CHARACTERIZATION OF RUBBER ISOLATOR NONLINEARITIES IN THE CONTEXT OF SINGLE- AND MULTI-DEGREE-OF-FREEDOM EXPERIMENTAL SYSTEMS

Key non-linear stiffness characterization issues of rubber isolators are clarified, and a process is proposed that includes experiments in single- and multi-degree-of-freedom configurations while different types of excitations are applied. Consequently, important characteristics, via experimental and analytical studies of three isolators, emerge that might not have been revealed in traditional non-resonant testing methods. First, static stiffness experiments are conducted to measure time-invariant load–deflection curves and influences from rubber durometer, isolator geometry and non-linear behavior on the dynamic-to-static stiffness ratio are illustrated. Next, dynamic excitations under random, frequency-sweep and fixed-frequency are employed to investigate how the behavior of each isolator is influenced by type of excitation. Also, the non-linear dynamic stiffness of each isolator is quantified in both single- and multi-degree-of-freedom configurations. Effects of isolator non-linearities on the effective vibration modes of the multi-degree-of-freedom (m.d.o.f.) experimental configuration are shown to be distributed differently for each isolator, yet some correlation is found with the single-degree-of-freedom (s.d.o.f.) experiment. For analytical characterization, the continuous system theory is used to develop a quasi-linear representation of the m.d.o.f. experimental configuration. Isolator dynamic properties determined from the s.d.o.f. experiment are used in this model. Finally, a discrete non-linear model consisting of a non-linear elastic force term is constructed. After execution of a procedure based upon numerical simulation, optimum parameters for this model are found. The characterization studies conducted here form an essential first step for the identification techniques that are improved by a priori knowledge of the types of non-linearities present.