NUMERICAL MODELLING OF RUBBER VIBRATION ISOLATORS: identification of material parameters

Rubber vibration isolators are used for vibration isolation of engines at high frequencies. To make a good prediction regarding the characteristics of a vibration isolator in the design process, numerical models can be used. However, for a reliable prediction of the dynamic behavior of the isolator, the rubber material parameters have to be known. In practice the material parameters have to be determined with help of experiments. Normally a Dynamic Mechanical Analyzer (DMA) is used to measure the dynamic material properties of test samples of the rubber. However, test samples of the rubber part of the mount are often not available. For this reason a procedure is developed to determine the parameters that describe the material behavior of an isolator with the help of measurements of the entire isolator. Two measurements are used: a static force-displacement and a dynamic transfer stiffness measurement. A finite element model (ABAQUS) of the mount is made and the material parameters are determined in an optimization procedure to fit the numerical response on the measured response. The static force-displacement measurement is used to determine the coefficients of the polynomial fit of the strain-energy function for the correct static behavior. After that a similar optimization procedure is performed to obtain the dynamic shear modulus of the isolator as function of the frequency with help of the measured dynamic transfer stiffness data. The procedure described above is illustrated for a cylindrical mount using a static and dynamic measurement in the transverse direction.