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

Abstract

The invention relates to a thrust chamber milling groove welding seam laser ultrasonic optical fiber coupling transmission-type detection system and method, and belongs to the technical field of nondestructive testing. According to the method disclosed by the invention, the brazing quality of the milling groove of the thrust chamber is quickly scanned and detected by using an optical fiber coupling laser ultrasonic detection method, and a defect detection imaging picture with high-precision display on parameters such as defect positions and sizes is formed in the detection process, so that nondestructive detection can be carried out on the quality detection of the milling groove brazing seam of the thrust chamber; meanwhile, the influence of the surface smoothness of the test piece on a detection result is reduced, the cost of detection equipment is reduced, rapid non-contact scanning is realized, and the detection and evaluation efficiency is improved through two-dimensional scanning and data post-processing.

Description

Technical Field

[0001] This invention belongs to the field of non-destructive testing technology and relates to a laser-ultrasonic fiber-optic coupled transmission testing system and method for thrust chamber milled groove welds. Background Technology

[0002] As a critical propulsion system for launch vehicles, the structural safety evaluation of liquid rocket engines is self-evident. To ensure the stability and reliability of liquid rocket engine performance during service, the thrust chamber typically employs a sandwich structure between its inner and outer walls for regenerative cooling. Common sandwich structures include corrugated plate structures and milled groove brazed structures. Due to factors such as manufacturing processes, incomplete penetration, brazing filler metal accumulation, and blockages in the sandwich structures can occur, severely impacting product performance. The quality of the brazed joints in the thrust chamber body is one of the key factors affecting rocket engine safety. Utilizing advanced non-destructive testing technologies for rapid and effective quality inspection is crucial for ensuring engine safety and reliability.

[0003] For the quality inspection of brazed seams in corrugated plate structures, conventional radiographic testing is currently the primary method, supplemented by hydraulic strength testing. However, for the quality inspection of brazed seams in milled groove structures, due to their structural characteristics, the gap after welding is extremely small, only 0.02 mm. Furthermore, the height of the milled groove ribs is relatively large, obscuring the brazed seams, making conventional radiographic testing methods unsuitable. Currently, hydraulic strength testing is the main method relied upon, lacking effective preventative non-destructive testing techniques. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art. This invention provides a laser-ultrasonic fiber-optic coupled transmission detection system and method for thrust chamber milled groove welds.

[0005] The solution of the present invention is: a laser-ultrasonic fiber-coupled transmission detection system and method for milling groove welds in thrust chambers, including a high-frequency pulsed laser, an optical fiber, a fiber-coupled laser focusing lens, a focusing air-coupled transducer, a preamplifier, a bandpass filter, an oscilloscope, a main control terminal, and a motion scanning mechanism;

[0006] A high-frequency pulsed laser emits a Gaussian-distributed pulsed laser beam, which is transmitted via optical fiber to a fiber-coupled laser focusing lens. The fiber-coupled laser focusing lens focuses the Gaussian-distributed pulsed laser beam into a pulsed spot and illuminates the inner wall area of ​​the thrust chamber. A focusing air-coupled transducer collects ultrasonic waves in the corresponding area on the outer wall of the thrust chamber. The ultrasonic waves are amplified and filtered sequentially by a preamplifier and a bandpass filter before being transmitted to an oscilloscope. The oscilloscope receives and displays the ultrasonic time-domain signal. A motion scanning mechanism synchronously controls the fiber-coupled laser focusing lens and the focusing air-coupled transducer. The main control terminal connects the oscilloscope and the motion scanning mechanism to control the motion scanning mechanism and to acquire, store, and process the ultrasonic signals.

[0007] Furthermore, the pulsed light spot is incident perpendicularly on the area above the milled groove ribs on the inner wall of the thrust chamber.

[0008] Furthermore, the presence of brazing defects in the inner wall area of ​​the thrust chamber will hinder the propagation of ultrasonic waves to the corresponding area on the outer wall of the thrust chamber.

[0009] Furthermore, the fiber-coupled laser focusing lens and the focusing air-coupled transducer are arranged in a transmission manner, aligning the excitation pulse laser and the air-coupled detection focus point on the same axis. Then, the thrust chamber sidewall is placed between the excitation pulse laser and the detection point, and the scanning and detection position is adjusted.

[0010] A laser-ultrasonic fiber-optic coupled transmission method for detecting milled weld seams in thrust chambers includes:

[0011] The laser-ultrasonic fiber-optic coupled transmission detection system for the milled groove weld of the thrust chamber is arranged according to the transmission scanning method.

