Thrust chamber milling groove welding seam optical fiber coupling laser-air coupling ultrasonic reflection type detection system and method

Abstract

The invention discloses an optical fiber coupling laser-air coupling ultrasonic reflection type detection system and method for a milling groove welding seam of a thrust chamber. The system comprises a high-frequency pulse laser, an optical fiber coupling laser focusing lens, a focusing type air coupling ultrasonic transducer, a control computer provided with ultrasonic signal acquisition and processing software, and a scanning movement mechanism. The detection method comprises the following steps: performing ultra-short pulse ultrasonic excitation on the inner wall surface of the milling groove of the thrust chamber by utilizing optical fiber coupling pulse laser, spreading ultrasonic waves in the milling groove structure, and hindering the spreading of the ultrasonic waves by a solder skipping defect of a brazing layer; the focusing type air coupling ultrasonic transducer collects ultrasonic signals of the position on the inner wall face so as to achieve detection of internal brazing defects, the motion scanning mechanism is controlled through a computer to conduct rapid scanning on the thrust chamber, and then overall evaluation of the brazing quality of the thrust chamber is achieved. The method effectively solves the problem that a conventional detection method for the milling groove brazing seam cannot detect the milling groove brazing seam, reduces the influence of the surface smoothness of the test piece on a detection result, reduces the cost of detection equipment, and improves the evaluation efficiency of the milling groove brazing seam defect of the thrust chamber.

Description

Technical Field

[0001] The present invention relates to the technical field of non-destructive testing, and particularly relates to a fiber-optic coupled laser-air coupled ultrasonic reflection detection system and method for the milled groove weld of a thrust chamber, which can realize the rapid detection and high-resolution imaging of defects in the brazed weld of the milled groove of a liquid rocket engine thrust chamber. Background Art

[0002] As a key power system of a launch vehicle, the safety evaluation of the structure of a liquid rocket engine is self-evident. To ensure the stability and reliability of the service performance of a liquid rocket engine, a sandwich structure is usually added between the inner and outer walls of the thrust chamber for regenerative cooling. The common sandwich structures mainly include a corrugated plate structure and a milled groove brazed structure. Due to factors such as manufacturing processes, the sandwich structure may have incomplete penetration, channel brazing material accumulation, blockage, etc. These defects will seriously affect the product performance. The quality of the brazed weld of the thrust chamber body is one of the key factors affecting the safety of the rocket engine. Using advanced non-destructive testing technologies to quickly and effectively detect its quality is crucial for ensuring the safe and reliable operation of the engine.

[0003] For the quality detection of the brazed weld of the corrugated plate structure, currently, it is mainly detected by conventional ray detection methods, and then hydraulic strength tests are used as auxiliary inspections. For the quality detection of the brazed weld of the milled groove structure, due to its structural characteristics, the gap is extremely small, only 0.02 mm, after welding, and at the same time, the height of the milled groove ribs is relatively large, and the brazed weld is blocked by the ribs, resulting in the inapplicability of conventional ray detection methods. Currently, it mainly relies on hydraulic strength tests and lacks effective preventive non-destructive testing technologies. With the gradual development and maturity of non-contact ultrasonic detection technologies such as laser ultrasonic and air-coupled ultrasonic, and at the same time, it is easy to achieve efficient detection and non-contact evaluation. Therefore, combining the advantages of laser and air-coupled ultrasonic, the fiber-optic coupled laser ultrasonic reflection detection system and method for the milled groove weld of the thrust chamber provide more feasibility for the detection of the milled groove brazed structure. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that the conventional detection methods for the milled groove brazed weld of the thrust chamber of a liquid rocket engine are not detectable, and to provide a fiber-optic coupled laser-air coupled ultrasonic reflection detection system and method for the milled groove weld of the thrust chamber.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] A fiber-coupled laser-air coupled ultrasonic reflection detection system for the milled groove weld of a thrust chamber, comprising: a high-frequency pulsed laser 1, an optical fiber 2, a fiber-coupled laser focusing lens 3, a focused air-coupled ultrasonic transducer 4, a preamplifier 7, a band-pass filter 8, an oscilloscope 9, a control computer 10 equipped with signal acquisition and processing software, and a motion scanning mechanism 11; wherein the fiber-coupled laser focusing lens 3 is connected to the high-frequency pulsed laser 1 through the optical fiber 2, the motion scanning control mechanism 11 synchronously controls the fiber-coupled laser focusing lens 3 and the focused air-coupled ultrasonic transducer 4, and after the oscilloscope 9 receives the trigger signal from the high-frequency pulsed laser 1, it starts to collect the time-domain signal measured by the focused air-coupled ultrasonic transducer 4 after passing through the preamplifier 7 and the band-pass filter 8, and the control computer 10 equipped with signal acquisition and processing software is responsible for collecting the signal from the oscilloscope 9 and storing it, and synchronously controls the motion scanning mechanism 11.

