Resonant ultrasound spectroscopy for measurement of mechanical damping: Comparison with broadband viscoelastic spectroscopy

This article compares resonant ultrasound spectroscopy (RUS) and other resonant methods for the determination of viscoelastic properties such as damping. RUS scans from 50 to 500 kHz were conducted on cubical specimens of several materials including brass, aluminum alloys, and polymethyl (methacrylate) (PMMA), a glassy polymer. Comparison of damping over the frequency ranges for broadband viscoelastic spectroscopy (BVS) and RUS for indium tin alloy in shear modes of deformation discloses a continuation of the tan δ power-law trend for ultrasonic frequencies up to 300 kHz. For PMMA, resonant peaks were sufficiently broad that higher modes in RUS began to overlap. Tan δ via RUS and BVS for PMMA agreed well in the frequency range where the methods overlap. RUS is capable of measuring tan δ as high as several percent at the fundamental frequency. Since higher modes are closely spaced, it is impractical to determine tan δ above 0.01-0.02 at frequencies other than the fundamental.