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

[1]

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. 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

Tabulation of n and K Values for Several Alloys [2][3][4]
MaterialnK (MPa)
Aluminum 1100–O (annealed)0.20180
2024 aluminum alloy (heat treated—T3)0.16690
5052-O 0.13 210
Aluminum 6061–O (annealed)0.20205
Aluminum 6061–T60.05410
Aluminum 7075–O (annealed)0.17400
Brass, Naval (annealed)0.49895
Brass 70–30 (annealed)0.49900
Brass 85–15 (cold-rolled)0.34580
Cobalt-base alloy (heat-treated)0.502,070
Copper (annealed)0.54315
AZ-31B magnesium alloy (annealed)0.16450
Low-carbon steel (annealed)0.26530
4340 steel alloy (tempered @ 315 °C)0.15640
304 stainless steel (annealed)0.4501275

References

  1. J. H. Hollomon, Tensile deformation, Trans. AIME, vol. 162, (1945), pp. 268-290.
  2. 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
  3. Kalpakjian, S (2014), Manufacturing engineering and technology (2nd ed.), Singapore: Pearson Education South Asia Pte, p. 62
  4. "41.2 Roll Formed Aluminum Alloy Components". ASM handbook (10th ed.). Materials Park, Ohio: ASM International. Handbook Committee. 2005. p. 482. ISBN 978-0-87170-377-4. OCLC 21034891.


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