ASTM E646 describes the determination of the tensile strain-hardening exponent (n-value) of metallic sheet materials exhibiting a continuous stress-strain curve in the plastic region. The metallic samples tested by this method should have thicknesses of at least 0.005 in (0.13 mm) but not greater than 0.25 in (6.4 mm). The stress-strain data is obtained in a uniaxial tension test. The displacement or strain is applied in a continuous and rate-controlled manner while the normal tensile load and strain are monitored.
The strain-hardening exponent quantifies the increase in hardness and strength caused by plastic deformation. This method is useful for estimating the strain at the onset of necking in a uniaxial tension test. Please note that the n-value may vary with the displacement rate or strain rate used, depending on the metal and test temperature.
Before conducting ASTM E646, it is important to read the entire specification in the relevant ASTM publication.