Comparison of substructuring techniques for experimental identification of rubber isolators dynamic properties

Hydraulic testing machines can be used to obtain dynamic stiffnesses of rubber isolators in translational degrees of freedom (DoF) up to a few hundred Hertz. Substructuring methods may identify the dynamic properties also in rotational DoF while requiring only standard vibration testing equipment. Results of two substructuring methods will be compared to those from a hydraulic machine. Both use rigid fixtures, mounted to the bottom and top of the isolators. Frequency based substructuring requires knowing the rigid fixtures dynamics to decouple them. Inverse Substructuring does not require the fixtures dynamics, but is assuming negligible mass and a special stiffness matrix topology of the isolator. Both methods produce accurate results for translational and rotational DoF up to the kilo Hertz range. Nevertheless, frequency based substructuring does not rely on specific isolator assumptions, which could not be justified.