Shear Damage

The model assumes that the equivalent plastic strain at the onset of damage, ${\overline{\epsilon }}_D^{pl}$ , is a function of the shear stress ratio and strain rate:

Here ${\theta }_s=(q+k_{s}p)/{\tau }_{\max }$ is the shear stress ratio, ${\tau }_{\max }$ is the maximum shear stress, and $k_s$ is a material parameter. The criterion for damage initiation is met when the following condition is satisfied:

where ${\omega }_S$ is a state variable that increases monotonically with plastic deformation proportional to the incremental change in equivalent plastic strain. At each increment during the analysis the incremental increase in ${\omega }_S$ is computed as

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

Input Data	Description
Ks	Material parameter, $k_s$ .
Fracture Strain	Equivalent fracture strain at damage initiation.
Shear Stress Ratio	The shear stress ratio is defined as ${\theta }_s=(q+k_{s}p)/{\tau }_{\max }$ , where $q$ is the von Mises equivalent stress, $p$ is the pressure stress, and ${\tau }_{\max }$ is the maximum shear stress.
Strain Rate	The equivalent plastic strain rate, ${\stackrel{\dot{¯}}{\epsilon }}^{pl}$
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.