| 摘要 |
A PLATE (12) OR PIPE WALL IS INSPECTED BY COUPLING AN ULTRASONIC TRANSDUCER (14, 16) TO ITS SURFACE SO AS TO GENERATE A COMPRESSION WAVE OR LATERAL WAVE (26) ALONG THE SURFACE AND A SHEAR WAVE OR HEAD WAVE (28) AT THE SHEAR-COMPRESSION CRITICAL ANGLE (THETA C). THE SAME TRANSDUCER (14, 16), OR AN ADDITIONAL TRANSDUCER (15, 16) ALSO COUPLED TO THE SURFACE, DETECTS A SERIES OF ULTRASONIC PEAKS CORRESPONDING TO EACH GENERATED ULTRASONIC PULSE. EACH SUCH DETECTED PEAK CORRESPONDS TO ULTRASONIC ENERGY TRAVELLING, PARTLY AS LATERAL WAVES (26, 32) ON ONE SURFACE OR THE OTHER, AND PARTLY AS HEAD WAVES (28, 30) CROSSING A CERTAIN NUMBER OF TIMES BETWEEN THE SURFACES. THE TRANSDUCER (14, 15) MAY BE OVER 0.5 M APART, AND SUBSTANTIALLY ALL THE INTERVENING PARTS OF THE PLATE (12) ARE INSPECTED.FIGURE 1
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