Yield Point

Definition - What does Yield Point mean?

A yield point is the stress level at which a metal or other material ceases to behave elastically. The stress divided by the strain is no longer constant. The point at which this occurs is known as the yield point. A yield point, in mechanical engineering, is the 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.

Knowledge of the yield point is vital when designing a component, since it generally represents an upper limit to the load that can be applied. It is also important for the control of many materials' production techniques such as forging, rolling, or pressing. In structural engineering, this is a soft failure mode which does not normally cause catastrophic failure or ultimate failure unless it accelerates buckling.

Yield point is typically measured in pounds per square inch (psi) or Newtons per square meter, also known as pascals (Pa).

Corrosionpedia explains Yield Point

The yield point marks the end of elastic behavior and the beginning of plastic behavior of a material. 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. 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.

When a yield point is not easily defined based on the shape of the stress-strain curve, an offset yield point is arbitrarily defined. The value for this is commonly set at 0.1 or 0.2% of the strain. High-strength steel and aluminum alloys do not exhibit a yield point, so this offset yield point is used on these materials.

Yield point is an important value to consider when selecting a material for design and building applications, particularly when there are significant loads or stresses being applied. For example, when building a structure with steel beams, it becomes necessary to know how much stress and weight the beams can handle in order to build a sound structure. Yield point is also a key factor in the processing of metals, which typically involves exposing the metal to high stresses during the manufacturing process.

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