Metal material rigidity measurement system and method based on intensity modulation laser ultrasound

Abstract

The invention discloses a metal material rigidity measurement system and method based on intensity modulation laser ultrasound. The measurement system comprises a function generator, an intensity modulation laser, a detection laser, a lock-in amplifier and a PC (Personal Computer), the function generator is used for generating a modulation signal and a synchronization signal; the intensity modulation laser is used for outputting modulation laser according to the modulation signal to act on metal to be detected; the detection laser is used for detecting a modulated ultrasonic signal generated by the metal to be detected; the lock-in amplifier is used for acquiring the amplitude and phase information of the modulated ultrasonic signal according to the modulated ultrasonic signal and the synchronizing signal; and the PC is used for acquiring the rigidity information of the metal material according to the amplitude and phase information of the modulated ultrasonic signal. The method is used for solving the destructive measurement problem of a traditional method, and the mechanical parameters of the sample are obtained by modulating the resonance response characteristic frequency of ultrasonic waves.

Description

Technical Field

[0001] The present invention belongs to the technical field of modulated laser ultrasonic detection, and in particular relates to a metal material rigidity measurement system and method based on intensity modulated laser ultrasonic. Background Art

[0002] With the continuous progress of materials science, new materials emerge in an endless stream, showing excellent mechanical properties. Therefore, accurate measurement of the mechanical parameters of materials is the key to ensure the effective application of these new materials. Among them, rigidity is an extremely important parameter for characterizing the mechanical properties of materials, and its measurement method is particularly important. At present, commonly used rigidity measurement methods include tensile test, nanoindentation and ultrasound. However, the tensile test and nanoindentation methods are not only cumbersome, but also require the sample to be processed into a standard size for measurement. Most importantly, they will damage the sample. The pulsed laser ultrasound method generates broadband ultrasound by applying a pulsed laser to a metal material, and obtains the mechanical properties of the metal material by measuring the sound velocity of ultrasound in different modes and combining it with the acoustic elasticity theory. However, the traditional sound velocity method requires the measurement of multiple sound velocities, which is complicated to operate. In addition, the pulsed laser has a low signal-to-noise ratio under thermoelastic conditions; although the problem of weak signal can be improved under ablation conditions, it will cause damage to the sample. Moreover, the cost of the pulsed laser ultrasound system is relatively high. Therefore, it is urgent to develop a metal material rigidity measurement system and method based on intensity modulated laser ultrasound to overcome the shortcomings of the existing technology. Summary of the invention

[0003] In order to solve the above technical problems, the present invention proposes a metal material rigidity measurement system and method based on intensity modulated laser ultrasound, which is used to solve the problems of complicated process and material damage measurement in traditional methods. The present invention can obtain the mechanical parameters of the sample by modulating the resonant response characteristic frequency of ultrasound, and the method also has significant advantages such as non-contact, non-destructive, low cost, and high signal-to-noise ratio.

[0004] The present invention provides a metal material rigidity measurement system based on intensity modulated laser ultrasound, comprising: a function generator, an intensity modulated laser, a detection laser, a phase-locked amplifier and a PC;

[0005] The function generator is used to generate a modulation signal and a synchronization signal;

[0006] The intensity modulated laser is used to output modulated laser according to the modulation signal to act on the metal to be detected;

[0007] The detection laser is used to detect the modulated ultrasonic signal generated by the metal to be detected;

[0008] The lock-in amplifier is used to obtain the amplitude and phase information of the modulated ultrasonic signal according to the modulated ultrasonic signal and the synchronization signal;

[0009] The PC is used to obtain the rigidity information of the metal material according to the amplitude and phase information of the modulated ultrasonic signal.

[0010] Optionally, an optical path device is provided between the intensity modulated laser and the metal to be detected;

[0011] The optical path device is used to limit the excitation point where the modulated laser acts on the material surface of the metal to be detected.

[0012] Optionally, the optical path device includes: a beam splitter, a reflector and a convex lens;

[0013] The modulated laser is incident on the beam splitter after the optical path is adjusted by the reflector, and then incident on the convex lens after the optical path is adjusted by the beam splitter to act on the metal to be detected.

[0014] Optionally, the metal to be detected is arranged on a three-axis mobile platform, and the three-axis mobile platform includes: an X-axis mobile platform, a Y-axis mobile platform and a Z-axis mobile platform;

[0015] The X-axis moving platform is used to drive the metal to be detected to move along the X-axis direction;

[0016] The Y-axis moving platform is used to drive the metal to be detected to move along the Y-axis direction;

[0017] The Z-axis moving platform is used to drive the metal to be detected to move along the Z-axis direction.

