Cars require a number of automotive body seals – passenger doors, windows, engine and trunk lids, and sunroofs. While static seals, such as those around windshields, are important, they are relatively simple. Dynamic seals on the other hand, such as door and window seals, are complex in function, and therefore in design. They not only need to maximize the seal between fixed and movable components, but also have compensate for the manufacturing tolerances of various body parts.
In terms of their material properties, automotive seals need to be resilient, weather resistant (including resistant to ultraviolet radiation effects), tear and abrasion resistant, strain resistant, and need to have bonding strength and a surface finish. Their mechanical requirements include the sealing of components against water, air, dust, and noise; ease of installation; and closing/cycling effort.
Designing and prototyping automotive seals historically relied on experience, empirical data, and “trial and error”. Today, however, most leading seal manufacturers use nonlinear FEA to optimize their seal designs early in the design cycle, significantly reducing the “error” in the trials, and helping bring parts to market much faster.
A typical car door seal (panel a) is subjected to three loading conditions: installation onto the door frame, door closure and window closure. The rubber is assumed to be isotropic, with a Mooney-Rivlin strain energy density function. Panel b shows the deformed geometry and the equivalent Cauchy stress distribution when the door frame moves downward. The window and door approach the seal simultaneously. Panel c shows the effects of door closure and panel d shows both door and window in their final position.
In this type of analysis, sliding contact and potential contact of the body with itself are important. This example illustrates how a modern nonlinear FEA code can easily handle difficulties with complex boundary conditions. An automated solution procedure which keeps track of the multibody movements and variable contact conditions is crucial to success. Such an analysis helps the designer to understand and improve the seal behavior by providing information about stresses, strains, reaction forces, and deformation histories. It also tells the designer where the rubber material is best used—leading to an optimum seal design for its expected dynamic loading histories.
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