In Brittle Damage: Johnson-Cook Plasticity Model (LAW27), a
damage model for brittle materials is presented. It is used in Radioss LAW27 valid for shell meshes. The damage is generated when the
shell works in traction only. A generalized damage model for ductile materials is
incorporated in Radioss LAW22 and LAW23. The damage is not only
generated in traction but also in compression and shear. It is valid for solids and shells.
The elastic-plastic behavior is formulated by Johnson-Cook model. The damage is introduced
by the use of damage parameter, . The damage appears in the material when the strain is larger than a
maximum value, :
If LAW 22 is identical to LAW2.
If and
This implies an isotropic damage with the same effects in tension and compression. The
inputs of the model are the starting damage strain and the slope of the softening curve as shown in Figure 1.
For brick elements the damage law can be only applied to the deviatoric part of stress
tensor and . This is the case of LAW22 in Radioss. However, if the application of damage law to stress tensor is expected, Radioss LAW23 may be
used.Figure 1. Ductile Damage Model
The strain rate definition and filtering for these laws are explained in Johnson-Cook Plasticity Model (LAW2). The
strain rate may or may not affect the maximum stress value
according to the user's choice, as shown in Table 1.