Defining Mohr-Coulomb plasticity

You can use the Mohr-Coulomb plasticity model for geotechnical engineering design applications. The model uses the classical Mohr-Coloumb yield criterion: a straight line in the meridional plane and an irregular hexagonal section in the deviatoric plane. However, the Abaqus Mohr-Coulomb model has a completely smooth flow potential instead of the classical hexagonal pyramid: the flow potential is a hyperbola in the meridional plane, and it uses the smooth deviatoric section proposed by Menétrey and Willam. See Mohr-Coulomb plasticity, for more information.

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

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

  2. Click the Plasticity tab, if necessary, to display the Plasticity tabbed page.

  3. Choose how you want to define Deviatoric eccentricity, e:

    • Select Calulated default to allow Abaqus to calculate the deviatoric eccentricity as e=(3-sin⁡ϕ)/(3+sin⁡ϕ), where ϕ is the Mohr-Coulomb Friction Angle that you specify in the Data table.

    • Select Specify, and enter a value for deviatoric eccentricity in the field provided. The range of values e can have is 1/2<e≤1.

  4. Enter a value for Meridional eccentricity, ϵ.

    The meridional eccentricity is a small positive number that defines the rate at which the flow potential approaches its asymptote.

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

    A column labeled Temp appears in the Data table.

  6. 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.

  7. Enter the following data in the Data table:

    Friction Angle

    Friction angle, ϕ, at high confining pressure in the p–Rm⁢c⁢q plane. Enter the value in degrees.

    Dilation Angle

    Dilation angle, ψ, at high confining pressure in the p–Rm⁢w⁢q plane. Enter the value in degrees.

    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. Click the Cohesion tab to display the Cohesion tabbed page.

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

    A column labeled Temp appears in the Data table.

  10. 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.

  11. Enter the following data in the Data table:

    Cohesion Yield Stress

    Cohesion yield stress.

    Abs Plastic Strain

    Absolute value of the corresponding plastic strain. (The first tabular value entered must always be zero.)

    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.

  12. If desired, toggle on Specify tension cutoff and click the Tension Cutoff tab to specify tension cutoff stress data to limit the load carrying capacity of the material model near the tensile region.

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

    A column labeled Temp appears in the Data table.

  14. 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.

  15. Enter the following data in the Data table:

    Tension Cutoff Stress

    Yield stress in uniaxial tension, σt.

    Tensile Plastic Strain

    Corresponding plastic strain. (The first tabular value entered must always be zero.)

    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.

  16. 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).