Numerical Controls for General Contact in Abaqus/Standard

By default, the general contact algorithm uses the finite-sliding, surface-to-surface contact formulation, which is discussed in Contact Formulations in Abaqus/Standard. In addition, it is supplemented by the edge-to-surface, edge-to-edge and vertex-to-surface formulations, which are also based on the finite-sliding tracking approach. Optionally, you can specify the small-sliding tracking approach for portions of the general contact domain and, by extension, the entire general contact domain.

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 associated with friction are discussed in Frictional Behavior.

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

The surface-to-surface contact formulation used by general contact generates individual contact constraints using a main-secondary approach, as discussed in Contact Formulations in Abaqus/Standard. Abaqus/Standard assigns default pure main-secondary surface roles of a contact formulation 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 main 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 main 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. Self-contact within a body is treated with balanced main-secondary contact by default, with each surface node acting as a main node in some constraints and as a secondary 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 main surface to the other two, and General_Contact_Faces_2 acts as a main surface 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 main 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 main-secondary 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 secondary surfaces s to other components by default. Contact between portions of crack surfaces are handled with balanced main-secondary contact since they all belong to a single component.

You can specify the small-sliding tracking approach for interactions involving portions of the entire general contact domain and, by extension, the entire contact domain. The small-sliding approach avoids repeated contact tracking and the need to re-establish the nodes involved in the constraint connectivity, which makes it more efficient than the default finite-sliding approach for general contact. However, you should be aware of the approximations involved in small sliding to decide whether they are appropriate (The Small-Sliding Tracking Approach). The small-sliding approach involves only the surface-to-surface contact over opposing surfaces; edges and vertices are deactivated. The surface pairs you specify to utilize small sliding are excluded automatically for the default finite-sliding approach. Subsequently, none of the types of contact based on finite-sliding assumptions (such as surface-to-surface contact or edge and vertex contact) are active over the pairings with the small-sliding specification.

You should not use the internally generated component surfaces when assigning the small-sliding approach; instead, you should define the surface names. Named XFEM-based crack surfaces are not allowed for specifying the small-sliding approach.

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 secondary 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.

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.