There are many kinds of the ultrasonic flaw detector, but in the actual flaw detection process, the pulse reflection ultrasonic flaw detector is the most widely used one. Generally, in homogeneous materials, the existence of defects will cause the discontinuity of materials, which often leads to the inconsistency of the acoustic impedance. The ultrasonic flaw detector working principle is as follows:
From the reflection theorem, it is known that the ultrasonic wave will reflect at the interface of two kinds of media with different acoustic impedance. The reflected energy is related to the difference of acoustic impedance between the two sides of the interface and the orientation and size of the interface. Pulse reflection ultrasonic flaw detector is designed according to this principle.
At present, major ultrasonic testing equipment suppliers use A-scan mode for most of the portable pulse reflection ultrasonic flaw detectors. The so-called A-scan display mode means that the abscissa of the displayer is the propagation time or distance of ultrasonic wave in the tested material, and the ordinate is the amplitude of the reflected ultrasonic wave.
For example, there is a defect in a steel workpiece. Because of this defect, an interface between the defect and the steel material is formed. The acoustic impedance between the two sides of the interface is different. When the ultrasonic wave emitted meets this interface, it will reflect. The reflected energy is received by the probe, and a reflected wave will be displayed at a certain position in the abscissa of the display screen. This position on the abscissa is the depth of the defect in the tested material. The height and shape of the reflected wave vary with different defects, reflecting the properties of the defect.