Specifying the offset of a conventional shell composite layup

In most cases you can use the midsurface of an element to indicate the reference surface. However, in some cases you need to define the reference surface as offset from the midsurface of the elements. For example, a model imported from a CAD system might assume that the shell is located at the top or bottom surface of the elements. In addition, you can specify a shell offset that defines a more precise surface geometry for contact problems where shell thickness is important. The offset value is defined as a fraction of the total thickness measured from the midsurface to the reference surface.

Context:

Positive values of the offset are in the positive element normal direction. When the offset is set equal to 0.5, the top surface of the element is the reference surface. When the offset is set equal to –0.5, the bottom surface is the reference surface. The default offset is 0, which indicates that the middle surface of the element is the reference surface. Figure 1 shows an offset to the top surface of the element.

Figure 1. An offset to the top surface of the element.

For more information, see Defining the initial geometry of conventional shell elements. You can use a discrete field to model elements with continuously varying offsets. For more information, see The Discrete Field toolset.

  1. From the Composite Layup editor, click the Offset tab.

  2. Do one of the following:

    • Choose the Middle surface, Top surface, or Bottom surface to represent the reference surface.

    • Choose Specify offset ratio, and enter a number.

    • Choose Distribution, and select an existing scalar discrete field that defines an offset that is varying spatially across the layup. Abaqus/CAE allows you to select only valid discrete fields, which, for an offset, are scalar discrete fields applied to elements. You can also create a new discrete field by clicking . For more information, see The Discrete Field toolset.

    • Choose From Geometry to use the thickness of the geometric section.