid of the cross-sectional area.This result is based on the fact that
the resultant normal force acting on the cross section must be zero.
• The flexure formula is based on the requirement that the resultant internal moment on the cross section is
equal to the moment produced by the normal stress distribution about the neutral axis.