Volume 1, Issue 7 (July 2004)
Material Properties for Use in FEA Modeling: Sealant Behavior with Ambient Laboratory Climate Aging
Stress relaxation uniaxial testing is used to define the behavior of elastomeric materials in their functional range. The stress-strain data obtained by this method are used in finite element analysis (FEA) to model the behavior of the material in a given application. The objective of this study is to determine the effect of aging on the uniaxial stress-strain properties of silicone sealants. This paper examines the material behavior changes that occur as these sealants continue to cure at ambient laboratory conditions. The study is intended as a first step toward developing simple working models that account for the effects of sealant aging in FEA modeling. Uniaxial stress relaxation testing was conducted on six commercially available silicone structural glazing, insulating glazing, and weatherproofing sealants in tension and in compression at temperatures of −20°C, 22°C, and 80°C. Testing was carried out immediately after cure, i.e., after three days for two-part and after 30 days for one-part sealants, and after an additional one-year storage period at ambient laboratory conditions. The test specimens were pre-loaded prior to testing in order to eliminate the Mullins effect. Testing was carried out over a strain range of −45–90%. The specimen was loaded to the desired strain level and then allowed to relax. The load at the end of the relaxation period was used to calculate the engineering stress. Coefficient of variance (CoV) was used to determine the significance of material property changes with continued sealant cure. No significant changes in engineering properties were observed for two sealants. For two further sealants, half or more of the test results were within CoV, and no clear trends in property drift could be derived. The changes in material properties of the final two sealants were well outside the CoV limit, and moderate to strong stiffening was observed.