Multipoint Constraint Element: Slot Joint

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MPC184 Slot Joint Element Description

The MPC184 slot joint element is a two-node element that has one relative displacement degree of freedom. The rotational degrees of freedom at nodes I and J are left free.

Figure 184slot.1:  MPC184 Slot Joint Geometry

MPC184 Slot Joint Geometry

MPC184 Slot Joint Input Data

Set KEYOPT(1) = 8 to define a two-node slot joint element.

Figure 184slot.1: MPC184 Slot Joint Geometry shows the geometry and node locations for this element. Two nodes (I and J) define the element.

A local Cartesian coordinate system must be specified at the first node, I, of the element. The second node, J, is constrained to move on the local e 1 axis specified at node I. The local coordinate system specified at node I evolves with the rotations at node I. Use the SECJOINT command to specify the identifiers of the local coordinate systems.

The constraints imposed on a slot joint element are easily described by referring to Figure 184slot.1: MPC184 Slot Joint Geometry. At any given instant of time, the constraints imposed in a 3-D slot joint are as follows:

Where, x I and x J are the position vectors of nodes I and J in the current configuration, and X I and X J are the position vectors of nodes I and J in the reference configuration. Essentially these constraints force the node J to move along the e 1 axis of the local coordinate system specified at node I. e I are in the current configuration, while E I are specified in the initial configuration.

The change in the relative position of the nodes I and J is given by:

Where u is the initial offset computed based on the initial configuration and the local coordinate system associated with node I, and

The constitutive calculations use the following definition of the joint displacement:


= reference length, length1, specified on SECDATA command.

If the reference length is not specified, the initial offset is used.

Other input data that are common to all joint elements (material behavior, stops and limits, locks, etc.) are described in "Joint Input Data" in the MPC184 element description.

MPC184 Slot Joint Input Summary

This input summary applies to the slot joint element option of MPC184: KEYOPT(1) = 8.


I, J

Note:  For a grounded joint element, specify either node I or node J in the element definition and leave the other node (the grounded node) blank.

Degrees of Freedom


Real Constants


Material Properties

Use the JOIN label on the TB command to define stiffness, damping, and Coulomb friction behavior. (See MPC184 Joint in the Material Reference for detailed information on defining joint materials.)

Surface Loads


Body Loads
Temperatures -- 

T(I), T(J)

Element Loads
Displacements -- 


Forces -- 


Special Features
Large deflection
Linear perturbation

Element behavior:

8  -- 

Slot joint element

MPC184 Slot Joint Output Data

The solution output associated with the element is in two forms:

These tables use the following notation:

A colon (:) in the Name column indicates the item can be accessed by the Component Name method [ETABLE, ESOL]. The O column indicates the availability of the items in the file Jobname.OUT. The R column indicates the availability of the items in the results file.

In either the O or R columns, Y indicates that the item is always available, a number refers to a table footnote that describes when the item is conditionally available, and a - indicates that the item is not available.

Table 184slot.1:  MPC184 Slot Joint Element Output Definitions

ELElement Number-Y
NODESElement node numbers (I, J)-Y
FYConstraint force in Y direction-Y
FZConstraint force in Z direction-Y
CSTOP1Constraint force if stop is specified on DOF 1-Y
CLOCK1Constraint force if lock is specified on DOF 1-Y
CSST1Constraint stop status[1]-Y
CLST1Constraint lock status[2]-Y
JRP1Joint relative position-Y
JCD1Joint constitutive displacement-Y
JEF1Joint elastic force-Y
JDF1Joint damping force-Y
JFF1Joint friction force-Y
JRU1Joint relative displacement-Y
JRA1Joint relative acceleration-Y
JRV1Joint relative velocity-Y
JTEMPAverage temperature in the element[3]-Y
JFST1Slip/stick status when friction is specified[4]-Y
JFNF1Normal moment in friction calculations-Y

  1. Constraint stop status:

    0 = stop not active, or deactivated
    1 = stopped at minimum value
    2 = stopped at maximum value
  2. Constraint lock status:

    0 = lock not active
    1 = locked at minimum value
    2 = locked at maximum value
  3. Average temperature in the element when temperatures are applied on the nodes of the element using the BF command, or when temperature are applied on the element using the BFE command.

