Strain hardening exponent
Encyclopedia
The strain hardening exponent (also called strain hardening index), noted as n, is a materials constant which is used in calculations for stress-strain behaviour
in work hardening
.
In the formula σ = K ε n, 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 an n value between 0.10 and 0.50.
Stress-strain curve
During tensile testing of a material sample, the stress–strain curve is a graphical representation of the relationship between stress, derived from measuring the load applied on the sample, and strain, derived from measuring the deformation of the sample, i.e. elongation, compression, or distortion...
in work hardening
Work hardening
Work hardening, also known as strain hardening or cold working, is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements within the crystal structure of the material. Any material with a reasonably high melting point such as metals and...
.
In the formula σ = K ε n, σ represents the applied stress
Stress (physics)
In continuum mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the body on which internal forces act. These internal forces are a reaction to external forces applied on the body...
on the material, ε is the strain
Strain (materials science)
In continuum mechanics, the infinitesimal strain theory, sometimes called small deformation theory, small displacement theory, or small displacement-gradient theory, deals with infinitesimal deformations of a continuum body...
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
Plasticity (physics)
In physics and materials science, plasticity describes the deformation of a material undergoing non-reversible changes of shape in response to applied forces. For example, a solid piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the...
solid, while a value of 1 represents a 100% elastic
Elasticity (physics)
In physics, elasticity is the physical property of a material that returns to its original shape after the stress that made it deform or distort is removed. The relative amount of deformation is called the strain....
solid. Most metals have an n value between 0.10 and 0.50.
Tabulation
| Material | n | K (MPa) |
|---|---|---|
| Low-carbon steel (annealed) | 0.21 | 600 |
| 4340 steel alloy (annealed) | 0.12 | 2650 |
| 304 stainless steel (annealed) | 0.5 | 1400 |
| Copper (annealed) | 0.44 | 530 |
| Naval brass (annealed) | 0.21 | 585 |
| 2024 aluminum alloy (heat treated—T3) | 0.17 | 780 |
| AZ-31B magnesium alloy (annealed) | 0.16 | 450 |