Multimode-Guided-Wave Ultrasonic Scanning of Materials

Two documents discuss a method of characterizing advanced composite materials by use of multimode-guided ultrasonic waves. The method at an earlier stage of development was described in “High-Performance Scanning Acousto-Ultrasonic System” (LEW-17601-1), NASA Tech Briefs, Vol. 30, No. 3 (March 2006), page 62. To recapitulate: A transmitting transducer excites modulated (e.g., pulsed) ultrasonic waves at one location on a surface of a plate specimen. The waves interact with microstructure and flaws as they propagate through the specimen to a receiving transducer at a different location. The received signal is analyzed to determine the total (multimode) ultrasonic response of the specimen and utilize this response to evaluate microstructure and flaws. The analysis is performed by software that extracts parameters of signals in the time and frequency domains. Scanning is effected by using computer controlled motorized translation stages to position the transducers at specified pairs of locations and repeating the measurement, data-acquisition, and data-analysis processes at the successive locations. The instant documents reiterate the prior description and summarize capabilities of the hardware and software of the method at the present state of development. One document presents results of a scan of a specimen containing a delamination.