Laser ultrasonic detection system for metal fatigue and plastic deformation process and detection method thereof

Abstract

The invention belongs to the technical field of metal fatigue and plastic deformation process detection, and particularly relates to a metal fatigue and plastic deformation process laser ultrasonic detection system and a detection method thereof. Comprising a laser ultrasonic signal excitation assembly, a laser ultrasonic signal detection assembly and a to-be-detected sample detection platform, the laser ultrasonic signal excitation assembly comprises a pulse laser, a phase grating and a 4F optical modulation unit; the laser ultrasonic detection assembly comprises a continuous laser, a double-wave mixing interference unit, a signal acquisition and processing unit and a lambda wave plate group; the to-be-detected sample detection platform comprises a 360-degree rotating table for realizing rotation of a to-be-detected sample and a two-dimensional scanning translation table for realizing translation of the to-be-detected sample. According to the invention, laser is irradiated on the detected workpiece, ultrasonic waves are generated based on a thermoelastic theory, contact with the detected workpiece is not needed, and non-contact measurement can be realized, so that a residual stress testing environment of a high-temperature, corrosive and radiated alloy material is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal fatigue and plastic deformation process detection, and in particular relates to a metal fatigue and plastic deformation process laser ultrasonic detection system and a detection method thereof. Background Art

[0002] Traditional ultrasonic monitoring equipment for fatigue and plastic deformation monitoring of metal materials typically utilizes piezoelectric sensors and electron diffraction. Due to limitations in piezoelectric sensor technology, the frequency of ultrasonic excitation and probe size result in a relatively long wavelength. This makes it difficult to accurately measure changes in grain size and orientation caused by fatigue testing and plastic deformation of metal materials using long-wavelength ultrasonic waves, resulting in low detection accuracy and limited to single-crystal structures or those with large grains. Furthermore, piezoelectric probes require coupling between the excitation and reception of ultrasonic waves and the inspected area through a coupling agent, making them unsuitable for testing in hazardous environments such as high temperatures, corrosion, and radiation. They also lack the ability to achieve long-range, rapid scanning. Furthermore, the inspection process requires full contact between the piezoelectric structure and the inspected workpiece. If this contact is poor, measurement errors can occur, making them unsuitable for fatigue testing and plastic deformation monitoring of complex workpieces. Inspection methods based on scanning electron microscopy and backscattered electron diffraction require the sample to be inspected in a vacuum, creating demanding testing conditions and preventing rapid, long-range scanning. Summary of the Invention

[0003] The purpose of the present invention is to provide a metal material fatigue detection and plastic deformation monitoring device based on laser ultrasonic detection technology and its method and process, which has the advantages of non-contact, rapid scanning, high time and spatial resolution, easy to achieve high-precision measurement, and convenient and fast detection process, so as to solve the problems in the existing technology.

[0004] To achieve the above objectives, the present invention adopts the following technical solutions.

[0005] A laser ultrasonic detection system for metal fatigue and plastic deformation process, comprising a laser ultrasonic signal excitation component, a laser ultrasonic signal detection component, and a detection platform for samples to be detected;

[0006] The laser ultrasonic signal excitation component is used to generate a wavelength-controllable laser ultrasonic signal, including: a pulsed laser, a phase grating, and a 4F optical modulation unit;

[0007] The pulse laser generates a high-energy pulse laser signal, which is passed through a phase grating that matches the laser wavelength. The phase grating weakens the energy of the 0th-order light beam, thereby generating ±1st-order diffracted laser light. A 4F optical modulation unit converges the ±1st-order diffracted laser light after passing through the phase grating. The focal lengths of the two cylindrical lenses in the 4F optical modulation unit are f1 and f2, respectively. The grating is located at the focal length f1 on the left side of the first cylindrical lens, and the distance between the two lenses is f1+f2. The sample to be tested is located at the focal length f2 behind the second lens. The ±1st-order diffracted light is converted into parallel light by the first lens of the 4F optical modulation unit, and then converged on the surface of the sample to be tested by the second cylindrical lens.

