Ductile Damage

The model assumes that the equivalent plastic strain at the onset of damage, ${\bar{ε}}_{D}^{p l}$ , is a function of stress triaxiality and strain rate:

{\bar{ε}}_{D}^{p l} = (η, {\overset{\dot{¯}}{ε}}^{p l}),

where $η = - p / q$ is the stress triaxiality, $p$ is the pressure stress, $q$ is the von Mises equivalent stress, and ${\bar{ε}}_{D}^{p l}$ is the equivalent plastic strain rate. The criterion for damage initiation is met when the following condition is satisfied:

ω_{D} = \int \frac{d {\bar{ε}}^{p l}}{{\bar{ε}}_{D}^{p l} (η, {\overset{\dot{¯}}{ε}}^{p l})} = 1 .

In this case, $ω_{D}$ is a state variable that increases monotonically with plastic deformation. At each increment during the analysis, the incremental increase in $ω_{D}$ is computed as

Δ ω_{D} = \frac{Δ {\bar{ε}}^{p l}}{{\bar{ε}}_{D}^{p l} (η, {\overset{\dot{¯}}{ε}}^{p l})} \geq 0 .

The ductile criterion can be used with the von Mises, Johnson-Cook, and Hill plasticity models, including equation of state.


Input Data	Description
Fracture Strain	Equivalent fracture strain at damage initiation.
Stress Triaxiality	The stress triaxiality is defined as $η = - p / q$ , where $p$ is the pressure stress and $q$ is the von Mises equivalent stress.
Strain Rate	The equivalent plastic strain rate, ${\bar{ε}}_{D}^{p l}$ .
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.
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. For more information, see Specifying Material Data as a Function of Temperature and Independent Field Variables.
Use damage evolution	Damage evolution defines how the material degrades after one or more damage initiation criteria are met. Select the check box and specify settings in the Damage Evolution group box; these settings are described in Damage Evolution.