Dynamic transfer stiffness measurements of vibration isolators in the audible frequency range

Abstract

An indirect measurement method for blocked dynamic transfer stiffness of vibration isolators in the audible frequency range, up to 1000 Hz, including static preload and all six degrees of freedom is presented, Techniques for improving the stiffness accuracy are discussed in some detail, To suppress (unwanted) coupling effects between different degrees of freedom an improved excitation and terminating arrangement is adopted. Source correlation technique and stepped sine excitation are applied, increasing the signal-to-noise ratio. Computationally, a heavy blocking mass is replaced by its effective mass in the high frequency region, while using an overdetermined stiffness equation system. This is possible by applying various blocking masses, measuring acceleration at several positions and repeating the measurements. The method applied to a cylindrical vibration isolator at four axial preloads, results in smooth stiffness magnitude and phase curves, displaying antiresonances, resonances and the expected preload dependence, The test rig flanking transmission is shown to be negligible, while applying an auxiliary isolator decoupled test set-up, embedded in a heavy rigid frame construction, The stiffness error due to non-vanishing motion of the blocking mass is also shown to be negligible,