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# 31.1 Connector elements

• “Connectors: overview,” Section 31.1.1   
• “Connector elements,” Section 31.1.2   
• “Connector actuation,” Section 31.1.3   
• “Connector element library,” Section 31.1.4   
• “Connection-type library,” Section 31.1.5

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# 31.1.1 CONNECTORS: OVERVIEW

Abaqus offers a library of connector types and connector elements to model the behavior of connectors.

# Overview

Connector modeling consists of:

• choosing and defining the appropriate connector elements (“Connector elements,” Section 31.1.2);   
• defining the connector behavior (“Connector behavior,” Section 31.2.1);   
• defining any connector actuations (“Connector actuation,” Section 31.1.3); and   
• monitoring connector output (“Connector elements,” Section 31.1.2, and “Connector element library,” Section 31.1.4).

# Typical applications

The analyst is often faced with modeling problems in which two different parts are connected in some way. Sometimes connections are simple, such as two panels of sheet metal spot welded together or a door connected to a frame with a hinge. In other cases the connection may impose more complicated kinematic constraints, such as constant velocity joints, which transmit constant spinning velocity between misaligned and moving shafts. In addition to imposing kinematic constraints, connections may include (nonlinear) force versus displacement (or velocity) behavior in their unconstrained relative motion components, such as a muscle force resisting the rotation of a knee joint in a crash-test occupant model. More complex connections may include the following:

• stopping mechanisms, which restrict the range of motion of an otherwise unconstrained relative motion;   
• internal friction, such as the lateral force or moments on a bolt generating friction in the translation of the bolt along a slot;   
• failure conditions, where excess force or displacement inside the connection causes the entire connection or a single component of relative motion to break free; and   
• locking mechanisms that engage after some force or displacement criteria is met, such as a snap-fit connector or a falling-pin locking mechanism on a satellite deployment arm.

In many situations the connection can be actuated either through displacement or force control, such as a hydraulic piston or a gear-driven robot arm.

In Abaqus/Standard if the two parts being connected are rigid bodies, multi-point constraints cannot be used to connect the bodies at nodes other than the reference nodes, since multi-point constraints use degree-of-freedom elimination and the other nodes on a rigid body do not have independent degrees of freedom. In Abaqus/Explicit this restriction does not apply. See “General multi-point constraints,” Section 35.2.2.

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Connector elements in Abaqus provide an easy and versatile way to model these and many other types of physical mechanisms whose geometry is discrete (i.e., node-to-node), yet the kinematic and kinetic relationships describing the connection are complex.

# Connector elements versus multi-point constraints

In many instances connector elements perform functions similar to multi-point constraints (“General multi-point constraints,” Section 35.2.2). However, in most cases multi-point constraints eliminate degrees of freedom at one of the nodes involved in the connection. This elimination has the advantage that the problem size is reduced; it has the disadvantage that output and other functionality provided with connector elements is not available. In addition, in Abaqus/Standard the degree of freedom elimination prevents the use of multi-point constraints between nodes without independent degrees of freedom (such as nodes on a rigid body whose degrees of freedom are dependent on the degrees of freedom at the reference node).

In contrast, connector elements do not eliminate degrees of freedom; kinematic constraints are enforced with Lagrange multipliers. These Lagrange multipliers are additional solution variables in Abaqus/Standard. The Lagrange multipliers provide constraint force and moment output. Since connector elements do not eliminate degrees of freedom, they can be used in many situations where multi-point constraints cannot be used or do not exist for the function required; for example, to connect two rigid bodies at nodes other than the reference node in Abaqus/Standard.

Multi-point constraints are more efficient than connector elements; and if the requirements of the analysis can be satisfied with multi-point constraints, they should be used in place of connector elements.

# Input file template

The following template shows the options used to define and activate the connector elements shown in Figure 31.1.1–1 and Figure 31.1.1–2. In the respective figures on the left is a schematic representation of a connection to be modeled; on the right is a representation of the equivalent finite element model. All options are discussed in detail in the following sections.

![](images/page-564_2c9da2e994875cf90815db440f578a5e2f72b6d3d0f38c8c0bd7b8eebca0010a.jpg)

<details>
<summary>text_image</summary>

extensible
range
7.5
</details>

![](images/page-564_bb4fd0e81de35fd46d62a244288da304be72125eba347fa3350b25498722eea2.jpg)

<details>
<summary>text_image</summary>

node 12
b
1 (local orientation)
node 11
a
2
</details>

Figure 31.1.1–1 Simplified connector model of a shock absorber.

