The program uses real constants to control contact parameters and properties for both general contact and pair-based contact. However, the assignment of these properties is handled differently for the two types of contact.
In a pair-based definition, the real constant ID is assigned to the contact and target
elements as one of the element attributes. In a general contact definition, the real
constant ID (REALID) is assigned via the
GCDEF command which controls the contact properties at a specific
general contact interface identified by section IDs (SECT1
and SECT2). Unlike pair-based contact, the real constant ID
(REALID) used on the GCDEF command is
not a contact element attribute.
If the REALID is not specified or is set to zero on GCDEF,
all default real constant values are used for the specified interface throughout the
entire analysis.
Most real constants used in a pair-based contact definition (see Real Constants) are also available in a general contact definition, with the following exceptions:
R1, R2, PPCN, FPAT, COR, FDMD, FDMS, BSRL, KSYM, and TFOR are not supported in a general contact definition.
General contact provides default values for TCC, ECC, MCC, PCC, and DCC based on the highest conductivity and element sizes of underlying elements from both sides of the contact interface. The default values of these real constants are not provided in the pair-based definition.
The program-provided defaults for certain real constants may not be identical for pair-based contact and general contact. For example, the resulting contact stiffness (FKN) and pinball radius (PINB) vary between the two contact definitions. The resulting pinball (PINB) in the general contact definition is no longer important for standard contact. However, it is critical in some situations such as for bonded contact (TB,INTER,,,ABOND) and for resolving initial interference fit (TB,INTER with TBDATA,,2). Specifying an absolute PINB value (negative input value) is highly recommended in these situations.
The table below compares default real constant values between pair-based contact and general contact and also indicates which real constants are not used in a general contact definition.
Table 8.2: Real Constant Defaults for Pair-Based vs. General Contact
| Real Constants | Description | Pair-Based Contact | General Contact | |
|---|---|---|---|---|
| No. | Name | |||
| 1 | R1 | Radius associated with target geometry |
0 | Not supported [5] |
|
Target radius (CONTA177) |
Calculated by program | |||
| 2 | R2 |
Radius associated with target geometry |
0 | Not supported [5] |
|
Superelement thickness |
1 | |||
|
Contact radius (CONTA177) |
Calculated by program | |||
| 3 | FKN | Normal penalty stiffness factor | 1 | 1 [1] |
| 4 | FTOLN | Penetration tolerance factor | 0.1 | 0.1 [1] |
| 5 | ICONT | Initial contact closure | 0 | 0 |
| 6 | PINB | Pinball region | [2] | [2] [1] |
| 7 | PZER | Pressure at zero penetration | [6] | [6] |
| 8 | CZER | Initial contact clearance factor | 0.01 | 0.01 |
| 9 | TAUMAX | Maximum friction stress | 1.00E+20 | 1.00E+20 |
| 10 | CNOF | Contact surface offset | 0 | 0 |
| 11 | FKOP | Contact opening stiffness | 1 | 1 [1] |
| 12 | FKT | Tangent penalty stiffness factor | 1 | 1 [1] |
| 13 | COHE | Contact cohesion | 0 | 0 |
| 14 | TCC | Thermal contact conductance | 0 | Auto [3] |
| 15 | FHTG | Frictional heating factor | 1 | 1 |
| 16 | SBCT | Stefan-Boltzmann constant | 0 | 0 |
| 17 | RDVF | Radiation view factor | 1 | 1 |
| 18 | FWGT | Heat distribution weighing factor | 0.5 | 0.5 |
| 19 | ECC | Electric contact conductance | 0 | Auto [3] |
| 20 | FHEG | Joule dissipation weighting factor | 1 | 1 |
| 21 | FACT | Static/dynamic ratio | 1 | 1 |
| 22 | DC | Exponential decay coefficient | 0 | 0 |
| 23 | SLTO | Allowable elastic slip | 1% | 1% [1] |
| 24 | TNOP | Maximum allowable tensile contact pressure | [4] | [4] |
| 25 | TOLS | Target edge extension factor | 2 | 2 |
| 26 | MCC | Magnetic contact permeance | 0 | Auto [3] |
| 27 | PPCN | Pressure-penetration criterion | 0 | Not supported |
| 28 | FPAT | Fluid penetration acting time | 0.01 | Not supported |
| 29 | COR | Coefficient of restitution | 1 | Not supported |
| 30 | STRM | Load step number for ramping penetration | 1 [7] | 1 [7] |
| 31 | FDMN | Normal stabilization damping factor | 1 | 1 [1] |
| 32 | FDMT | Tangential stabilization damping factor | 0.001 | 0.001 [1] |
| 33 | FDMD | Destabilizing squeal damping factor | 1 | Not supported |
| 34 | FDMS | Stabilizing squeal damping factor | 0 | Not supported |
| 35 | TBND | Critical bonding temperature | No default | No default |
| 36 | WBID | Internal contact pair ID (used only by the Results Tracker in Workbench Mechanical) | n/a | n/a |
| 37 | PCC | Pore fluid contact permeability coefficient | 0 | Auto [3] |
| 38 | PSEE | Pore fluid seepage coefficient | 0 | 0 |
| 39 | ABPP | Ambient pore pressure | 0 | 0 |
| 40 | FPFT | Gap pore fluid flow participation factor | 0 | 0 |
| 41 | FPWT | Gap pore fluid flow distribution weighting factor | 0.5 | 0.5 |
| 42 | DCC | Contact diffusivity coefficient | 0 | Auto [3] |
| 43 | DCON | Diffusive convection coefficient | 0 | 0 |
| 44 | ABDC | Ambient concentration | 0 | 0 |
| 45 | BSRL | Real ID of base contact pair (after contact pair-splitting) | 0 | Not supported |
| 46 | KSYM | Real ID of the companion pair for symmetric contact or self contact (after contact pair-splitting) | 0 | Not supported |
| 47 | TFOR | Pair-based force convergence tolerance | No default | Not supported |
| 48 | TEND | Ending time for ramping contact stiffness | 0 | 0 |
The internal default may be different for pair-based contact and general contact.
The program-provided defaults for pinball region varies between the two contact definitions.
The default value is calculated as a function of highest conductivity and mesh size at the interface.
TNOP defaults to the force convergence tolerance divided by contact area at contact nodes.
The R1 and R2 real constants are not used in a general contact definition. However, you can input radius values required by contact and target elements via a section definition (SECTYPE and SECDATA commands). This includes the radius of a general contact surface that represents 3D beam-to-beam or 3D edge-to-edge contact, and radius values associated with rigid target segments. See Applying Surface Geometry Correction for details.
If TEND is specified as a positive value, STRM defaults to zero.
Examples
When you assign a non-zero REALID on the
GCDEF command, you will typically input the same number in the
real constant set ID field (NSET) on the R
and RMODIF commands.
The following example defines a contact stiffness factor (FKN) of 10 at a specific
contact interface. REALID = 14 is used to identify the
non-default property:
GCDEF,,SECT1,SECT2,,14 R,14,,,10
If the REALID has been specified by a previous
GCDEF command, you can use the RMODIF command
to add any non-default real constant values regardless of whether or not an associated
R command was issued.
Use NSET = GCN on the RMODIF command to define or modify real constants
for all real constant sets that were previously assigned by GCDEF.
For example:
RMODIF,GCN,STLOC,V1,V2,V3,V4,V5,V6
Note that the GCN label only acts on real constant sets predefined by
GCDEF commands. The default real constant set
(REALID = 0 or undefined) is not affected.
For example, the following command defines a contact stiffness factor (FKN) of 10 for all real constant sets previously specified by GCDEF commands:
RMODIF,GCN,3,10