Bending Stresses

There is no single bending stress as such, but bending stress means stresses (both tensile at bottom and compressive at top) developed due to bending. When a load is applied to a beam at right angles to its axis, it gets deflected. The beam can be simply supported at its ends or as a cantilever, fixed only at one end.

Neutral axis of a beam is, where the stress is zero. For a beam of rectangular cross-section it is at the middle as shown in Figure 6.1(a). The load can be a single point load [Figure 6.1(b)], or point loads at many places along its axis, or a Uniformly Distributed Load (UDL)

[Figure 6.1(c)] The area above the Neutral Axis (NA) undergoes compression, while the area below the NA is under tension. Stress pattern is shown in Figure 6.2. The stress is proportional to the distance Y from the NA. In addition to compressive and tensile stress, the load also tries to shear the beam at the ends.

Flexural Strength

Flexural strength is same as the tensile strength for homogeneous materials. Due to various defects in materials, some local weakness is caused. When bending occurs, a material may fail at a stress lesser than its tensile strength, if there is a large flaw at the extreme fibre. Stress caused by bending is known as flexural or bending stress. The formula to calculate this strength is given in the following section by Equation (6.1).

Bending Moment

In simple terms, a bending force is a force that causes bending to any part. Bending moments occur when a bending force is applied at a given distance away from a fixed reference point.