Optical fiber type laser ultrasonic measurement device and method suitable for seawater high-pressure environment

Abstract

The invention discloses an optical fiber type laser ultrasonic measuring device and method suitable for a seawater high-pressure environment, and the device comprises a deep sea pressure tank part, and is characterized in that an optical fiber type laser ultrasonic system is arranged, a compression-resistant optical fiber is arranged in the optical fiber type laser ultrasonic system, and the compression-resistant optical fiber is located in the deep sea pressure tank part; an integrated receiving head is arranged at one end of the compression-resistant optical fiber and installed on a tank body of the deep sea pressure tank component to receive incident light, an ultrasonic surface wave excitation module of the laser ultrasonic system excites surface waves in a target area of a to-be-detected sample, and an ultrasonic detection module detects the excited surface waves. And processing the signal carrying the surface wave information to obtain the material property of the sample to be detected. The device realizes laser ultrasonic in-situ detection in the deep sea pressure ground simulation environment, and has the advantages of high time resolution, external vibration resistance, suitability for rough surfaces, suitability for the deep sea pressure environment and the like.

Description

Technical Field

[0001] This invention relates to a laser ultrasonic testing device and method, specifically to a laser ultrasonic testing device and method suitable for high-pressure seawater environments, particularly a fiber optic laser ultrasonic measuring device suitable for defect measurement. Background Technology

[0002] Deep-sea equipment serves as a core carrier supporting deep-sea safety, resource development, and scientific research. Its service reliability is tested through ground-based simulation devices that reproduce extreme deep-sea environments (high pressure, low temperature, corrosion, etc.). Currently, deep-sea equipment requires ground-based simulation devices for pressure resistance performance assessment and design optimization; however, the coupling of existing in-situ characterization technologies with ground-based simulation devices still faces bottlenecks. Traditional methods (such as high-speed photography and strain gauges) can capture macroscopic information such as sample surface deformation and crack propagation, but they cannot obtain key internal parameters of the material in real time (such as residual stress distribution, microscopic defect evolution, phase transformation behavior, etc.). This results in a blind spot in equipment performance evaluation—"visible on the surface, but unclear on the internal structure"—limiting the iteration efficiency of deep-sea equipment.

[0003] Laser ultrasound belongs to the field of ultrasonic testing and combines the advantages of both lasers and ultrasound, featuring non-contact, high-resolution, and non-destructive testing. Its principle is as follows: an excitation laser is used to generate ultrasonic waves on the sample surface through the thermoelastic effect. Surface wave displacement information is then obtained through a probe laser and an interferometer. By inverting the detected surface wave displacement, internal material information such as residual stress and defects can be obtained. For example, Chinese invention application CN 111257236 A discloses a dual-pulse laser ultrasonic testing device and its testing method. The device comprises a pulsed laser emitting device and a continuous laser emitting device respectively arranged on the front and rear sides of a sample. The pulsed laser emitting device has a first beam splitter and a reflector directly in front of it to split the pulsed laser beam into two beams perpendicular to the front surface of the sample. A lens is provided between the first beam splitter and the sample surface. A photorefractive two-wavelength mixing interferometer and a photodetector are also provided on one side of the rear surface of the sample. The continuous laser emitting device has a second beam splitter in front of it, which splits the continuous laser beam into two beams. One beam is angled towards the rear surface of the sample and then reflected into the photorefractive two-wavelength mixing interferometer, while the other beam is directly directed towards the photorefractive two-wavelength mixing interferometer. This invention has the advantages of reducing damage and improving measurement accuracy.

[0004] However, existing laser ultrasound systems have the following limitations if they are to be used in deep-sea high-pressure environments: (1) Poor vibration resistance: Traditional laser vibration meters have extremely high requirements for equipment stability, while deep-sea pressure simulation devices are accompanied by strong vibrations during operation, resulting in a decrease in detection accuracy; (2) Insufficient environmental adaptability: The high pressure environment in the deep sea (up to 30 MPa) poses a challenge to the pressure resistance of optical fibers, and existing laser ultrasound systems are unable to stably transmit laser signals; (3) Difficulty in detecting rough surfaces: There are often processing marks or corrosion on the surface of deep-sea equipment materials, and traditional optical systems are easily affected by scattering interference.

