Nondestructive characterization of material properties by an automated ultrasonic technique

Ultrasonic velocity and/or attenuation measurement is a versatile tool for nondestructive characterization of material properties such as residual stress, texture, porosity, elastic constants, microstruture etc. In this contribution, an automated, computer-controlled system is described which enables fast and accurate measurement of the time-of-flight of ultrasonic signals as well as the frequency dependent attenuation alpha (f). A high speed digitiser is used for signal recording of the ultrasonic backwall-echoes. The evaluation of the recorded signals is performed involving Fast Fourier Transforms (FFT) for attenuation measurement and cross-correlation technique for time-of-flight measurement. Time resolution better than 1 ns is achieved by applying additional data interpolation. As examples of practical application, the determination of porosity in sintered material and the measurement of grain size in this ferritic sheets are demonstrated.