Ultrasonic Testing

Ultrasonic Testing

Acoustic impedance

Posted Sun, 14/03/2010 - 10:44

Sound travels through materials under the influence of sound pressure. Because molecules or atoms of a solid are bound elastically to one another, the excess pressure results in a wave propagating through the solid.

The acoustic impedance Z of a material is defined as the product of its density p [kg/m^3] and acoustic velocity V [m/s].

Z = pV

The acoustic inpedance Z can be expressed in:

  • N.s/m^3
  • Pa.s/m
  • kg/(m^2.s) = 1 Rayl (S.I. unit of acoustic impedance is MRayl or Megarayls)

1 Rayl = 1 dyne.s/cm^3

Guided Waves

Posted Sun, 14/03/2010 - 10:26

Lamb waves are guided acoustic waves which propagate in the plane of a plate and, like bulk acoustic waves, their interaction with defects means that they can be used for inspection purposes. Because they propagate in the plane of a plate, a reasonably large area of a suitable structure can potentially be inspected from a single location although with some reduction in resolution and sensitivity compared to the conventional single point ultrasonic inspection described above.

Introduction to Ultrasonic Testing

Posted Sun, 14/03/2010 - 10:25

Why use ultrasonics for nondestructive material testing?

Phased array

Posted Sun, 14/03/2010 - 10:21

The Phased Array concept concerns multielement transducers. Each element of these transducers is connected to a different electronic channel, either directly or through multiplexors, according to electronic device performances.

Each element can be activated or not for each shot. The size and the location of the active aperture of a phased array transducer depends on the activated elements.

Pulse-Echo Inspection

Posted Sun, 14/03/2010 - 10:17

This process uses a transducer to both transmit and receive the ultrasonic pulse. The received ultrasonic pulses are separated by the time it takes the sound to reach the different surfaces from which it is reflected. The size (amplitude) of a reflection is related to the size of the reflecting surface. The pulse-echo ultrasonic response pattern is analyzed on the basis of signal amplitude and separation. Alternatively, the specimen may be immersed in water, with the probe immersed as well.

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The Power of Ultrasonic Inspection

Posted Sun, 14/03/2010 - 10:16

Ultrasonic inspection is a powerful, effective form of nondestructive testing in aviation maintenance. But it is also a technique that has room for error due to improper equipment setup, calibration, and an inexperienced tester.

To get a clear picture of ultrasonic inspection, Christine Murner answered a few questions. She is the aerospace marketing leader for GE Sensing & Inspection Technologies.

What is ultrasonic inspection?

Ultrasonic inspection uses high frequency sound energy to detect internal flaws or to characterize materials.

Through-Transmission Inspection

Posted Sun, 14/03/2010 - 10:16

This inspection employs two transducers, one to generate and a second to receive the ultrasound. A defect in the sound path between the two transducers will interrupt the sound transmission. The magnitude (the change in the sound pulse amplitude) of the interruption is used to evaluate test results. Through-transmission inspection is less sensitive to small defects than is pulse-echo inspection.

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