Strain hardening exponent

 The strain hardening exponent (also called the strain hardening index), usually denoted , a constant often used in calculations relating to stress–strain behavior in work hardening. It occurs in the formula known as Hollomon's equation (after John Herbert Hollomon Jr.) who originally posited it as

${\displaystyle \sigma =K\epsilon ^{n}}$^[1]

where ${\displaystyle \sigma }$ represents the applied true stress on the material, ${\displaystyle \epsilon }$ is the true strain, and ${\displaystyle K}$ 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 ${\displaystyle n}$-value between 0.10 and 0.50.

TabulationEdit

Tabulation of ${\displaystyle n}$- and ${\displaystyle K}$-values for several alloys ^[2][3][4]

Material	n	K (MPa)
Aluminum 1100–O (annealed)	0.20	180
2024 aluminum alloy (heat treated—T3)	0.16	690
5052-O	0.13	210
Aluminum 6061–O (annealed)	0.20	205
Aluminum 6061–T6	0.05	410
Aluminum 7075–O (annealed)	0.17	400
Brass, Naval (annealed)	0.49	895
Brass 70–30 (annealed)	0.49	900
Brass 85–15 (cold-rolled)	0.34	580
Cobalt-base alloy (heat-treated)	0.50	2,070
Copper (annealed)	0.54	325
AZ-31B magnesium alloy (annealed)	0.16	450
Low-carbon steel (annealed)	0.26	530
4340 steel alloy (tempered @ 315 °C)	0.15	640
304 stainless steel (annealed)	0.450	1275