[0008] The laser ultrasonic testing component is used to detect the propagation speed and frequency of the fixed wavelength surface acoustic wave signal generated by pulsed laser excitation in the material, including: continuous laser, dual-wave mixing interference unit, signal acquisition and processing unit, and lambda wave plate group;

[0009] The continuous laser excites the continuous wave band laser as the detection light, and the detection light passes through the first The wave plate and the first polarization beam splitter (PBS-1) split the light into detection light and reference light;

[0010] The reference light passes through the second The wave plate reaches the photorefractive crystal, and the detection light passes through the second polarization beam splitter prism (PBS-2), the first The wave plate reaches the sample to be tested and interacts with the surface vibration of the sample to be tested to form reflected light. The reflected light passes through the third The wave plate reaches the photorefractive crystal;

[0011] The reference light and the reflected light reach the photorefractive crystal, which produces a photorefractive effect and generates an enhanced detection ultrasonic signal corresponding to the sample to be tested;

[0012] Enhanced detection of ultrasonic signal once through the second Wave plate and polarizer reach the optical signal detection unit

[0013] Here, the λ wave plate mainly controls the deflection of lasers with different polarization states, thereby realizing dual-wave laser interference.

[0014] The detection platform for the sample to be tested is a 360-degree rotating table used to realize the rotation of the sample to be tested and a two-dimensional scanning translation table used to realize the translation of the sample to be tested.

[0015] A further improvement or preferred embodiment of the aforementioned laser ultrasonic detection system for metal fatigue and plastic deformation process is that the optical signal detection unit includes a photodetector, an amplifier, an oscilloscope, and a PC.

[0016] A further improvement or preferred embodiment of the aforementioned laser ultrasonic detection system for metal fatigue and plastic deformation processes is characterized in that the pulse laser is a 1064nm Q-switched pulse laser, and the phase grating is a fixed-size grating that adjusts the 1064nm wavelength laser to cancel the 0th-order signal.

[0017] A further improvement or preferred embodiment of the aforementioned laser ultrasonic detection system for metal fatigue and plastic deformation processes is that the continuous laser is a 532nm wavelength laser, and the photorefractive crystal, lambda wave plate, polarization beam splitter, and polarizer are all optical devices corresponding to the continuous laser wavelength.

[0018] This application also provides a laser ultrasonic detection method for metal fatigue and plastic deformation process, comprising the following steps:

[0019] Step 1. First, debug the laser ultrasonic excitation platform. Select pulsed lasers with different pulse widths and gratings of different sizes based on the grain size of the metal sample to be tested. This stimulates a laser ultrasonic surface acoustic wave signal that matches the grain size of the metal sample to be tested. The wavelength of the laser ultrasonic surface acoustic wave signal is smaller than the grain size. The acoustic signal wavelength is calculated by controlling the 4F system and the diffraction laser interference angle.

[0020] Step 2. Debug the laser ultrasonic signal excitation component. Use the 4F optical modulation unit to focus the probe light path on the surface of the sample to be tested, ensuring that the size of the probe laser spot on the sample surface is smaller than the wavelength of the high-energy pulse laser. The vibration signal of the surface acoustic wave will affect the reflected signal of the probe light. After acting on the photorefractive crystal, the photorefractive effect is detected by the photodetector. The vibration signal of the surface acoustic wave on the sample surface can be measured through the preamplifier and signal processing.

[0021] Step 3. Pre-treat the sample to be tested so that the surface roughness of the sample can meet the normal reflection of the detection laser signal, ensure that there is no diffuse reflection phenomenon that affects the detection after the detection laser acts on the surface of the sample to be tested, and the surface roughness of the sample to be tested is smaller than the focused spot size of the detection laser;

[0022] Step 4. Fix the sample to be tested on the translation stage and scan the area to be tested. The excitation laser and the detection laser should be on concentric circles and act on the area to be tested of the sample to be tested.

[0023] Step 5. Set the translation step size of the two-dimensional translation stage to be less than one tenth of the grain size, and record the corresponding positions of the sample to be tested for different translation areas;

[0024] Step 6. Set the translation time of the two-dimensional translation stage. By synchronizing the repetition time of the pulse laser and the translation wait time of the translation stage, the detection signal is averaged to reduce the signal-to-noise ratio of the detection signal. Since the pulse laser has a certain repetition frequency, it can stimulate the same laser ultrasonic signal multiple times in a short period of time. The signal-to-noise ratio is reduced by taking an average of multiple detections.

[0025] Step 7. Rotate and scan the test area of ​​the sample to be tested to obtain surface acoustic wave signals in different directions. By analyzing the angular dispersion characteristics of the surface acoustic wave, the angular dispersion characteristics at different positions in the scan area are obtained to analyze the grain orientation information;

[0026] Step 8. Analyze the acquired laser ultrasonic signal data and the surface profile of the sample to be tested, and analyze the grain orientation and grain size information of the sample to be tested based on the measured change information of the surface acoustic wave speed;

[0027] Step 9. Perform fatigue testing and plastic deformation testing on the sample to be tested, change the grain and stress information inside the metal material, and repeat steps 4-8 to obtain laser ultrasonic excitation surface acoustic wave signal information in the sample to be tested after fatigue testing and plastic deformation;

[0028] Step 10. Compare and analyze the changing patterns of the laser ultrasonic signal to realize fatigue detection and plastic deformation monitoring of metal materials.