[0007] When detecting the milled groove thrust chamber after brazing, the high-frequency pulsed laser 1 emits a Gaussian pulsed laser beam, which reaches the fiber-coupled laser focusing lens 3 through the optical fiber 2. The focused pulsed light spot irradiates above the rib on the inner wall surface of the thrust chamber, and ultrasonic waves 5 are formed and propagate outward along the rib to the outer wall surface. The brazing defect 6 inside the thrust chamber will reflect the ultrasonic waves and propagate towards the inner wall surface, thereby forming local ultrasonic signal characteristics on the inner wall surface. The out-of-plane displacement ultrasonic signal in this area is collected non-contact by the focused air-coupled ultrasonic transducer 4 to realize the detection at this position; the fiber-coupled laser focusing lens 3 and the focused air-coupled ultrasonic transducer 4 are scanned and collected through the motion scanning mechanism 11, that is, the overall brazing quality of the thrust chamber is detected.

[0008] The detection method of the fiber-coupled laser-air coupled ultrasonic reflection detection system for the milled groove weld of a thrust chamber described above includes the following steps:

[0009] Step 1: Install the fiber-coupled laser-air coupled ultrasonic reflection detection system for the milled groove weld of the thrust chamber, and adopt the reflection layout scanning and collection method, that is, the ultrasonic excitation end and the detection end are on the same side. First, place the fiber-coupled laser focusing lens 3 obliquely and make the incident pulsed laser obliquely incident and coincide with the air-coupled detection focus of the focused air-coupled ultrasonic transducer 4, and adjust the scanning and detection position.

[0010] Step 2: Set the scanning length in the x-axis direction to be L 1 , the spacing to be Δx, the number of scanning points to be m = L 1 ÷Δx + 1, the scanning length in the y-axis direction to be L 2 , the scanning spacing to be Δy, the number of scanning points to be n = L 2 ÷Δy + 1, and the total area of the scanning region to be L 1 ×L 2, the total number of points in the scanning area is m×n, and the test piece is reciprocally moved along the scanning area 13 for two-dimensional scanning detection;

[0011] Step 3: Obtain the body wave time-domain signals S 1,1 (t), S 1,2 (t)…S 1,m (t), S 2,1 (t), S 2,2 (t)…S 2,m (t)…S n,1 (t), S n,2 (t)…S n,m (t), and sequentially form a two-dimensional signal data matrix S(t, m×n);

[0012] Step 4: Perform band-pass digital filtering on the translated and aligned two-dimensional signal data matrix S′(t, m×n), and then intercept the ratio of the peak value at the defect position to the peak value of the bottom echo as the defect feature to obtain a two-dimensional signal matrix A(x, y) corresponding to the ratio and the scanning point coordinates;

[0013] Step 5: Take the two-dimensional signal matrix A(x, y) corresponding to the ratio and the scanning point coordinates, set the interpolation step size, and obtain a two-dimensional signal matrix V(x, y) after interpolation and normalization;

[0014] Step 6: Perform imaging processing on the two-dimensional signal matrix V(x, y) after interpolation and normalization processing to obtain a defect detection imaging diagram of the defect position and size of the test piece, that is, a one-dimensional B-scan diagram, a synthetic aperture algorithm imaging diagram, and a two-dimensional C-scan diagram.

