Ultrasonic velocity technique for monitoring property changes in fiber-reinforced ceramic matrix composites

Abstract : A novel technique for measuring ultrasonic velocity was used to monitor changes that occur during processing and heat treatment of a silicon carbides/RBSN composite. Results indicated that correlations exist between the ultrasonic velocity data and elastic modulus and also interfacial shear strength data determined from mechanical tests. The ultrasonic velocity data can differentiate changes in axial modulus as well as in interfacial shear strength. The mechanical performance of fiber-reinforced ceramic matrix composites depends upon fiber, fiber/matrix interface and matrix properties. Changes in component properties either during fabrication or service will influence mechanical properties. It is desirable to have a nondestructive method for monitoring changes in these properties. The purpose of the present work was to devise and use an ultrasonic velocity method to monitor changes in matrix properties and interfacial shear strength in a unidirectionally reinforced SiC/RBSN composite. Two modes of ultrasonic wave propagation were measured along the fiber direction for specimens prepared under various conditions of density, SiC fiber surface coating, and heat treatment history. Differences in velocity between these conditions were then compared to differences in mechanical properties as determined by destructive testing.