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

An indirect measurement method for blocked dynamic transfer stiffness of vi bration 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 improve d excitation and terminating arrangement is adopted. Source correlation tec hnique and stepped sine excitation are applied, increasing the signal-to-no ise ratio. Computationally, a heavy blocking mass is replaced by its effect ive mass in the high frequency region, while using an overdetermined stiffn ess 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 prelo ads, results in smooth stiffness magnitude and phase curves, displaying ant iresonances, resonances and the expected preload dependence, The test rig f lanking transmission is shown to be negligible, while applying an auxiliary isolator decoupled test set-up, embedded in a heavy rigid frame constructi on, The stiffness error due to non-vanishing motion of the blocking mass is also shown to be negligible, (C) 2001 Institute of Noise Control Engineeri ng.