In
materials science, the Zener–Hollomon parameter, typically denoted as ''Z'', is used to relate changes in temperature or strain-rate to the stress-strain behavior of a material. It has been most extensively applied to the forming of steels at increased temperature, when
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[''Fire Safety Engineering'', J.A. Purkiss, 2007, 2nd ed. Butterworth-Heinemann. Oxford] It is given by
:
where
is the
strain rate, ''Q'' is the
activation energy
In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules pe ...
, ''R'' is the
gas constant, and ''T'' is the temperature. The Zener–Hollomon parameter is also known as the temperature compensated strain rate, since the two are inversely proportional in the definition. It is named after
Clarence Zener and
John Herbert Hollomon, Jr. who established the formula based on the stress-strain behavior in steel.
When plastically deforming a material, the
flow stress
In materials science the flow stress, typically denoted as Yf (or \sigma_\text), is defined as the instantaneous value of stress required to continue plastically deforming a material - to keep it flowing. It is most commonly, though not exclusivel ...
depends heavily on both the strain-rate and temperature. During
forming processes, ''Z'' may help determine appropriate changes in strain-rate or temperature when the other variable is altered, in order to keep material flowing properly. ''Z'' has also been applied to some metals over a large range of strain rates and temperatures and shown comparable microstructures at the end-of-processing, as long as ''Z'' remained similar. This is because the relative activity of various deformation mechanisms is typically inversely proportional to temperature or strain-rate, such that decreasing strain rate or increasing temperature will increase ''Z'' and promote plastic deformation.
See also
*
Hollomon–Jaffe parameter
The Hollomon–Jaffe parameter (HP), also generally known as the Larson–Miller parameter, describes the effect of a heat treatment at a temperature for a certain time.
This parameter is especially used to describe the tempering of steels, so ...
References
{{DEFAULTSORT:Zener-Hollomon parameter
Metallurgy