Specifying clay plasticity behavior

The Abaqus/Standard clay plasticity model describes the inelastic response of cohesionless soils. This model provides a reasonable match to the experimentally observed behavior of saturated clays. You can define the inelastic material behavior by a yield function that depends on the three stress invariants, an associated flow assumption to define the plastic strain rate, and a strain hardening theory that changes the size of the yield surface according to the inelastic volumetric strain.

Context:

For more information, see Critical state (clay) plasticity model.

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

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

  2. Click the arrow to the right of the Hardening field, and select the hardening law form of your choice:

    • Select Exponential to specify an exponential hardening/softening law.

    • Select Tabular to specify a piecewise linear hardening/softening relationship.

    See Hardening law, for more information.

  3. If you selected the Exponential form of the hardening law, you have the option of entering a value for Intercept. This parameter corresponds to e1, the intercept of the virgin consolidation line with the void ratio axis in a plot of void ratio versus the logarithm of pressure stress.

    If you specify a value for Intercept, Abaqus ignores any value specified for the initial yield surface size, a0, in the Data table.

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

    A column labeled Temp appears in the Data table.

  5. 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.

  6. If you selected the Exponential form of the hardening law, enter the following data in the Data table:

    Log Plas Bulk Mod

    Logarithmic plastic bulk modulus, λ (dimensionless).

    Stress Ratio

    Stress ratio at critical state, M.

    Init Yld Surf Size

    Initial yield surface size, a0 (units of FL−2). Abaqus ignores this data item if you have specified a value for Intercept.

    Wet Yld Surf Size

    Parameter defining the size of the yield surface on the “wet” side of critical state, β. If this value is omitted or set to zero, a value of 1.0 is assumed.

    Flow Stress Ratio

    Ratio of the flow stress in triaxial tension to the flow stress in triaxial compression, K. 0.778≤K≤1.0. If this value is left blank or set to zero, a value of 1.0 is assumed.

    Temp

    Temperature.

    Field n

    Predefined field variables.

    You may need to expand the dialog box to see all the columns in the Data table. For detailed information on how to enter data, see Entering tabular data.

  7. If you selected the Tabular form of the hardening law, enter the following data in the Data table:

    Stress Ratio

    Stress ratio at critical state, M.

    Init Vol Plas Strain

    Initial volumetric plastic strain, εvolp⁢l|0 corresponding to pc|0.

    Wet Yld Surf Size

    Parameter defining the size of the yield surface on the “wet” side of critical state, β. If this value is omitted or set to zero, a value of 1.0 is assumed.

    Flow Stress Ratio

    Ratio of the flow stress in triaxial tension to the flow stress in triaxial compression, K. 0.778≤K≤1.0. If this value is left blank or set to zero, a value of 1.0 is assumed.

    Temp

    Temperature.

    Field n

    Predefined field variables.

    You may need to expand the dialog box to see all the columns in the Data table. For detailed information on how to enter data, see Entering tabular data.

  8. If you selected the Tabular form of the hardening law, select Compressive Clay Hardening from the Suboptions menu to provide the hydrostatic compression yield stress as a function of volumetric plastic strain to define piecewise linear hardening/softening of the Cam-clay plasticity yield surface. See Defining compressive clay hardening for a clay plasticity model” for detailed instructions.

  9. If you selected the Tabular form of the hardening law, select Tensile Clay Hardening from the Suboptions menu to provide the hydrostatic tension yield stress as a function of volumetric plastic strain to define piecewise linear hardening/softening of the Cam-clay plasticity yield surface. See Defining tensile clay hardening for a clay plasticity model” for detailed instructions.

  10. If desired, select Potential from the Suboptions menu to specify anisotropic yield behavior. See Defining anisotropic yield and creep” for more information.

  11. If desired, select Softening Regularization from the Suboptions menu to specify a regularization scheme to mitigate potential mesh independence of the results. See Specifying softening regularization for a clay plasticity model” for detailed instructions.

  12. 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).