In a general contact definition, the default contact interface behavior is frictionless standard contact. You can assign non-default interface behaviors to specific surfaces via the GCDEF command:
GCDEF,,SECT1,SECT2,MATID
The non-default interface behavior is identified by a material number
(MATID), and the general contact surfaces are identified
by section IDs (SECT1 and SECT2).
If MATID is zero or undefined, the default frictionless
standard contact is assumed.
When you assign a non-zero MATID on the
GCDEF command, you will typically input the same number in the
material reference number field (MAT) on one or both of the
following commands:
MP,MU,MATID ! Friction TB,INTER,MATID ! Contact interaction
Unlike pair-based contact, the material ID (MATID) used on
the GCDEF command is not a contact element attribute in a general
contact definition.
Similar to pair-based contact, the friction coefficient used in the general
contact definition can be specified via the MP,MU or
TB,FRIC command. See Coefficient of Friction for
details. User-defined friction is also available. See Writing Your Own Friction Law (USERFRIC) for details.
The following example defines frictional contact with a coefficient of 0.2 at a
specific contact interface. MATID = 10 is used to
identify the non-default behavior:
GCDEF,,SECT1,SECT2,10 MP,MU,10,0.2
8.10.2. Contact Interaction Options Specified via TB
Contact interactions for general contact definitions are specified via
TB,INTER,MATID,,,TBOPT, where the
interaction option is input as a TBOPT label. (KEYOPT(12)
is not used to specify the contact interaction, as it is for pair-based contact.)
The following example defines always-bonded contact behavior at a contact
interface. MATID = 12 is used to identify the non-default
behavior:
GCDEF,,SECT1,SECT2,12 TB,INTER,12,,,ABOND
The table below lists all possible interaction options.
| TBOPT Label | Interaction Behavior | Description |
|---|---|---|
| STANDARD | Standard unilateral contact | Normal pressure equals zero if separation occurs. (Similar to KEYOPT(12) = 0 for pair-based contact elements.) |
| ROUGH | Rough (no sliding) | Perfectly rough frictional contact where there is no sliding. (Similar to KEYOPT(12) = 1 for pair-based contact elements.) |
| NOSEPE | No separation (sliding permitted) | No separation contact in which the target and contact surfaces are tied for the remainder of the analysis once contact is established (although sliding is permitted). (Similar to KEYOPT(12) = 2 for pair-based contact elements.) |
| BONDED | Bonded contact (no separation, no sliding) | Bonded contact in which the target and contact surfaces are bonded in all directions (once contact is established) for the remainder of the analysis. (Similar to KEYOPT(12) = 3 for pair-based contact elements.) |
| ANOSEP | No separation (always) | No separation contact in which contact detection points that are either initially inside the pinball region or that once involve contact always attach to the target surface along the normal direction to the contact surface (sliding is permitted). (Similar to KEYOPT(12) = 4 for pair-based contact elements.) |
| ABOND | Bonded (always) | Bonded contact in which contact detection points that are either initially inside the pinball region or that once involve contact always attach to the target surface along the normal and tangent directions to the contact surface (fully bonded). (Similar to KEYOPT(12) = 5 for pair-based contact elements.) |
| IBOND | Bonded (initial contact) | Bonded contact in which the contact detection points that are initially in a closed state will remain attached to the target surface, and the contact detection points that are initially in an open state will remain open throughout the analysis. (Similar to KEYOPT(12) = 6 for pair-based contact elements.) |
| USER | User-defined | User-defined interaction model programmed via the user
subroutine, USERINTER. See Defining Your Own Contact Interaction (USERINTER) for details.
|
All of the above options use material constant (C1) on the TBDATA command. The value of C1 defines the effect of initial penetration or gap, as described in the table below.
| C1 Value | Description |
|---|---|
| 0 | Include both initial geometrical penetration or gap and offset. (Similar to KEYOPT(9) = 0 for pair-based contact elements.) |
| 1 | Exclude both initial geometrical penetration or gap and offset. (Similar to KEYOPT(9) = 1 for pair-based contact elements.) |
| 2 | Include both initial geometrical penetration or gap and offset, but with ramped effects. (Similar to KEYOPT(9) = 2 for pair-based contact elements.) |
| 3 | Include offset only (exclude initial geometrical penetration or gap). (Similar to KEYOPT(9) = 3 for pair-based contact elements.) |
| 4 | Include offset only (exclude initial geometrical penetration or gap), but with ramped effects. (Similar to KEYOPT(9) = 4 for pair-based contact elements.) |
| 5 | Include offset only (exclude initial geometrical penetration or gap) regardless of the initial contact status (near-field or closed). (Similar to KEYOPT(9) = 5 for pair-based contact elements.) |
| 6 | Include offset only (exclude initial geometrical penetration or gap), but with ramped effects regardless of the initial contact status (near-field or closed). (Similar to KEYOPT(9) = 6 for pair-based contact elements.) |
Note that the effects of C1 input are dependent on which
TBOPT label was previously defined. The indicated
initial gap effect is considered only if TBOPT = ANOSE or
TBOPT = ABOND is defined.
Note: If TBDATA is not issued, the program uses C1 = 1 (exclude both initial geometrical penetration or gap and offset) by default.
You can modify the friction coefficient between load steps or in a restart by
re-issuing MP,MU or TB,FRIC commands. You can
also modify contact interface behaviors between load steps or in a linear
perturbation analysis by resetting TBOPT on the
TB,INTER command.