[0029] In a further improvement or preferred embodiment of the aforementioned laser ultrasonic detection method for metal fatigue and plastic deformation processes, the center of the high-energy pulse laser signal and the detection light spot reaching the sample to be inspected coincide with the rotation axis of the turntable.

[0030] A further improvement or preferred embodiment of the aforementioned laser ultrasonic detection method for metal fatigue and plastic deformation processes further includes a step of controlling the interference angle by controlling the focal length and distance of the two cylindrical lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structure of the laser ultrasonic detection system for metal fatigue and plastic deformation process;

[0032] Figure 2 It is a flow chart of the laser ultrasonic testing method for metal fatigue and plastic deformation process;

[0033] Figure 3 It is a time domain signal diagram of surface acoustic wave signal, thermal signal and surface echo signal;

[0034] Figure 4 It is a frequency domain signal diagram of surface acoustic wave signal, thermal signal and surface echo signal;

[0035] Figure 5 It is a schematic diagram of the two-dimensional scanning of the laser ultrasonic signal in the plastic deformation area of ​​the aluminum alloy material. DETAILED DESCRIPTION

[0036] The present invention is described in detail below with reference to specific embodiments.

[0037] The present invention's laser ultrasonic detection system and method for metal fatigue and plastic deformation processes provide a highly accurate product and technical solution suitable for testing in aerospace and specialized industries. This system utilizes a laser ultrasonic excitation system to excite surface acoustic wave signals. By controlling the accuracy of the excitation ultrasonic signal and the detection ultrasonic system, it enables rapid scanning and detection of metal structures with varying grain sizes. Laser light is irradiated onto the workpiece, generating ultrasonic waves based on thermoelastic theory. This system eliminates the need for contact with the workpiece, enabling non-contact measurement. This allows for testing residual stress in alloy materials subjected to high temperatures, corrosion, and radiation.

[0038] like Figure 1 As shown, the laser ultrasonic detection system for metal fatigue and plastic deformation process of the present invention includes a laser ultrasonic signal excitation component, a laser ultrasonic signal detection component, and a detection platform for samples to be detected;

[0039] The laser ultrasonic signal excitation component is used to generate a wavelength-controllable laser ultrasonic signal, including: a pulsed laser, a phase grating, and a 4F optical modulation unit;

[0040] The pulse laser generates a high-energy pulse laser signal, which is passed through a phase grating that matches the laser wavelength. The phase grating weakens the energy of the 0th-order light beam, thereby generating ±1st-order diffracted laser light. A 4F optical modulation unit converges the ±1st-order diffracted laser light after passing through the phase grating. The focal lengths of the two cylindrical lenses in the 4F optical modulation unit are f1 and f2, respectively. The grating is located at the focal length f1 on the left side of the first cylindrical lens, and the distance between the two lenses is f1+f2. The sample to be tested is located at the focal length f2 behind the second lens. The ±1st-order diffracted light is converted into parallel light by the first lens of the 4F optical modulation unit, and then converged on the surface of the sample to be tested by the second cylindrical lens.

[0041] The laser ultrasonic testing component is used to detect the propagation speed and frequency of the fixed wavelength surface acoustic wave signal generated by pulsed laser excitation in the material, including: continuous laser, dual-wave mixing interference unit, signal acquisition and processing unit, and lambda wave plate group;

[0042] The continuous laser excites the continuous wave band laser as the detection light, and the detection light passes through the first The wave plate and the first polarization beam splitter (PBS-1) split the light into detection light and reference light;

[0043] The reference light passes through the second The wave plate reaches the photorefractive crystal, and the detection light passes through the second polarization beam splitter prism (PBS-2), the first The wave plate reaches the sample to be tested and interacts with the surface vibration of the sample to be tested to form reflected light. The reflected light passes through the third The wave plate reaches the photorefractive crystal;

[0044] The reference light and the reflected light reach the photorefractive crystal, which produces a photorefractive effect and generates an enhanced detection ultrasonic signal corresponding to the sample to be tested;

[0045] Enhanced detection of ultrasonic signal once through the second Wave plate and polarizer reach the optical signal detection unit

[0046] Here, the λ wave plate mainly controls the deflection of lasers with different polarization states, thereby realizing dual-wave laser interference.

