Operating Principle Of Ultrasonic Flaw Detectors-UFD
Operating Principle Of Ultrasonic Flaw Detectors-UFD
- March 3, 2022
Operating Principle Of Ultrasonic Flaw Detectors-UFD
1)The Principle of ultrasonic testing
The ultrasonic inspection refers to non-destructive methods. This method is widely used for welded joints testing for different materials: low-alloyed and low-carbon steel, aluminium, copper and their alloys. Mechanical oscillations propagate in the elastic “body”. They are divided into: infrasonic (frequency of vibrations up to 30 Hz), sonic (20 – 20* 103 Hz), ultrasonic (2 * 104 to 109 Hz) and hypersonic (over 109 Hz). During acoustic waves propagation, the particles of the medium, that the waves are passing though, oscillate relatively of their equilibrium points. If particles oscillate along, these waves are called longitudinal, if perpendicular – transverse.
Ultrasonic wave carries a certain amount of energy along the direction of it’s propagation, which is characterized by intensity of ultrasound (quantity of energy that is transferred along with the wave into the object body through area, which is perpendicular to the direction of propagation).
The longer ultrasonic wave propagates, the less is it’s intensity. The length of the path travelled by wave can be measured by the value of the damping coefficient. High hardness materials have their own absorption and scattering coefficients.
Piezoelectricity is the electric charge that accumulates in certain solid materials such as crystals, certain ceramics in response to applied mechanical stress. The piezoelectric effect is a reversible process. The reverse piezoelectric effect manifest as internal generation of a mechanical strain resulting from an applied electrical field. High-frequency electrical oscillations given by generator are converted through the piezoelectric crystals into mechanical vibrations with frequency up to 500 – 1000 MHz.
So a high frequency generator sends impulse to piezoelectric element that issues ultrasonic oscillations, that being reflected from a flaw, or the opposite surface fall onto the other piezoelectric element that being stressed by those oscillations sends electrical impulse to the instrument’s input. After processing thus obtained signal is displayed on the device’s monitor.
