Defining Contact Properties in Structural Steps

In structural steps, you can use contact properties to define the tangential and normal interaction between two surfaces.

Note: You can also define contact properties in thermal steps to specify the conductive and radiative interaction between two surfaces. For more information, see Defining Contact Properties in Thermal Steps.

Two friction modes are available when you define tangential behavior:

  • Rough: Prevents all relative sliding motion between two contacting surfaces while the corresponding normal-direction contact constraints are active.
  • Coulomb: Relates the maximum allowable frictional (shear) stress across an interface to the contact pressure between the contacting bodies.

This task shows you how to:

Before you begin:
See Also
About Contact Properties
Defining Surface-Based Contact in Implicit Steps
Defining Surface-Based Contact in Explicit Dynamic Steps
In Other Guides
Feature Manager

Define Tangential Contact Properties Using Rough Friction

  1. From the Interactions section of the action bar, click Contact Property .
  2. Optional: Enter a descriptive Name.
  3. Expand the Tangential behavior section to access more options.
  4. Select Specify tangential behavior options.
  5. From the Friction type options, select Rough.
  6. Click OK.

Define Tangential Contact Properties Using Coulomb Friction

  1. From the Interactions section of the action bar, click Contact Property .
  2. Optional: Enter a descriptive Name.
  3. Expand the Tangential behavior section to access more options.
  4. Select Specify tangential behavior options.
  5. From the Friction type options, select Coulomb.
  6. For implicit steps, select one of the Enforcement options:
    OptionDescription
    Penalty Enforces frictional constraints with a stiffness, which permits some relative motion of the surfaces (an "elastic slip") when they would normally stick.
    Lagrange Enforces sticking constraints exactly so that there is no relative motion between two closed surfaces until the critical shear stress is reached.
  7. Specify the Friction Dependences:
    1. Select Slip rate to define the velocity parallel to the surface when friction is overcome.
    2. Select Contact pressure to define the pressure between two surfaces in contact.
    3. Select Temperature to define the temperature of the contact surface.
    4. In the table, enter the Friction coefficient and values for any friction-dependent options that you selected.
  8. For explicit dynamic steps, enter a value as the Tau max, which is the maximum achievable value of the equivalent shear stress.

    Sliding occurs if the equivalent shear stress reaches this value, regardless of the contact pressure stress.

  9. For implicit dynamic steps, enter a value as the Slip tolerance, which is the magnitude of allowable elastic slip when using the penalty enforcement method.
  10. Click OK.

Define Normal Contact Properties

  1. From the Interactions section of the action bar, click Contact Property .
  2. Optional: Enter a descriptive Name.
  3. Expand the Normal behavior section to access more options.
  4. Select Specify normal behavior options.
  5. From the Pressure-overclosure type options, select one of the following:
    OptionDescription
    Hard contact Minimizes the penetration of the secondary surface into the main surface and prevents the transfer of tensile stress across the interface. This option uses the default Lagrange multiplier method of constraint enforcement.
    Tabular Defines a linear pressure-overclosure relationship. Enter pressure-overclosure data in the table, or use the context menu to import data from an external file. Tabular data must be monotonically increasing.
    Exponential Specifies a zero clearance distance and initial pressure at that clearance. Pressure increases exponentially as the clearance diminishes (past the initial value).
  6. If you chose tabular pressure-overclosure, enter values for Pressure and Overclosure in the table.
  7. If you chose exponential pressure-overclosure, enter values for Clearance and Pressure.
  8. Clear Allow separation to prevent separation of surfaces once contact has been established.
  9. From the Enforcement type options, select one of the following:
    OptionDescription
    Solver Default Specifies an appropriate constraint enforcement type based on your model.
    Augmented Lagrange Uses an augmentation iteration scheme with the penalty method to drive down the penetration distance.
    Direct Enforces contact constraints directly without approximation or use of augmentation iterations.
    Penalty Approximates hard pressure-overclosure behavior by using a contact force proportional to the penetration distance; therefore, some degree of penetration will occur.

    Enforcement options are not available for contact interaction properties in explicit dynamic steps.

  10. For augmented Lagrange or penalty enforcement, enter a value as the Stiffness scale factor to scale the penalty stiffness.

    The penalty stiffness is 10 times the stiffness of a representative underlying element. The scale factor acts as an additional multiplier on any scale factor specified in the surface behavior definition. It is generally recommended that you only consider order-of-magnitude changes in this scale factor.

  11. Click OK.