Characterizing the Frequency Response of Compliant Materials by Laser Döppler Vibrometry Coupled Acoustic Excitation

Low-stiffness or compliant materials are inherently difficult to characterize in terms of dynamic mechanical properties. Their free-vibration behavior is not frequently analyzed, given that performing classic vibration testing in these type of materials may imply the tampering of the results by external sources, either by changes in the geometry of the sample, by gravity-induced buckling, or the instrumentation itself (e.g., the mass of accelerometers). This study proposes an approach to determine the frequency response of these types of materials, using a noncontact methodology based on acoustic excitation and displacement measurement by Laser Döppler Vibrometry. The detailed method may be optimized by changing the sample design into a half-cane configuration to increase sample stiffness. This approach significantly increases the sample eigenmodes, facilitating their excitation by the acoustic pressure source. Numerical analysis using the values of the dynamic Young’s modulus from the experimental approaches validates the overall procedure. It is shown that the combination of numerical analysis and the proposed experimental method is a possible route for the determination of the dynamic Young’s modulus of these types of materials by inverse engineering.