A better way to Simulate Gaskets

The gasket feature includes a range of 2D and 3D gasket or interface elements. The 3D, eight-node version, for example, lets users apply different temperatures at each node and assign several thermalloading schemes. The graph shows experimental pressure versus displacement (relative displacement of top and bottom gasket surfaces) for a graphite composite. Part of gasket complexity is that their material behaves nonlinearly. The sample was loaded (blue curves) and unloaded (brown curves) five times along the loading path and then unloaded at the end of the test to determine the materials unloading stiffness. Ansys 6.1 has calculated deflections for a gasket and the surrounding cylinder head. The lower view shows deflections on the gasket surface. Gaskets seem fairly simple. Seen one, you've seen them all. But they are not. And until now, gasket design has been a trial-and-error effort. A recent software release from Ansys devotes special features to gasket design and simulation. Gaskets are usually thin with layers of several materials. Before applying a gasket, its material should have a known behavior in the thickness direction (from top to bottom) to ensure that joints remain sealed under complex loading cycles. "This behavior has been difficult to characterize with standard material models," says Guoyu Lin, a development engineer with Ansys, Cannonsburg, Pa. "It's also impractical to directly model gaskets using conventional solid elements because it requires such a large number due to the elements' aspect ratios." When gaskets are thin, say 0.003 in., aspect ratios (heightto-width ratios) for the elements that mesh them can reach 25:1, much higher than the recommended 3:1. With a courser mesh or thinner gasket, the ratio heads up. So a standard element typically will not give good answers. The simulation software overcomes these hurdles by including several elements and material options to simulate gaskets. New elements