Nastran Contact Options

This page describes the available options for the default contact definition or for explicitly defined contact pairs. There are no Nastran-specific options associated with the General Contact Settings.

Access the Nastran-specific contact options in one of the following ways:

• Double-click the Contact (Default:___) heading in the browser (tree view), or right-click this heading and choose Edit Settings from the context menu. Then, select Nastran contact (CONTACTGENERATE) options from the drop-down menu at the top of the Contact Options dialog. When accessing the Nastran contact settings for the default contact declaration, only the General tab is available. (See the General Tab section of this page.)

  Options and values that you specify here are output to the Nastran deck as parameters of a CONTACTGENERATE card.

• Double-click an explicitly defined contact pair heading in the browser, or right-click the heading and choose Edit Settings from the context menu. Then, select Nastran contact (BSCONP) options from the drop-down menu at the top of the Contact Options dialog. When accessing the Nastran contact settings for an explicit contact pair, the General and Advanced tabs are available. (See the General Tab and Advanced Tab sections of this page.)

  Options and values that you specify here are output to the Nastran deck as parameters of BSCONP cards.

The Nastran-specific settings within the General and Advanced tabs of the Contact Options dialog contain the same parameters for all analysis and contact types. The contents of those tabs are detailed on this page. The listed parameters remain the same for all cases, but options and input fields that are not applicable to the current analysis or contact type are inactive.

There is one additional tab that is only applicable to nonlinear static stress analyses—the Weld Damage Model tab. Please refer to the Nastran Weld Failure Determination page within the Nonlinear Analyses branch to see the Weld Damage Model options.

Contact Surface Designation

The order in which you select surfaces or parts when defining contact pairs is important in some situations. In Simulation Mechanical, the first part/surface selected is the Primary one. The second part/surface selected is the Secondary one. The order can be reversed after a contact pair is created by right-clicking the contact pair heading in the browser and choosing Flip Primary and Secondary.

In Autodesk Nastran, the terms Master and Slave are analogous to the Simulation Mechanical terms Primary and Secondary, respectively. The first part/surface listed in a contact pair is the Master and the second is the Slave.

Contact Accomplished Through Merging of Nodes

Attention: Nastran-specific contact options are ignored when the following two conditions are both satisfied:

• You specify Bonded contact in the browser (either at the default or explicit contact pair level), and
• You generate a matched mesh

Under these conditions, the coincident nodes where two parts meet become merged together, and the Nastran-specific contact options have no effect on the simulation results. Part interaction is handled by virtue of the merged nodes rather than CONTACTGENERATE or BSCONP cards in the Nastran deck.

General Tab

Contact type: The available Nastran-specific contact types depend on the analysis type and the basic contact type specified in the browser (Bonded, Welded, or Surface). All possible contact types are listed below, but only those applicable to the current analysis and basic contact type will be available for selection:

