Comparative Assessment of Frequency Dependent Joint Properties Using Direct and Inverse Identification Methods

Elastomeric joints are utilized in many automotive applications, and exhibit frequency and excitation amplitude dependent properties. Current methods commonly identify only the cross-point joint property using displacement excitation at stepped single frequencies. This process is often time consuming and is limited to measuring a single dynamic stiffness term of the joint stiffness matrix. This study focuses on developing tractable laboratory inverse experiments to identify frequency dependent stiffness matrices up to 1000 Hz. Direct measurements are performed on a commercial elastomer test system and an inverse experiment consisting of an elastic beam (with a square cross section) attached to a cylindrical elastomeric joint. Sources of error in the inverse methodology are thoroughly examined and explained through simulation which include ill-conditioning of matrices and the sensitivity to modeling error. The identified translational dynamic stiffness and loss factor values show good agreement between the two identification methods, though challenges remain for the rotational and coupling stiffness terms. The experimental methods are applied to two different elastomeric materials of the same geometry.