A method for measuring the mechanical quality factor (Q factor) of materials in large-amplitude flexural
vibrations was devised on the basis of the original definition of the Q factor. The Q factor, the ratio of the
reactive energy to the dissipated energy, was calculated from the vibration velocity distribution. The bar
thickness was selected considering the effect of the thickness on the estimation error. In the experimental
setup, a 1-mm-thick polymer-based bar was used as a sample and fixed on the top of a longitudinal transducer.
Using transducers of different lengths, flexural waves in the frequency range of 20–90 kHz were
generated on the bar. The vibration strain in the experiment reached 0.06%. According to the
Bernoulli–Euler model, the reactive energy and dissipated energy were estimated from the vertical velocity
distribution on the bar, and the Q factors were measured as the driving frequency and strain were varied.
The experimental results showed that the Q factors decrease as the driving frequencies and strains
increase. At a frequency of 28.30 kHz, the Q factor of poly(phenylene sulfide) (PPS) reached approximately
460 when the strain was smaller than 0.005%. PPS exhibited a much higher Q factor than the other
tested polymers, which implies that it is a potentially applicable material as the elastomer for high-power
ultrasonic devices.