The yield point (Re) or yield strength is one of the values of physical properties found through tensile tests for materials such as metals (e.g., ISO 6892), plastics, composites (e.g., ISO 527).

The yield point means the end of the elastic behavior and the beginning of the plastic behavior in the material.

Exceeding the yield point means that the material cannot return to its original form.

Parts and structures can no longer be safely used if the yield point is locally or partially exceeded.

The upper yield point (ReH) refers to the stress at which no permanent plastic deformation of the material occurs when the load is released.

If the load is released by ending the test before the upper yield point, the tensioned material can be returned to its original form.

If the material is tensioned above the upper yield point, the material cannot return to its original form even after the load has been released.

The upper yield point represents the peak value when the initial tensile graph takes a peak load and begins to drop significantly. Plastic deformation begins to occur after the upper yield point. 

When the yield point is clear, the material begins to flow and the stress decreases slightly, but the elongation increases. The aforementioned situations are only in steel with little/no alloy.

The upper yield point is defined in ISO 6892-1 as follows.

After the maximum stress has been reached, there must be a stress reduction of at least 0.5%, and subsequent flow of at least 0.05% with no tensile stress again exceeding the yield point.

The lower yield point (ReL) is the lowest stress value in the flow interval after the upper yield point.

The upper yield point is called the yield point if it does not span a wide range or is not identified and a yield occurs at a constant load.

The offset yield point is used when the yield point of the material cannot be reliably measured during the tensile test.

In this case, measure with the 0.2 offset yield point of the plastic elongation.

Offset yield is any point on the stress-strain curve and is mainly used for materials with no apparent yield strength.

The elasticity and plastic range of the material are constantly diverted, making the yield strength unclear. Offset yield 0.2% is frequently used.

0.2 offset yield (Rp0.2) is the tensile stress that the plastic elongation in the short tensile test is consistent with the elongation meter measurement length ratio (0.2%).

Cold rolled or cold molded materials have no obvious yield point. These materials are determined and specified as offset yield of 0.2%.

The 0.2% offset yield is always clearly visible in the stress-strain diagram (the upper yield point is not always the case).

The yield ratio is calculated to find the point at which material damage begins and shows how much tensile stress the material used can withstand.

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