Maximum or quadratic nominal stress damage

The Maxs and Quads damage initiation criteria are used to predict damage initiation in cohesive elements where the cohesive layers are defined in terms of traction-separation. Both forms evaluate the stress ratios between a given stress value and the peak nominal stress value in each of three directions. t n o , t s o , and t t o represent the peak values of the nominal stress when the deformation is either purely normal to the interface or purely in the first or the second shear direction, respectively. The Maxs criterion is based on the maximum value of the three ratios, whereas the Quads criterion is based on a quadratic combination of all three ratios.

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In Other Guides
Defining the Constitutive Response of Cohesive Elements Using a Traction-Separation Description
  1. From the menu bar in the Edit Material dialog box, select Mechanical Damage for Traction Separation Laws Maxs Damage or Quads Damage.

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

  2. If you are using the extended finite element method (XFEM) to model fracture, you can choose the crack propagation direction when the damage initiation criterion is satisfied. The crack can extend at a direction normal to the element local 1-direction (default) or parallel to the element local 1-direction.
  3. Enter the Tolerance. The value should be equal to the tolerance within which the damage initiation criterion must be satisfied.
  4. To define the separate tolerance used for crack growth, toggle on Growth Tolerance and enter the Growth Tolerance.

    If this parameter is included but no value is specified, keep the toggle on for default.

  5. To define the separate tolerance used for unstable crack growth, toggle on Unstable Growth Tolerance and enter the Unstable Growth Tolerance.

    If this parameter is included but no value is specified, keep the toggle on for infinite.

  6. Select the arrow to the right of the Position field, and select the method for computing the stress/strain fields ahead of the crack tip to determine if the damage initiation criterion is satisfied and to determine the crack propagation direction (if needed):

    • Select Centroid to use the stress/strain at the element centroid.

    • Select Crack tip to use the stress/strain extrapolated to the crack tip.

    • Select Combined to use the stress/strain extrapolated to the crack tip to determine if the damage initiation criterion is satisfied and to use the stress/strain at the element centroid to determine the crack propagation direction (if needed).

  7. To define the material damage data that depend on effective rate of separation, toggle on Use rate-dependent data.

    A column labeled rate-dependent appears in the Data table.

  8. To define material damage data that depend on temperature, toggle on Use temperature-dependent data.

    A column labeled Temp appears in the Data table.

  9. To define behavior data that depend on field variables, click the arrows to the right of the Number of field variables field to increase or decrease the number of field variables.

    Field variable columns appear in the Data table.

  10. Enter damage parameters in the Data table:

    Maximum Nominal Stress Normal-only Mode

    Nominal stress at damage initiation in a normal-only mode.

    Maximum Nominal Stress Shear-only mode First Direction

    Nominal stress at damage initiation in a shear-only mode that involves separation only along the first shear direction.

    Maximum Nominal Stress Shear-only mode Second Direction

    Nominal stress at damage initiation in a shear-only mode that involves separation only along the second shear direction.

    Temp

    Temperature, θ .

    Field n

    Predefined field variables.

    You might 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.

  11. Select Suboptions Damage Evolution to define the material degradation that takes place once damage begins.

    For more information, see Damage evolution.”

  12. Select Suboptions Damage Stabilization Cohesive to enter viscous coefficients and improve the model convergence.

    For more information, see Damage stabilization.”

  13. Click OK to exit the material editor.