[0015] Both the fiber-coupled laser focusing lens 3 and the focused air-coupled ultrasonic transducer 4 described in Step 1 are non-contact type, and a reflection arrangement scanning and acquisition method is adopted. The pulsed laser is obliquely incident on a small area above the milled groove rib of the thrust chamber, and the size of the laser spot is controlled to be the same as the width of the rib, so as to achieve the precise excitation of the ultrashort pulsed ultrasonic wave, effectively reduce the interference of the reflected signals from the inner wall and rib boundary of the thrust chamber, and at the same time reduce the blind area effect of the bottom surface of the outer wall of the thrust chamber; by adjusting the size and shape of the pulsed laser spot to excite a small area, higher directivity can be obtained. The pulsed laser is more suitable for ultrasonic excitation of metal materials with a large acoustic impedance, while the focused air-coupled ultrasonic transducer 4 is more suitable for exciting ultrasonic waves in materials with a low acoustic impedance. In addition, different waveforms are generated by the pulsed laser in the metal material. By adding a constraint layer on the surface of the test piece, that is, coating a transparent liquid film on the surface of the test piece, the heat in the laser irradiation area causes the liquid to evaporate and generate a greater reaction force, so as to enhance the amplitude of the longitudinal wave signal and change the directivity of the ultrasonic wave.

[0016] The ratio of the peak value at the defect position intercepted in Step 4 to the peak value of the bottom echo, which is used as the defect feature, belongs to the signal feature collected in the reflection arrangement. If the distance between the focused air-coupled ultrasonic transducer 4 and the surface of the test piece changes, resulting in partial offset of the time-domain signal, the offset signal is corrected for its time-domain position before signal processing.

[0017] The interpolation step size set in Step 5 is adjusted according to the scanning step size. For better interpolation results, the scanning step size is set to one-tenth of the minimum scanning step size, that is, min(Δx,Δy) / 10.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] Aiming at the problem that the conventional detection methods for the existing milled groove brazed welds are not detectable, the present invention uses a fiber-coupled laser-air-coupled ultrasonic detection system and method to quickly scan and detect the quality of the milled groove brazing of the thrust chamber. During the detection process, a defect detection imaging diagram of the defect position and size is formed, thereby providing a feasible detection system and method for the quality detection of the milled groove brazed weld of the thrust chamber. Since the focused air-coupled ultrasonic transducer does not require optical focusing like optical detection equipment (such as a laser interferometer, etc.), it only needs to be placed directly above the rib, and the distance between the focused air-coupled ultrasonic transducer and the surface of the test piece is controlled to be one focal length of the focused air-coupled ultrasonic transducer. In addition, compared with the optical detection equipment, the focused air-coupled ultrasonic transducer is smaller in size, lower in price, convenient to install and simple to use. Therefore, the influence of the surface finish of the test piece on the detection result is reduced, the cost of the detection equipment is reduced, rapid non-contact scanning is realized, and the efficiency of detection and evaluation is improved through two-dimensional scanning and data post-processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the laser air-coupled ultrasonic reflection scanning detection related to the present invention;

[0021] Figure 2 It is a flow chart of the specific implementation steps of the present invention;