  4. Stick/slip status when friction is active:

    0 = friction is not activated
    1 = sticking
    2 = slipping or sliding

The following table shows additional non-summable miscellaneous (NMISC) output available for the slot joint element.

Note:  This output is intended for use in the ANSYS Workbench program to track the evolution of local coordinate systems specified at the nodes of joint elements.

Table 184slot.2:  MPC184 Slot Joint Element - NMISC Output

E1X-I, E1Y-I, E1Z-IX, Y, Z components of the evolved e1 axis at node I-Y
E2X-I, E2Y-I, E2Z-IX, Y, Z components of the evolved e2 axis at node I-Y
E3X-I, E3Y-I, E3Z-IX, Y, Z components of the evolved e3 axis at node I-Y
E1X-J, E1Y-J, E1Z-JX, Y, Z components of the evolved e1 axis at node J-Y
E2X-J, E2Y-J, E2Z-JX, Y, Z components of the evolved e2 axis at node J-Y
E3X-J, E3Y-J, E3Z-JX, Y, Z components of the evolved e3 axis at node J-Y
JFX, JFY, JFZConstraint forces expressed in the evolved coordinate system specified at node I-Y
JMX, JMY, JMZConstraint moments expressed in the evolved coordinate system specified at node I-Y

Table 184slot.3: MPC184 Slot Joint Item and Sequence Numbers - SMISC Items and Table 184slot.4: MPC184 Slot Joint Item and Sequence Numbers - NMISC Items list output available via the ETABLE command using the Sequence Number method. See The General Postprocessor (POST1) in the Basic Analysis Guide and The Item and Sequence Number Table for further information. The table uses the following notation:


output quantity as defined in the Element Output Definitions table.


predetermined Item label for ETABLE command


sequence number for single-valued or constant element data

Table 184slot.3:  MPC184 Slot Joint Item and Sequence Numbers - SMISC Items

Output Quantity Name ETABLE and ESOL Command Input

Table 184slot.4:  MPC184 Slot Joint Item and Sequence Numbers - NMISC Items

Output Quantity Name ETABLE and ESOL Command Input

MPC184 Slot Joint Assumptions and Restrictions

  • Boundary conditions cannot be applied on the nodes forming the slot joint.

  • Rotational degrees of freedom are activated at the nodes forming the element. When these elements are used in conjunction with solid elements, the rotational degrees of freedom must be suitably constrained. Since boundary conditions cannot be applied to the nodes of the slot joint, a beam or shell element with very weak stiffness may be used with the underlying solid elements at the nodes forming the joint element to avoid any rigid body modes.

  • Stops (SECSTOP) and locks (SECLOCK) can only be applied on the relative x-direction. These are not applicable to the rotational degrees of freedom.

  • If both stops and locks are specified, then lock specification takes precedence. That is, if the degree of freedom is locked at a given value, then it will remain locked for the rest of the analysis.

  • In a nonlinear analysis, the components of relative motion are accumulated over all the substeps. It is essential that the substep size be restricted such that these rotations in a given substep are less than π for the values to be accumulated correctly.

  • The element currently does not support birth or death options.

  • The equation solver (EQSLV) must be the sparse solver or the PCG solver. The command PCGOPT,,,,,,,ON is also required in order to use the PCG solver.

  • The element coordinate system (/PSYMB,ESYS) is not relevant.

MPC184 Slot Joint Product Restrictions

When used in the product(s) listed below, the stated product-specific restrictions apply to this element in addition to the general assumptions and restrictions given in the previous section.

ANSYS Mechanical Pro 

  • Linear perturbation is not available.

Release 18.2 - © ANSYS, Inc. All rights reserved.