Measuring Frequency Dependent Material Properties by Use of N-Parameter Models

The measurement of material properties is an important task. Quantities such as Young's modulus and the shear modulus, Poisson's ratio and material damping must be known when dealing with noise problems in analytical and numerical calculations. By classical methods, often only a single number is obtained which is real and independent of frequency. Sometimes, however, this is not sufficient. If a material behaves visco-elastically, we can use N-parameter-models to describe its behaviour. Then, the aforesaid properties can be described as complex numbers and in dependence of frequency, often with just a fistful of parameters which are valid for a wide frequency range. This paper gives a short introduction into the theory of visco-elastic materials and presents three different measurement examples of parameter identification.