Complex Stiffness Identification by Inverse Methods

The basic principle of an inverse method for material stiffness identification is to compare measured values of a test specimen with computed values from a numerical model of the test specimen. The parameters in the numerical model are the unknown material stiffness properties and they are iteratively updated starting from an initial set of parameters until the computed output matches the measured values. This paper first outlines the general procedure used for material stiffness identification with inverse methods. The procedure is next illustrated with an example on the identification of complex engineering constants of composite materials. In this example the vibration behaviour of a freely suspended test plate is used as the information source. The measured quantities are the resonance frequencies of the test plates and the damping ratios of their associated mode shapes. The resonance frequencies are used to tune the real part of the complex moduli, while the damping ratios are used to identify the imaginary part.