CFAST and CWELD Connections (Nastran)

Use the CFAST/CWELD Connection command to create Nastran CFAST and CWELD type connections in Pre/Post. In Nastran you use CFAST and CWELD elements to model connections, such as fasteners, spot welds, or rivets, between multiple sheet bodies. You can use CFAST and CWELD elements to connect patches of elements either within a single FE model or between FE models in an assembly FEM.

CFAST and CWELD connections:

• Are not actual elements. They are simply connection definitions. Nastran internally generates the constraint equations that define the stiffness for the CFAST or CWELD connections when you solve the model.

• Provide alternatives to traditional Nastran connection methods, such as CBAR, RBE2, or RBE3 elements or MPC constraints. In general, CWELD and CFAST connections are easier to create and use.

For more information on connection elements in Simcenter Nastran, see:

• CFAST and CWELD in the Simcenter Nastran Quick Reference Guide

• CWELD Connector Element in the Simcenter Nastran Element Library Reference Manual

In the following graphic, (A) shows the location of rivets which represent the points on which to create the CWELD elements. (B) shows the two different meshes (physical property table IDs) that are connected by the CWELD elements. (C) shows the CWELD connections that the software creates at those locations.

Note:

The Spot Weld command is an alternative approach for creating connections at weld locations using either universal connections or using 1D beam and elements, such as CBEAM, CBAR, RBAR, and CGAP elements. For more information, see Universal connections or Creating a series of spot weld connections.

Defining the patches of elements

In Pre/Post, you can define the patches of elements to connect with a CFAST or CWELD connection by either selecting:

• The individual elements to connect on either side of the connection.For more information, see Selecting elements to create CFAST and CWELD connections (Nastran).

• The physical property tables to connect on either side of the connection.For more information, see Selecting physical property tables to create CFAST and CWELD connections (Nastran).

Defining properties for CFAST and CWELD connections

You can use the PFAST and PWELD physical property table dialog boxes to define properties for the CFAST and CWELD connections.

• For CFAST and CFAST1D elements, you can use the PFAST dialog box to define the translational and rotational stiffness properties of the element, the mass of the weld connection, and the structural damping value.

• For CWELD and CWELD1D elements, you can use the PWELD dialog box to define the axial rod diameter of the connection.

In the Simulation file, you can create a CWELD/CFAST Connection Parameters modeling object to specify values for various parameters that Nastran uses to create the CFAST or CWELD connections during the solve. These options correspond to the fields on the SWLDPRM bulk data entry. See Defining properties and parameters for CFAST/CWELD connections for more information.

CFAST and CWELD connections in the Simulation Navigator

The software places all CWELD and CFAST connections in either the 0D Connections or 1D Connections node in the Simulation Navigator. For example:

0D Connections
CWeld_Collector(1)
CWeld_Mesh_1

You can edit an existing CFAST or CWELD connection and modify the connection's properties, such as the connection type.

• For CFAST and CWELD connections that you import into Pre/Post, you cannot edit a connection that was created with a Path Selection of Patch by Element and a Location Type of **Projection Point (GS)**as the software cannot accurately determine the Search Distance data.

• After you create CFAST or CWELD connections, if you delete or modify one of the elements or physical property tables involved in the connection, then the software cannot automatically update the connection.

Note:

You cannot modify the specified element type when you edit an existing CFAST or CWELD connection.

Displaying CFAST and CWELD elements

By default, the software does not display the marker and associated text (the abbreviated element name) for 0D elements, including CFAST and CWELD elements. Not displaying the marker and text can improve the performance when you load or import a FEM file that contains a large number of 0D meshes. To display the marker or text for CFAST and CWELD elements, right-click the appropriate CFAST or CWELD mesh collector in the Simulation Navigator and select Edit Display. Then, use the Marker Type and Text options in the Mesh Display dialog box to select the marker type and turn on the text display.

For more information about display settings for 0D elements in large models, see Display settings for large models with 0D meshes.

Where do I find it?

Application	Pre/Post
Prerequisite	An active FEM file with Nastran as the specified solver.
Command Finder	CFAST/CWELD Connection

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

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CFAST and CWELD Connections (Nastran), Simcenter 3D 2021.1 Series

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