[0047] The sample detection platform is used to realize the rotation and translation of the sample to be tested.

[0048] The optical signal detection unit includes a photodetector, an amplifier, an oscilloscope, and a PC.

[0049] As a preferred solution, the pulsed laser is a 1064nm Q-switched pulsed laser, and the phase grating is a fixed-size grating that modulates the 1064nm wavelength laser to cancel the zero-order signal. The continuous laser is a 532nm wavelength laser, and the photorefractive crystal, lambda wave plate, polarization beam splitter, and polarizer are all optical components corresponding to the continuous laser wavelength.

[0050] This application also provides a laser ultrasonic detection method for metal fatigue and plastic deformation process, such as Figure 2 As shown, it mainly includes the following steps:

[0051] Step 1. First, debug the laser ultrasonic excitation platform. Select pulsed lasers with different pulse widths and gratings of different sizes based on the grain size of the metal sample to be tested. This stimulates a laser ultrasonic surface acoustic wave signal that matches the grain size of the metal sample to be tested. The wavelength of the laser ultrasonic surface acoustic wave signal is smaller than the grain size. The acoustic signal wavelength is calculated by controlling the 4F system and the diffraction laser interference angle.

[0052] Step 2. Debug the laser ultrasonic detection equipment. Use a high-performance lens system to focus the detection light path on the surface of the sample to be tested, ensuring that the size of the detection laser spot on the sample surface is smaller than the wavelength of the excitation laser ultrasonic signal. The vibration signal of the surface acoustic wave will affect the photorefractive effect of the reflected signal after acting on the photorefractive crystal, and then be measured by the photodetector. The vibration signal of the surface acoustic wave on the sample surface can be measured through a preamplifier and signal processing.

[0053] Step 3. Pre-treat the sample to be tested so that the surface roughness of the sample can meet the normal reflection of the detection laser signal, ensure that there is no serious diffuse reflection after the detection laser acts on the surface of the sample to be tested, and the surface roughness of the sample to be tested is smaller than the focus spot size of the detection laser;

[0054] Step 4. Fix the sample to be tested on the translation stage and scan the area to be tested. The excitation laser and the detection laser should be on concentric circles and act on the area to be tested of the sample to be tested.

[0055] Step 5. Set the translation step size of the two-dimensional translation stage to be less than one tenth of the grain size, and record the corresponding positions of the sample to be tested for different translation areas;

[0056] Step 6. Set the translation time of the two-dimensional translation stage. By synchronizing the repetition time of the pulse laser and the translation wait time of the translation stage, the detection signal is averaged to reduce the signal-to-noise ratio of the detection signal. Since the pulse laser has a certain repetition frequency, it can stimulate the same laser ultrasonic signal multiple times in a short period of time. The signal-to-noise ratio is reduced by taking an average of multiple detections.

[0057] Step 7. Rotate and scan the test area of ​​the sample to be tested to obtain surface acoustic wave signals in different directions. By analyzing the angular dispersion characteristics of the surface acoustic wave, the angular dispersion characteristics at different positions in the scan area are obtained to analyze the grain orientation information;

[0058] Step 8. Analyze the acquired laser ultrasonic signal data and the surface profile of the sample to be tested, and analyze the grain orientation and grain size information of the sample to be tested based on the measured change information of the surface acoustic wave speed;

[0059] Step 9. Perform fatigue testing and plastic deformation testing on the sample to be tested, change the grain and stress information inside the metal material, and repeat steps 4-8 to obtain laser ultrasonic excitation surface acoustic wave signal information in the sample to be tested after fatigue testing and plastic deformation;

[0060] Step 10. Compare and analyze the changing patterns of the laser ultrasonic signal to realize fatigue detection and plastic deformation monitoring of metal materials.

[0061] To ensure the detection effect, the direction of the light and the angular position of the platform should be controlled to ensure that the high-energy pulse laser signal reaching the sample to be inspected and the center of the detection light spot coincide with the rotation axis of the turntable.

[0062] In particular, in actual implementation, the interference angle control step can be achieved by controlling the focal length and distance of the two cylindrical lenses.

[0063] The following is a test of the plastic deformation area of ​​a certain aluminum alloy material to be tested based on the aforementioned metal fatigue and plastic deformation process laser ultrasonic detection system and detection method.

