Creating or editing a free body cut

To create a free body cut, select the nodes and elements that comprise your free body cross-section; that is, select the surface of your model across which you want to investigate the resultant force and moment. Abaqus/CAE provides several methods for selecting the nodes and elements for a cross-section:

  • For three-dimensional objects, you can select individual element faces to include in the cross-section. The contribution from all elements connected to the nodes of the selected faces will be considered.

  • For two- or three-dimensional objects, you can select individual element edges to include in the cross-section. Each edge provides Abaqus/CAE with an element definition and two or three nodes to include in the cross-section. The contribution from all elements connected to the nodes of the selected edges will be considered.

  • For any type of model, you can select the nodes and elements you want to include individually. This method is recommended for selecting nodes and elements from geometrical areas, such as the ends of beams, in which it might be awkward or difficult to select nodes and elements using their edges or faces. The contribution from only the selected elements will be considered.

You can also display a free body cut on a view cut. For more information, see Understanding view cuts.

Related Topics
Displaying, hiding, and highlighting free body cuts
Customizing free body cut display

Context:

When you define a cross-section using element faces or element edges, Abaqus/CAE provides three additional selection methods that enable you to select the nodes and elements for this definition:

  • You can select the faces or edges by picking components in the viewport, either individually or by angle.

  • You can select a surface set, which is defined in the output database.

  • You can select one or more display groups to use as part of your surface definition.

When you define a cross-section by selecting nodes and elements individually, you can specify the nodes or elements you want to include in the definition by typing their labels directly into the Free Body Cross-Section dialog box.

Abaqus/CAE also enables you to customize the summation point for a free body cut, which is the three-dimensional location about which resultant moments are taken. By default, the summation point is placed at the area centroid of the element faces contributing to the free body computation, but you can move the summation point to the centroid location of the nodes for the cross-section or to any three-dimensional location in your model.

You can also adjust the orientation of component vector display for a free body cut. In many cases the most desirable coordinate system for a free body cut is one in which one axis is normal to the surface of the model and another axis is tangential to the surface. This “normal and tangential” coordinate system is created internally and used by default for the display of component vectors. However, you can change the orientation to use any custom coordinate system available in your session, or you can create a new datum coordinate system.

When you edit a free body cut, Abaqus/CAE enables you to change the components included in the free body cross-section, the summation point settings, and the component resolution settings. However, you cannot change the selection method that was used to define a free body cut; for example, if you defined the free body cut using three-dimensional element faces, your subsequent edits to the free body cut will also use this method.

By default, free body cuts persist only for the duration of your session. If you want to retain a free body cut that you have defined to make it available in subsequent sessions, you can save it to an XML file, to the model database, or to an output database. For more information, see Managing session objects and session options.

  1. Locate the options for creating or editing a free body cut:

    • To create a free body cut, select ToolsFree Body CutCreate from the main menu bar in the Visualization module.

      Tip: You can also create a free body cut using the tool in the Visualization module toolbox.

    • To edit a free body cut, select ToolsFree Body CutEdit from the main menu bar in the Visualization module, and select the free body cut you want to edit.

      Tip: You can also use the free body cut manager to edit a free body cut. From the main menu bar, select ToolsFree Body CutManager, and click Edit from the dialog box that appears.
      The Free Body Cross-Section dialog box opens, from which you can customize the edges, faces, or elements and nodes that constitute the cross-section.

  2. If you are creating a free body cut, choose one of the following from the Selection Method options, and click OK:

    • Select Based on view cut to calculate and display a free body cut based on the current view cut. If you choose this selection method, Abaqus/CAE opens the View Cut Manager, from which you can display and position a view cut for your model and customize the display of an associated free body cut. For more information, see Customizing display and calculation of resultant force and moment on the active view cuts.

    • Select 2D element edges to specify the nodes and elements implicitly (or indirectly) by selecting element edges. This method is recommended for two-dimensional models.

    • Select 3D element faces to specify the nodes and elements implicitly (or indirectly) by selecting element faces. This method is recommended for three-dimensional models.

    • Select Elements and nodes to select the elements or nodes individually for your free body cross-section.

    The Free Body Cross-Section dialog box opens, from which you can select the edges, faces, or elements and nodes that constitute the cross-section.

  3. From the Item list at the top left of the dialog box, select Surfaces, Display groups, Elements, or Nodes as the type of model component to use for the free body cross-section.

    Abaqus/CAE refreshes the Method list.

  4. Choose a selection method from the Method list; and/or select the specific items for the free body cross-section by picking from the viewport, selecting items from the list that appears on the right side of the dialog box, or entering data in the right side of the dialog box.

    For more information about selection options, see Selection methods for free body cross-sections.

    Certain items can be highlighted in the viewport to verify your selection. Toggle Highlight items in viewport if available.

  5. When you have completed your selections, click OK to close the Free Body Cross-Section dialog box.

    The Edit Free Body Cut dialog box opens.

  6. If desired, customize the summation point or the coordinate system transformation options for the selected free body cut.

    1. From the Summation point options, select the three-dimensional location from which the vectors in the free body cut originate.

      • Select Centroid of cut to place the summation point automatically at the area centroid of the element faces contributing to the free body computation.

      • Select Nodal average to place the summation point automatically at the averaged deformed coordinates of all nodes included in the free body cut.

      • Select User-defined, and specify a custom three-dimensional location in space or click to select the summation point from the viewport. The summation point is highlighted in the viewport.

    2. From the Component resolution options, you can specify the coordinate system transformation that takes place when vectors are displayed in component form. (See Customizing general display options for free body cuts, for more information about displaying force and moment vectors in component form.)

      • Select Normal and tangential to orient the component vectors with the normal and the tangent of the surface you select.

      • Select CSYS and a coordinate system to transform the component vectors to a custom coordinate system. Alternatively, you can click Create to create a new datum coordinate system.

      The Component resolution options affect display of free body cuts only when component vector display is selected in the Free Body Plot Options dialog box.

  7. Click OK.

    Abaqus/CAE creates the free body cut and displays it in the viewport.