Yield point, also known as yield strength or elastic limit, is an important value to consider when selecting a material for design applications, particularly when there are significant loads or stresses being applied. It is also a key factor in the processing of metals, which typically involves exposing the metal to high stresses during the manufacturing process. In design applications, yield point is often used as an upper bound for the allowable stress that can be applied. It is especially important in material applications that require precise dimensional tolerances to be maintained in the presence of high stresses and loads.

Most matter has a predictable and measurable relationship between the stress applied and the resulting strain, or deformation, that occurs. This relationship can be plotted in a stress-strain curve, which generally shows the yield point. The yield point defines the stress that will cause an onset of permanent deformation to occur in a material.

A material that is exposed to tensile, or pulling, stress will experience strain and elongate, resulting in a dimensional change. At low levels of stress, this strain can be reversible. This means that, after the stress is removed, the material may return to its original dimensions. This is known as elastic strain.

When the applied stress exceeds the yield point, a material will deform to the point where it can no longer return to its original dimensions once the load is removed. This is referred to as plastic deformation or plastic strain, which is the result of permanent displacement of atoms within the material. Yield point is typically measured in pounds per square inch (psi) or Newtons per square meter, also known as pascals (Pa).

Yield point is most common in ductile materials. Ductility is a measure of how much deformation occurs before complete failure. These materials, such as steel, can experience a significant amount of plastic deformation before such a breakdown. Brittle materials, such as concrete and glass, have very low elasticity and usually exhibit little or no plastic deformation before failure. For this reason, brittle matter does not have a yield point, and tends to fail immediately after a critical value of stress has been exceeded.