Methods of measuring mechanical properties of plastics with high-frequency ultrasound

Two methods are described for measuring ultrasonic wave velocities and attenuations in plastics at very high ultrasonic frequencies. The first is a variation of the "water immersion" method, and involves measuring the differential loss and phase shift resulting from removal of the specimen from the ultrasonic beam. Longitudinal wave data can be obtained to about 100 MC. For the second method, which is applicable to both shear and longitudinal waves, the specimen is cemented or thermally bonded between two solid rods of quartz, andt he desired quantitieasr e obtained from measurement of wave amplitudes as a function of frequency. Measurements for mechanical Q and velocity of propagation are presented for polystyrene, linear polyethylene, and a polystyrene fluid used as a coupling medium. It is demonstrated that results for longitudinal waves at frequencieass high as 1000 Mc an be obtained.