Plastic Options


Type	Description
Yield criterion	The following yield criteria are available: von Mises yield begins when the von Mises stress reaches the yield strength. Hill's criterion is used for anisotropic plasticity and has a quadratic form for which six yield ratio entries are required. When you select this option, the Potential options appear.
Hardening	The following hardening models are available: Isotropic: The yield surface changes size uniformly in all directions such that the yield stress increases (or decreases) in all stress directions as plastic straining occurs. Kinematic: A constant rate of hardening under cyclic loading conditions. Combined: Nonlinear isotropic/kinematic hardening under cyclic loading conditions. User: You can define your own hardening law with a user subroutine.

Isotropic Plasticity

Isotropic plasticity is defined using either tabular hardening or Johnson-Cook hardening. For tabular hardening, each row in the table includes a True Plastic Strain value and the corresponding Yield Stress at that strain. Plastic strain to stress relationships are interpolated linearly between data points; the stress remains constant at strains outside the specified data range. You can also specify strain rate-dependent data for tabular hardening.

For Johnson-Cook hardening, several material parameters are required, along with the melting and transition temperatures for the material.

Tip: To add or delete rows from the table, right-click in the table region and select an option from the menu that appears.


Input Data	Description
Yield Stress	(Tabular data entry) The true—or logarithmic—stress value at the corresponding true plastic strain.
Plastic Strain	(Tabular data entry) The plastic component of the true—or logarithmic—strain in the material (i.e., true strain that will not be recovered after the stress is removed).
Use strain rate-dependent data	(Tabular data entry) Select this option to enter test data showing yield stress values versus equivalent plastic strain at different equivalent plastic strain rates. Enter strain rates in the Strain Rate column that appears.
A, B, n, m	(Johnson-Cook hardening) Material parameters measured at or below the transition temperature.
Melting Temperature	(Johnson-Cook hardening) Temperature above which the material behaves as a fluid.
Transition Temperature	(Johnson-Cook hardening) The yield stress is not temperature dependent at or below this temperature.
Use temperature-dependent data	Specifies material parameters that depend on temperature. A Temperature field appears in the data table. For more information, see Specifying Material Data as a Function of Temperature and Independent Field Variables.

Kinematic Plasticity

Kinematic plasticity defines a nonlinear hardening material property. You can also define linear kinematic hardening by using a single backstress and setting Gamma=0. The linear hardening response is valid only for relatively small strains—less than 5%.


Input Data	Description
Number of backstresses	The backstresses are calculated responses at different strain rates. They are combined to provide a better overall picture of the material response.
Yield Stress	The stress at which plastic deformation begins.
C	Kinematic hardening modulus, which must be provided for each backstress term.
Gamma	Material parameter, which must be provided for each backstress term.
Use temperature-dependent data	Specifies material parameters that depend on temperature. A Temperature field appears in the data table.

Combined Plasticity

The combined plasticity hardening model uses both an isotropic and a nonlinear kinematic component to define the material response. The isotropic response parameters are included in the table below. The kinematic response is defined as described in Kinematic Plasticity.


Input Data	Description
Yield Stress	The true—or logarithmic—stress value at the corresponding true plastic strain.
Plastic Strain	For Tabular data entry, the plastic component of the true—or logarithmic—strain in the material (i.e., true strain that will not be recovered after the stress is removed).
Q-infinity	Isotropic hardening parameter, $Q_{\infty}$ .
Hardening Param b	Isotropic hardening parameter, b.
Use temperature-dependent data	Specifies material parameters that depend on temperature. A Temperature field appears in the data table.

User-defined Hardening

For implicit analyses you can define the yield stress, $σ^{0}$ , through a user subroutine (UHARD). For explicit time integration you can use VUHARD.


Input Data	Description
Hardening Properties	Hardening properties for your hardening user subroutine.

Potential Options

The Potential table appears when you select Hill's yield criterion.


Input Data	Description
R11, R22, R33, R12, R23, and R13	The six yield ratios: $R_{11}$ , $R_{22}$ , $R_{33}$ , $R_{12}$ , $R_{23}$ , and $R_{13}$ , respectively.
Use temperature-dependent data	Specifies material parameters that depend on temperature. A Temperature field appears in the data table.
Number of field variables	Specify material parameters that depend on field variables. Field columns appear in the data table for each field variable you add.