Abaqus Interaction

[Muredac Ford]

Ifyour model includes complex geometries and numerous contact interactions, you may want to customize the variables that control the contact algorithms to obtain cost-effective solutions. These controls are intended for advanced users and should be used with great care. For more information, see “Contact controls editors,” Section 15.8.4.

General contact (ABAQUS/Explicit only)General contact interactions allow you to define contact between many or all regions of the model with a single interaction. Typically, general contact interactions are defined for an all-inclusive surface that contains all exterior faces, shell perimeter edges, and edges based on beams and trusses in the model. To refine the contact domain, you can include or exclude specific surface pairs. Unlike surface-to-surface contact or self-contact interactions, surfaces used in general contact interactions can span many disconnected regions of the model. Attributes, such as contact properties, surface properties, and contact formulation, are assigned as part of the contact interaction definition but independently of the contact domain definition, which allows you to use one set of surfaces for the domain definition and another set of surfaces for the attribute assignments. For detailed instructions on creating this type of interaction, see “Defining general contact,” Section 15.12.5.

General contact interactions and surface-to-surface or self-contact interactions can be used together in the same analysis. Only one general contact interaction can be active in a step during an analysis.

The interaction definition and its optional associated property are used to define the basic aspects of the interaction, but the user must provide user subroutine UEL to supply the specific formulae for how actuation depends on sensor readings. You specify the name of the file containing the user subroutine when you create the analysis job in the Job module. Warning: This feature is intended for advanced users only. Its use in all but the simplest test examples will require considerable coding by the user/developer. “User-defined elements,” Section 18.15.1 of the ABAQUS Analysis User's Manual, should be read before proceeding.

Surfaces of the same type can be combined to create new surfaces (see Operating on surfaces). However, with regard to contact a combined surface can be used only with general contact in Abaqus/Explicit.

When the general contact algorithm is used, Abaqus also provides a default all-inclusive, automatically defined surface that includes all element-based surface facets (in Abaqus/Standard and in Abaqus/Explicit), all crack surfaces for enriched elements (in Abaqus/Standard only), all analytical rigid surfaces (in Abaqus/Explicit only), and all Eulerian materials (in Abaqus/Explicit only) in the model.

Contact interactions for contact pairs and general contact are defined by specifying surface pairings and self-contact surfaces. General contact interactions typically are defined by specifying self-contact for the default surface, which allows an easy, yet powerful, definition of contact. (Self-contact for a surface that spans multiple bodies implies self-contact for each body as well as contact between the bodies.)

At least one surface in an interaction must be a non-node-based surface, and at least one surface in an interaction must be a non-analytical rigid surface. Additional restrictions and guidelines for contact surfaces are discussed for each contact definition approach. The definition of contact pairs is discussed in detail in About contact pairs in Abaqus/Standard and About contact pairs in Abaqus/Explicit. The definition of general contact interactions is discussed in detail in About general contact in Abaqus/Standard and About general contact in Abaqus/Explicit.

Nondefault surface properties (such as thickness and, in some cases, offset) can be defined for particular surfaces in a contact model. In addition, you can control which edges of a surface will be included in the general contact domain in Abaqus/Explicit. Surface properties for contact pairs are discussed in Assigning surface properties for contact pairs in Abaqus/Standard and Assigning surface properties for contact pairs in Abaqus/Explicit. Surface properties for general contact are discussed in Surface properties for general contact in Abaqus/Standard and Assigning surface properties for general contact in Abaqus/Explicit.

Contact interactions in a model can refer to a contact property definition, in much the same way that elements refer to an element property definition. By default, the surfaces interact (have constraints) only in the normal direction to resist penetration. The other mechanical contact interaction models available depend on the contact algorithm and whether Abaqus/Standard or Abaqus/Explicit is used (see About mechanical contact properties). Some of the available models are:

The thermal, thermal-electrical, and pore-fluid surface interaction models available in Abaqus are discussed in Thermal contact properties, Electrical contact properties, and Pore fluid contact properties, respectively.

