Characterizing the nonlinear viscoelastic properties of sealant, including its Mullins effect

Quantification of mechanical properties, such as nonlinear viscoelastic behavior, for a cured sealant is complicated by the presence of the Mullins effect. This article examines the mechanical behavior of five different sealants materials encompassing the range of currently available commercial sealant formulations. The Mullins effect was observed for all materials and was present in both tensile and compression experiments. If a previously tested sample was allowed to rest (remain unloaded) for a sufficiently long period of time, however, the Mullins effect was partially recovered; that is, the modulus measured during the first mechanical loading following the rest period was greater than that obtained on subsequent loadings. Samples were then preloaded to remove the Mullins effect, and their nonlinear viscoelastic properties were examined using stress–relaxation experiments. Although the behavior was complex, the time and strain dependences were sufficiently independent so that time–strain superposition could be used to simplify modeling and characterization without introducing significant errors. A simple empirical equation was formulated to describe the behavior for all five sealants over the range of strains and time scales examined. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers