Elastic Hysteresis is the difference between the strain energy required to generate a given stress in a material, and the material's elastic energy at that stress. This energy is dissipated as internal friction (heat) in a material during one cycle of testing (loading and unloading).
When mechanical test data is plotted on a stress/strain curve, a material exhibiting elastic hysteresis will display one path during the loading phase of the test, and a different path during the unloading phase. The two paths will clearly diverge due to hysteresis loss (energy loss in the form of heat), with the area between the curves representing the energy dissipated.
Different materials display varying degrees of elastic hysteresis. Hard metals, for example, display less hysteresis than high-elongation materials such as elastomers. High-speed testing tends to generate the most noticeable results, as forces on the specimen will be greater over a shorter elongation, followed by a much quicker drop in load when unloading over that same elongation.
The damping capacity of a material can be found by dividing a material’s elastic hysteresis by its elastic deformation energy. By comparing the elastic hysteresis and damping capacities of different materials, engineers can make sure they are using a material appropriate for their intended application. For instance, a rubber with a more pronounced hysteresis is able to disperse a large amount of energy and might be a good choice for absorbing vibrations or sound.