[0005] Currently, there are no publicly reported laser ultrasonic testing systems suitable for deep-sea high-pressure simulation environments. Summary of the Invention

[0006] The purpose of this invention is to provide a fiber optic laser ultrasonic measurement device suitable for high-pressure seawater environments, so as to improve the stability, anti-interference and adaptability of material internal defect detection under high-pressure seawater environments.

[0007] Another objective of this invention is to provide a fiber optic laser ultrasonic measurement method suitable for high-pressure seawater environments.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: a fiber optic laser ultrasonic measurement device suitable for high-pressure seawater environments, comprising a deep-sea pressure tank component, wherein the deep-sea pressure tank component simulates applying a predetermined hydrostatic pressure to the sample under test and maintains stable pressure through the deep-sea pressure environment; a fiber optic laser ultrasonic system is provided, wherein a pressure-resistant optical fiber is provided within the fiber optic laser ultrasonic system, the pressure-resistant optical fiber is located within the deep-sea pressure tank component, and an integrated receiver head is provided at one end of the pressure-resistant optical fiber, the integrated receiver head is installed on the tank body of the deep-sea pressure tank component to receive incident light; the ultrasonic surface wave excitation module of the laser ultrasonic system excites surface waves in the target area of ​​the sample under test, the ultrasonic detection module detects the excited surface waves, and processes the signal carrying surface wave information to obtain the material properties of the sample under test.

[0009] A further technical solution, the fiber optic laser ultrasound system includes a picosecond pulsed laser, a 1×2 polarization-maintaining fiber coupler, an acousto-optic modulator, a BBO crystal, a dichroic mirror, a fiber optic optical delay line, a manual fiber polarization controller, a fiber optic circulator, a first polarization beam combiner / splitter, a second polarization beam combiner / splitter, a pressure-resistant integrated lens assembly, a polarization controller, a third polarization beam combiner / splitter, a balanced photodetector, a waveform generator, and a lock-in amplifier. The picosecond pulsed laser emits a pulsed laser with wavelength λ, which is split into two beams with an intensity ratio of 9:1 by the 1×2 polarization-maintaining fiber coupler. The stronger laser beam is modulated by the acousto-optic modulator, with the modulation signal provided by the waveform generator, exhibiting a sinusoidal intensity distribution. The modulated beam enters the BBO crystal, where the wavelength is converted from λ to λ / 2 using the frequency doubling effect. The excited beam is transmitted through the dichroic mirror into the pressure-resistant fiber and, under the focusing of the pressure-resistant integrated lens assembly, is transmitted to the surface of the sample to be tested, generating an ultrasonic signal. The weaker laser beam is time-delayed by the fiber optic optical delay line and enters the polarization beam... The polarization controller rotates the polarization direction of the laser by 45°, splitting it into two optical paths through a first polarization beam combiner / splitter. These paths are transmitted to fiber arms of different lengths. A fixed time delay occurs when the laser reaches the second polarization beam combiner / splitter. The probe laser, after being reflected by a dichroic mirror, enters a pressure-resistant fiber and is focused onto the sample surface by optical components in an integrated receiver. The returning beam, carrying surface wave information, is transmitted back through the fiber. The returned beam contains two delayed waves from the long and short fiber arms, but their polarization directions are interchanged, ensuring that the two beams returning from the first polarization beam combiner / splitter have no path difference. The two beams return to the polarization controller and interfere. The interfering beam is split into two beams by a third polarization beam combiner / splitter, which enter the input of a balanced photodetector with a 270° phase deviation. The output signal of the balanced photodetector enters a lock-in amplifier. The reference signal is the same as that from the waveform generator used in the acousto-optic modulator. After signal processing, the system finally obtains a signal output proportional to the surface wave vibration velocity or displacement.

[0010] In a preferred embodiment, the pressure-resistant integrated lens assembly comprises two high-precision aspherical lenses to focus the laser onto the sample surface. This enables efficient focusing of the laser onto the sample surface, ensuring energy utilization and beam quality during the excitation process.

[0011] In a preferred embodiment, the integrated receiver head comprises two aspherical lenses and a quarter-wave plate. The aspherical lenses are used to focus and collect scattered light from the sample surface, and the quarter-wave plate is used to exchange the polarization directions of the two beams. This ensures the interference stability of the returned light.

[0012] A further technical solution involves a scanning mechanism within the deep-sea pressure tank component. The scanning mechanism includes a rotating mechanism and a Y-axis electric guide rail. The other end of the pressure-resistant optical fiber is fixed to the moving part of the scanning mechanism and is driven by the scanning mechanism.

