Definition - What does Yield Stress mean?
Yield Stress, also known as yield strength, is the maximum stress that can be applied to a material without causing plastic deformation. It is the stress at which a material will exhibit specified permanent deformation. In engineering structural design, yield strength is very important, e.g., when designing a component, it must support the force incurred during use, and the component must not deform. In design applications, the yield strength is often used as an upper limit for the allowable stress that can be applied.
Petropedia explains Yield Stress
The value of yield strength is important in the construction of structures, since the structures are able to perform in the elastic region under normal servicing conditions. However, when faced with unexpected impact loads such as explosions, fires or natural disasters such as earthquakes, etc., the plastic region of the material becomes crucial, as a large portion of the energy being absorbed by the materials under such circumstances is mainly contributed by the plastic region. As such, having a higher toughness implies that the materials are able to withstand such unforeseen loading for a long period of time so as to allow more time for safety measures to be carried out. Prior to the yield point, a material will deform elastically and return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible.
In general, yield strength increases with strain rate and decreases with temperature. When the latter is not the case, the material is said to exhibit yield strength anomaly, which is typical for super-alloys. Yield strength anomaly is also referred to as yield stress anomaly.