[0022] Figure 3 It is a schematic diagram of the signal processing process related to the present invention, where (a) is the signal processing process of the scan, (b) is the signal processing process of the translation alignment scan, and (c) is the schematic diagram of the two-dimensional C-scan imaging of the scan area. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0024] As Figure 1As shown in the figure, the present invention discloses a fiber-coupled laser-air-coupled ultrasonic reflection detection system and method for a milled groove weld of a thrust chamber, including: a high-frequency pulsed laser 1, an optical fiber 2, an optical fiber-coupled laser focusing lens 3, a focused air-coupled ultrasonic transducer 4, a preamplifier 7, a band-pass filter 8, an oscilloscope 9, a control computer 10 equipped with signal acquisition and processing software, and a motion scanning mechanism 11; wherein the optical fiber-coupled laser focusing lens 3 is connected to the high-frequency pulsed laser 1 through the optical fiber 2, and the motion scanning control mechanism 11 synchronously controls the optical fiber-coupled laser focusing lens 3 and the focused air-coupled ultrasonic transducer 4. After receiving the trigger signal from the high-frequency pulsed laser 1, the oscilloscope 9 starts to collect the time-domain signal measured by the focused air-coupled ultrasonic transducer 4 after passing through the preamplifier 7 and the band-pass filter 8. The control computer 10 equipped with signal acquisition and processing software is responsible for collecting the signal from the oscilloscope 9 and storing it, and synchronously controls the motion scanning mechanism 11. When detecting the milled groove thrust chamber after brazing, the high-frequency pulsed laser 1 emits a Gaussian pulsed laser beam, which reaches the optical fiber-coupled laser focusing lens 3 through the optical fiber 2. The focused pulsed light spot irradiates above the inner wall rib of the thrust chamber 14, and ultrasonic waves 5 are formed and propagate outward along the rib to the outer wall. The brazing defect 6 inside the thrust chamber will reflect the ultrasonic waves and propagate towards the inner wall, thereby forming local ultrasonic signal characteristics on the inner wall. The out-of-plane displacement ultrasonic signal in this area is collected non-contact by the focused air-coupled ultrasonic transducer 4 to achieve the detection at this position; the optical fiber-coupled laser focusing lens 3 and the focused air-coupled ultrasonic transducer 4 are scanned and collected by the motion scanning mechanism 11, that is, the overall brazing quality of the thrust chamber is detected.

[0025] The detection method of the fiber-coupled laser-air-coupled ultrasonic reflection detection system for the milled groove weld of a thrust chamber is as follows Figure 2 shown and is described in detail as follows:

[0026] Step 1: Install the fiber-coupled laser-air-coupled ultrasonic reflection detection system for the milled groove weld of a thrust chamber. This method adopts a reflection layout, that is, the optical fiber-coupled laser focusing lens 3 and the focused air-coupled ultrasonic transducer 4 are placed on the same side of the test piece. First, the excitation pulsed laser is obliquely incident to coincide with the detection focus of the focused air-coupled ultrasonic transducer, and the scanning detection position is adjusted.

[0027] Step 2: Set the scanning length in the x-axis direction to L 1 , the spacing is Δx, and the number of scanning points is m = L 1 ÷Δx + 1. The scanning length in the y-axis direction is L 2 , the scanning spacing is Δy, and the number of scanning points is n = L 2 ÷Δy + 1. The total area of the scanning region is L 1 ×L 2, the total number of points in the scanning area is m×n, and the test piece is reciprocally moved along the scanning area 13 for two-dimensional scanning detection;

[0028] Step 3: Obtain the body wave time-domain signals S 1,1 (t), S 1,2 (t)…S 1,m (t), S 2,1 (t), S 2,2 (t)…S 2,m (t)…S n,1 (t), S n,2 (t)…S n,m (t), and sequentially form a two-dimensional signal data matrix S(t, m×n), as shown in Figure 3 (a);

[0029] Step 4: As shown in Figure 3 (b), perform band-pass digital filtering on the translated and aligned two-dimensional signal data matrix S′(t, m×n), and then intercept the ratio of the peak value at the defect position to the peak value of the bottom echo as the defect feature to obtain a two-dimensional signal matrix A(x, y) corresponding to the ratio and the scanning point coordinates;

