Non-Destruction Test

Last Updated on September 15, 2022 by You Ling

Ultrasonic testing is a kind of nondestructive testing

Ultrasonic testing, also known as ultrasonic testing and ultrasonic flaw detection, is a kind of non-destructive testing

Non destructive testing is a testing method to inspect the surface and internal quality of the inspected invisible without damaging the working state of the workpiece or raw materials. Ultrasonic nondestructive testing (NDI) is a development and application of ultrasonic nondestructive testing. Its equipment includes ultrasonic flaw detector, probe, coupling agent and standard test block. Its purpose is to detect shrinkage cavity, bubble, welding crack, slag inclusion, incomplete fusion, incomplete penetration and other defects of castings and thickness measurement.

Basic principle of ultrasonic nondestructive testing

1、There are many kinds of ultrasonic nondestructive testing instruments, but in the actual nondestructive testing process, the pulse reflection ultrasonic flaw detector is the most widely used. Generally, in uniform materials, the existence of defects will cause material discontinuities, which often lead to inconsistent acoustic impedance. From the reflection theorem, we know that ultrasonic waves will be reflected at the interface of two media with different acoustic impedance, and the amount of reflected energy is related to the difference in acoustic impedance of the media on both sides of the interface and the orientation and size of the interface. The pulse reflection ultrasonic nondestructive testing flaw detector is designed according to this principle.

2、At present, most of the portable pulse reflection ultrasonic nondestructive testing flaw detectors are in A-scan mode. The abscissa of the so-called A-scan display mode is the propagation time or distance of the ultrasonic wave in the tested material, and the ordinate is the amplitude of the ultrasonic wave reflection. For example, there is a defect in a steel workpiece. Because of the defect, an interface between the defect and the steel material is formed. The acoustic impedance between the interfaces is different. When the emitted ultrasound meets this interface, it will reflect, and the reflected energy is received by the probe. A reflected wave waveform will be displayed at a certain position of the abscissa in the display screen, This position of the abscissa is the depth of the defect in the tested material. The height and shape of this reflected wave vary with different defects, reflecting the nature of defects.

Main characteristics of ultrasonic nondestructive testing

1、When the ultrasonic wave propagates in the medium, it has the characteristics of reflection on the interface of different substances. If a defect is encountered and the size of the defect is equal to or greater than the ultrasonic wave length, the ultrasonic wave will reflect back on the defect, and the NDT flaw detector can display the reflected wave; If the defect size is even smaller than the wavelength, the sound wave will bypass the ray and cannot be reflected;

2、The directivity of wave sound is good. The higher the frequency, the better the directivity. It radiates into the medium with a very narrow beam, which is easy to determine the location of defects.

3、The propagation energy of ultrasonic wave is large. For example, the propagation energy of ultrasonic wave with a frequency of 1MHZ (1MHz) is equivalent to one million times of the sound wave with the same amplitude and a frequency of 1000HZ (Hz).

As an important nondestructive testing technology, ultrasonic testing not only has the fundamental advantages of strong penetrability, simple equipment, good use conditions and safety, and wide detection range, but also its output signal is reflected in the form of waveform. So that the current rapid development of computer signal processing, pattern recognition and artificial intelligence and other high-tech can be conveniently applied to the detection process, so as to improve the accuracy and reliability of detection.

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