What is the stress that causes yielding called?

The stress that causes yielding is referred to as yield stress. Yield stress defines the point at which a material begins to deform plastically, meaning that it undergoes permanent deformation rather than returning to its original shape once the load is removed. This critical value is an essential parameter in material science and engineering because it helps engineers understand how materials behave under different loading conditions.

When a material is subjected to stress below its yield stress, it will return to its original form upon removal of the load, exhibiting elastic behavior. However, once the stress exceeds this yield point, the material will not only deform but will also retain that deformation even after the external forces are no longer applied. Recognizing yield stress helps in selecting appropriate materials for structural applications to ensure safety and functionality.

The other terms provided encompass different ideas within the domain of material mechanics and failure analysis. Ultimate stress, for example, refers to the maximum stress a material can withstand before failure, while shear stress is a measure of how much force is acting parallel to a given surface. The elastic limit is closely related to yield stress, as it is the maximum stress that can be applied without causing the material to yield, but yield stress is the more precise term for the onset of permanent deformation.