An axis of a figure, a circle or a sphere, which is indistinct from any other axis of the figure; an imaginary line in the cross section of a beam, shaft, or the like along which no stresses occur
the internal axis of a member in bending along which the strain is zero; on one side of the neutral axis the fibers are in tension, on the other side the fibers are in compression
The surface in a member where the stresses change from compression to tension, i e , represents zero strain and therefore zero stress The neutral axis is perpendicular to the line of applied force