Simultaneous ultrasonic velocity and sample thickness measurement and application in composites

Ultrasonic velocity is widely used in the investigation of material properties. In cases where thickness of the test piece is not precisely known or varies spatially, it is desirable to determine the wave velocity and the sample thickness in the same ultrasonic measurements. For tests in an immersion tank or using squirters, both wave velocity and the specimen thickness may be deduced from the time of flight of several ultrasonic pulses. In this paper four different configurations of pulse echo and through transmission are described for the ‘‘simultaneous’’ velocity and thickness determination. The method is then applied to investigate the porosity content in graphite/polyimide and graphite/epoxy composite laminates. Good results were obtained for both the wave velocity and the part thickness, and a clear correlation between velocity and void content is demonstrated.