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Principle of ultrasonic testing

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ultrasonic testing is a nondestructive testing method to test the internal defects of materials by using the reflection of ultrasonic propagation waveform and the energy change of penetration time caused by the difference of acoustic properties of materials and their defects

pulse reflection method uses longitudinal wave in vertical flaw detection and transverse wave in oblique flaw detection. Pulse reflection method includes longitudinal wave flaw detection and transverse wave flaw detection. On the wave display screen of ultrasonic instrument, the abscissa represents the propagation time of sound wave and the ordinate represents the amplitude of echo signal

for the same homogeneous medium, the propagation time of pulse wave is directly proportional to the sound path. Therefore, the existence of defects can be judged by the appearance of defect echo signal; The distance between the defect and the detection surface can be determined by the position of the echo signal, so as to realize the defect location; The equivalent size of the defect is judged by the echo amplitude


extended data:

advantages of ultrasonic testing:

1. It is suitable for nondestructive testing of metal, non-metal and composite materials

2. The defect location is more accurate

3. The detection rate of area defects is high

4. It has high sensitivity and can detect defects with small internal size

5. It is harmless to human body and the environment

6 Do not destroy samples

reference source: Baidu Encyclopedia – Ultrasonic Testing

when ultrasonic wave acts on the contact surface of thermoplastic plastics, it will produce tens of thousands of high-frequency vibrations per second. This high-frequency vibration with a certain amplitude will transmit ultrasonic energy to the welding area through the upper weldment. Due to the large acoustic resistance at the interface between the two welding areas, local high temperature will be generated. In addition, due to the poor thermal conductivity of the plastic, it can not be distributed in time at the moment and gathered in the welding area, resulting in the rapid melting of the contact surface of the two plastics. After adding a certain pressure, it will be integrated into one. When the ultrasonic stops, let the pressure last for a few seconds to solidify and form, so as to form a solid molecular chain to achieve the purpose of welding, and the welding strength can be close to the strength of raw materials. The quality of ultrasonic plastic welding depends on three factors: the amplitude of the transducer welding head, the applied pressure and the welding time. The welding time and the welding head pressure can be adjusted, and the amplitude is determined by the transducer and horn. When the energy exceeds the appropriate value, the melting amount of plastic is large and the weldment is easy to deform; If the energy is small, it is not easy to weld firmly, and the added pressure cannot be large. This optimum pressure is the product of the side length of the welding part and the optimum pressure of every 1mm at the edge
in contemporary society, various plastic products have penetrated into all fields of people’s daily life. At the same time, they are also widely used in aviation, shipbuilding, automobile, electrical appliances, packaging, toys, electronics, textile and other industries. However, due to the limitations of injection molding process and other factors, a considerable part of plastic products with complex shapes cannot be injection molded at one time, which requires bonding. However, the plastic bonding and heat sealing process used for many years is quite backward, which not only has low efficiency, but also has a certain toxicity of the adhesive, causing problems such as environmental pollution and labor protection. The traditional process can no longer meet the development needs of modern plastic industry, so a novel plastic processing technology ultrasonic plastic welding stands out for its advantages of high efficiency, high quality, beauty and energy saving. When welding plastic products, ultrasonic plastic welding machine does not add any adhesive, filler or solvent, and does not consume a large amount of heat source. It has the advantages of simple operation, fast welding speed, high welding strength and high production efficiency. Therefore, ultrasonic welding technology is more and more widely used.

there are many kinds of ultrasonic flaw detectors, but in the actual flaw detection process, pulse reflection ultrasonic flaw detector is most widely used. Generally, in uniform materials, the existence of defects will cause discontinuity of materials, which often leads to inconsistency of acoustic impedance. From the reflection theorem, we know that ultrasonic will be reflected at the interface of two media with different acoustic impedance, and the reflected energy is related to the difference of acoustic impedance between the media on both 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, most portable pulse reflection ultrasonic flaw detectors are in A-scan mode. The so-called A-scan display mode is that the abscissa of the display is the propagation time or distance of ultrasonic wave in the tested material, and the ordinate is the amplitude of ultrasonic reflected wave. For example, there is a defect in a steel workpiece. Due to the existence of this defect, an interface between different media is formed between the defect and the steel material. The acoustic impedance between the interfaces is different. When the emitted ultrasonic meets this interface, it will reflect (see Figure 1), 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 the reflected wave vary with different defects, reflecting the nature of the defects

if you need more questions about ultrasonic flaw detector, you can contact online!

very simple:
sound wave (continuous wave with adjustable frequency) propagates in the inspected workpiece. When the thickness of the workpiece is an integral multiple of the half wavelength of ultrasonic wave, it will cause resonance. The instrument displays the resonance frequency. If there are defects in the workpiece, the resonance frequency will change. The difference of resonance frequency is used to judge the internal state of the workpiece

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