USING A SINGLE TRANSDUCER ULTRASONIC-IMAGING METHOD TO ELIMINATE THE EFFECT OF THICKNESS VARIATION IN THE IMAGES OF CERAMIC AND COMPOSITE PLATES

This article describes a single transducer ultrasonic imaging method b ased on ultrasonic velocity measurement that eliminates the effect of thickness variation in the images of ceramic and composite plate sampl es. The method is based on using a reflector located behind the sample and acquiring echoes off the sample and reflector surfaces in two sca ns. As a result of being thickness-independent, the method isolates ul trasonic variations due to material microstructure. Its use can result in significant cost savings because the ultrasonic image can be inter preted correctly without the need for precision thickness machining du ring nondestructive evaluation stages of material development. Velocit y images obtained using the thickness-independent methodology are comp ared with apparent velocity maps and c-scan echo peak amplitude images for monolithic ceramic (silicon nitride), metal matrix composite and polymer matrix composite materials having thickness and microstructura l variations. It was found that the thickness-independent ultrasonic i mages reveal and quantify correctly areas of global microstructural (p ore and fiber volume fraction) variation due to the elimination of thi ckness effects. A major goal achieved in this study was to move the th ickness-independent imaging technology out of the lab prototype enviro nment and into the commercial arena so that it would be available to u sers worldwide.