Contact interference in LS-DYNA models

In the LS-DYNA environment, there are multiple settings that you can use to apply contact thickness values. When you use the Interference Check command to check for intersections and penetrations between Contact definitions in LS-DYNA models, the software must examine these settings to compute the appropriate thickness value to apply to the elements.

Defining thickness values for LS-DYNA models

In the LS-DYNA environment, you can specify options in the FEM and Simulation file that affect the thickness of 2D elements in contact.

• In the FEM file, you can specify element thickness values in physical property tables.

• In the Simulation file, you can specify contact thickness options in the Controls, Contact Card 2 Card 3, and Contact Card A Card B modeling object dialog boxes. You then include these modeling objects in the Contact definition or in the appropriate solution.

Note:

The Interference Check command does not compute contact thickness values from contact definitions that you specify with the Connection Options list in the Mesh Associated Data dialog box in the FEM file.

Specifying contact thickness options in the Simulation file

The following table details all the different options that control contact thickness.

Option	Description	Dialog box location	LS-DYNA keyword	Notes
Default contact thickness (TH)	Specifies the default contact thickness value.	Controls modeling object, Contact page, Card 3 options	*CONTROL_CONTACT	This option applies to Contact definitions where the Contact Type is set to the following types only:AUTOMATIC_GENERALAUTOMATIC_SINGLE_SURFACEAUTOMATIC_NODES_TO_SURFACEAUTOMATIC_SURFACE_TO_SURFACEEAUTOMATIC_ONE_WAY_SURFACE_TO_SURFACEE
Default thickness scale factor (TH_SF)	Specifies the default scale factor to apply to contact thickness.	Controls modeling object, Contact page, Card 3 options	*CONTROL_CONTACT
Flag for using actual shell thickness in single surface types (SSTHK)	Controls whether LS-DYNA uses the defined shell element thickness values in the contact analysis.LS-DYNA ignores this value when the Soft constraint option (SOFT) is set to (2) Segment-based contact.	Controls modeling object, Contact page, Card 2 options**Soft constraint option (SOFT)**Contact Card A Card B modeling object (Card A) options	*CONTROL_CONTACT	This option applies to Contact definitions where the Contact Type is set to the following types only:AUTOMATIC_GENERAL****AUTOMATIC_SINGLE_SURFACE
Optional thickness for slave surface (SST)	Specifies an optional thickness value for 2D elements on the slave surface. This value overrides any specified element thickness value.	Contact Card 2 Card 3 modeling object, Card 3 options	*CONTACT_
Optional thickness for master surface (MST)	Specifies an optional thickness value for 2D elements on the master surface. This value overrides any specified element thickness value.	Contact Card 2 Card 3 modeling object, Card 3 options	*CONTACT_
Scale factor for slave surface thickness (SFST)	Specifies a scale factor for the thickness value for 2D elements on the slave surface.	Contact Card 2 Card 3 modeling object, Card 3 options	*CONTACT_
Scale factor for slave surface thickness (SFMT)	Specifies a scale factor for the thickness value for 2D elements on the master surface.	Contact Card 2 Card 3 modeling object, Card 3 options	*CONTACT_

Calculating contact thickness during the Interference Check process

The Interference Check command calculates the appropriate contact thickness value to apply to the selected elements according to the following criteria:

• When all other thickness options are either undefined or set to 0, the software computes the default contact thickness value as: Default contact thickness (TH) * Default thickness scale factor (TH_SF). For example, the software computes the default contact thickness value when:The Optional thickness for slave surface (SST) and Optional thickness for master surface (MST) options are not defined and the Flag for using actual shell thickness in single surface types (SSTHK) option is set to (0) Actual shell thickness is not used.When Flag for using actual shell thickness in single surface types (SSTHK) is set to (1) Use actual shell thickness and the Shell Thickness (T1) value is not specified in the physical property table associated with the mesh (SECTION_SHELL dialog box).

• When both selected surfaces in the contact definition have the Optional thickness for slave surface (SST) and Optional thickness for master surface (MST) options defined, the software computes the contact thickness as:Thickness of the slave surface = Optional thickness for slave surface (SST) * **Scale factor for slave surface thickness (SFST)**Thickness of the master surface = Optional thickness for master surface (MST) * **Scale factor for master surface thickness (SFMT)**Note: The software does not compute any contact thickness values for any selected 2D elements that are not included in the master or slave surfaces in the Contact definition.

• When Flag for using actual shell thickness in single surface types (SSTHK) is set to (1) Use actual shell thickness and the Contact Type in the Contact Definition is set to AUTOMATIC_GENERAL or AUTOMATIC_SINGLE_SURFACE, the software uses the Shell Thickness (T1) value in the physical property table associated with the mesh (SECTION_SHELL dialog box) as the contact thickness value.

• When all thickness values are set to 0 or are not defined, the software sets the contact thickness value to 0.

Applying thickness values to the appropriate elements

The software applies the computed contact thickness value to all 2D elements associated with the Contact definitions that you select when you define the interference set in the Interference Check dialog box.

You can use the Interference Check command to check for interference between contacting faces that are meshed with 2D elements only. The Interference Check does not analyze contact definitions that include 1D or 3D elements.

Where do I find it?

Application	Pre/Post
Prerequisite	A Simulation file activeLS-DYNA as the specified solver
Command Finder	Interference Check

Learn more

Detecting interference and clearance issues between meshes

Working with the Interference Check Navigator

Repairing interference and clearance issues between elements

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Contact interference in LS-DYNA models, Simcenter 3D 2021.1 Series

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