A METHOD FOR EVALUATING TRANSDUCER LOADING EFFECTS ON ULTRASONIC TRANSIT TIME MEASUREMENTS.
NAVAL RESEARCH LAB WASHINGTON D C
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Measurements of ultrasonic pulse velocities in specimens of structural materials offers a means of nondestructive stress analysis. An ultrasonic measurement technique and data processing scheme has been devised in which time intervals are measured between transducer resonance oscillations within the structure of successive unrectified echoes of an initial square-wave pulse rather than between echo leading edges. When the echo round trip transit times obtained using a series of transducers of different thicknesses are plotted against the transducer resonance periods, these time intervals determine a straight line. Actually, the data processing method yields several equally spaced values, one of which is the echo transit time while the others differ from it in steps of one cycle period of the resonant transducer vibrations which form the pulses. The result is a family of straight lines which have a single point in common at zero transducer resonance period. It is proposed that the transit time associated with this common point is the true travel time for sound in the medium unperturbed by transducer effects. Author