CN211179651U - A New Ultrasonic Detection System for Metal Internal Defects - Google Patents

Abstract

The utility model discloses a novel ultrasonic testing system of metal internal defect, the system includes that the circulator passes through the optic fibre Fizeau interferometer detecting system, fiber optic regulator, electronic accurate displacement platform, convex lens, spectroscope, space pulse laser instrument, photoelectric detector, oscilloscope and the signal analysis identification module that isolator and narrow linewidth laser instrument are connected and are constituteed, arouse the supersound at the metal surface with pulse laser, carry out non-contact detection to ultrasonic signal with optic fibre Fizeau interferometer detecting system, cooperate electronic accurate displacement platform, the metal sample that drives to be measured carries out two-dimensional optical scanning and detects, acquire the ultrasonic signal of metal surface; and processing the detection time domain signal by using a signal analysis and identification module to obtain the information of the position and the size of the defect in the metal. The system is simple to build, flexible to use, high in detection precision, nondestructive and non-contact to detect, achieves ultra-high precision photoacoustic detection of metal internal defects, and has important application prospects in the field of ultrasonic precision detection.

Description

A New Ultrasonic Detection System for Metal Internal Defects

technical field

The utility model belongs to the field of laser ultrasonic nondestructive testing, in particular to a novel ultrasonic testing system for metal internal defects.

Background technique

As a new type of ultrasonic non-destructive testing method, laser ultrasonic testing technology is mainly used for the detection of defects on the surface and interior of materials. This technology utilizes lasers to realize the excitation and detection of ultrasound. Compared with traditional piezoelectric ultrasonic technology, laser ultrasonic testing technology has the advantages of non-contact, wide frequency band, high spatial resolution, and can work normally in special environments such as high temperature, high pressure, corrosion, radiation, etc., and has strong environmental adaptability. sex. Therefore, laser ultrasonic testing technology has been widely used in material characterization, defect detection, process monitoring and so on.

There are many kinds of ultrasonic detection systems at this stage, and the difference is mainly in the difference between the ultrasonic excitation equipment and the ultrasonic detector. For ultrasonic detectors, the commonly used devices are PZT piezoelectric ceramics, EMAT electromagnetic ultrasonic sensors, laser interferometers, and Doppler vibrometers. In 2017, Chuanyong Wang et al. published "Width gauging of surface slot using laser-generated Rayleigh waves" in "Optics & LaserTechnology". In this paper, a pulsed laser is used to excite ultrasonic waves, and a laser interferometer is used to detect the ultrasonic signals, so as to realize the quantitative measurement of the width and position information of rectangular defects on the surface of aluminum plates. In 2017, Zhong Yunjie et al. published "Simulation of Laser Ultrasonics for Detection of Surface-Connected Rail Defects" in the "Journal of Nondestructive Evaluation", using a laser ultrasonic inspection system to detect tiny cracks on the rail surface.

Based on laser ultrasound, the present application combines optical fiber sensing technology to realize the identification and measurement of ultrasound signals. The system effectively reduces the purchase cost of equipment while maintaining high temporal and spatial resolution and high signal-to-noise ratio. It is flexible to use, easy to debug, and the precision can reach 0.01 mm. It can effectively detect various types of defects such as the surface and the interior of the sample, and has certain application potential in the field of laser ultrasonic nondestructive testing.

Utility model content

The purpose of the utility model is to overcome the deficiencies of the prior art, and provide a new type of ultrasonic detection system for metal internal defects, which can perform ultrasonic scanning detection on metal internal defects without damage, and detect the defect position, Ultra-high-precision detection of horizontal and vertical size information.