[0013] To achieve another objective of this invention, a fiber optic laser ultrasonic measurement method suitable for high-pressure seawater environments is provided. This method utilizes the aforementioned fiber optic laser ultrasonic measurement device suitable for high-pressure seawater environments and includes the following steps: (1) Place the sample to be tested inside the deep-sea pressure tank component, seal the pressure tank, apply a predetermined pressure intensity inside the pressure tank through the pressurization system and the hydraulic control system and keep the pressure stable to simulate the environmental pressure of the sample to be tested at the expected seawater depth. (2) Control the scanning mechanism inside the deep-sea pressure tank components to move the integrated lens group of the laser ultrasonic system to the measurement position; (3) The laser ultrasound system uses the thermoelastic effect to excite and detect ultrasonic signals on the surface of an object, and stores the measured ultrasonic signals in a computer. (4) Change the distance of the optical delay line in the laser ultrasound system and repeat step (3) until the surface wave signal within the required time range is measured. By reconstructing the surface wave signal under different delay times, the surface wave within the time range is obtained. (5) Change the position of the integrated lens group of the laser ultrasound system relative to the sample to be measured, and repeat steps (3) to (4) until all areas are detected.

[0014] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: This invention relates to a device and method for laser ultrasonic testing of samples in a deep-sea pressure environment using a fiber optic laser ultrasonic system. The fiber optic laser ultrasonic system ensures system stability and reduces interference from external mechanical vibrations. Pressure-resistant optical fibers are used to achieve ultrasonic excitation and detection under deep-sea pressure (30 MPa), making it suitable for rough surface testing and enabling in-situ laser ultrasonic testing in a simulated deep-sea pressure environment. This invention offers advantages such as high temporal resolution, resistance to external vibrations, applicability to rough surfaces, and suitability for deep-sea pressure environments. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the optical path of the device according to an embodiment of the present invention.

[0016] The components include: 1. Picosecond pulsed laser; 2. 1×2 polarization-maintaining fiber coupler; 3. Acousto-optic modulator; 4. BBO crystal; 5. Dichroic mirror; 6. Fiber optic optical delay line; 7. Manual fiber polarization controller; 8. Fiber circulator; 9. First polarization beam combiner / splitter; 10. Second polarization beam combiner / splitter; 11. Compression-resistant integrated lens assembly; 12. Polarization controller; 13. Third polarization beam combiner / splitter; 14. Balanced photodetector. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments: Example: A fiber optic laser ultrasonic measuring device suitable for high-pressure seawater environments, comprising a deep-sea pressure tank component, a scanning system, and a fiber optic laser ultrasonic system.

[0018] The main body of the deep-sea pressure tank is made of stainless steel, with an internal anti-corrosion coating to prevent corrosion of the pressure tank during testing, which could lead to water turbidity and excessive absorption of laser intensity. Scanning system 2 is placed inside the deep-sea pressure tank and mainly consists of a bottom rotating mechanism and a side Y-axis scanning displacement rail. The bottom rotating mechanism enables axial rotation of the sample under test, while the side Y-axis scanning rail displacement stage is equipped with pressure-resistant optical fibers. Computer control of the rotating mechanism and Y-axis displacement stage enables full-field scanning of the sample under test within the deep-sea pressure tank.

[0019] See Figure 1 The device of the present invention includes a picosecond pulse laser 1, a 1×2 polarization-maintaining fiber coupler 2, an acousto-optic modulator 3, a BBO crystal 4, a dichroic mirror 5, a fiber optic optical delay line 6, a manual fiber polarization controller 7, a fiber optic circulator 8, a first polarization beam combiner / splitter 9, a second polarization beam combiner / splitter 10, a pressure-resistant integrated lens assembly 11, a polarization controller 12, a third polarization beam combiner / splitter 13, and a photoelectric balance detector 14.

