Abaqus/CAE User's Guide  


69.7.7 Offset faces

You can create faces by offsetting them from existing faces. Abaqus/CAE creates the new faces as a shell. The offset operation is stored as a feature of the part; therefore, you can use the Model Tree to delete faces that you created. You can use offset faces when creating a midsurface model; for information, see Chapter 35, “Midsurface modeling.”

You can use target faces to compute an offset distance as shown in Figure 69–9, or you can specify an offset distance.

Figure 69–9 A constant offset distance between diverging faces.

Regardless of the offset distance method that you choose, Abaqus/CAE creates all new faces at a constant offset distance from the selected faces, as shown in the figure. However, if you use target faces to compute the offset distance, Abaqus/CAE uses the selected faces and the target faces to calculate the thickness and offset distance at each node in the offset faces such that the behavior of the offset faces approximates the behavior of the original sections. You can view the result of these calculations after the part is meshed by showing the native mesh and toggling on Render shell thickness with a Scale factor of 1 in the Part Display Options dialog box.

You can review and edit the shell thickness values with the Assign thickness and Offset tool (for more information, see “Assigning thicknesses and offsets,” Section 35.5.2), or you can specify a thickness for the new faces when you assign a section to them.

To create new faces by offsetting faces:

  1. From the main menu bar, select ToolsGeometry Edit.

    Abaqus/CAE displays the Geometry Edit dialog box.

    Tip:  You can also offset faces using the tool, located with the edit tools in the Part module toolbox. For a diagram of the edit tools in the toolbox, see “Using the Geometry Edit toolset,” Section 69.1.

  2. From the dialog box, select the Face category and the Offset method.

  3. Select the faces to offset. You can select faces individually, by face angle, or by face curvature; and you can select an existing set containing the faces. For more information on selecting objects in the viewport, see “Selecting objects within the current viewport,” Section 6.2.

    Note:  The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.

  4. From the prompt area, click Done.

    Abaqus/CAE displays the Offset Faces dialog box.

  5. Choose one of the available options to determine the offset distance:

    Note:  Regardless of the calculation method, Abaqus/CAE applies a constant offset to the faces as shown in Figure 69–9. You must use another method to create new faces centered between converging or diverging faces.

    Use target faces to compute distance

    Select a target face or faces. Abaqus/CAE computes the distance between the faces to be offset and the target faces by sampling the faces at several points. Use one of the following distance options:

    • Select Half the average distance to offset the new faces by this amount.

    • Select Fraction distance to closest point on face, and enter a value.

      Abaqus/CAE offsets the new faces by the distance to the closest point on the target faces times the entered value.

    • Select Fraction distance to farthest point on face, and enter a value.

      Abaqus/CAE offsets the new faces by the distance to the farthest point on the target faces times the entered value.

    You can select the target faces using the same methods you used in Step 3. If your original faces are part of the reference representation for a midsurface model, you can click Auto Select to have Abaqus/CAE select appropriate faces from the opposite side of the reference representation. Varying distances between potential target faces may result in selections that only partially match the original faces. If necessary, click Edit to modify the selections in the viewport.

    Distance

    Enter an offset distance, or select to measure and enter a distance between objects in the viewport.

    Negative values for the fraction or actual distance create an offset in the face normal direction; positive values create an offset in the opposite direction. If you are uncertain of the normal directions, use the Shell element normals general query to view the normal directions for shells in the model. For more information, see “Obtaining general information about the model,” Section 71.2.2. The normals for solids point toward the outside, so a positive offset will create a face inside the part unless the offset distance is greater than the part thickness.

  6. If the model contains a reference representation, toggle Auto trim to reference representation to control whether Abaqus/CAE matches the offset faces to the reference representation.

    If this option is toggled on, Abaqus/CAE extends the offset faces along their free edges and trims them where they intersect with the reference representation.

    Note:  Face extension may fail for complex faces. If face extension fails, Abaqus/CAE indicates the error and trims any unextended faces that intersect with the reference representation.

  7. Click OK.

    Abaqus/CAE creates new faces at the prescribed distance from the originals, and the procedure restarts at Step 3.

  8. To exit the offset procedure, either

    • click the cancel button in the prompt area, or

    • click mouse button 2 anywhere in the Abaqus/CAE window, or

    • select another operation from the Geometry Edit toolset or from the tools in the Part module.


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