The technical scheme that realizes the purpose of the present utility model is:

A new ultrasonic inspection system for metal internal defects, including narrow linewidth lasers, isolators, circulators, fiber conditioners, motorized precision displacement stages, convex lenses, beam splitters, space pulse lasers, photodetectors, oscilloscopes, and signal analysis and identification Module, the metal sample to be tested is fixed on the electric precision mobile platform, and one side of the electric precision mobile platform is sequentially provided with a convex lens, a beam splitter and a space pulse laser. The space photodetector receives and converts the electrical signal and transmits it to the oscilloscope as a trigger signal. The other part of the laser is focused on the surface of the metal sample to be tested fixed on the electric precision moving platform through the convex lens, which is used to excite the ultrasonic wave; the circulator is set on the electric precision moving platform The other side of the platform is adjusted and fixed as a probe head through an optical fiber adjuster. The circulator is connected to a narrow linewidth laser through an isolator to form a fiber-optic Fizeau interferometer detection system. The output end of the circulator is also connected to the input end of the photodetector. , the output end of the photodetector is connected to the input end of the oscilloscope, the output end of the oscilloscope is connected to the input end of the signal analysis and identification module, the detection head transmits the signal to the photoelectric detector, the photoelectric detector outputs the interference signal, and the interference signal is input In the oscilloscope, the oscilloscope outputs the detection signal, and the detection signal is integrated and processed by the signal analysis and identification module to obtain the detection result.

In the space pulse laser, the output laser focusing point and the fiber probe at the end of the circulator are respectively located on both sides of the metal sample to be measured, and are in the same straight line.

The space pulse laser is a Nd:YAG solid-state laser with a laser wavelength of 1064 nm and a pulse width of 6 ns.

The optical fiber adjuster can be adjusted in the X-Y-Z direction, and the adjustment precision is 0.01mm.

The narrow linewidth laser, optical isolator, circulator, and photodetector all have an operating wavelength of 1550 nm.

The signal analysis and identification module adopts the prior art to process the detection signal through computer algorithm programming to obtain the detection result, including the filtering processing of the detection signal, the signal identification of the longitudinal wave and the transverse wave, the ratio calculation of the amplitude of the longitudinal wave and the transverse wave, These four parts are extracted from the signal reception time variation.

The working principle of the system is as follows: using pulsed laser radiation to the surface of the material, if the laser energy is controlled to be lower than the material damage threshold, the thermoelastic effect can be induced, resulting in the generation of Rayleigh waves, transverse waves, longitudinal waves and other types of ultrasonic waves. When there are defects in the sample, the above-mentioned ultrasonic waves will be affected by the defects during the transmission process, so that the characteristics of the signal shape, amplitude, receiving time and other characteristics will change to different degrees. The utility model determines the position, size, shape and other information of defects by extracting the time domain signal features of different scanning positions and calculating the signal features.

Beneficial effects: The utility model provides a new type of ultrasonic detection system for metal internal defects. The system uses a pulsed laser to excite ultrasonic waves and realizes non-contact and non-destructive ultrasonic detection; uses a fiber-optic Fizeau interferometer detection system to detect ultrasonic waves, which has the advantages of: Extremely high temporal and spatial resolution; using the signal analysis and identification module, the defect information can be accurately analyzed; the system is simple to build, easy to adjust, and can work normally in harsh environments such as high temperature, high pressure, and strong electromagnetic interference; it can detect There are many types of defects, and ultrasonic testing can be performed on surface cracks, gaps, grooves, internal pores, cavities and other types of defects.

Description of drawings

FIG. 1 is a schematic structural diagram of a new type of ultrasonic inspection system for metal internal defects;

Fig. 2 is the internal defect imaging image obtained by scanning detection;

In the picture: 1. Narrow linewidth laser 2. Isolator 3. Circulator 4. Fiber conditioner 5. Photodetector 6. Sample to be tested 7. Electric precise displacement platform 8. Space pulse laser 9. Beam splitter 10. Convex lens 11. Space photodetector 12. Oscilloscope 13. Signal analysis and identification module.

Detailed ways

The present utility model is further described below in conjunction with the accompanying drawings and embodiments, but is not intended to limit the present utility model.

