| Matrix or Vector | Shape Functions | Integration Points |
|---|---|---|
| Stiffness Matrix | Linear in x, quadratic in y and z directions | 2 x 2 |
| Thermal Load Vector | Same as stiffness matrix | Same as stiffness matrix |
| Load Type | Distribution |
|---|---|
| Element temperature | Based on element shape function, constant through the direction perpendicular to element plane |
| Nodal temperature | Same as element temperature distribution |
The element is designed specially for simulation of gasket joints, where the primary deformation is confined to the gasket through-thickness direction. The through-thickness deformation of gasket is decoupled from the other deformations and the membrane (in-plane) stiffness contribution is neglected. The element offers a direct means to quantify the through-thickness behavior of the gasket joints. The pressure-deformation behavior obtained from experimental measurement can be applied to the gasket material. See Gasket Material for detailed description of gasket material options.
The element is composed of bottom and top surfaces. An element midplane is created by averaging the coordinates of node pairs from the bottom and top surfaces of the elements. The numerical integration of interface elements is performed in the element midplane. The element formulation is based on a corotational procedure. The virtual work in an element is written as:
 | (13–353) |
where:
| t = traction force across the element |
| d = closure across the element |
| Sint = midplane of the interface surfaces |
The integration is performed in the corotational equilibrium configuration and the Gauss integration procedure is used.
The relative deformation between top and bottom surfaces is defined as:
 | (13–354) |
where, uTOP and uBOTTOM are the displacement of top and bottom surfaces of interface elements in the local element coordinate system based on the midplane of element.
The thickness direction is defined as the normal direction of the mid plane of the element at the integration point.