Stress-Strain Curve for Rubber

When you stretch a rubber cord to a few times its natural length, it returns to its original length after removal of the forces. That is, the elastic region is large and there is no well defined plastic flow region. Substances having large strain are called elastomers. This property arises from their molecular arrangements. The stress-strain curve for rubber is distinctly different from that of a metallic wire.

Firstly, there is no region of proportionality. Secondly, when the deforming force is gradually reduced, the original curve is not retraced, although the sample finally acquires its natural length. The work done by the material in returning to its original shape is less than the work done by the deforming force. This difference of energy is absorbed by the material and appears as heat. This phenomenon is called elastic hysteresis.

Elastic hysteresis has an important application in shock absorbers. A part of energy transferred by the deforming force is retained in a shock absorber and only a small part of it is transmitted to the body to which the shock absorber is attached.