As shown in Figure 1, a new type of ultrasonic inspection system for metal internal defects, including narrow linewidth laser, isolator, circulator, fiber conditioner, electric precision displacement platform, convex lens, beam splitter, space pulse laser, photodetector , oscilloscope and signal analysis and identification module, the metal sample to be tested is fixed on the electric precision mobile platform, and one side of the electric precision mobile platform is sequentially provided with a convex lens, a beam splitter and a space pulse laser. The laser beam emitted by the space pulse laser is divided into two parts by the beam splitter. Part of the energy, part of the energy is received by the space photodetector and converted into an electrical signal, and then transmitted to the oscilloscope as a trigger signal, and the other part of the laser is focused on the surface of the metal sample to be measured fixed on the motorized precision moving platform through a convex lens to excite ultrasound; annular; The circulator is located on the other side of the electric precision mobile platform and is adjusted and fixed as a probe head through an optical fiber adjuster. The circulator is connected to a narrow linewidth laser through an isolator to form a fiber optic Fizeau interferometer detection system. The output end of the circulator is also connected to the photoelectric The input end of the detector is connected, the output end of the photodetector is connected to the input end of the oscilloscope, the output end of the oscilloscope is connected to the input end of the signal analysis and identification module, the detection head transmits the signal to the photoelectric detector, and the photoelectric detector outputs interference The interference signal is input into the oscilloscope, the oscilloscope outputs the detection signal, and the detection signal is integrated and processed by the signal analysis and identification module to obtain the detection result.

The described oscilloscope adopts a high-resolution oscilloscope, and its maximum sampling frequency is 20GSa/s.

In the space pulse laser, the output laser focusing point and the fiber probe at the end of the circulator are respectively located on both sides of the metal sample to be tested, and are in the same straight line. During scanning, the positions of the two remain unchanged, and only the testing sample is moved.

The space pulse laser is a Nd:YAG solid-state laser with a laser wavelength of 1064 nm and a pulse width of 6 ns.

The optical fiber adjuster can be adjusted in the X-Y-Z direction, and the adjustment precision is 0.01mm.

The narrow linewidth laser, optical isolator, circulator, and photodetector all have an operating wavelength of 1550 nm.

The signal analysis and identification module adopts the prior art to process the detection signal through computer algorithm programming to obtain the detection result, including the filtering processing of the detection signal, the signal identification of the longitudinal wave and the transverse wave, the ratio calculation of the amplitude of the longitudinal wave and the transverse wave, These four parts are extracted from the signal reception time variation.

The metal sample to be tested is fixed on the electric precision displacement platform, driven by the electric precision displacement platform and realizes scanning detection in a two-dimensional area. The electric precision displacement platform includes a control motor, and the scanning stroke is 200×200mm. The step size is 0.01mm.

Example:

The detection was carried out using an aluminum plate sample with a sample size of 300 × 100 × 10 mm. On the upper side of the aluminum plate, drill a cylindrical hole with a diameter of 2 mm and a depth of 10 mm to create internal defects for detection; fix the sample to be tested on a precision electric displacement platform, and adjust the position of the sample so that the defect position is within the scanning range.

The above-mentioned connected ultrasonic detection system is used for detection. Before detection, the fiber Fizeau interferometer detection system is first debugged, and the relative distance between the fiber end face and the sample surface is changed by the fiber adjuster, thereby changing the fiber interference cavity length. Observe the output signal of the photodetector. When the output light intensity reaches a predetermined intensity, the interferometer is in a stable working state and can detect the ultrasonic signal; on the other side of the sample, control the pulsed laser to emit laser light, and adjust the output intensity of the pulsed laser to make The laser energy is less than the sample damage threshold, and the single-shot emission mode is selected to ensure that the interferometer can receive the ultrasonic signal stably.

Adjust the relative position of the fiber end face and the laser irradiation point so that the two are in the same straight line in space. During detection, the pulsed laser is turned on to emit a single-shot laser. Through the detection system, the ultrasonic detection waveform can be obtained on the oscilloscope. After that, the above detection steps were repeated, and the precision electric displacement platform was controlled to drive the sample to perform point-by-point scanning detection in a 5 × 5 mm area with a step size of 0.2 mm. During scanning, keep the position of the fiber probe and the laser irradiation spot unchanged, and only the detection sample moves.