• The following Nastran contact types are available when the basic Simulation Mechanical contact type specified in the browser is Bonded or Welded. The specific options you see depend upon whether you are editing settings for the default contact type or for an explicitly defined contact pair:
  • Welded (symmetric): This option is applicable to explicitly defined contact pairs (BSCONP card). All nodes on the master surface are connected to the nodes around the element faces they contact on the slave surface (but limited by the Maximum activation distance parameter). In addition, all nodes on the slave surface are connected to the nodes around the element faces they contact on the master surface. This type of contact generates more connections between the parts than the unsymmetric variant does.
  • Welded (unsymmetric): This option is applicable to explicitly defined contact pairs (BSCONP card). All nodes on the master surface are connected to the nodes around the element faces they contact on the slave surface (but limited by the Maximum activation distance parameter).
  • Welded: This option is applicable to the default contact definition (CONTACTGENERATE card). Since the master surface and slave surface are not known for default contact definitions, all possible contact elements are generated (slave-to-master and master-to-slave). This setting is equivalent to the Welded (symmetric) option for BSCONP cards.
  • Offset Weld (symmetric): This option is applicable to explicitly defined contact pairs (BSCONP card). All nodes on the master surface are connected to the nodes around the element faces to which they are bonded on the slave surface (but limited by the Maximum activation distance parameter). In addition, all nodes on the slave surface are connected to the nodes around the element faces to which they are bonded on the master surface. Offset weld (symmetric) contact provides the same type of connection as the Welded (symmetric) option previously introduced, except that it support surfaces that are not in contact in the CAD model. You must specify the Penetration surface offset, which defines the distance between the surfaces that are to be bonded to each other. An example of when to use this type of contact is to connect shell elements to another part. Assume that the CAD surface of the shell element part is drawn at the midplane of the thickness the elements represent, which is the proper technique. Therefore, an adjacent brick part would be separated from the shell elements by half of the shell element thickness.
  • Offset Weld (unsymmetric): This option is applicable to explicitly defined contact pairs (BSCONP card). All nodes on the master surface are connected to the nodes around the element faces to which they are bonded on the slave surface (but limited by the Maximum activation distance parameter). Offset weld (unsymmetric) contact provides the same type of connection as the Welded (unsymmetric) option previously introduced, except that it supports surfaces that are not in contact in the CAD model. You must specify the Penetration surface offset, which defines the distance between the surfaces that are to be bonded to each other.
  • Offset Weld: This option is applicable to the default contact definition (CONTACTGENERATE card). Since the master surface and slave surface are not known for default contact definitions, all possible contact elements are generated (slave-to-master and master-to-slave). This setting is equivalent to the Offset Weld (symmetric) option for BSCONP cards.
  Note: Do not confuse the term Welded Contact within its two different contexts:
  • Nastran Solver: For Nastran solutions, the term Welded Contact is analogous to Bonded Contact or Smart Bonding in Simulation Mechanical.
  • SimMech Solver: For solutions run using the native Simulation Mechanical solver, the meaning of Welded contact is quite different. The nodes along the edges of the contact surfaces act the same as if the Bonded option had been selected. However, the nodes along the interior of these surfaces act the same as if the Free/No Contact option had been selected. This contact type simulates the connection between two parts when a weld bead is added around the perimeter of the part interface. Loads are transmitted from one part to the other only through the perimeter weld. Interior surface nodes are free to separate from, or even penetrate through, each other.

  When you run a simulation using the Nastran solver, the basic Bonded and Welded Simulation Mechanical contact settings produce the same results, assuming that the same Nastran-specific options are used in both cases. SimMech bonded and welded contact are both mapped to Nastran welded contact by default.

