12. Viscoelastic Properties for PMMA Bar over a Wide Range of Frequencies

Viscoelastic properties for a polymethyl methacrylate (PMMA) bar were examined using both ultrasonic wave propagation experiments in the higher frequency range of 25–200 kHz and longitudinal wave propagation experiments in the lower frequency range of up to 15 kHz. Since the geometrical dispersion due to three-dimensional deformation was caused by higher frequency components involved in the ultrasonic waves, the three-dimensional wave theory was employed to analyze experimental data of wave propagation. It was found that the 5-element model based on the three-dimensional theory could evaluate the viscoelastic properties of a wide range of frequencies. The peak value of the attenuation coefficient moved to the higher frequency as the diameter of the bar became small. Moreover, the viscoelastic properties could be evaluated only by the solution of the first mode based on the three-dimensional wave theory when the diameter of the bar was thin.