Bending wave and transfer function based material characterization

Abstract

The goal of this thesis is to develop a method capable of determining the viscous and elastic properties of materials over the broad range of building acoustics frequencies (20 Hz-5 kHz). Careful consideration is given to the drawbacks and limitations of existing material characterization techniques. The method is developed up to the point of accommodating isotropic and homogeneous materials of plate form factor. Three polyurea aerogel samples with different densities and distinct nanomorphologies are measured using the approach. Dynamic testing aids in determining the suitability of polyurea aerogels for noise and vibration control applications. Complex elastic moduli in line with more traditionally obtained static measurements partially validate the technique. Polyurea aerogels are confirmed to have remarkably high elastic moduli given such low material densities. Material loss factors calculated with this method are less consistent than desired. Contributing factors to this deficiency are discussed and remediating steps are proposed. The low frequency limit of the method as implemented is approximately 600 Hz while the upper target of 5 kHz is shown attainable. Lower frequencies may be reached and the course of actions to do so is discussed. Overall the technique is well suited for the determination of dynamic mechanical properties at frequencies not measurable using commercial equipment and without reliance on modal behavior or extrapolation from ultrasonic measurements.