• The following Nastran contact types are available when the basic Simulation Mechanical contact type specified in the browser is Surface. The specific options you see depend upon whether you are editing settings for the default contact type or for an explicitly defined contact pair:
  • General (symmetric): This option is applicable to explicitly defined contact pairs (BSCONP card). Surfaces do not have to be initially in contact in the CAD model. Nodes on the slave surface cannot penetrate the element faces on the master surface. Additionally, nodes on the master surface cannot penetrate the face of elements on the slave surface.
  • General (unsymmetric): This option is applicable to explicitly defined contact pairs (BSCONP card). Surfaces do not have to be initially in contact in the CAD model. Nodes on the slave surface cannot penetrate the element faces on the master surface. However, unsymmetric contact does not prevent nodes on the master surface from penetrating the face of elements along the slave surface. The surfaces can separate freely and can slide along each other.
  • General: This option is applicable to the default contact definition (CONTACTGENERATE card). Since the master surface and slave surface are not known for default contact definitions, all possible contact is detected (slave-to-master and master-to-slave). This setting is equivalent to the General (symmetric) option for BSCONP cards.
• The following Nastran contact types are available when the basic Simulation Mechanical contact type specified in the browser is Sliding/no separation. The specific options you see depend upon whether you are editing settings for the default contact type or for an explicitly defined contact pair:
  • Slide (symmetric): This option is applicable to explicitly defined contact pairs (BSCONP card). Surfaces do not have to be initially in contact in the CAD model. Nodes on the slave surface can neither penetrate the element faces on the master surface nor separate from them. The same contact behavior is imposed between the nodes on the master surface and the element faces on the slave surface.
  • Slide (unsymmetric): This option is applicable to explicitly defined contact pairs (BSCONP card). Surfaces do not have to be initially in contact in the CAD model. Nodes on the slave surface can neither penetrate the element faces on the master surface nor separate from them. However, unsymmetric contact does not prevent nodes on the master surface from penetrating or separating from the face of elements along the slave surface.
  • Slide: This option is applicable to the default contact definition (CONTACTGENERATE card). Since the master surface and slave surface are not known for default contact definitions, all possible contact is detected (slave-to-master and master-to-slave). This setting is equivalent to the Slide (symmetric) option for BSCONP cards.
• The following Nastran contact types are available when the basic Simulation Mechanical contact type specified in the browser is Sliding/no separation. The specific options you see depend upon whether you are editing settings for the default contact type or for an explicitly defined contact pair:
  • Rough (symmetric): This option is applicable to explicitly defined contact pairs (BSCONP card). Surfaces do not have to be initially in contact in the CAD model. Nodes on the slave surface can neither penetrate the element faces on the master surface nor slide along them. However, the slave nodes can separate from the master surface. The same contact behavior is imposed between the nodes on the master surface and the element faces on the slave surface.
  • Rough (unsymmetric): This option is applicable to explicitly defined contact pairs (BSCONP card). Surfaces do not have to be initially in contact in the CAD model. Nodes on the slave surface can neither penetrate the element faces on the master surface nor slide along them. However, unsymmetric contact does not prevent nodes on the master surface from penetrating or sliding relative to the face of elements along the slave surface.
  • Rough: This option is applicable to the default contact definition (CONTACTGENERATE card). Since the master surface and slave surface are not known for default contact definitions, all possible contact is detected (slave-to-master and master-to-slave). This setting is equivalent to the Rough (symmetric) option for BSCONP cards.

Stiffness factor: (Nastran SFACT parameter; Real number > 0.0; Default = 1.0) – This input is the stiffness scaling factor used to scale the penalty values that are determined automatically. The use of a scale factor less than one is recommended when convergence problems arise. A value greater than one when excessive penetration occurs. To deviate from the default behavior, activate the checkbox and enter a suitable floating point value in the input field.

Coefficient of friction: (Nastran MU parameter; Real number ≥ 0.0; Default = 0.0). – This option is applicable to general surface contact. Activate the checkbox and specify an appropriate coefficient of static friction in the input field to include static friction forces in the contact solution. When deactivated, surface contact is frictionless.

Penetration surface offset: (Nastran W0 parameter; Real number; Default = 0.0) – This option is applicable to Offset weld and General surface contact types. By default, the contact plane is the face of the master surface elements, with contact detected when a slave node touches that plane. For symmetric contact types, contact is also detected when a master node touches the face of an element on the slave surface. A positive W0 value offsets the contact plane in the direction normal to the element face. This offset results in a contact condition occurring when a node on one part is located at or penetrates the offset plane of the other part. That is, contact occurs at a specified distance away from the actual element faces. An example of when to use this parameter is to provide proper interaction between shell elements and another part. Assume that the CAD surface of the shell element part is drawn at the midplane of the thickness the elements represent, which is the proper technique. Therefore, an adjacent brick part would be separated from the shell elements by half of the shell element thickness. Offsetting the contact plane by half of the shell thickness causes part interaction to occur at the correct distance between the meshes.

Maximum activation distance: (Nastran MAXAD parameter; Real number ≥ 0.0; Default = AUTO) – This parameter is applicable to all types of contact, but it is especially useful for Offset weld and General surface contact. Normally, the program calculates the default MAXAD value from a number of model characteristics and parameters. The AUTO setting (option deactivated) is recommended for optimal performance when little or no sliding is expected. If significant sliding is expected, or if the contact surfaces are initially separated, activate this option and specify a suitable distance in the input field. Potential contact will only be considered for master and slave nodes that are within the specified distance from each other.

