An evaluation of several experimental techniques for determination of dynamic modulus of urethane
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The estimation of the dynamic modulus of a material with frequency dependent properties is often difficult and plays a crucial role in predicting the vibrational characteristics of the structures utilizing them. In this thesis, different experimental techniques such as tripod testing, laser scanning technique and Oberst bar method are used to estimate the damping properties of a particular viscoelastic material namely urethane over a broad frequency range. In the tripod test, cylindrical urethane samples arc excited by means of a shaker and the resulting vibrations are fed to a dual channel FFT analyzer which gives the complex modulus values as a continuous function of frequency. Using the laser scanning vibrometer, the natural frequencies, damping ratios and modes shapes of a composite bar with urethane sandwiched symmetrically between two steel bars are obtained. Using these results and established equations, the dynamic modulus of urethane can be determined at the resonant frequency points. Once the properties are determined, the sandwiched Oberst bars are analyzed by a finite element method to determine the natural frequencies and mode shapes. These results are again correlated with those obtained by laser testing to verify the modulus values obtained by the tripod testing.