Ultrasonic Non destructive Testing
Principle: The basic principle behind the ultrasonic inspection is the transmission of the Ultrasound with the medium and the reflection or scattering at any surface or internal discontinuity in the medium due to the change in the acoustic impedance. The Discontinuity means the existence of the flaw or detect or cracks or hole in the material. The reflected or scattered sound waves are received and amplified and hence, the defects in the specimen are suitably characterized.
Block diagram of the Ultrasonic Flaw detector
Whenever there is a change in the medium, then the Ultrasonic waves will be reflected. This is the principle used in Ultrasonic flaw detector. Thus, from the intensity of the reflected echoes, the flaws are detected without destroying the material and hence this method is known as a Non Destructive method.
a. The pulse generator generates high frequency waves and is applied to the Piezo-electric transducer and the same is recorded in the CRO.
b. The piezo electric crystals are resonated to produce Ultrasonic waves.
c. These Ultrasonic waves are transmitted through the given specimen.
d. These waves travel through the specimen and is reflected back by the other end.
e. The reflected Ultrasonic are received by the transducer and is converted into electric signals. These reflected signals are amplified and is recorded in the CRO.
f. If the reflected pulse is same as that o the transmitted pulse, then it indictes that there is no defect in the specimen.
g. On the other hand, if there is any defect on the specimen like a small hole or pores, then the Ultrasonic will be relected bby the holes(i.e.) defects due to change in the medium.
h. From the time delay between the transmitted and received pulses, the position of the hole can be found.
i. From the height o the pulse received the depth of the hole can also be determined.