Bending stress is a form of stress seen when loads are applied perpendicularly to an object, forcing it to deflect under the load. The degree of bending an object will tolerate before it becomes permanently deformed varies, depending on the construction materials, size, and other variables. Testing products for their bending stress tolerances is an important part of safety testing, especially for things like elements being used in construction, where deformation under stress could lead to structural collapses and fatal consequences.
Many types of objects can bend, with a simple example of bending stress being seen in many closets around the world. Closets typically have one or more rods supported at either end. When these rods are loaded up with clothing, shoe racks, and other belongings, they can deflect under the weight of the load. A sturdy hanging rod will bounce back into position when the load is removed. Eventually, the load can become so high that the rod is permanently bent or snaps as a result of the stress.
During bending, several different physical phenomena are occurring. As an object bends, one side becomes compressed because it is being partially folded under the weight of the load. The other side becomes stretched. Repeated sessions of bending, followed by a reduction of the load can result in cracks, creases, and other problems caused by the stretching and compression. This can weaken the object and make it more at risk of permanent deformation or breakage in the future, even under the same load.
People sometimes use this characteristic to their advantage. For example, some products come packaged in containers with tops designed to be removed with the use of bending stress. During transit, the top can bend and flex under stress. Once someone is ready to use it, the top is bent back and forth several times, causing it to weaken and then snap off. People can also use stress to bend or snap objects of varying lengths for projects.
Various formulas describing bending stress can be used in stress calculations. These formulas take the weight and type of materials involved under account to determine when they will cross the threshold between being able to bend and recover and permanent damage. Engineers and architects use these formulas while designing buildings, equipment, and other projects, developing safe tolerances to ensure that stress will not permanently damage the finished product.