The primary deformation behavior of gasket joints is through-thickness deformation. It is therefore difficult to use solid continuum elements to effectively model gasket joints. The interface elements, which are based on the relative deformation of the top and bottom surfaces, offer a direct means to quantify through-thickness deformation of the gasket joints. Thus the pressure versus closure behavior can be directly applied to characterize the gasket material.
The element formulation is based on a corotational procedure. Refer to Gasket Material in the Mechanical APDL Theory Reference for further details.
An interface element is composed of bottom and top surfaces. Mechanical APDL provides several types of interface elements for the analysis of the gasket joints. Figure 10.1: Element Topology of a 3D 8-Node Interface Element shows the geometry of a 3D 8-node interface element. 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 Gauss integration scheme is used for the numerical integration.
The thickness direction is defined as the normal direction of the mid plane of the element at the integration point, and calculated inside of Mechanical APDL. The positive direction is defined by the right-hand rule going around the nodes in the midplane. The through-thickness deformation is quantified by the relative deformation of bottom and top surfaces along the thickness direction. The thickness direction is then noted as the X-direction according to the Mechanical APDL notation convention. The ESYS coordinate system is used only to define in-plane element directions.