[0020] First, a picosecond pulsed laser 1 emits a pulsed laser beam with a wavelength of λ, which is split into two beams with an intensity ratio of 9:1 by a 1×2 polarization-maintaining fiber coupler 2. The stronger laser beam is modulated by an acousto-optic modulator 3, with the modulation signal provided by a waveform generator, exhibiting a sinusoidal intensity distribution (sin ωt). The modulated beam enters a BBO crystal 4, where the wavelength of the laser is converted from λ to λ / 2 using the frequency doubling effect. This wavelength conversion distinguishes the wavelengths of the excitation laser from those of the probe laser to avoid interference. Subsequently, the excitation beam passes through a dichroic mirror 5, is transmitted into the interior of a pressure-resistant fiber, and is focused by a pressure-resistant integrated lens assembly 11 onto the surface of the sample under test, exciting an ultrasonic signal. The pressure-resistant integrated lens assembly comprises two high-precision aspherical lenses, capable of efficiently focusing the laser onto the sample surface, ensuring energy utilization and beam quality during the excitation process. The weaker beam is introduced with a time delay via a fiber-optic optical delay line 6, ensuring a stable time difference between the measured excitation laser and the surface wave excitation laser. The distance of the optical delay line is adjusted to measure surface wave signals at different times; the time resolution of the laser ultrasound system depends on the distance difference of the optical delay line after each measurement. Subsequently, the laser passing through the fiber-optic optical delay line 6 enters the polarization controller 7, which rotates the laser's polarization direction by 45°. The laser is then transmitted through the fiber optic circulator 8 to the first polarization beam combiner / splitter 9, splitting it into two optical paths, which are then transmitted to fiber arms of different lengths. The different lengths of the fiber arms ensure a fixed time delay between the two beams when they reach the second polarization beam combiner / splitter 10. The probe laser, after being reflected by the dichroic mirror 5, enters the pressure-resistant fiber and is focused onto the sample surface by the optical components in the pressure-resistant integrated lens assembly 11. The receiver head includes two aspherical lenses and a quarter-wave plate. The aspherical lenses are used to focus and collect scattered light from the sample surface, while the quarter-wave plate is used to exchange the polarization directions of the two beams, ensuring the interference stability of the returned light. The returned beam carries surface wave information and is transmitted back through the optical fiber, containing two delayed waves from the long and short fiber arms, but with their polarization directions exchanged. The light wave initially propagating in the short arm propagates through the long arm upon return, and vice versa. The two beams returning to the first polarization beam combiner / splitter 9 have no path difference and interfere upon returning to the third polarization beam combiner / splitter 13. The interfering beam is split into two beams by the third polarization beam combiner / splitter 13, which enter the input of the balanced photodetector 14 with a phase deviation of 270°. The output signal of the balanced photodetector enters the lock-in amplifier. The reference signal is the same as that from the waveform generator used in the acousto-optic modulator, mainly to modulate the noise signal to a high frequency and then filter out the noise using the low-pass filter of the lock-in amplifier. After signal processing, the system finally obtains a signal output that is proportional to the surface wave vibration velocity or displacement.

[0021] The usage method of this embodiment includes the following steps: Step 1: Using the device proposed in this invention, high hydrostatic pressure resistant optical fibers are introduced into the interior of a deep-sea pressure tank.

[0022] Step 2: Control the scanning system inside the deep-sea pressure tank to move the integrated lens group of the laser ultrasound system to the measurement position.

[0023] Step 3: The laser ultrasound system uses the thermoelastic effect to excite and detect ultrasonic signals on the surface of an object, and stores the measured ultrasonic signals in a computer.

[0024] Step 4: Change the distance of the optical delay lines within the laser ultrasound system and repeat Step 3 until the surface wave signal within the desired time range is obtained. The surface wave within the time range is acquired by reconstructing the surface wave signals at different delay times.

[0025] Step 5: Change the position of the sample to be measured and repeat steps 3-4.

Claims

1. A fiber optic laser ultrasonic measuring device suitable for high-pressure seawater environments, comprising a deep-sea pressure tank component, wherein the deep-sea pressure tank component simulates applying a predetermined hydrostatic pressure to the sample under test through a deep-sea pressure environment and maintains stable pressure; characterized in that: A fiber optic laser ultrasound system is provided, which contains a pressure-resistant optical fiber located inside the deep-sea pressure tank component. One end of the pressure-resistant optical fiber is equipped with an integrated receiver head, which is installed on the tank body of the deep-sea pressure tank component to receive incident light. The ultrasonic surface wave excitation module of the laser ultrasound system excites surface waves in the target area of ​​the sample to be tested. The ultrasonic detection module detects the excited surface waves and processes the signal carrying the surface wave information to obtain the material properties of the sample to be tested.

