General Contact

General contact allows you to create a very simple definition of contact in your model during a Nonlinear Structural or an Explicit Dynamics case. You select multiple faces that can interact and rely on Abaqus to track the interactions between the faces. You typically define general contact by selecting all surfaces in your model (including analytical rigid surfaces). To refine the contact domain, you can include or exclude specific pairs of surface groups. The surfaces that you select can span multiple unattached bodies, so self-contact is not limited to contact of a single body with itself. For example, self-contact of a surface that spans two bodies implies contact between the bodies as well as contact of each body with itself. See Defining general contact in Abaqus/Standard in the Abaqus Interactions Guide, and Defining general contact in Abaqus/Explicit in the Abaqus Interactions Guide for more information.

Alternatively, Abaqus for CATIA V5 allows you to choose selected surface pairs to include in the interaction and selected surface pairs to exclude. The primary motivation for specifying contact exclusions is to avoid physically unreasonable contact interactions. For example, your model may contain multiple forming tools, but not all of the tools participate in the forming process simultaneously. If you specify contact exclusions, you can prevent certain tools from participating in the contact model in certain steps. You do not need to be concerned with specifying contact exclusions for parts of the model that are not likely to interact, since these exclusions typically will have minimal effect on computational performance.

You can use general contact in conjunction with contact pairs (i.e., some interactions can be modeled with general contact, while others are modeled with contact pairs). General contact uses only the finite-sliding, surface-to-surface contact formulation in a Nonlinear Structural case or the finite-sliding contact formulation in an Explicit Dynamics case. These formulations allow for arbitrary separation, sliding, and rotation of the surfaces.

You cannot specify an initial clearance for general contact. However, during the first step of the analysis Abaqus adjusts the positions of surfaces to remove small initial overclosures that exist in the general contact domain. The adjustments are made with strain-free initial displacements. This automatic adjustment of surface position is intended to correct only minor mismatches associated with mesh generation.

The following topics are discussed in this section:

Creating a General Contact Interaction

General contact in a Nonlinear Structural case is defined in the Initialization step and will appear in the Connections container for that step. You must define a general contact initialization property for use in the Initialization Behavior tabbed page of the General Contact dialog box. In addition, master and slave surfaces are assigned automatically and cannot be modified. Only one general contact interaction can be created in a Nonlinear Structural case.

The default contact property model in an Explicit Dynamics case assumes “hard” contact in the normal direction, no friction, no thermal interactions, etc. You can select a mechanical connection behavior that modifies the default contact property model. The mechanical connection behavior can apply to the entire model or to selected surface pairs. See Creating a Mechanical Connection Behavior for more information. You can use contact pairs and general contact interactions in the same Explicit Dynamics case. However, only one general contact interaction can be active in an explicit dynamics step.

When you are selecting a surface pair to include or exclude in the interaction or to associate with a mechanical connection behavior, you can select a surface pair that represents all of the surfaces in your model by selecting Nodes and Elements from the specification tree. Individual points that you created with the point tool are not included in the selection of all surfaces. (In most cases you use the point tool to create a handler point for a part constraint.)

This task shows you how to create a general contact interaction.

  1. Click the General Contact icon .

    The General Contact dialog box appears. For an Explicit Dynamics case, a General Contact object appears in the specification tree under the Connections objects set for the current step. For a Nonlinear Structural case, a General Contact object appears in the specification tree under the Connections objects set for the Initialization step.

  2. You can change the identifier of the contact pair by editing the Name field.

  3. Toggle on Stabilize rigid body modes for entire model to activate stabilization.

  4. To define the surfaces that will interact, do either of the following from the Contact Domain tabbed page:

    • Choose All to include all surfaces of your model in the contact domain. If you choose All, Abaqus for CATIA V5 selects all exterior faces, beam segments, and analytical rigid surfaces; however, stand-alone points are not selected. Shell edges are also included for Explicit Dynamics cases only.

    • Choose Selected Surface Pairs, and select pairs of surface groups to include in the contact domain. You cannot select surfaces directly; you must select surface groups that include the desired surfaces. To select a surface group that represents all surfaces in the model, select Nodes and Elements from the specification tree. See Creating Groups for more information.

  5. To exclude surfaces from the contact interaction, select the Exclusion Domain tabbed page, and select pairs of surface groups to exclude from the contact domain. Abaqus excludes contact for the surface groups that you specify, even if you included the same pair of surface groups directly or indirectly in the contact domain. To select a surface group that represents all surfaces in the model, select Nodes and Elements from the specification tree.

  6. To modify the default contact property model, do the following from the Connection Behavior tabbed page:

    • From the specification tree, select a Global Connection Behavior that Abaqus for CATIA V5 will apply to the entire model.

    • Select pairs of surface groups and a Local Connection Behavior that applies to the selected groups. In many cases you will select a global connection contact behavior for the entire model, but you will assign a specific local connection behavior to a subset of the model. Local connection behaviors take precedence over the global connection behavior. Abaqus ignores any contact property assignments for surface groups that fall outside of the general contact domain. To select a surface group that represents all surfaces in the model, select Nodes and Elements from the specification tree. See Assigning contact properties for general contact in Abaqus/Explicit in the Abaqus Interactions Guide for more information.

  7. For a Nonlinear Structural case, you must define initialization behaviors. In the Initialization Behaviors tabbed page, select the surface groups and a general contact initialization property to complete the table. See General Contact Initialization Properties for more information on defining initialization properties.

  8. For an Explicit Dynamics case, you can view the propagation status of the general contact from the Status tabbed page. The page shows the following:

    • Whether the general contact was Created in this step or Propagated into this step.

    • Whether the general contact is Active or Inactive.

General Contact Initialization Properties

General contact initialization properties are used with general contact for Nonlinear Structural cases.

This task shows you how to create a general contact initialization property.

  1. Click the General Contact Initialization Property icon .

    The General Contact Initialization Property dialog box appears, and a General Contact Initialization Property object appears in the specification tree under the Nonlinear and Thermal Properties objects set.

  2. You can change the identifier of the property by editing the Name field.

  3. Specify the treatment of initial overclosures between surfaces:

    • Select Resolve with strain-free adjustments to adjust certain surfaces to be exactly touching at the beginning of the analysis without creating strain in the model. Only portions of surfaces that lie within the specified distance range are adjusted.

    • Select Treat as interference fits to resolve surface overclosures gradually over the course of the first step in the analysis; this technique creates strain in the model as the surfaces are displaced. Only portions of surfaces that lie within the specified overclosure distance range are adjusted using the interference fit.

  4. Specify a distance beyond which initial overclosures can be ignored. Smaller overclosures will be treated as specified in the previous step.

    • Select Analysis default to let Abaqus calculate a maximum overclosure adjustment distance based on the size of the elements on each surface.

    • Select Specify value to enter a maximum overclosure adjustment distance directly. If you enter a value that is smaller than the calculated analysis default for a surface, Abaqus uses the analysis default value for that surface.

      Warning:  If there are any regions with initial overclosures greater than the specified distance, contact between these regions will not be recognized in the analysis.

  5. If you selected Resolve with strain-free adjustments in Step 3, you can also specify treatment of initially open nodes.

    • Select Analysis default to ignore all open nodes during the initialization adjustments.

    • Select Specify value to enter a maximum opening adjustment distance directly.

      Nodes separated from the opposing surface by a value less than the specified distance are adjusted to lie exactly on the opposing surface.

General contact initialization properties are applied to the model using the Initialization Behavior tabbed page in the General Contact dialog box. For more information, see Creating a General Contact Interaction.