MULTIPLE ULTRASONIC ECHO SIGNALS IN A PLATE. DETERMINATION AND APPLICATION
Journal: NDT WORLD
Volume 19 № 1
, 2016
Rubrics: ULTRASONIC INSPECTION
Authors:
2.
Acoustic Control Systems, Ltd
employee
Moskva, Russian Federation
employee
Moskva, Russian Federation
Type:
Article
Pages:
from 36
to 39
Status:
Published
Received:
02.03.2016
Accepted:
30.03.2016
Published:
30.03.2016
Language:
Russian
Keywords:
ultrasonic pulses, multiple echo signals, longitudinal wave velocity, transversal wave, bottom echo, piezoelectric transducer, EMAT, Poisson ratio
Abstract (English):
Introduction. Multiple echo signals arise within a plate being tested with a normal ultrasonic transducer. Besides some weaker pulses with unequal recurrence intervals are seen on the screen. Although their amplitude is rather small, they can prevent the device, for example a thickness gauge, from normal operation. The task was to ascertain the reasons and to determine the points of time when these weak pulses arise. Method. Any mechanical perturbation of the solid body’s surface generates a pair of ultrasound waves that propagate into its volume. The plate was tested with longitudinal and transversal ultrasonic waves originated by different normal transducers; the waves’ velocities in the plate material were known. Thus the time points when several initial pulses were to come to the oscillogram were calculated. Results. The coincidence of the measured time points with the calculated ones showed that each small pulse is a result of ultrasonic signal propagation within the plate thickness: one or more times as a longitudinal wave and one or more times as a transversal wave. Strict determinateness of pulse registration points for all the pulses, depending only on the plate thickness and the actual sound velocities within the plate, allows the both velocities and a Poisson ratio to be measured using any of a normal transducer, including a piezoelectric transducer of longitudinal waves. When the ratio “transversal wave velocity / longitudinal wave velocity” is equal or close to 0.5, some pairs of pulses or more arise at the same point of time. Conclusion. The given simple way to measure a velocity of both transversal and longitudinal waves makes it possible to evaluate physical and mechanical properties of the material.
Introduction. Multiple echo signals arise within a plate being tested with a normal ultrasonic transducer. Besides some weaker pulses with unequal recurrence intervals are seen on the screen. Although their amplitude is rather small, they can prevent the device, for example a thickness gauge, from normal operation. The task was to ascertain the reasons and to determine the points of time when these weak pulses arise. Method. Any mechanical perturbation of the solid body’s surface generates a pair of ultrasound waves that propagate into its volume. The plate was tested with longitudinal and transversal ultrasonic waves originated by different normal transducers; the waves’ velocities in the plate material were known. Thus the time points when several initial pulses were to come to the oscillogram were calculated. Results. The coincidence of the measured time points with the calculated ones showed that each small pulse is a result of ultrasonic signal propagation within the plate thickness: one or more times as a longitudinal wave and one or more times as a transversal wave. Strict determinateness of pulse registration points for all the pulses, depending only on the plate thickness and the actual sound velocities within the plate, allows the both velocities and a Poisson ratio to be measured using any of a normal transducer, including a piezoelectric transducer of longitudinal waves. When the ratio “transversal wave velocity / longitudinal wave velocity” is equal or close to 0.5, some pairs of pulses or more arise at the same point of time. Conclusion. The given simple way to measure a velocity of both transversal and longitudinal waves makes it possible to evaluate physical and mechanical properties of the material.
Keywords:
ultrasonic pulses, multiple echo signals, longitudinal wave velocity, transversal wave, bottom echo, piezoelectric transducer, EMAT, Poisson ratio
ultrasonic pulses, multiple echo signals, longitudinal wave velocity, transversal wave, bottom echo, piezoelectric transducer, EMAT, Poisson ratio
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