[0012] Two-dimensional area scanning of the test piece is performed using laser and air coupling at equal intervals.

[0013] The time-domain signals of each measurement point are obtained, and a signal matrix is ​​formed in sequence and then translated and aligned.

[0014] The signal matrix after translation and alignment is bandpass filtered, and then the time domain signal of the weld area in the key period of interest is extracted for power spectrum analysis to obtain a two-dimensional signal matrix I with frequency and amplitude.

[0015] The amplitude at the center frequency position and the coordinates of the scanning point are used to form a two-dimensional signal matrix II, which is then subjected to interpolation and normalization.

[0016] The interpolated and normalized two-dimensional signal matrix II is subjected to imaging processing to obtain the processed image.

[0017] Furthermore, the two-dimensional region scanning is set as follows: the scanning length in the x-axis direction is L1, the scanning interval in the x-axis direction is Δx, and the number of scanning points is m = L1 ÷ Δx + 1; the scanning length in the y-axis direction is L2, the scanning interval in the y-axis direction is Δy, and the number of scanning points is n = L2 ÷ Δy + 1; the total area of ​​the scanning region is L1 × L2, and the total number of scanning points in the scanning region is m × n.

[0018] Furthermore, the interpolation process is to set the interpolation step size to one-tenth of the smallest of the scanning spacing Δx in the x-axis direction and the scanning spacing Δy in the y-axis direction.

[0019] Furthermore, the key period of focus is the first four pulses of the transmission ultrasound signal.

[0020] Furthermore, the processed images include one-dimensional B-scan images, synthetic aperture imaging images, and two-dimensional C-scan images.

[0021] The advantages of this invention compared to the prior art are:

[0022] This invention utilizes fiber-coupled laser ultrasonic testing to rapidly scan and inspect the brazing quality of thrust chamber milled grooves. During the inspection process, a defect detection image is generated with high precision display of parameters such as defect location and size. This enables non-destructive testing of the quality of thrust chamber milled groove brazing seams, while reducing the impact of specimen surface finish on the test results, lowering the cost of testing equipment, and achieving rapid non-contact scanning. Furthermore, the efficiency of inspection and evaluation is improved through two-dimensional scanning and data post-processing. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the laser-coupled ultrasonic transmission scanning detection method involved in the present invention;

[0024] Figure 2 This is a flowchart illustrating the specific implementation steps of the present invention;

[0025] Figure 3 This is the scanning signal of the present invention;

[0026] Figure 4 This is the translational alignment scanning signal of the present invention;

[0027] Figure 5 This is the power spectrum analysis scan signal of the present invention;

[0028] Figure 6 This is a peak C-scan imaging image obtained from power spectrum analysis in this invention. Detailed Implementation

[0029] The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1 As shown, a laser-ultrasonic fiber-coupled transmission detection system for milled groove welds in a thrust chamber includes: a high-frequency pulsed laser 1, an optical fiber 2, a fiber-coupled laser focusing lens 3, a focusing air-coupled transducer 10, a preamplifier 11, a bandpass filter 12, an oscilloscope 13, a control computer 14 equipped with signal acquisition and processing software, and a motion scanning mechanism 15. The fiber-coupled laser focusing lens 3 is connected to the high-frequency pulsed laser 1 via the optical fiber 2. The motion scanning control mechanism 15 synchronously controls the fiber-coupled laser focusing lens 3 and the focusing air-coupled transducer 10. After receiving a trigger signal from the pulsed laser 1, the oscilloscope 13 begins to acquire the time-domain signal from the air-coupled ultrasonic transducer 10 after passing through the preamplifier 11 and the bandpass filter 12. The control computer 14 equipped with signal acquisition and processing software is responsible for acquiring and storing the signal from the oscilloscope 13 and synchronously controlling the motion scanning mechanism 15.

[0031] The high-frequency pulsed laser 1 has a frequency of approximately 1000Hz. When inspecting the milled thrust chamber after brazing, the high-frequency pulsed laser 1 emits a Gaussian pulsed laser beam that travels through fiber optic 2 to the fiber-coupled laser focusing lens 3. The focused pulsed spot 4 irradiates a certain area of ​​the inner wall of the thrust chamber 16, forming ultrasonic waves 5 that propagate along the narrow ribs (0.8–1.2 mm wide) towards the outer wall. The brazing defects 7 inside the thrust chamber hinder the propagation of ultrasonic waves to the outer wall, resulting in a localized weakening of the ultrasonic signal on the outer wall. The out-of-plane displacement ultrasonic signal of this area is collected non-contactly by the air-coupled ultrasonic transducer 10, thus enabling detection at this location. The fiber-coupled focusing lens 3 and the air-coupled transducer 10 are scanned and collected by the motion scanning mechanism 15, thereby achieving the overall inspection of the brazing quality of the thrust chamber.

