# PCONT

Bulk Data Entry Defines properties of a CONTACT interface.

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PCONT PID GPAD STIFF MU1 MU2 CLEARANCE SEPARATION
FRICESL
The following optional continuation lines are used to define nonlinear penalty for the S2S contact interface. Only one of each of these continuation lines are allowed on a single PCONT entry.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
+ STFEXP C0 P0
+ STFQDR C0 ALPHA1 ALPHA2 ALPHA3
+ STFTAB STFTID

## Examples

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PCONT 34     0.3 0.25
Enforced stick condition:
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PCONT 34     STICK

## Definitions

Field Contents SI Unit Example
PID Property identification number.
Integer
Specifies an identification number for this entity.
<String>
Specifies a user-defined string label for this entity. 6

No default (Integer > 0)

GPAD "Padding" of the interface to account for additional layers, such as shell thickness. This value is subtracted from the contact gap opening as calculated from the location of nodes. 1

Default = THICK (Real, NONE or THICK)

STIFF Relative stiffness of contact interface. 2.

Positive value (STIFF = Real > 0.0) is directly prescribed stiffness.

Negative value (STIFF = Real < 0.0) defines a stiffness scaling factor. The stiffness scaling factor is equal to |Real < 0.0|. The scaling is applied to the automatic stiffness value (the stiffness value when STIFF = AUTO).

Default = AUTO (AUTO, SOFT, HARD, Real > 0.0, or Real < 0.0)

MU1 Coefficient of static friction ( $\mu$ s) or Friction coefficient table (integer) referencing a TABLES1 or TABLEG entries. 3

Default = 0.0 (Real ≥ 0.0, Integer > 0, STICK or FREEZE)

MU2 Coefficient of kinetic friction ( $\mu$ k). (Ignored in linear analysis). 3

Default = MU1 (0.0 < Real < MU1)

CLEARANCE Initial gap opening between main and secondary, irrespective of the actual distance between the nodes. 5

Default = not prescribed (Real or blank).

SEPARATION Flag indicating whether the main and secondary can separate after the contact has been closed. Applied only to frictional, SLIDE, and STICK contacts with S2S or large-displacement N2S.
YES (Default)
Separation could happen even after the contact is closed.
NO
No separation happens once the contact is closed.

FRICESL Frictional elastic slip - distance of sliding up to which the frictional transverse force increases linearly with slip distance. Specified in physical distance units (similar to U0 and GPAD). 3
AUTO (Default) or Blank
Friction model based on Elastic Slip Distance, with the distance selected as 0.5% of the average characteristic edge length of all the CONTACTs.
LONG
Friction model based on Elastic Slip Distance, with the distance selected as 1% of the average characteristic edge length of all the CONTACTs.
Real > 0.0
Friction model based on Elastic Slip Distance, with the distance selected as Real > 0.0.
0.0
Friction model based on fixed transverse stiffness KT.

STFEXP Indicates that the exponential nonlinear penalty parameters are to follow:
C0, P0 Parameters defining the exponential function. 2

C0: Default = AUTO (Real > 0.0 or AUTO)

P0: Default = AUTO (Real > 0.0 or AUTO)

STFQDR Indicates that the quadratic nonlinear penalty parameters are to follow:
C0, ALPHA1, ALPHA2, ALPHA3 Parameters defining the quadratic function. 2

C0: Default = 0.0 (Real ≥ 0.0)

ALPHA1: Default = AUTO (Real > 0.0 or AUTO)

ALPHA2: Default = AUTO (1.0>Real > 0.0 or AUTO)

ALPHA3: Default = AUTO (1.0>Real > 0.0 or AUTO)

STFTAB Flag indicating that the contact pressure-overclosure relationship is defined.
STFTID Identification number of a TABLES1 or TABLEG entry for the pressure-overclosure relationship. 4

