Numerical controls for general contact in Abaqus/Standard

Numerical controls associated with the general contact algorithm in Abaqus/Standard:

  • should not be modified from their default settings for the majority of problems;

  • can be used for problems where the default settings do not provide cost-effective solutions;

  • can be used to control the master-slave roles and the sliding formulation; and

  • in some cases can be applied selectively to particular regions within a general contact domain.

The following topics are discussed:

Related Topics
About general contact in Abaqus/Standard
In Other Guides
*CONTACT
*CONTACT FORMULATION
*CONTACT CONTROLS
Specifying master-slave assignments for general contact

ProductsAbaqus/StandardAbaqus/CAE

Contact formulation

The general contact algorithm uses the finite-sliding, surface-to-surface contact formulation, which is discussed in Contact formulations in Abaqus/Standard. Other contact formulations are not available for general contact in Abaqus/Standard.

Constraint enforcement method

The general contact algorithm uses a penalty method to enforce active contact constraints by default. Other constraint enforcement methods can be specified as part of the surface interaction (i.e., contact property) definition, as discussed in Contact constraint enforcement methods in Abaqus/Standard. Assignment of contact properties to general contact interactions is discussed in Contact properties for general contact in Abaqus/Standard.

Numerical controls for friction

Numerical controls associated with friction are discussed in Frictional behavior.

Beam-to-beam contact

Activation of beam-to-beam contact is discussed in About general contact in Abaqus/Standard.

Master and slave roles

The surface-to-surface contact formulation used by general contact generates individual contact constraints using a master-slave approach, as discussed in Contact formulations in Abaqus/Standard. Abaqus/Standard assigns default pure master-slave roles for contact involving disconnected bodies within the general contact domain. Bodies consisting of connected beam and truss elements are considered disconnected bodies even though these bodies may share nodes with other faceted bodies. Internal surfaces are generated automatically using the naming convention General_Contact_Faces_k, where k corresponds to an automatically assigned component number. By default, the lower-numbered component surfaces act as master surfaces to the higher-numbered component surfaces. An exception is when component surfaces consisting of beam and truss elements interact with faceted component surfaces in the edge-to-surface contact formulation. A component surface consisting of beam and truss elements acts as the master surface in the edge-to-surface formulation if half of the average element radius is larger than the average smallest facet length of the faceted component surface. You can determine the default pure master-slave roles by viewing the automatically generated internal surfaces in the Visualization module of Abaqus/CAE (see Using display groups to display subsets of your model). Self-contact within a body is treated with balanced master-slave contact by default, with each surface node acting as a master node in some constraints and as a slave node in other constraints.

For example, if the general contact domain spans three disconnected bodies, the following three internal “component-surfaces” for general contact are created automatically:

  • General_Contact_Faces_1

  • General_Contact_Faces_2

  • General_Contact_Faces_3

By default, the first surface listed acts as a master to the other two, and General_Contact_Faces_2 acts as a master to General_Contact_Faces_3. If any of these surfaces contain beam or truss elements interacting with other faceted surfaces in the edge-to-surface contact formulation, the decision to use these as the master surfaces will depend on the average element radius and the average smallest facet length of the faceted surfaces. By default, self-contact within each of these three surfaces is modeled with balanced master-slave contact.

All XFEM-based crack surfaces in the general contact domain are assigned to a separate component and assigned the highest component number. Therefore, crack surfaces act as slaves to other components by default. Contact between portions of crack surfaces are handled with balanced master-slave contact since they all belong to a single component.

Specifying non-default master-slave roles

You can override the default master-slave roles by specifying pure master-slave roles or by specifying that balanced master-slave contact should be used. The default master-slave treatment works well in most cases. Keep the following points in mind when modifying the master-slave assignments, in addition to other factors discussed in this section:

  • Do not use the internally generated component surfaces when assigning alternative master-slave roles (instead, use surface names that you define). Named XFEM-based crack surfaces are not supported for specifying master-slave roles.

  • The master-slave role assignments are part of the model definition and cannot be modified from step to step.

  • The guidelines for assigning pure master-slave roles for contact pairs discussed in Defining contact between two separate surfaces are also applicable for situations in which you reassign pure master-slave roles for general contact.

