ABSTRACT
Measurements of flexural, longitudinal, and torsional resonant frequencies of bars provide means of determining the elastic moduli and Poisson’s ratio of materials, which are quantities of engineering importance. These measurements have been valuable in determining the quality, including strength, of ceramic materials and of powder–metal compacts. This chapter presents ultrasonic methods of determining viscosity and of determining the properties of fluids and slurries and plastic and high polymers. The sing-around method is useful for measuring the velocity of sound to moderately high accuracy. However, it is good for monitoring changes in ultrasonic velocity to very high accuracy. The group velocity in a nondispersive medium such as aluminum is essentially equal to the phase velocity, that is, the velocity associated with a discrete frequency. The pulse-superposition and pulse-echo-overlap techniques are useful for measuring the velocity of sound in materials in which multiple echoes can be established.