[0064] Figure 3 This is a schematic diagram of an exemplary laser ultrasonic signal according to the present invention. The left figure shows the time domain signal. The detection laser acquires a high-frequency laser ultrasonic surface acoustic wave signal, a low-frequency thermal signal, and echo signals from the upper and lower surfaces of the sample. The right figure shows the frequency domain signal of the laser signal. The center frequency of the high-frequency surface acoustic wave is approximately 22 MHz.

[0065] Figure 4 This is a schematic diagram of a two-dimensional scanning of a laser ultrasonic signal of an exemplary scanning of a plastic deformation area of ​​an aluminum alloy material according to the present invention. The plastic deformation area can be detected by analyzing the change in the center frequency of the surface acoustic wave of the two-dimensional scanning laser ultrasonic signal.

[0066] In the figure, due to the changes in the internal mechanical properties, grain properties, density and other properties of the metal material in the fatigue and plastic deformation areas, when the laser ultrasonic signal acts on the sample surface after plastic deformation and fatigue changes, the acoustic field model characteristics change significantly. Here, the plastic deformation and fatigue characteristics of the material can be monitored based on the change law of the laser ultrasonic signal acoustic field signal.

[0067] The laser ultrasonic detection technology of this application is a new non-contact, high-precision, long-distance scanning non-destructive testing technology. This technology combines the advantages of high sensitivity of traditional ultrasonic monitoring and non-contact optical detection, and has the advantages of high precision (sub-nanometer level) and high detection bandwidth (GHz).

[0068] During the detection process, pulsed laser is used to excite high-frequency narrow-band ultrasonic signals, and the photorefractive effect of continuous laser is used to detect high-frequency laser ultrasonic signals. The dual-wave mixing interferometry method based on the photorefractive effect can realize the dynamic detection of high-frequency laser ultrasonic signals in rough surface samples. The two-dimensional scanning platform and the rotating scanning platform are used to scan the high-frequency laser ultrasonic signals on the sample surface to realize the implementation detection of high-frequency acoustic surface signals in different areas, and then the change law of the fatigue area and plastic deformation area of ​​the metal sample is calculated through the change law of the surface acoustic wave signal.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A laser ultrasonic detection system for metal fatigue and plastic deformation process, characterized in that: It includes a laser ultrasonic signal excitation component, a laser ultrasonic signal detection component, and a detection platform for samples to be tested; The laser ultrasonic signal excitation component is used to generate a wavelength-controllable laser ultrasonic signal, including: a pulsed laser, a phase grating, and a 4F optical modulation unit; The pulse laser generates a high-energy pulse laser signal, which is passed through a phase grating that matches the laser wavelength. The phase grating weakens the energy of the 0th-order light beam, thereby generating ±1st-order diffracted laser light. A 4F optical modulation unit converges the ±1st-order diffracted laser light after passing through the phase grating. The focal lengths of the two cylindrical lenses in the 4F optical modulation unit are f1 and f2, respectively. The grating is located at the focal length f1 on the left side of the first cylindrical lens, and the distance between the two lenses is f1+f2. The sample to be tested is located at the focal length f2 behind the second lens. The ±1st-order diffracted light is converted into parallel light by the first lens of the 4F optical modulation unit, and then converged on the surface of the sample to be tested by the second cylindrical lens. The laser ultrasonic testing component is used to detect the propagation speed and frequency of the fixed wavelength surface acoustic wave signal generated by pulsed laser excitation in the material, including: continuous laser, dual-wave mixing interference unit, signal acquisition and processing unit, and lambda wave plate group; The continuous laser excites the continuous wave band laser as the detection light, and the detection light passes through the first The wave plate and the first polarization beam splitter (PBS-1) split the light into detection light and reference light; The reference light passes through the second The wave plate reaches the photorefractive crystal, and the detection light passes through the second polarization beam splitter prism (PBS-2), the first The wave plate reaches the sample to be tested and interacts with the surface vibration of the sample to be tested to form reflected light. The reflected light passes through the third The wave plate reaches the photorefractive crystal; The reference light and the reflected light reach the photorefractive crystal, generating a photorefractive effect to generate an interference-enhanced detection ultrasonic signal corresponding to the sample to be tested; Here, the detection light entering the photorefractive crystal meets the reference light in the nonlinear medium. When phase matching is satisfied, a new frequency component is generated due to the nonlinear effect of the medium. The new light intensity distribution is then detected by the photodetector. The weak vibration signal is transmitted through the second The wave plate and polarizer reach the optical signal detection unit and amplify the detected surface wave signal; Enhanced detection of ultrasonic signal once through the second The wave plate and polarizer reach the optical signal detection unit; The λ-wave plate controls the deflection of lasers with different polarization states to achieve phase matching, thereby realizing dual-wave laser interference; The detection platform for the sample to be tested uses a 360-degree rotating table to realize the rotation of the sample to be tested, and uses a two-dimensional scanning translation table to realize translation.

