Ultrasonic Measurement of Phase and Group Velocity and Attenuation Using Continuous Wave Transmission Techniques.

摘要

The main purpose of the program was to measure the frequency-dependence of phase velocity,group velocity,and attenuation,for longitudinal and shear waves,in seven different dispersive three-dimensional reinforced woven composites,using continuous wave ultrasonic techniques. A secondary purpose was to determine the errors associated with the usual rf burst zero crossing techniques,when applied to dispersive materials,under the constraints of fixed-path and fixed-frequency. To measure phase velocity V and group velocity U in the composites,we used,for the most part,the fixed-path,variable frequency technique demonstrated by the authors in a previous program. V and U data were thereby obtained over an approximately 50:1to approximately 100:1frequency range,up to the low megahertz range,the limit depending on specimen attenuation. The principal limitation of the methods utilized stems from the nonhomogeneous nature of the specimens,and the corresponding difficulty of precisely defining V, U and the attenuation coefficient. (Modified author abstract)