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The gasket element behavior is unique in the following areas:

• Only compressive stresses through the thickness are developed and transmitted. Stresses and forces in the plane of the gasket are ignored. So even though the gasket part may be bonded to the mating part (by virtue of using the same nodes on each part), the connection is better thought of as a 0 friction surface since no shear forces are developed in the gasket.
• The mesh must be created with just one element through the thickness.
• In some situations, the user needs to indicate which surfaces are the top and the bottom. This occurs when the thickness dimension (in the compression direction) of the gasket is larger than the width (normal to the compression direction). See below.
• The material properties are specific to a given thickness of gasket.

3D gasket elements can have these geometric forms: bricks (8 corner nodes, 6 quadrilateral sides), wedges (6 corner nodes, 2 triangular sides, 3 quadrilateral sides), pyramids (5 corner nodes, 4 triangular sides, 1 quadrilateral side), and tetrahedral (4 corner nodes, 4 triangular sides). Since only one element is permitted through the thickness, at least one of the faces of the tetrahedral element must be on the top or bottom of the gasket.

The material model of the gasket element includes the capability of a multi-linear elastic curve, a yield point, multi-linear plastic curve, and multiple unloading curves, each of which is defined by multi-linear curves.

Uniform pressure, traction, and hydrostatic pressure can be applied only to the top face or bottom face of the 3D gasket element, but not to both.

If the model originated from a CAD solid model and has not been altered manually, the pressure can be applied by selecting the surface of the face where the pressure is appropriate. The surface numbers of the individual lines making the face are not critical. A pure CAD model knows what faces belong to the surface. The pressure will be applied if the selected surface is the top or bottom face of the gasket.

For parts that were meshed by hand, or if the CAD model was altered (and therefore you are working with the equivalent of a hand meshed model), the lines making up the face of the element need to have a majority of the lines on the same surface number in order for the pressure to be applied to the face. For a four node face, any three of the four lines on the same surface number determines the surface number of that face. For a three node face, any two of the three lines on the same surface number determines the surface number of that face, Then, the highest surface number among the faces that define the 3D gasket element determines the surface number of the element. The pressure will be applied if the selected surface is the top or bottom face of the gasket.

## Basic Steps for Use of 3D Gasket Elements

1. Be sure that a unit system is defined.
2. Be sure that the model is using a nonlinear analysis type.
3. When creating the mesh of the gasket, use one element through the thickness. Note that the mesher for CAD solid models has a special setting for creating a mesh with one element. (See Meshing CAD Solid Models)
4. Right-click the Element Type heading for the part that you want to be 3D gasket elements.
5. Select the 3D Gasket command.
6. Right-click the Element Definition heading.
7. Select the Edit Element Definition command.
8. Specify the appropriate input in the Element Definition dialog to specify the solution parameters for the gasket element.
9. Press the OK button.
10. Right-click the Material heading for the part and choose Edit Material. Enter the material properties for the gasket.
11. Select the surface or surfaces that define the top face and bottom face of the gasket. This can be done in the display area (Selection Select Surfaces) or in the Surfaces branch of the tree view. (The two faces can be on the same surface number or different surface numbers.) Right-click and choose Gasket's Top/Bottom Surface. When working with a hand-built mesh, the lines on the sides of the gasket that connect the top and bottom faces should not be on the same surface number as the top or bottom surface.