Ultrasonic Longitudinal and Surface Wave Methods for in situ Monitoring of Damage in Metal Matrix and Ceramic Matrix Composites

Abstract

This paper discusses the development of a unique set of integrated Nondestructive Evaluation (NDE)/Mechanical test techniques for characterization of ceramic matrix composites (CMC) and metal matrix composites (MMC). These techniques are sensitive to the initiation and accumulation of damage in CMC and MMC. These techniques use longitudinal (bulk) wave and surface wave ultrasonic energy to interrogate the composite specimens, in situ, during mechanical testing. Changes in surface and longitudinal wave characteristics are compared with stiffness changes for extensometer measurements during tension, creep and fatigue testing of SiC/BMAS (barium-magnesium alumino-silicate) CMC. Surface waves were used to identify the onset of surface and near-surface cracks in CMC. Changes in the surface wave characteristics provide a better indicator of impending failure during fatigue testing of Sigma/Ti-6242 MMC than extensometer data. Longitudinal wave propagation was successfully used to monitor the changes in the stiffness of the composite during fatigue loading conditions of CMC and MMC. The changes in the peak-to-peak amplitude of the transmitted wave signal appears to be an equal or better indicator of impending failure of the composite than the extensometer data.