Strain hardening exponent
The strain hardening exponent, usually denoted, is a measured parameter that quantifies the ability of a material to become stronger due to strain hardening. Strain hardening is the process by which a material's load-bearing capacity increases during plastic strain, or deformation. This characteristic is what sets ductile materials apart from brittle materials. The uniaxial tension test is the primary experimental method used to directly measure a material's stress–strain behavior, providing valuable insights into its strain-hardening behavior.
The strain hardening exponent is sometimes regarded as a constant and occurs in forging and forming calculations, as well as the formula known as the Hollomon equation, originally posited as:
where represents the applied true stress on the material, is the true strain, and is the strength coefficient.
The value of the strain hardening exponent lies between 0 and 1, with a value of 0 implying a perfectly plastic solid and a value of 1 representing a perfectly elastic solid. Most metals have an -value between 0.10 and 0.50. In one study, strain hardening exponent values extracted from tensile data from 58 steel pipes from natural gas pipelines were found to range from 0.08 to 0.25, with the lower end of the range dominated by high-strength low alloy steels and the upper end of the range mostly normalized steels.
Tabulation
| Material | n | K |
| Aluminum 1100–O | 0.20 | 180 |
| 2024 aluminum alloy | 0.16 | 690 |
| 5052-O | 0.13 | 210 |
| Aluminum 6061–O | 0.20 | 205 |
| Aluminum 6061–T6 | 0.05 | 410 |
| Aluminum 7075–O | 0.17 | 400 |
| Brass, Naval | 0.49 | 895 |
| Brass 70–30 | 0.49 | 900 |
| Brass 85–15 | 0.34 | 580 |
| Cobalt-base alloy | 0.50 | 2,070 |
| Copper | 0.54 | 325 |
| AZ-31B magnesium alloy | 0.16 | 450 |
| Low-carbon steel | 0.26 | 530 |
| Low-carbon steel | 0.08 | 700 |
| 4340 steel alloy | 0.15 | 640 |
| 304 stainless steel | 0.450 | 1275 |