[0030] Step 5: Take the two-dimensional signal matrix A(x, y) corresponding to the ratio and the scanning point coordinates, set the interpolation step size to one-tenth of the minimum scanning step size, that is, min(Δx, Δy) / 10, and obtain a two-dimensional signal matrix V(x, y) after interpolation and normalization;

[0031] Step 6: Perform imaging processing on the two-dimensional signal matrix V(x, y) after interpolation and normalization processing to obtain a defect detection imaging map of the defect position and size of the test piece, such as a one-dimensional B-scan image, a synthetic aperture algorithm imaging map, a two-dimensional C-scan image. Figure 3 As shown in (c), it is a schematic diagram of two-dimensional C-scan imaging of the scanning area. The entire area of the image represents the experimental scanning area. The positions parallel to the y-axis are the positions of the milled groove ribs. The cooling channels are between the ribs, and the discontinuity above the ribs is the brazing seam defect.

Claims

1. A thrust chamber milling groove weld fiber-coupled laser-air-coupled ultrasonic reflection detection system, characterized in that: include: A high-frequency pulse laser (1), an optical fiber (2), an optical fiber-coupled laser focusing lens (3), a focused air-coupled ultrasonic transducer (4), a preamplifier (7), a bandpass filter (8), an oscilloscope (9), a control computer (10) equipped with signal acquisition and processing software, and a motion scanning mechanism (11); wherein the optical fiber-coupled laser focusing lens (3) is connected to the high-frequency pulse laser (1) through the optical fiber (2); the motion scanning control mechanism (11) synchronously controls the optical fiber-coupled laser focusing lens (3) and the focused air-coupled ultrasonic transducer (4); the oscilloscope (9) receives a trigger signal from the high-frequency pulse laser (1) and starts to collect the time domain signal measured by the focused air-coupled ultrasonic transducer (4) after passing through the preamplifier (7) and the bandpass filter (8); the control computer (10) equipped with the signal acquisition and processing software is responsible for collecting and storing the signal from the oscilloscope (9), and synchronously controlling the motion scanning mechanism (11).

2. According to claim 1, a thrust chamber milling groove weld fiber-coupled laser-air-coupled ultrasonic reflection detection system is characterized in that: When inspecting the milled groove thrust chamber after brazing, a high-frequency pulse laser (1) emits a Gaussian pulse laser beam through an optical fiber (2) to reach a fiber-coupled laser focusing lens (3), and the focused pulse light spot is irradiated onto the upper part of the inner wall rib of the thrust chamber, and forms an ultrasonic wave (5) that propagates along the rib to the outer wall surface. The brazing defect (6) inside the thrust chamber will reflect the ultrasonic wave and propagate to the inner wall surface, thereby forming a local ultrasonic signal feature on the inner wall surface. The off-surface displacement ultrasonic signal of the area is collected in a non-contact manner by a focused air-coupled ultrasonic transducer (4), thereby realizing the detection at the position; the fiber-coupled laser focusing lens (3) and the focused air-coupled ultrasonic transducer (4) perform scanning and collection through a motion scanning mechanism (11), thereby realizing the detection of the overall brazing quality of the thrust chamber.

