Question

Difference between centroidal axis and neutral axis

Answer 1

Neutral axis is the axis at which strain (and consequently stress) is zero when the beam is subjected to bending. Neutral axis is perpendicular to the plane of the loads. Centroidal axis is any axis that passes through the centroid of the cross section. There can be an infinite number of centroidal axes. Two of these are the principal axes. Major principal axis is the centroidal axis about which the second moment of area is the largest (out of all the possible centrodal axes) and minor principal axis is the one about which the second moment of area is the least.If stresses are linear and within the yield stress, neutral axis passes through the centroid (that is, neutral axis is one of the centroidal axes).If stresses are greater than the yield stress, and if all fibres across the depth of the section have yielded (fully plastic section), the neutral axis is the equal area axis (an axis perpendicular to the plane of loads that divides the cross section area into two equal halves). Equal area axis may be a centroidal axis, but depending on the shape, equal area axis may not pass through the centroid.