Characterization of Material Properties

For materials that display an almost linear stress-strain response within the given range of loads, such as glass, aluminum, and steel, the key physical properties required for FEA modeling—Young’s modulus of elasticity and Poisson’s ratio—are available in a number of engineering handbooks [5]. The response of elastomeric seals and sealants, however, generally is nonlinear, even at lower strains. For silicone sealants, which by nature are closer in behavior to ideal elastomers, nonlinear response must be considered once strains exceed the range of about -15 % to +30%. Linear FEA modeling becomes fairly inaccurate outside this limited range; therefore, a nonlinear stress-strain curve is required for the characterization of sealant behavior.

Uniaxial tensile and compressive stress relaxation testing was used to determine the behavior of two silicone insulating glass sealants (DOW CORNING 982 and DOW CORNING 3-0117)[44] within the func­tional range of strain of the materials. These tests characterize the stress-strain behavior of the sealant at a specific temperature and after the sealant has had time to relax under strain. This approach is more representative of a quasistatic design condition where the applied sealant strains occur slowly, providing sufficient time for the sealant to relax and reach a uniform temperature [6]. The tensile and compressive stress-strain curves are used with a curve fit program to create coefficients for a material constitutive equation. The constitutive equation provides strain energy density material functions for the elastomer portion of the model.