1. The initial contact gap opening is calculated automatically based on the relative location of secondary and main nodes (in the original, undeformed mesh). To account for additional material layers covering main and secondary objects, the GPAD entry can be used. GPAD option THICK automatically accounts for shell thickness on both sides of the contact interface (this also includes the effects of shell element offset ZOFFS or composite offset Z0), when the main and/or secondary are shell surfaces (SET of shell element types or SURF of shell element faces). The THICK option will only apply automatic padding if shells are selected for main/secondary in the contact interface (for example, padding is not applied for "skinned" solid elements that are selected as a main/secondary in the contact interface). For further information, refer to Contact Interface Padding (GPAD) in the User Guide.
2. Option STIFF=AUTO determines the value of normal stiffness for each contact element using the stiffness of surrounding elements. Additional options SOFT and HARD create respectively softer or harder penalties. SOFT can be used in cases of convergence difficulties and HARD can be used if undesirable penetration is detected in the solution. A negative value for STIFF indicates that a stiffness scaling factor equal to |Real < 0.0| is defined. This scaling is applied on the stiffness value via STIFF = AUTO. For further information, refer to Penalty-based Contact in the User Guide.

Optional continuation lines STFEXP and STFQDR are available for the definition of exponential and quadratic penalties. These penalties do not apply to FREEZE contact, they are also ignored for contacts in linear analysis.

For further information, refer to Linear Penalty Curve (Nonlinear Analysis) and Nonlinear Penalty Curve (Nonlinear Analysis) in the User Guide.

3. MU1=STICK is interpreted in OptiStruct as an enforced stick condition - such contact interfaces will not enter the sliding phase. Of course, the enforced stick only applies to contacts that are closed.
Note: In order to effectively enforce the stick condition, frictional offset may need to be turned off. For further information, refer to Friction in the User Guide.

MU1=FREEZE enforces zero relative motion on the contact surface - the contact gap opening remains fixed at the original value and the sliding distance is zero. Also, rotations at the secondary node are matched to the rotations of the main patch. The FREEZE condition applies to all respective contact elements, no matter whether open or closed. Also, this condition is effective irrespective of the frictional offset setting.

MU1 set to an integer value references a TABLES1 or TABLEG ID. TABLES1 or TABLEG entries (xi,yi) correspond to pseudo time-friction coefficient values. For nonlinear subcases, table lookup is performed to compute a value for the coefficient of friction based on the pseudo-time value of the current increment. An error message is issued and OptiStruct will stop, if a negative value is returned. If a zero value is returned, the CONTACT that refers to the PCONT entry will be treated as frictionless. For linear subcases, the friction coefficient at pseudo-time zero will be used. MU2 will be ignored, if MU1 is provided as TABLES1 or TABLEG ID.

If FRIC is not explicitly defined on the PCONTX/PCNTX# entries, the MU1 value on the CONTACT or PCONT entry is used for FRIC in the /INTER entries for Geometric Nonlinear Analysis. Otherwise, FRIC on PCONTX/PCNTX# overwrites the MU1 value on CONTACT/PCONT. For further information, refer to Friction in the User Guide.

4. TABLES1 or TABLEG entries can be used to define the contact pressure-overclosure relationship, as outlined below.
x – values Overclosure values The values must be in ascending order.

The values can be negative and will refer to gap opening values in this case.

y – values Pressure values The values must be in ascending order.

The values must be positive.

Under the above conditions, the slope of the pressure-overclosure curve (penalty) will not be negative or zero.

5. For more information on clearance, refer to Contact Interface Parameters (Contact Control) in the User Guide.
6. String based labels allow for easier visual identification, including when being referenced by other entries. For more details, refer to String Label Based Input File.
7. CONTPRM, KTLIN can be used to control the tangential stiffness KT for closed contact in linear analysis when STIFF = Real > 0.0 and MU1 = Real > 0.0 on the PCONT entry referenced by the contact.
8. This card is represented as a property in HyperMesh.