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![](images/page-565_01a4d7d1e2260a1c2ee31d542f9b6fadf63c4b0cfbf374d135a0dfd2cfab62e1.jpg)

<details>
<summary>text_image</summary>

2.0
15.0
body 2
node 120
node 110
body 1
45°
Rightarrow
node 120
2
1 (local orientation)
node 110
2
1
global directions
</details>

Figure 31.1.1–2 A pin-in-slot connection modeled with SLOT and CARDAN connection types.   
```prolog
*HEADING
...
*ELEMENT, TYPE=CONN3D2, ELSET=shock
101, 11, 12
*ELEMENT, TYPE=CONN3D2, ELSET=pininslot
1010, 110, 120
...
*ORIENTATION, NAME=ori60
0.5, 0.866025, 0.0, -0.866025, 0.5, 0.0
*ORIENTATION, NAME=ori45
0.707, 0.707, 0.0, -0.707, 0.707, 0.0
*CONNECTOR SECTION, ELSET=shock, BEHAVIOR=sbehavior
revolute, slot
ori60,
...
*CONNECTOR BEHAVIOR, NAME=sbehavior
*CONNECTOR DAMPING, COMPONENT=1
1500.0
*CONNECTOR LOCK, COMPONENT=3, LOCK=4
, , -500.0, 500.0
*CONNECTOR ELASTICITY, COMPONENT=4, NONLINEAR
-900., -0.7
0., 0.0
1250., 0.7
*CONNECTOR CONSTITUTIVE REFERENCE 
```