[0032] A fiber-coupled laser-air-coupled ultrasonic transmission method for detecting milled groove welds in thrust chambers includes the following steps:

[0033] Step 1: Install the laser-ultrasonic fiber-coupled transmission detection system for the milled groove weld of the thrust chamber. This method adopts a transmission arrangement. First, align the excitation pulse laser and the empty coupling detection focus point on the same axis. Then, place the test piece between the excitation and detection points and adjust the scanning and detection position.

[0034] Both the pulsed laser and the air-coupled probe are non-contact, employing a transmission-type scanning acquisition method. The laser achieves vertical incidence and precise excitation of ultra-short pulse ultrasonic waves in a tiny area above the milled groove reinforcement, effectively reducing interference from reflected signals from the inner wall and reinforcement boundary, while also minimizing the blind zone effect on the outer wall bottom surface. Using a pulsed laser allows for excitation of a tiny area by adjusting the spot size, achieving higher directivity. It is more suitable for ultrasonic excitation of metallic materials with high acoustic impedance, while the air-coupled probe is better suited for exciting ultrasonic waves in materials with low acoustic impedance. Furthermore, the laser source can generate different waveforms in metallic materials, and the amplitude of the longitudinal wave signal and the directivity of the ultrasonic waves can be enhanced and altered by adding a constraint layer to the specimen surface.

[0035] Step 2: Set the scanning length in the x-axis direction to L1, the spacing to Δx, and the number of scanning points to m = L1 ÷ Δx + 1. Set the scanning length in the y-axis direction to L2, the scanning spacing to Δy, and the number of scanning points to n = L2 ÷ Δy + 1. Set the total area of ​​the scanning region to L1 × L2 and the total number of scanning points to m × n. Move the test piece back and forth along the direction shown in the figure to perform two-dimensional scanning detection. The x-axis direction is the circumferential direction of the thrust chamber, and the y-axis direction is the direction along the generatrix of the thrust chamber.

[0036] Step 3: Obtain the volume wave time-domain signal S at each measurement point using two-dimensional scanning. 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), where t is time;

[0037] Step 4: Bandpass filter the translated and aligned two-dimensional signal data matrix S′(t,m×n), and then extract the time-domain signal within the time period of interest for power spectrum analysis to obtain the two-dimensional signal matrix A(f,v) with frequency and amplitude, where f is the frequency and v is the amplitude.

[0038] The period of interest is the first four pulses of the transmission signal. If the distance between the air-coupled probe and the surface of the specimen changes, causing a partial shift in the time domain signal, the shifted signal can be corrected in the signal processing section.

[0039] Step 5: Take the amplitude at the center frequency position and the coordinates of the scan point to form a two-dimensional signal matrix U(u,w). Set the interpolation step size to one-tenth of the minimum scan step size, i.e., min(Δx,Δy) / 10. After interpolation and normalization, a new two-dimensional signal matrix V(u,w) is obtained, where u is the amplitude at the center frequency position and w represents the coordinates of the scan point.

[0040] Step 6: Perform imaging processing on the two-dimensional signal matrix V(u,w) of the amplitude at the center frequency position and the coordinates of the scan point after interpolation and normalization to obtain the one-dimensional B-scan (Brightness-modulated scan), synthetic aperture image, and two-dimensional C-scan (Constant-depth scan) of the specimen.

[0041] like Figure 3 The image shows the scanning signal of this invention; as shown... Figure 4 As shown, this is the translational alignment scanning signal of the present invention; as Figure 5 The image shows the power spectrum analysis scan signal of this invention; as shown... Figure 6 The image shown is a peak C-scan image obtained from power spectrum analysis according to the present invention.

