Bending Stress and the Flexure Formula

Bending Stress and the Flexure Formula

Imagine taking a simple, straight rubber eraser and bending it with your fingers. As you apply that force, the top surface visibly squishes together, while the bottom surface stretches out. This simple observation is the key to understanding bending stress in engineering.

Let's look closely at a segment of this bent beam. The top fibers are in compression, getting shorter. The bottom fibers are in tension, getting longer. But notice the magic in the middle: there is a line that neither stretches nor compresses. We call this the Neutral Axis.

Because the deformation changes smoothly from squished at the top to stretched at the bottom, the internal stress does too. It is zero at the neutral axis and reaches its maximum values at the very outer edges of the beam.