Key non-linear sti!ness characterization issues of rubber isolators are clari"ed, and a process is proposed that includes experiments in single-and multi-degree-of-freedom con"gurations while di!erent 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 sti!ness experiments are conducted to measure time-invariant load}de#ection curves and in#uences from rubber durometer, isolator geometry and non-linear behavior on the dynamic-to-static sti!ness ratio are illustrated. Next, dynamic excitations under random, frequency-sweep and "xed-frequency are employed to investigate how the behavior of each isolator is in#uenced by type of excitation. Also, the non-linear dynamic sti!ness of each isolator is quanti"ed in both single-and multi-degree-of-freedom con"gurations. E!ects of isolator non-linearities on the e!ective vibration modes of the multi-degree-of-freedom (m.d.o.f.) experimental con"guration are shown to be distributed di!erently 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 con"guration. 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 "rst step for the identi"cation techniques that are improved by a priori knowledge of the types of non-linearities present.
2001 Academic Press