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Viscoelastic Response of Closed-Cell Polyurethane Foams From Half Hour-Long Creep Tests: Identification of Lomnitz Behavior

In this paper, a protocol for interpretation of static creep tests on closed-cell polyurethane foams is defined, considering the influence of a finite loading duration when identifying creep compliance parameters. Experiments were conducted at isothermal conditions with temperatures ranging from 20 to 120 °C. The experimental results indicate Lomnitz, i.e., logarithmic-type creep behavior. We discuss uniqueness of the backcalculated parameters. Furthermore, the viscoelastic material parameters obtained were verified in independent experiments: elastic compliance by ultrasonic wave velocity measurements, viscous material parameters by relaxation tests.