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7. Reliability of Structural Ceramics

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A commercially available scanning-laser-acoustic-microscope {SLAM) has been developed which provides new and unique analytical capabilities for materials science and non-destructive testing. By employing 100 MHz acoustic waves to create images, the "elastic microstructure" of complex materials is visualized directly. The "acoustic micrographs" which contain 2 x 104 image points, are displayed on a real time TV monitor. The sample remains accessible to the investigator during the procedure and stressing fixtures can be employed. Dynamic activities can be recorded either on movie film or video tape. There are two acoustic imaging modes which appear to be essential for flaw and defect characterization. The first mode displays the acoustic transmission level through the sample (normal mode) and the second mode displays fringes related to the acoustic phase (interference mode). The presence of a defect within a sample may be evidenced by a change in transmission level or a change in phase or both. The nature of the defect (e.g. high density inclusion or void) can be determined through the combined analysis of the interference and normal mode micrographs. The SLAM technique has been applied to a wide variety of materials including ceramics, metals, glasses, polymers, etc. Defect localization down to 25 μm has been achieved. Samples can be systematically searched, area by area, by simply repositioning the part on the stage of the microscope and observing the acoustic image on the TV monitor.



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4 p.