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—- - Session 1626

Frequency-Domain Vibration Analysis for Characterizing the Dynamic Mechanical Properties of Materials P. Raju Mantena Department of Mechanical Engineering The University of Mississippi University, MS 38677

ABSTRACT

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.

INTRODUCTION

Structural members when put into service are susceptible to extraneous vibration. Apart from the static load carried by the design member, it is subjected to fatigue and other mechanical loadings due to vibrations. If the amplitude of vibration is high then the component is likely to experience high induced stresses. Hence, the usefulness of intrinsic material damping to curtail the induced vibration amplitudes is an important design parameter for modeling real world problems. 1’2 Damping is a measure of the total energy dissipated in any vibrating structure. Damping can be generated within the material of the structure (material damping), by the fluid surrounding the structure (fluid damping) or by the impact and scraping at joints (friction damping). There are a large number of mechanisms which may cause damping; some of these are now well understood, others less so. In solids, material damping attributed to internal friction may be

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Mantena, P. R. (1996, June), Frequency Domain Vibration Analysis For Characterizing The Dynamic Mechanical Properties Of Materials Paper presented at 1996 Annual Conference, Washington, District of Columbia. 10.18260/1-2--6064