3. A detection method of a thrust chamber milling groove weld fiber-coupled laser-air-coupled ultrasonic reflection detection system according to claim 1 or 2, characterized in that: The steps include: Step 1: Install the thrust chamber milling groove weld fiber-coupled laser-air-coupled ultrasonic reflection detection system, adopt a reflection arrangement scanning and collection method, that is, the ultrasonic excitation end and the detection end are on the same side, firstly, the fiber-coupled laser focusing lens (3) is tilted and the excitation pulse laser is tilted to coincide with the air-coupled detection focus point of the focused air-coupled ultrasonic transducer (4), and the scanning detection position is adjusted; Step 2: Set the scanning length in the x-axis direction to L1, the spacing to Δx, the number of scanning points to m=L1÷Δx+1, the scanning length in the y-axis direction to L2, the scanning spacing to Δy, the number of scanning points to n=L2÷Δy+1, the total area of ​​the scanning area to L1×L2, the total number of scanning points to m×n, and reciprocate the test piece along the scanning area (13) to perform two-dimensional scanning detection; Step 3: Two-dimensional scanning to obtain the body wave time domain signal S of each measuring point 1,1 (t), S 1,2 (t)…S 1,m (t), S 2,1 (t), S 2,2 (t)…S 2,m (t)…S n,1 (t), S n,2 (t)…S n,m (t), sequentially forming a two-dimensional signal data matrix S(t,m×n); Step 4: Perform bandpass digital filtering on the translationally aligned two-dimensional signal data matrix S′(t,m×n), and then intercept the peak value ratio of the peak value at the defect position to the peak value of the bottom echo as the defect feature, and obtain the two-dimensional signal matrix A(x,y) corresponding to the ratio and the scanning point coordinates; Step 5: Take the two-dimensional signal matrix A(x,y) corresponding to the ratio and the scan point coordinates, set the interpolation step size, interpolate and normalize to obtain the two-dimensional signal matrix V(x,y); Step 6: Perform imaging processing on the two-dimensional signal matrix V(x, y) after interpolation and normalization processing to obtain a defect detection imaging image containing the defect position and size of the test piece, namely, a one-dimensional B-scan image, a synthetic aperture algorithm imaging image, and a two-dimensional C-scan image.

4. The detection method of the thrust chamber milling groove weld fiber-coupled laser-air-coupled ultrasonic reflection detection system according to claim 3 is characterized in that: The fiber-coupled laser focusing lens (3) and the focused air-coupled ultrasonic transducer (4) described in step 1 are both non-contact types, and adopt a reflective arrangement scanning and collection method. The excitation pulse laser is incident obliquely on a small area above the milling groove rib of the thrust chamber, and the size of the laser spot is controlled to be the same as the width of the rib, thereby achieving accurate excitation of ultra-short pulse ultrasonic waves, effectively reducing the interference of the reflected signals of the inner wall and the rib boundary of the thrust chamber, and reducing the blind area effect of the bottom surface of the outer wall of the thrust chamber; by adjusting the size and shape of the pulse laser spot to achieve excitation of the small area, a higher directivity is obtained. The pulse laser is more suitable for ultrasonic excitation of metal materials with large acoustic impedance, while the focused air-coupled ultrasonic transducer (4) is more suitable for exciting ultrasonic waves in low acoustic impedance materials. In addition, the pulse laser generates different waveforms in the metal material. By adding a constraint layer on the surface of the specimen, that is, coating a transparent liquid film on the surface of the specimen, the heat in the laser irradiation area causes the liquid to evaporate and generate a greater reaction force, thereby enhancing the amplitude of the longitudinal wave signal and changing the directivity of the ultrasonic wave.

5. The detection method of the thrust chamber milling groove weld fiber-coupled laser-air-coupled ultrasonic reflection detection system according to claim 3 is characterized in that: The ratio of the peak value at the intercepted defect position to the peak value of the bottom echo described in step 4 is taken as the defect feature and belongs to the signal feature collected by the reflective arrangement. If the distance between the focused air-coupled ultrasonic transducer (4) and the surface of the test piece changes, resulting in a partial offset in the time domain signal, the offset signal is corrected in the time domain before signal processing.

6. The detection method of the thrust chamber milling groove weld fiber-coupled laser-air-coupled ultrasonic reflection detection system according to claim 3 is characterized in that: The interpolation step size setting described in step 5 is adjusted according to the scanning step size. In order to obtain a better interpolation result, the scanning step size is set to one tenth of the minimum scanning step size, that is, min(Δx,Δy) / 10.

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