Defining constrained joint connections for LS-DYNA models

You can create the following types of LS-DYNA constrained joints as 1D connection elements in Pre/Post:

Element type	LS-DYNA keyword	Description
CONSTRAINED_INTERPOLATION	*CONSTRAINED_INTERPOLATION	A spider type element that you can use to connect a single independent node to multiple dependent nodes with weighting factors on each node. For example, you can use a *CONSTRAINED_INTERPOLATION element to connect a point or node to an edge.Use the Element Associated Data dialog box to define the node weighting factors.
CONSTRAINED_JOINT	*CONSTRAINED_JOINT	Joint element with different types. Use the Joint Type option in the Mesh Associated Data dialog box to select the type of joint to create, such as Spherical, Revolute, or Cylindrical.Use the Constrained Joint Options modeling object to specify additional options, such as variables for the FAILURE keyword.
CONSTRAINED_NODAL_RIGID_BODY	*CONSTRAINED_NODAL_RIGID_BODY	Models rigid, non-breakable connections between components, such as spot welds and other weld types. In explicit analyses, for example, you can use rigid bodies to represent stiff structural components that undergo negligible deformations but significant translations and rotations. Typically, you use a CONSTRAINED_NODAL_RIGID_BODY to connect a single independent node to dependent multiple nodes to create a spider-like connection. LS-DYNA considers all nodes that are connected by a CONSTRAINED_NODAL_RIGID_BODY connection to be a rigid body.Use the Constrained Nodal Rigid Body Optional dialog box to specify additional optional options, such as selecting an optional node for post-processing rigid body data.Note: You can also use the Constrained Keywords command in the Simulation file to use the *CONSTRAINED_NODAL_RIGID_BODY keyword to create a rigid connection between components. For more information, see Constrained keywords for rigid body creation (LS-DYNA).
CONSTRAINED_SPOTWELD	*CONSTRAINED_SPOTWELD	A rigid link that you can use to connect two shell elements (top to bottom). You can also specify properties, such as a failure time that specifies when the spot-weld fails.
CONSTRAINED_RIVET	*CONSTRAINED_RIVET	A special type of spot weld that you can use to model a rivet connection.Note: In Pre/Post, to create a *CONSTAINED_RIVET element, you must create *CONSTAINED_SPOTWELD element first, then modify the Element Type in the Mesh Associated Data dialog box *CONSTAINED_RIVET.

In Pre/Post, you use the 1D Mesh or 1D Connection command and the options in the Element Associated Data and Mesh Associated Data dialog boxes to define these keywords.

Note:

In LS-DYNA, these connection keywords are not elements, though they act as elements. Because they are not elements, your LS-DYNA input file does not need to include *PART or *MAT/*SECTION keywords.

Limitations

• In Pre/Post, you can define one coordinate system for a node. In LS-DYNA, you can define multiple coordinate systems for a single node. When you import one of these connection element keywords, Pre/Post uses the coordinate system that is defined on the independent node. If the independent node does not have a coordinate system, then the software uses the coordinate system that is defined on the first dependent node. When this occurs, Pre/Post displays a warning in the Information window and prints a message in the .lis file.

• In LS-DYNA, you can define different degrees of freedom for the dependent nodes of these connection elements. In Pre/Post, you can define a single degree of freedom only for all dependent nodes. If you import an element that has dependent nodes with different degrees of freedom, Pre/Post applies the degrees of freedom assigned to the first dependent node to all dependent nodes. The software then displays a warning in the Information window and prints a message in the .lis file.

• You cannot define dependent degree of freedom data in the Element Associated Data dialog box.

• When you import an LS-DYNA input file and then export the same file, Pre/Post does not preserve the element IDs for these connection elements. In LS-DYNA, an ID value must be unique within a *CONSTRAINED_ keyword. It does not have to be unique among all connections that use the CONSTRAINED_ keyword. In Pre/Post, ID values must be unique across all elements. If you import an input file that containsCONSTRAINED_ keywords with undefined ID values or ID values that are not unique, then Pre/Post changes the element ID to a unique value.

Look up more details

LS-DYNA elements

Manually creating connections in LS-DYNA models

Modeling spot welds for LS-DYNA

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Defining constrained joint connections for LS-DYNA models, Simcenter 3D 2021.1 Series

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