Noncontact Determination of Antisymmetric Plate Wave Velocity in Ceramic Matrix Composites

Abstract

A 13 mJ NdYAG 1064 nm, 4 ns, laser pulse was employed to produce ultrasonic plate waves in 20 percent porous SiC/SiC composite tensile specimens of three different architectures.An air coupled 0.5 MHz transducer was used to detect and collect the waveforms which contained first antisymmetric plate wave pulses for determining the shear wave velocity (VS). These results were compared to VS values determined on the same specimens with Repeated laser pulsing at the same location always lead to deterioration of the ultrasonic signal. The signal would recover in about 24 hr in air however, indicating that no permanent damage was produced.