yield point

Stress-strain curveAs a material is stretched with increasing stress, it suffers strain (a fractional change in length). As stress increases from zero, the strain on the material increases linearly until the proportional limit at A. From A to B the material enters a new regime, and at the yield point B the material will not return to its original state when the stress is removed. The material has been permanently deformed. If the stress is removed at point C, for example, the material will have a permanent set; that is, the strain is not zero even when there is no stress. At D the material is at its ultimate strength, and, even if the force is reduced, fracture occurs at E.

yield point, in mechanical engineering, load at which a solid material that is being stretched begins to flow, or change shape permanently, divided by its original cross-sectional area; or the amount of stress in a solid at the onset of permanent deformation. The yield point, alternatively called the elastic limit, marks the end of elastic behavior and the beginning of plastic behavior. When stresses less than the yield point are removed, the material returns to its original shape. For many materials that do not have a well-defined yield point, a quantity called yield strength is substituted. Yield strength is the stress at which a material has undergone some arbitrarily chosen amount of permanent deformation, often 0.2 percent. A few materials start to yield, or flow plastically, at a fairly well-defined stress (upper yield point) that falls rapidly to a lower steady value (lower yield point) as deformation continues. Any increase in the stress beyond the yield point causes greater permanent deformation and eventually fracture. See deformation and flow.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Erik Gregersen.
Citation Information
Article Title: yield point
Website Name: Encyclopaedia Britannica
Publisher: Encyclopaedia Britannica, Inc.
Date Published: 03 November 2026
Access Date: November 13, 2026