After all the scanning work is completed, the internal defect imaging diagram as shown in Figure 2 is obtained, and the ultrasonic shape data of all scanning points are collected. Use the signal analysis and identification module data for analysis and processing. By using MATLAB software, the waveform data is filtered to improve the signal-to-noise ratio of the waveform, which is convenient for analysis and processing. After observation, it was found that the longitudinal wave and shear wave signals were detected at 1.6 μs and 3.3 μs, respectively. In the defect-free area, the amplitude intensity of the longitudinal wave is significantly stronger than that of the transverse wave, which is consistent with the transmission characteristics of the two types of ultrasonic waves. As the position of the scanning point gradually approaches the defect, the longitudinal wave intensity gradually decreases. At the same time, compared with the longitudinal wave, the attenuation amplitude of the shear wave signal strength is smaller. When scanning to the edge of the defect, the amplitude intensity of the longitudinal wave decays below the shear wave. As the scan point gradually moves out of the defect area, the longitudinal wave intensity increases and again exceeds the shear wave intensity at the edge of the defect. And through the analysis of the difference of the receiving time of the longitudinal wave and the transverse wave, the depth of the detection point defect is judged by the propagation speed of the longitudinal wave and the transverse wave in the object to be tested.

According to the above-mentioned waveform change law, the defect can be judged by observing the relative amplitudes of the longitudinal wave and the transverse wave. Definition When the amplitude and intensity of the longitudinal wave is smaller than the transverse wave, the scanning point is at the defect position, otherwise it means that there is no defect in the test sample. Using MATLAB software for programming, an ultrasonic judgment program was designed. Using the longitudinal wave as the standard, normalize the data of all scanning points. After processing, the P-wave intensity of all data is unity. The shear wave intensity of each set of data is then extracted. In the defect-free area, the longitudinal wave intensity is greater than the shear wave intensity, so the shear wave intensity is less than one. At the defect position, the longitudinal wave intensity is smaller than the shear wave, and the shear wave intensity is greater than one. Collecting all the shear wave intensity data and arranging them according to the scanned spatial position, the shear wave intensity distribution data in the two-dimensional scanning area can be obtained. Then, the amplitude intensity is plotted with the color depth, and the scanning image of the internal defects of the sample can be obtained. Finally, the time when the longitudinal wave and the transverse wave are received in each set of data is extracted, and the longitudinal size of the defect here is obtained through calculation and analysis.

Claims (5)

1. a novel ultrasonic detection system for metal internal defects, is characterized in that, comprises narrow linewidth laser, isolator, circulator, optical fiber regulator, electric precision displacement platform, convex lens, beam splitter, space pulse laser, photodetector , oscilloscope and signal analysis and identification module, the metal sample to be tested is fixed on the electric precision mobile platform, and one side of the electric precision mobile platform is sequentially provided with a convex lens, a beam splitter and a space pulse laser. The laser beam emitted by the space pulse laser is divided into two parts by the beam splitter. Part of the energy, part of the energy is received by the space photodetector and converted into an electrical signal, and then transmitted to the oscilloscope as a trigger signal, and the other part of the laser is focused on the surface of the metal sample to be measured fixed on the motorized precision moving platform through a convex lens to excite ultrasound; annular; The circulator is located on the other side of the electric precision mobile platform and is adjusted and fixed as a probe head through an optical fiber adjuster. The circulator is connected to a narrow linewidth laser through an isolator to form a fiber optic Fizeau interferometer detection system. The output end of the circulator is also connected to the photoelectric The input end of the detector is connected, the output end of the photodetector is connected to the input end of the oscilloscope, the output end of the oscilloscope is connected to the input end of the signal analysis and identification module, the detection head transmits the signal to the photoelectric detector, and the photoelectric detector outputs interference The interference signal is input into the oscilloscope, the oscilloscope outputs the detection signal, and the detection signal is integrated and processed by the signal analysis and identification module to obtain the detection result. 2. The novel ultrasonic detection system for metal internal defects according to claim 1, wherein the space pulse laser, the output laser focus point and the fiber probe at the end of the circulator are respectively located in the metal sample to be tested on both sides and in the same straight line. 3 . The novel ultrasonic detection system for metal internal defects according to claim 1 , wherein the space pulse laser is a Nd:YAG solid-state laser with a laser wavelength of 1064 nm and a pulse width of 6 ns. 4 . 4 . The novel ultrasonic detection system for metal internal defects according to claim 1 , wherein the optical fiber adjuster can be adjusted in the X-Y-Z direction, and the adjustment accuracy is 0.01 mm. 5 . 5 . The novel ultrasonic detection system for metal internal defects according to claim 1 , wherein the operating wavelengths of the narrow linewidth lasers, optical isolators, circulators, and photodetectors are all 1550 nm. 6 .

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