The procedure for defining general contact is simplified compared to pair-based contact. The GCGEN command and the GCDEF command are key components to this simplified procedure.
The GCGEN command automatically creates all required contact elements for the general contact definition, including:
Surface contact elements (CONTA172, CONTA174) overlaid on the exterior surfaces of deformable bodies
3D line contact elements (CONTA177) overlaid on 3D beams, on feature edges of 3D deformable bodies, and on perimeter edges of 3D shell structures
Vertex-to-surface contact elements (CONTA175) overlaid on the convex corners of deformable bodies and shell structures (2D or 3D) and on endpoints of 3D beam structures
Target elements (TARGE169, TARGE170) overlaid on the surfaces of standalone rigid bodies can also be part of the general contact definition, but must be defined manually.
By default, frictionless standard contact is assumed for all general contact interactions, and default values are used for other contact settings and properties (element key options and real constants). The GCDEF command enables you to further define specific contact interactions between surfaces or to exclude contact interaction for surfaces that should never come into contact.
Following are characteristics of the general contact method:
The general contact surfaces are generated automatically by the GCGEN command based on physical parts and geometric shapes in the model.
Because the general contact surfaces are represented by existing contact and target elements, you can easily display the surfaces and the contact results.
All contact and target elements in the general contact definition are assigned a real constant ID equal to zero and a material ID equal to zero. This is a notable difference between general contact and pair-based contact.
Each general contact surface is assigned a unique section ID and a unique element type ID.
The material ID and real constant ID input on the GCDEF command are associated with the interface properties (defined via MP or TB commands) and the contact control parameters (defined via the R or RMODIF commands) for the specified contact interaction.
Contact searching takes place among all general contact surfaces. This is especially advantageous for contact between multiple, very thin layers.
General contact automatically designates asymmetric contact and target pairing for contact interactions. The automatic asymmetric pairing logic is also used for self-contact within a surface.
General contact and pair-based contact can exist together in a model. The program automatically excludes general contact interactions that overlap with pair-based contact definitions.
In a general contact definition, surface-to-surface contact elements (CONTA172 and CONTA174) are used as the primary contact constraints. 3D edge-to-surface elements (CONTA177) and the 2D or 3D vertex-to-surface elements (CONTA175) can also be included as supplemental constraints. The additional edge-to-surface contact can more accurately resolve contact involving feature edges of solid bodies and perimeter edges of shell structures penetrating into other surfaces. The vertex-to-surface contact formulation is intended to prevent penetrations between convex corners of solid bodies and shell surfaces as well as endpoints of beam structures into other surfaces.
CONTA177 can also be used to model 3D beam-to-beam contact in a general contact definition. Three scenarios are available: crossing beams in contact, nearly parallel beams in contact, and a beam sliding inside a hollow beam. Use KEYOPT(3) to control whether only one or all of these scenarios are included in the model.