Neutral Layer and Neutral Axis
In the beam or cantilever, there is one layer which retains the original length of it even after bending. So in this layer tensile stress and compressive stress both are not set up. This layer is called as neutral layer.
Neutral axis is line of intersection of neutral layer with any normal section of beam. If cutting plane YY is passed across length of beam, the line NA becomes line of intersection of neutral layer and normal section of the beam. Thus, NA is the neutral axis. As no bending stress is set up in neutral layer, the same is true to neutral axis, that is, no bending stress is set tip in neutral axis. It will be proved that neutral axis passes through C.G. of section of beam or cantilever.