2. The laser ultrasonic detection system for metal fatigue area and plastic deformation process according to claim 1, characterized in that: The optical signal detection unit includes a photodetector, an amplifier, an oscilloscope, and a PC.

3. The laser ultrasonic detection system for metal fatigue area and plastic deformation process according to claim 1, characterized in that: The pulse laser is a 1064nm Q-switched pulse laser, and the phase grating is a fixed-size grating that adjusts the 1064nm wavelength laser to cancel out the 0th-order signal.

4. The laser ultrasonic detection system for metal fatigue area and plastic deformation process according to claim 1, characterized in that: The continuous laser is a 532nm wavelength laser, and the photorefractive crystal, lambda wave plate, polarization beam splitter prism, and polarizer are all optical devices corresponding to the continuous laser wavelength.

5. The laser ultrasonic detection method for metal fatigue and plastic deformation process according to claim 1, characterized in that: The steps include: Step 1. First, debug the laser ultrasonic excitation platform. Select pulsed lasers with different pulse widths and gratings of different sizes according to the grain size of the metal sample to be tested, and then stimulate the laser ultrasonic surface acoustic wave signal that matches the grain size of the metal sample to be tested. The wavelength of the laser ultrasonic surface acoustic wave signal is smaller than the grain size. Step 2. Debug the laser ultrasonic signal excitation system. Use the 4F optical modulation unit to focus the probe light path on the surface of the sample to be tested, ensuring that the size of the probe laser spot on the sample surface is smaller than the wavelength of the surface acoustic wave signal. The vibration signal of the surface acoustic wave will affect the reflected signal of the probe laser. After acting on the photorefractive crystal, the photorefractive effect is detected by the photodetector. The vibration signal of the surface acoustic wave on the sample surface can be measured through the preamplifier and signal processing. Step 3. Pre-treat the sample to be tested so that the surface roughness of the sample can meet the normal reflection of the detection laser signal, ensure that there is no diffuse reflection that affects the detection effect after the detection laser acts on the surface of the sample to be tested, and the surface roughness of the sample to be tested is smaller than the focused spot size of the detection laser; Step 4. Fix the sample to be tested on the translation stage and scan the area to be tested. The excitation laser and the detection laser should be on concentric circles and act on the area to be tested of the sample to be tested. Step 5. Set the translation step size of the two-dimensional translation stage to be less than one tenth of the grain size, and record the corresponding positions of the sample to be tested for different translation areas; Step 6. Set the translation time of the two-dimensional translation stage and average the detection laser signal within the translation time to reduce the signal-to-noise ratio of the detection signal. Since the pulse laser has a certain repetition frequency and can stimulate the same laser ultrasonic signal multiple times in a short period of time, the signal-to-noise ratio is reduced by averaging multiple detections. Step 7. Rotate and scan the test area of ​​the sample to be tested to obtain surface acoustic wave signals in different directions. By analyzing the angular dispersion characteristics of the surface acoustic wave, the angular dispersion characteristics at different positions in the scan area are obtained to analyze the grain orientation information; Step 8. Analyze the acquired laser ultrasonic signal data and the surface profile of the sample to be tested, and analyze the grain orientation and grain size information of the sample to be tested based on the measured change information of the surface acoustic wave speed; Step 9. Perform fatigue testing and plastic deformation testing on the sample to be tested, change the grain and stress information inside the metal material, and repeat steps 4-8 to obtain laser ultrasonic excitation surface acoustic wave signal information in the sample to be tested after fatigue testing and plastic deformation; Step 10. Compare and analyze the changing patterns of the laser ultrasonic signal to realize fatigue detection and plastic deformation monitoring of metal materials.

6. The laser ultrasonic detection method for metal fatigue area and plastic deformation process according to claim 5, characterized in that: The high-energy pulse laser signal and the center of the detection light spot reaching the sample to be tested coincide with the rotation axis of the rotating stage.

7. The detection method for the laser ultrasonic detection method of metal fatigue area and plastic deformation process according to claim 5, characterized in that: The method also includes the step of controlling the interference angle by controlling the focal length and distance of the two cylindrical lenses.

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