  • The limitations of balanced (symmetric) master-slave contact pairs discussed in Using symmetric master-slave contact pairs to improve contact modeling are also applicable for situations in which you reassign balanced master-slave contact for general contact. Balanced master-slave contact can result in reduced robustness due to the increased number of constraints and the possibility of overconstraints.

Input File Usage

Use the following option to indicate that the first surface should be considered the slave surface:

CONTACT FORMULATION, TYPE=MASTER SLAVE ROLES
surf_1, surf_2, SLAVE

Use the following option to indicate that the first surface should be considered the master surface:

CONTACT FORMULATION, TYPE=MASTER SLAVE ROLES
surf_1, surf_2, MASTER

If the first surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. The second surface name must be specified.

Use the following option to specify that balanced master-slave contact should be used between two surfaces:

CONTACT FORMULATION, TYPE=MASTER SLAVE ROLES
surf_1, surf_2, BALANCED

If the first surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. If the second surface name is omitted, contact between the first surface and itself is assumed.

Abaqus/CAE Usage

Interaction module: Create Interaction: General contact (Standard): Contact Formulation: Master-slave assignments: Edit: 
select the surfaces in the columns on the left, and click the arrows in the middle 
to transfer them to the list of master-slave assignments.
In the First Surface Type column, enter SLAVE to indicate that the first surface should be considered the slave surface, enter MASTER to indicate that the first surface should be considered the master surface, or enter BALANCED to specify that balanced master-slave contact should be used between the two surfaces.

Automatically generated contact exclusions

Abaqus/Standard automatically generates contact exclusions for the master-slave roles opposite to specified pure master-slave roles; therefore, self-contact is excluded for any regions of the two surfaces that overlap. For example, specifying that the general contact interaction between surf_A and surf_B should use pure master-slave contact with surf_A considered to be the slave surface would result in exclusions being generated internally for master faces of surf_A contacting slave faces of surf_B; self-contact would be excluded for the region of overlap between surf_A and surf_B. An error message is issued if the second surface name is omitted or is the same as the first surface name since this input would result in the exclusion of self-contact for the surface.

Smoothness of contact force redistribution upon sliding

You can control the smoothness of nodal contact force redistribution upon sliding. The default setting, which is generally appropriate, results in the smoothness of the nodal force redistribution being of the same order as the elements underlying the slave surface; that is, linear redistribution smoothness for linear elements, and quadratic redistribution smoothness for second-order elements. Quadratic redistribution smoothness usually tends to improve convergence behavior and improve resolution of contact stresses within regions of rapidly varying contact stresses. However, quadratic redistribution smoothness tends to increase the number of nodes involved in each constraint, which can increase the computational cost of the equation solver. Linear redistribution smoothness tends to provide better resolution of contact stresses near edges of active contact regions and, therefore, occasionally results in better convergence behavior.

Input File Usage

Use the following option to indicate that the smoothness of the contact force redistribution upon sliding should be of the same order as the elements underlying the slave surface:

CONTACT FORMULATION, TYPE=SLIDING TRANSITION
surf_1, surf_2, ELEMENT ORDER SMOOTHING

If the first surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. If the second surface name is omitted, contact between the first surface and itself is assumed.

Use the following option to indicate linear smoothness of the contact force redistribution upon sliding:

CONTACT FORMULATION, TYPE=SLIDING TRANSITION
surf_1, surf_2, LINEAR SMOOTHING

If the first surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. If the second surface name is omitted, contact between the first surface and itself is assumed.

Use the following option to indicate quadratic smoothness of the contact force redistribution upon sliding:

CONTACT FORMULATION, TYPE=SLIDING TRANSITION
surf_1, surf_2, QUADRATIC SMOOTHING

If the first surface name is omitted, a default surface that encompasses the entire general contact domain is assumed. If the second surface name is omitted, contact between the first surface and itself is assumed.

Additional global numerical controls for general contact

Some additional numerical contact controls can be modified globally from step-to-step for general contact; you cannot specify contact controls for individual surface pairings within the general contact domain. You can apply contact stabilization to address rigid body modes that occur prior to the establishment of contact in the model, and you can adjust the tolerances used by Abaqus/Standard to determine contact penetrations and separations; both techniques are discussed in Adjusting contact controls in Abaqus/Standard.