[0042] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A laser-ultrasonic fiber-optic coupled transmission detection system for milled groove welds in thrust chambers, characterized in that: It includes a high-frequency pulsed laser (1), an optical fiber (2), an optical fiber coupled laser focusing lens (3), a focusing air-coupled transducer (10), a preamplifier (11), a bandpass filter (12), an oscilloscope (13), a main control terminal (14), and a motion scanning mechanism (15); A high-frequency pulsed laser (1) emits a Gaussian-distributed pulsed laser beam, which is transmitted to a fiber-coupled laser focusing lens (3) via an optical fiber (2). The fiber-coupled laser focusing lens (3) focuses the Gaussian-distributed pulsed laser beam into a pulsed spot (4) and irradiates the inner wall area of ​​the thrust chamber (16). A focusing air-coupled transducer (10) collects ultrasonic waves (5) in the corresponding area on the outer wall of the thrust chamber (16). The ultrasonic waves (5) are amplified and filtered by a preamplifier (11) and a bandpass filter (12) in sequence, and then transmitted to an oscilloscope (13). The oscilloscope (13) receives and displays the time-domain signal of the ultrasonic waves (5). A motion scanning mechanism (15) synchronously controls the fiber-coupled laser focusing lens (3) and the focusing air-coupled transducer (10). A main control terminal (14) connects the oscilloscope and the motion scanning mechanism (15) to complete the control of the motion scanning mechanism (15) and the acquisition, storage and processing of the ultrasonic wave (5) signal.

2. The laser-ultrasonic fiber-optic coupled transmission detection system for thrust chamber milled groove welds according to claim 1, characterized in that: The pulsed light spot (4) is incident vertically on the area above the milled groove rib on the inner wall of the thrust chamber (16).

3. The laser-ultrasonic fiber-optic coupled transmission detection system for thrust chamber milled groove welds according to claim 1, characterized in that: The location of the brazing defect (7) on the inner wall of the thrust chamber (16) will hinder the propagation of ultrasonic waves (5) to the corresponding area on the outer wall of the thrust chamber (16).

4. The laser-ultrasonic fiber-optic coupled transmission detection system for thrust chamber milled groove welds according to claim 1, characterized in that: The fiber-coupled laser focusing lens (3) and the focusing air-coupled transducer (10) are arranged in a transmission manner, aligning the excitation pulse laser and the air-coupled detection focus point on the same axis. Then, the side wall of the thrust chamber (16) is placed between the excitation pulse laser and the detection point, and the scanning and detection position is adjusted.

5. A laser-ultrasonic fiber-optic coupled transmission method for detecting milled groove welds in thrust chambers, characterized in that... include: The laser-ultrasonic fiber-optic coupled transmission detection system for the milled groove weld of the thrust chamber is arranged according to the transmission scanning method. Two-dimensional area scanning of the test piece is performed using laser and air coupling at equal intervals. The time-domain signals of each measurement point are obtained, and a signal matrix is ​​formed in sequence and then translated and aligned. The signal matrix after translation and alignment is bandpass filtered, and then the time domain signal of the weld area in the key period of interest is extracted for power spectrum analysis to obtain a two-dimensional signal matrix I with frequency and amplitude. The amplitude at the center frequency position and the coordinates of the scanning point are used to form a two-dimensional signal matrix II, which is then subjected to interpolation and normalization. Imaging processing is performed on the interpolated and normalized two-dimensional signal matrix II to obtain the processed image.

6. The laser-ultrasonic fiber-optic coupled transmission detection system for thrust chamber milled groove welds according to claim 5, characterized in that, The two-dimensional region scanning is set as follows: the scanning length in the x-axis direction is L1, the scanning interval in the x-axis direction is Δx, and the number of scanning points is m = L1 ÷ Δx + 1; the scanning length in the y-axis direction is L2, the scanning interval in the y-axis direction is Δy, and the number of scanning points is n = L2 ÷ Δy + 1; the total area of ​​the scanning region is L1 × L2, and the total number of scanning points in the scanning region is m × n.

7. The laser-ultrasonic fiber-optic coupled transmission detection system for thrust chamber milled groove welds according to claim 6, characterized in that, The interpolation process involves setting the interpolation step size to one-tenth of the smallest of the scanning intervals Δx in the x-axis direction and Δy in the y-axis direction.

8. The laser-ultrasonic fiber-optic coupled transmission detection system for thrust chamber milled groove welds according to claim 5, characterized in that, The key period of focus is the first four pulses of the transmission ultrasound signal.

9. The laser-ultrasonic fiber-optic coupled transmission detection system for thrust chamber milled groove welds according to claim 5, characterized in that, The processed images include one-dimensional B-scan images, synthetic aperture imaging images, and two-dimensional C-scan images.

Images