Steinberg-Lund Hardening

In the Steinberg-Lund hardening law, the yield stress is given by

      [math]\displaystyle{ \sigma_y = \left(\min\left\{\sigma_0\bigl(1 + \beta \alpha\bigr)^n,\sigma_y^{max}\right\}+\min\left\{Y_T(\dot\alpha,T),Y_P\right\}\right){G(T,P)\over G_0} }[/math]

where [math]\displaystyle{ Y_T(\dot\alpha,T) }[/math] is a strain rate and temperature dependent term, σ₀ is the initial yield stress, β and n are hardening law properties, α is the cumulative equivalent plastic strain, G(T,P) is the shear modulus (which may depend on temperature and pressure), and G₀ is the initial shear modulus. The strain rate and temperature dependent term is defined in inverse form:

      [math]\displaystyle{ {d\alpha(Y_T,T)\over dt} = \left[{1\over C_1}\exp\left({2U_k\over kT}\left(1 - {Y_T\over Y_P}\right)^2\right)+{C_2\over Y_T} \right]^{-1} }[/math]

where C₁, C₂, U_k, and Y_P are hardening law parameters. The shear modulus temperature and pressure dependence is given by the same function as in the Steinberg-Cochran-Guinan Hardening law:

      [math]\displaystyle{ {G(T,P)\over G_0} = 1 + {G_P'\over G_0} P J^{1/3} + {G_T'\over G_0}(T-T_0) }[/math]

where J is the relative volume change (V/V₀), G_P' and G_T' are coefficients for pressure and temperature affects, T is current temperature, and T₀ is a reference temperature. For more details, see paper by Steinberg and Lund.

Hardening Law Properties

This hardening law can set the following properties:

Property	Description
yield	Initial yield stress (σ0 at zero pressure and the reference temperature). Enter in units of MPa.
betahard	Yield stress hardening term β. It is dimensionless.
nhard	Exponent on cumulative equivalent plastic strain in hardening term. It is dimensionless.
GPpG0	The (Gp'/G0) ratio term for pressure dependence of shear modulus. Enter in units MPa-1. Enter 0 to omit pressure dependence in shear modulus.
GTpG0	The (GT'/G0) ratio term for temperature dependence of shear modulus. Enter in units K-1. Enter 0 to omit temperature dependence in shear modulus.
C1SL	The C1 constant in this law entered in units of 1/sec.
C2SL	The C2 constant in this law entered in units of MPa-sec.
YP	The Peierls stress (YP) and also the maximum rate-dependent yield stress. Enter in units of MPa.
Uk	An energy associated with forming kinks (Uk). It has units eV.
yieldMax	Maximum yield stress. Enter in units of MPa.

The reference temperature, T₀, is set using the simulation's stress free temperature and not set using hardening law properties.

History Data

This hardening law defines three history variables, wihich are the cumulative equivalent plastic strain (absolute) defined as:

      [math]\displaystyle{ \alpha = \sum \sqrt{2\over3}\ ||d\varepsilon_p|| }[/math]

where dε_p is the incremental plastic strain tensor in one time step, the current rate- and temperature-dependent yield stress (Y_T) in MPa, and the current plastic strain rate (dα/dt in 1/sec). These variables are stored as history variables #1, #2, and #3.