Abaqus
offers a library of connector types and connector elements to model the
behavior of connectors.
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.
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).
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 1
and
Figure 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.
Figure 1. Simplified connector model of a shock absorber. Figure 2. A pin-in-slot connection modeled with
SLOT and CARDAN
connection types.