Maximum allowable penetration: (Nastran TMAX parameter; Real number ≥ 0.0; Default = 0.0) – This parameter is the maximum allowable penetration used in the adjustment of penalty values normal to the contact plane. A positive value activates the penalty value adjustment. When TMAX ≠ 0.0, the displacement based stiffness update method is selected. The value you specify defines the allowable penetration of the slave node into the master surface. The recommended TMAX value is between 1% and 10% of the element thickness for plates or the equivalent thickness for other elements that are connected to the contact element. When this option is left deactivated, the program determines when to adjust the penalty values based on the model characteristics and other parameters.

Frictional stiffness for stick: (Nastran FSTIF parameter; Real number ≥ 0.0; Default is model dependent) – Activate this option to provide a user-specified frictional stiffness. The FSTIF value should be chosen carefully. A method of choosing a value is to divide the expected frictional strength (MU * expected normal force) by a reasonable value of the relative displacement before slipage occurs. A large stiffness value may cause poor convergence, while too small a value may result in reduced accuracy.

Advanced Tab

Maximum allowable adjustment ratio: (Nastran MAR parameter; Real number ≥ 1.0; Default = 100.0) – MAR is the maximum allowable adjustment ratio for adaptive penalty values K and FSTIF. The Nastran TRMIN parameter is used for the penalty value adjustment and defines the lower limit for the allowable penetration computed by TRMIN * TMAX. The penalty values are decreased if the penetration is below the lower limit.

Fraction of maximum allowable penetration: (Nastran TRMIN parameter; 0.0 ≤ Real number ≤ 1.0; Default = 0.001) – This parameter is the fraction of the TMAX parameter, and it defines the lower limit for the allowable penetration.

Maximum radial activation distance: (Nastran MAXRAD parameter; Real number ≥ 0.0; Default = 0.0) – MAXRAD and MAXNAD are an alternative to MAXAD. If either one is set to a non-zero value MAXAD is ignored and MAXRAD and/or MAXNAD is used instead. When MAXRAD is specified elements are only generated if the element in-plane distance from any contact surface master node to the potential slave node is less than (1.0E-5) * l₁₃ + MAXRAD, where l₁₃ is the distance from node 1 to node 3 of the contact surface.

Maximum normal activation distance: (Nastran MAXNAD parameter; Real number ≥ 0.0; Default = 0.0) – MAXRAD and MAXNAD are an alternative to MAXAD. If either one is set to a non-zero value MAXAD is ignored and MAXRAD and/or MAXNAD is used instead. When MAXNAD is specified elements are only generated if the element normal distance from any contact surface master node to the potential slave node is less than MAXNAD.

Maximum allowable slip: (Nastran SMAX parameter; Real number ≥ 0.0; Default = 0.0) – Maximum allowable slip used in the adjustment of penalty values parallel to the contact plane (FSTIF). A positive value activates the penalty value adjustment. If SMAX ≠ 0.0, the displacement based update method is selected. The FSTIF value is adjusted internally to achieve the SMAX displacement specified. When SMAX = 0.0 (default), the proximity stiffness based update method is used.

Thermal contact conductance: (Nastran CTC parameter; Real number ≥ 0.0; Default = ∞) – This parameter is only applicable to heat transfer analyses. CTC is defined as q/ΔT, where ΔT is the change in temperature between the slave node and the average of the master nodes, and q is the heat flux through the contact surface.

Weld Damage Model Tab

This tab is only applicable to explicitly defined contact pairs in Static Stress with Nonlinear Material Models analyses. Additionally, it is only applicable when the basic contact type defined in the browser is Bonded or Welded.

Please see the Nastran Weld Failure Determination page in the Nonlinear Analyses branch for details concerning the parameters in the Weld Damage Model tab.