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```txt
, , , 22.5,
*CONNECTOR STOP, COMPONENT=1
7.5, 15.0
...
*CONNECTOR FRICTION
0.34, 0.55, 0.0
0.34, 0.10, 0.45
*FRICTION
.15
...
*CONNECTOR SECTION, ELSET=pininslot
cardan, slot
ori45,
*CONNECTOR MOTION
pininslot, 4
pininslot, 5
...
*STEP
...
*CONNECTOR MOTION, TYPE=VELOCITY
pininslot, 6, 0.7854
...
*CONNECTOR LOAD
pininslot, 1, 1000.0
...
*END STEP 
```

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# 31.1.2 CONNECTOR ELEMENTS

Products: Abaqus/Standard Abaqus/Explicit Abaqus/CAE

# References

• “Connectors: overview,” Section 31.1.1   
• “Connector element library,” Section 31.1.4   
• “Connection-type library,” Section 31.1.5   
• \*CONNECTOR SECTION   
• “Creating connector sections,” Section 15.12.11 of the Abaqus/CAE User’s Guide, in the HTML version of this guide   
• “Creating and modifying connector section assignments,” Section 15.12.12 of the Abaqus/CAE User’s Guide, in the HTML version of this guide

# Overview

# Connector elements:

• are available for two-dimensional, axisymmetric, and three-dimensional analyses;   
• can define a connection between two nodes (each node can be connected to a rigid part, a deformable part, or not connected to any part);   
• can define a connection between a node and ground;   
• have relative displacements and rotations that are local to the element, which are referred to as components of relative motion;   
• are functionally defined by specifying the connector attributes;   
• have comprehensive kinematic and kinetic output; and   
• can be used to monitor kinematics in local coordinate systems.

# Choosing an appropriate element

Two connector elements are provided. The element type to be chosen depends on the dimensionality of the analysis: CONN2D2 for two-dimensional and axisymmetric analyses and CONN3D2 for threedimensional analyses. Both connector elements have at most two nodes. The position and motion of the second node on the connector element are measured relative to the first node.

# Naming convention

Connector elements in Abaqus are named as follows:

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![](images/page-568_7f5b3f72645c472f01b7de467f3814fbfd7b5ba0d8321458f09078c717466786.jpg)

<details>
<summary>text_image</summary>

CONN
3D
2
number of nodes
two-dimensional (2D) or three-dimensional (3D)
connector
</details>

For example, CONN2D2 is a two-dimensional, 2-node connector element.

# Defining a connection between points

A connector element can be used to connect two points.

Input File Usage: \*ELEMENT, TYPE=name connector element number, node\_1, node\_2

Abaqus/CAE Usage: Interaction module: Connector→Assignment→Create: select wires

# Defining a connection between a point and ground

A connector element can be connected to ground, and the ground “node” can be the first or second point on the connector element. The initial position of the ground node used for calculating relative position and displacement is the initial position of the other point on the element. All displacements and rotations at the ground node, if they exist, are fixed.

Input File Usage: Use one of the following options: \*ELEMENT, TYPE=name connector element number, node number on the body \*ELEMENT, TYPE=name connector element number, , node number on the body

Abaqus/CAE Usage: Interaction module: Connector→Assignment→Create: select wires connected to ground

# Components of relative motion

Connector elements have relative displacements and rotations that are local to the element. These relative displacements and rotations are referred to as components of relative motion. In the three-dimensional case connector elements use 12 nodal degrees of freedom to define six relative motion components: three displacements and three rotations in element local directions. In two dimensions six nodal degrees of

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freedom define three relative motion components: two displacements and one rotation. The components of relative motion are either constrained or unconstrained (“available”), depending upon the definition of the connector element.

# Constrained components of relative motion

Constrained components of relative motion are displacements and rotations that are fixed by the connector element.

In connector elements with constrained components of relative motion, Abaqus/Standard uses Lagrange multipliers to enforce the kinematic constraints. Accordingly, in Abaqus/Standard the constraint forces and moments carried by the element appear as additional solution variables. The number of additional solution variables is equal to the number of constrained components of relative motion. In Abaqus/Explicit the constraints are enforced using an augmented Lagrangian technique for which no additional solution variables are needed.

# Available components of relative motion

Available components of relative motion are displacements and rotations that are not constrained kinematically and, hence, remain available for defining material-like behavior, specifying time-dependent motion, applying loading, or assigning complex interactions, such as contact or friction. Many connection types have available components of relative motion, and their meaning is described in “Connection-type library,” Section 31.1.5, for each individual connection type.

# Defining the connection attributes

The connection attributes define the connector element’s function. In the most general case you specify the following attributes:

• the connection type or types,   
• the local directions associated with the connector’s nodes,   
• additional data for certain connection types, and   
• the connector behavior.

The connector definition that is defined with these attributes is associated with a set of connector elements.

Input File Usage: \*CONNECTOR SECTION, ELSET=name

Abaqus/CAE Usage: Interaction module:

Connector→Geometry→Create Wire Feature

Connector→Section→Create: Name: connector section name

Connector→Assignment→Create: select wires: Section:

connector section name

# Defining the connection type

Abaqus provides a comprehensive library of connection types. See “Connection-type library,” Section 31.1.5, for the available connection types. The connection types are divided into three categories: basic connection components, assembled connections, and complex connections. The basic

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connection components affect either translations or rotations on the second node. A connector element may include one translational basic connection component and/or one rotational basic connection component. The assembled connections are constructed from the basic connection components. They are provided for convenience and cannot be combined in the same connector element definition with a basic connection component or other assembled connections. Complex connections affect a combination of degrees of freedom at the nodes in the connection and cannot be combined with other connection components.

The connection type is specified as:

• a single basic connection type (translational or rotational),   
• one translational and one rotational basic connection type,   
• one assembled connection type, or   
• one complex connection type.

Input File Usage: Use one of the following options:

```txt
*CONNECTOR SECTION, ELSET=name basic connection type, basic connection type
*CONNECTOR SECTION, ELSET=name assembled connection or complex connection 
```

Abaqus/CAE Usage: Interaction module:

```txt
Connector→Section→Create: Connection Category: Basic, Translational type: translational basic connection type and/or Rotational type: rotational basic connection type or
Connector→Section→Create: Connection Category: Assembled/Complex, Assembled/Complex type: assembled connection or complex connection 
```

# Defining the local connector directions

Local directions at the nodes are often required to define the connection types used to define the connector element. The local directions and how they are used to define the connection are described in “Connection-type library,” Section 31.1.5. In the most general case the connection type uses two sets of local directions, which are defined as described in “Orientations,” Section 2.2.5. The names associated with the two orientation definitions must be referred to from the connector section definition.

Input File Usage: Use the following options for the most general case:

```txt
*ORIENTATION, NAME=orientation_1
*ORIENTATION, NAME=orientation_2
*CONNECTOR SECTION, ELSET=name
basic connection type(s) or assembled connection
orientation_1 for first node (or ground), orientation_2 for
second node (or ground) 
```
