| Matrix or Vector | Shape Functions | Integration Points |
|---|---|---|
| Stiffness Matrix | Linear in x, quadratic in y and z directions | 2 x 2 |
| 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 interface delamination and fracture, where the interface surfaces are represented by a group of interface elements, in which an interfacial constitutive relationship characterizes the traction separation behavior of the interface. The element offers a direct means to quantify the interfacial separation behavior. See Cohesive Zone Material (CZM) Model for detailed description of interface material options.
The virtual work of the element is written as:
 | (13–355) |
where:
| t = traction force across the element |
| d = separation 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 separation, d, is defined as the relative deformation between top and bottom surfaces as:
 | (13–356) |
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 midplane of the element at the integration point.