2. The fiber optic laser ultrasonic measuring device suitable for high-pressure seawater environments according to claim 1, characterized in that: The fiber-optic laser ultrasound system includes a picosecond pulsed laser, a 1×2 polarization-maintaining fiber coupler, an acousto-optic modulator, a BBO crystal, a dichroic mirror, a fiber-optic optical delay line, a manual fiber polarization controller, a fiber circulator, a first polarization beam combiner / splitter, a second polarization beam combiner / splitter, a pressure-resistant integrated lens assembly, a polarization controller, a third polarization beam combiner / splitter, a balanced photodetector, a waveform generator, and a lock-in amplifier. The picosecond pulsed laser emits a pulsed laser with wavelength λ, which is split into two beams with an intensity ratio of 9:1 by the 1×2 polarization-maintaining fiber coupler. The stronger laser beam is modulated by the acousto-optic modulator, with the modulation signal provided by the waveform generator, exhibiting a sinusoidal intensity distribution. The modulated beam enters the BBO crystal, where the wavelength is converted from λ to λ / 2 using the frequency doubling effect. This excited beam is transmitted through the dichroic mirror into the pressure-resistant fiber and, under the focusing of the pressure-resistant integrated lens assembly, is transmitted to the surface of the sample to be tested, generating an ultrasonic signal. The weaker laser beam undergoes a time delay through the fiber-optic optical delay line before entering the polarization controller. The laser's polarization direction is rotated by 45° and split into two optical paths by a first polarization beam combiner / splitter. These paths are transmitted to fiber arms of different lengths. A fixed time delay occurs when the laser reaches the second polarization beam combiner / splitter. The probe laser, after being reflected by a dichroic mirror, enters a pressure-resistant fiber and is focused onto the sample surface by optical components in an integrated receiver. The returning beam carries surface wave information and is transmitted back through the fiber. The returned beam contains two delayed waves from the long and short fiber arms, but their polarization directions are interchanged, ensuring that the two beams returning from the first polarization beam combiner / splitter have no path difference. The two beams return to the polarization controller and interfere. The interfering beam is split into two beams by a third polarization beam combiner / splitter, which enter the input of a balanced photodetector with a 270° phase deviation. The output signal of the balanced photodetector enters a lock-in amplifier. The reference signal is the same as that from the waveform generator used in the acousto-optic modulator. After signal processing, the system finally obtains a signal output proportional to the surface wave vibration velocity or displacement.

3. The fiber optic laser ultrasonic measuring device suitable for high-pressure seawater environments according to claim 1, characterized in that: The pressure-resistant integrated lens assembly includes two high-precision aspherical lenses that focus the laser onto the sample surface.

4. The fiber optic laser ultrasonic measuring device suitable for high-pressure seawater environments according to claim 1, characterized in that: The integrated receiver head includes two aspherical lenses and a quarter-wave plate. The aspherical lenses are used to focus and collect scattered light from the sample surface, and the quarter-wave plate is used to exchange the polarization directions of the two beams of light.

5. The fiber optic laser ultrasonic measuring device suitable for high-pressure seawater environments according to claim 1, characterized in that: A scanning mechanism is provided inside the deep-sea pressure tank component. The scanning mechanism includes a rotating mechanism and a Y-axis electric guide rail. The other end of the pressure-resistant optical fiber is fixed on the moving part of the scanning mechanism and is driven by the scanning mechanism.

6. A fiber optic laser ultrasonic measurement method suitable for high-pressure seawater environments, implemented using any of the fiber optic laser ultrasonic measurement devices suitable for high-pressure seawater environments as described in claims 1-5, comprising the following steps: (1) Place the sample to be tested inside the deep-sea pressure tank component, seal the pressure tank, apply a predetermined pressure intensity inside the pressure tank through the pressurization system and the hydraulic control system and keep the pressure stable to simulate the environmental pressure of the sample to be tested at the expected seawater depth. (2) Control the scanning mechanism inside the deep-sea pressure tank components to move the integrated lens group of the laser ultrasonic system to the measurement position; (3) The laser ultrasound system uses the thermoelastic effect to excite and detect ultrasonic signals on the surface of an object, and stores the measured ultrasonic signals in a computer. (4) Change the distance of the optical delay line in the laser ultrasound system and repeat step (3) until the surface wave signal within the required time range is measured. By reconstructing the surface wave signal under different delay times, the surface wave within the time range is obtained. (5) Change the position of the integrated lens group of the laser ultrasound system relative to the sample to be measured, and repeat steps (3) to (4) until all areas are detected.

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