Strain hardening exponent
The strain hardening exponent (also called strain hardening index), noted as n, is a material's constant which is used in calculations for stress–strain behavior in work hardening. It occurs in the formula known as Hollomons equation after John Herbert Hollomon Jr. who originally proposed it[1]:
σ = K ε n,
where σ represents the applied stress on the material,
ε is the strain,
and K is the strength coefficient.
The value of the strain hardening exponent lies between 0 and 1. A value of 0 means that a material is a perfectly plastic solid, while a value of 1 represents a 100% elastic solid. Most metals have a n value between 0.10 and 0.50.
Tabulation
| Material | n | K (MPa) |
|---|---|---|
| Aluminum 1100–O (annealed) | 0.20 | 180 |
| 2024 aluminum alloy (heat treated—T3) | 0.16 | 690 |
| 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 | 315 |
| 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 |
References
- J. H. Hollomon, Tensile deformation, Trans. AIME, vol. 162, (1945), pp. 268-290.
- Callister, Jr., William D (2005), Fundamentals of Materials Science and Engineering (2nd ed.), United States of America: John Wiley & Sons, p. 199, ISBN 978-0-471-47014-4
- Kalpakjian, S (2014), Manufacturing engineering and technology (2nd ed.), Singapore: Pearson Education South Asia Pte, p. 62
External links
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