Question

What Causes Elastic Hysteresis?

Answer 1

1. 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.
2. This energy is dissipated as internal friction (heat) in a material during one cycle of testing (loading and unloading)
3. 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.
4. 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.
   
5. A string with the load connected can be used to demonstrate the effect. It will stretch and get longer if the top of the piece of string is suspended on a hook and a little weight is put on the bottom of the string one at a time.
6. The forward curve in the graph corresponds to the string stretching when more weights are added to it because the force exerted by the weights on the string is rising.
7. The backward curve occurs when the string is shrinking and the force is lowered as each weight is removed.
8. As the weights are removed from the band, each weight that created a given length while loaded compresses less, resulting in a somewhat higher strain for the same amount of stress, as we can see in the graph.
9. The gap between the strain energy required to achieve certain stress in a material and the material's elastic energy at that tension is known as elastic hysteresis.
10. During stretching, the differential energy is released as internal resistive heat energy in the material.