Frequency Domain Vibration Analysis For Characterizing The Dynamic Mechanical Properties Of Materials

Dynamic stiffness and internal damping are referred to as the dynamic mechanical properties of a material and are often expressed in terms of a complex stiffness or complex modulus. The measurement of dynamic mechanical properties of structural materials is of interest for at least two reasons; (a) accurate numerical values of such intrinsic material properties are needed as input to design equations, and (b) dynamic mechanical property measurements can be used for quality control operations during fabrication and/or for periodic in-situ inspection during the service life of the components. The increasing use of composite materials in the aerospace, aircraft and automobile industries has brought about the need for rapid and reliable experimental techniques to characterize their mechanical properties. In the field of vibrations frequency-domain testing is increasingly becoming state-of-the-art as opposed to time-domain experimentation. In this paper the details of a non-destructive experimental technique for characterizing materials using the impulsive excitation frequency-domain vibration analysis, is described. The relationship between the resonant frequency of vibration and half-power bandwidth on the dynamic mechanical properties of different materials is underscored. Experiments are performed on metallic, polymeric and composite materials to determine their dynamic modulus and loss factor (a measure of damping), and comparison is made with data obtained from the conventional time-domain based free-vibration decay tests. This experiment has been successfully incorporated as a laboratory exercise for the past few years in the undergraduate mechanical engineering curriculum at The University of Mississippi.