Specifying cap plasticity behavior

You can use the modified Drucker-Prager/Cap plasticity model to simulate geological materials that exhibit pressure-dependent yield. The addition of a cap yield surface helps control volume dilatancy when the material yields in shear and provides an inelastic hardening mechanism to represent plastic compaction. You can also define inelastic time-dependent (creep) behavior coupled with the plastic behavior in an Abaqus/Standard analysis.

Context:

For more information on cap plasticity, see Modified Drucker-Prager/Cap model.

  1. From the menu bar in the Edit Material dialog box, select MechanicalPlasticityCap Plasticity.

    (For information on displaying the Edit Material dialog box, see Creating or editing a material.)

  2. Toggle on Use temperature-dependent data to define data that depend on temperature.

    A column labeled Temp appears in the Data table.

  3. Click the arrows to the right of the Number of field variables field to increase or decrease the number of field variables on which the data depend.

  4. In the Data table, enter the following data:

    Material Cohesion

    Material cohesion, d, in the p–t plane (Abaqus/Standard) or in the p–q plane (Abaqus/Explicit). (Units of FL−2.)

    Angle of Friction

    Material angle of friction, β, in the p–t plane (Abaqus/Standard) or in the p–q plane (Abaqus/Explicit). Enter the value in degrees.

    Cap Eccentricity

    Cap eccentricity parameter, R. Its value must be greater than zero (typically 0.0001≤R≤1000.0).

    Init Yld Surf Pos

    Initial cap yield surface position, εv⁢o⁢lp⁢l|0.

    Transition Surf Rad

    Transition surface radius parameter, α. Its value should be a small number compared to unity. If you leave this field blank, the default is 0.0 (i.e., no transition surface). If you include creep properties in the material model, you must set α equal to zero.

    Flow Stress Ratio

    The ratio of the flow stress in triaxial tension to the flow stress in triaxial compression, K. The value of K should be such that 0.778≤K≤1.0. If you leave this field blank or enter a value of 0.0, Abaqus uses a value of 1.0 by default. If you include creep properties in the material model, you should set K equal to 1.0. This parameter applies only to Abaqus/Standard analyses.

    Temp

    Temperature.

    Field n

    Predefined field variables.

  5. To define the hardening part of the cap plasticity model, select Cap Hardening from the Suboptions menu. See Defining hardening parameters for a cap plasticity model” for detailed instructions.

  6. If you want to specify cap creep behavior, select one of the following options from the Suboptions menu:

    • Select Cap Creep Cohesion to choose a cohesion creep mechanism that follows the type of plasticity active in the shear-failure plasticity.

    • Select Cap Creep Consolidation to choose a consolidation mechanism that follows the type of plasticity active in the cap plasticity region.

    See Defining creep parameters for a cap plasticity model” for detailed instructions. For more information on cap creep behavior, see Creep formulation.

  7. Click OK to create the material and to close the Edit Material dialog box. Alternatively, you can select another material behavior to define from the menus in the Edit Material dialog box (see Browsing and modifying material behaviors, for more information).