Ultrasonic Flaw Detection in Ceramics,
ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
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High frequency ultrasonic approach for determining defects in ceramic materials in the size range required for failure prediction have been outlined. A 200 MHz A-scan device pulsed with a short 2 ns pulse has been constructed and shown to have a good dynamic range 70 dB and a depth resolution of at least 25 micrometers. A B-scan system for defect detection studies has al so been developed and is ready for use. Techniques for accurate attenuation measurements in ceramics have been developed and automated. Preliminary data have also been obtained on a range of ceramic polycrystals. Calculations of the scattering defects in ceramics, and of bond losses in thin gold foils, have been used in cylinders with the attenuation data to predict typical defect detectabilities. These calculations predict that defects in the size range 20-100 micrometers should be detectable with the present transducers in fully-dense, fine-grained ceramics. Preliminary defect detection studies have confirmed that defects at least as small as 100 micrometers are readily detectable in these materials.