The property of certain materials that enables them to return to their original dimensions after an applied stress has been removed. In general, if a stress is applied to a wire, the strain will increase in proportion (see OA on the illustration) until a certain point called the limit of proportionality is reached. This is in accordance with Hooke’s law. Thereafter there is at first a slight increase in strain with increased load until a point L is reached. This is the elastic limit; up to this point the deformation of the specimen is elastic, i.e. when the stress is removed the specimen returns to its original length. Beyond the point L there is permanent deformation when the stress is removed, i.e. the material has ceased to be elastic and has become plastic. In the plastic stages individual materials vary somewhat; in general, however, at a point B there is a sudden increase in strain with further increases of stress—this is the yield point. Beyond the point C, the breaking stress, the wire will snap (which occurs at point D).

Elasticity.