Contact interaction models are defined as model data except for contact pairs in Abaqus/Explicit, in which case they are defined as history data. Information on assigning contact properties to contact pairs can be found in Assigning contact properties for contact pairs in Abaqus/Standard and Assigning contact properties for contact pairs in Abaqus/Explicit. Information on assigning contact properties to general contact interactions can be found in Contact properties for general contact in Abaqus/Standard and Assigning contact properties for general contact in Abaqus/Explicit.

The crush stress associated with the CZone analysis capability is specified as a material property and has the effect of limiting the contact stress under specific circumstances discussed in CZone analysis.

The default algorithmic controls for contact analyses are usually sufficient, but you can adjust numerical controls for some special cases. For example, depending on the contact algorithm used, the numerical controls for the contact formulation, the main and secondary roles for the contact surfaces, and the sliding formulation are provided. Information on contact formulations and numerical methods used by the contact algorithms is provided in Contact formulations in Abaqus/Standard and Contact formulations for contact pairs in Abaqus/Explicit. The available numerical controls for the various contact algorithms are discussed in Numerical controls for general contact in Abaqus/Standard, Adjusting contact controls in Abaqus/Standard, Contact controls for general contact in Abaqus/Explicit, and Contact controls for contact pairs in Abaqus/Explicit.

Abaqus/Standard provides the following approaches for defining contact interactions: general contact, contact pairs, and contact elements. Contact pairs and general contact both use surfaces to define contact; comparisons of these approaches are provided later in this section. Contact elements are provided for certain interactions that cannot be modeled with either general contact or contact pairs; however, it is generally recommended to use general contact or contact pairs if possible.

Contact between two deformable bodies. The structures can be either two-or three-dimensional, and they can undergo either small or finite sliding.Examples of such problems include the assembly of a cylinder head gasket andthe slipping between two components of a threaded connector.

Contact between a rigid surface and a deformable body. The structurescan be either two- or three-dimensional, and they can undergo either small orfinite sliding. Examples of such problems include metal forming simulations andanalyses of rubber seals being compressed between two components.

Small-sliding or finite-sliding interaction between a set of points anda rigid surface. These models can be either two- or three-dimensional. Anexample of this type of problem is the pull-in of an underwater cable that isresting on the seabed, with the seabed modeled as a rigid surface.

Contact between a set of points and a deformable surface. These modelscan be either two- or three-dimensional. An example of this class of contactproblem is the design of a bearing where one of the bearing surfaces is modeledwith substructures.

For most contact problems you have a choice of whether to define contact interactions using general contact or contact pairs. In Abaqus/Standard the distinction between general contact and contact pairs lies primarily in the user interface, the default numerical settings, and the available options. The general contact and contact pair implementations share many underlying algorithms.

The contact interaction domain, contact properties, and surface attributes are specified independently for general contact, offering a more flexible way to add detail incrementally to a model. The simple interface for specifying general contact allows for a highly automated contact definition; however, it is also possible to define contact with the general contact interface to mimic traditional contact pairs. Conversely, specifying self-contact of a surface spanning multiple bodies with the contact pair user interface (if the surface-to-surface formulation is used) mimics the highly automated approach often used for general contact.

In Abaqus/Standard traditional pairwise specifications of contact interactions may result in more efficient analyses as compared to an all-inclusive self-contact approach to defining contact. Therefore, there is often a trade-off between ease of defining contact and analysis performance. Abaqus/CAE provides a contact detection tool that greatly simplifies the process of creating traditional contact pairs for Abaqus/Standard (see Understanding contact and constraint detection).

Contact formulation: By default, general contact uses the finite-sliding, surface-to-surface formulation supplemented by the finite-sliding, edge-to-surface; finite-sliding, edge-to-edge; and finite-sliding, vertex-to-surface formulations. For crack surfaces on enriched elements, edges and vertices are deactivated. In addition, you can specify the small-sliding tracking approach over portions of the general contact domain. Edges and vertices are deactivated over regions where small sliding is active. Contact pairs use the finite-sliding, node-to-surface formulation by default except when the contact detection tool in Abaqus/CAE is used to create the contact pairs, in which case the finite-sliding, surface-to-surface formulation is used by default. See Contact formulations in Abaqus/Standard for a discussion of contact formulations.

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