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What is yield strength?

Yield strength is the term used to refer to an indication of the maximum stress that can be developed in a substance without causing it to plastically deform. Yield strength is the stress point at which a material becomes permanently deformed, providing a useful approximation of that material’s elastic limit.

Before reaching the yield point, the material will deform elastically, but it will always revert to its original shape upon removal of the applied stress. Once the yield point is exceeded, a small fraction of the deformation experienced will become permanent and irreversible.

An understanding and knowledge of a material’s yield strength is vital when designing and manufacturing components, as it represents the upper load limit for that substance. Consequently, yield strength is very important in the production processes used for many materials such as pressing, rolling, or forging.

Yield strength typically decreases with temperature and increases with strain rate. With the former, when this is not the case, the substance is said to exhibit “yield strength/yield stress anomaly”, which is often seen in super-alloys. Materials that fall into this category are often preferred for applications where high strength is required at high temperatures.

The yield strength of a material is especially important in the construction of buildings that may be exposed to unexpected impact loads such as earthquakes. Under these stresses, the plastic region of the substance becomes vital, as much of the energy that it absorbs is largely contributed by the plastic region. Therefore, a material’s ability to withstand unforeseen forces and loading for a longer period of time will allow longer for safety measures to be implemented.