How is ultimate tensile stress calculated from a tensile test?

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In a tensile test, the ultimate tensile stress (UTS)—also referred to as tensile strength—is calculated by dividing the maximum load a material supports during the test by its initial cross-sectional area.12

As a sample is stretched during the test, it may undergo plastic strain. If the test continues past the point of yielding, the load reaches a maximum value as the material begins to localize strain and form a constricted region known as a neck. This maximum load value is the figure used in the calculation to determine the material's ultimate tensile stress.2