How to Create, Edit and Remove a Joint

You can use the joint creation utility within the CAD Solid Model environment to automatically create truss or beam elements between the axis of the joint and the rotating part(s). This capability is often used to simulate joints in areas of the model where stress is not a concern. If stress in the joints is a concern, you would model detailed joint components and use surface-to-surface contact.

To create a joint with this utility, perform the following steps:

• Select all of the surfaces that are involved in the joint. You can do so by either clicking on the surfaces in the model display (hold down the "Ctrl" key to select multiple surfaces) or clicking on the surface names in the model tree.
   
• Right click anywhere in the working area. A pop-up menu of options for the selected surfaces will appear (see Figure 1).

Figure 1: After selecting surfaces in this model of a piston assembly with a rotating crank, right clicking in the working area accessed a pop-up menu with the "Create Joint" option.

• Choose the "Create Joint" option. The "Create Joint" dialog will appear (see Figure 2). (Alternatively, you can use the "Mesh:Joint Browser..." command sequence to access the "Joint Browser" dialog and then click on the "Create" button to access the "Create Joint" dialog.)

• The selected surfaces are listed in the "Participating surfaces" section. In the "Joint type" field, you can specify the type of joint that you want to create by choosing between two options:
   
  • "Pin joint (lines to axis endpoints)" - The nodes on the selected surfaces are connected to the opposite end of the joint axis, which will allow the model to rotate around the axis.
     
  • "Universal joint (lines to axis midpoint)" - The nodes at either end of the model are connected to the midpoint of the axis, which will allow the model to rotate about the axis as well as swivel about the center point of the axis.
     

You can choose between automatic and manual specification of the axis/center-point. If you choose "Manual axis/center-point specification", then you can enter the X, Y and Z coordinates (for a pin joint, enter coordinates for the two end points of the axis; for a universal joint, enter coordinates for the center point).

• Click on the "OK" button to accept the settings and create the joint.
   
• Use the "Mesh:Create Mesh..." command sequence to access the "Create Mesh" screen. Click on the "Mesh" button. The surface mesh will be created including the lines that will be defined as the truss or beam elements for each joint. In addition, each joint will be placed in its own part number as shown in the model tree of Figure 3.

Figure 3: After meshing, the lines that will be defined as the truss or beam elements of the joints can be seen in the piston assembly model. The lines of each joint are placed in distinct part numbers as shown in the model tree.

In addition to the method described above, you can use the "Mesh:Joint Browser..." command sequence to access the "Joint Browser" dialog (see Figure 4), which enables you to do the following:

• Create joints
   
• Edit previously created joints
   
• Remove previously created joints

You can use the "Joint Browser" dialog to examine and modify joints that were created via the surface selection method that was shown in Figures 1-3.

Here are some additional considerations for joints:

• Joints can be added before or after meshing. If added after meshing, the joints will be automatically created when you click on "OK" in the "Create Joint" dialog.
   
• If you want to apply a prescribed rotation to a joint, then the joint must have both translational and rotational degrees of freedom; however, truss elements have only translational degrees of freedom. Therefore, you must modify the element type of the joint part to beam elements in the FEA Editor environment.

For more information about creating, editing and removing joints, see the ALGOR User's Guide.