[0018] The present invention also provides a method for measuring the rigidity of metal materials based on intensity modulated laser ultrasound, comprising:

[0019] S1. Input the modulation signal to the intensity modulated laser through the function generator to obtain the current modulated laser and the current synchronization signal;

[0020] S2, applying the current modulated laser to the surface of the metal material to be detected to generate the current modulated ultrasonic wave;

[0021] S3, based on the current modulated ultrasonic wave, using a detection laser to detect the current modulated ultrasonic wave signal;

[0022] S4, inputting the current modulated ultrasonic signal into the input end of the phase-locked amplifier, and performing phase-locked analysis with the synchronization signal to obtain the amplitude and phase of the current modulated ultrasonic signal;

[0023] S5. Based on the amplitude and phase of the current modulated ultrasonic signal, a classical spring model is introduced to obtain the resonance response of the metal material to the modulated ultrasonic wave, and according to the resonance response, the current rigidity characteristics of the metal material are obtained;

[0024] S6. Repeat steps S1-S5 to obtain the rigidity distribution state of the metal surface to be detected.

[0025] Optionally, obtaining the amplitude and phase of the current modulated ultrasonic signal includes:

[0026] The current modulated ultrasonic signal is subjected to phase-locked analysis to obtain the amplitude and phase of the current modulated ultrasonic signal.

[0027] Optionally, the classical spring model is:

[0028]

[0029] in, is the inertia term in the spring system, is the spring term in the spring system, the external force term βI0cos(ωt) is the external force term of the spring system, λ and μ are Lame constants, β is the thermal expansion coefficient, I0 is the power of the intensity modulated laser source, ω is the modulation frequency, and t is time.

[0030] Optionally, obtaining the current rigidity characteristic of the metal material according to the resonance response includes:

[0031] Since the external force term is in the form of resonance, it is assumed that the steady-state solution of the spring system is also in the form of harmonic u(t)=Acos(ωt-θ), where A is the amplitude and θ is the phase. The amplitude A is solved as:

[0032]

[0033] Based on the amplitude, the resonant frequency is obtained:

[0034]

[0035] Among them, k is the spring stiffness. The higher the stiffness, the higher the resonant frequency.

[0036] Compared with the prior art, the present invention has the following advantages and technical effects:

[0037] The present invention is based on the theory of multi-physics field coupling of light, heat and sound, introduces the classic spring model, and establishes the relationship between the rigidity characteristics of metal materials and their resonant response characteristic frequencies. The surface of the metal material is irradiated with an intensity modulated laser to generate modulated ultrasonic waves. The ultrasonic signal is obtained by combining a detection laser, and a phase-locked amplifier is used to perform time domain signal analysis to accurately obtain the resonant response characteristic frequency of the ultrasonic wave. The present invention proposes a new method for measuring the rigidity of metal materials. By using the C-scan form, the rigidity distribution state of the metal material can be obtained, achieving the effects of non-contact measurement, non-destructive measurement, low cost and high signal-to-noise ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings that constitute part of this application are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation on this application. In the drawings:

[0039] Figure 1 This is a schematic diagram of a metal material rigidity measurement system based on intensity modulated laser ultrasound according to an embodiment of the present invention, wherein: 1. a function generator; 2. a modulated laser; 3. a reflector; 4. a spectroscope; 5. a convex lens; 6. a sample; 7. a detection platform; 8. a detection laser; 9. a lock-in amplifier; 10. a PC; and 11. an FPGA module;

[0040] Figure 2 This is a flow chart of a method for measuring the rigidity of metal materials based on intensity modulated laser ultrasound according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0042] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0043] The present invention proposes a metal material rigidity measurement system based on intensity modulated laser ultrasound, such as Figure 1 As shown, specifically including:

[0044] Function generator, intensity modulated laser, detection laser, lock-in amplifier and PC computer;

[0045] Function generator, used to generate modulation signal and synchronization signal;

[0046] An intensity modulated laser is used to output a modulated laser according to a modulation signal and act on the metal to be detected;

[0047] A detection laser for detecting the modulated ultrasonic signal generated by the metal to be detected;

[0048] A lock-in amplifier is used to obtain amplitude and phase information of the modulated ultrasonic signal according to the modulated ultrasonic signal and the synchronization signal;

[0049] A PC is used to obtain the rigidity information of metal materials based on the amplitude and phase information of the modulated ultrasonic signal.

[0050] Specifically, the function generator, the detection laser, and the FPGA module are electrically connected to the lock-in amplifier, and the lock-in amplifier is electrically connected to the PC. The function generator is also electrically connected to the intensity modulated laser and the lock-in amplifier, and the FPGA module 11 is electrically connected to the lock-in amplifier and the three-axis mobile drive module.

[0051] The intensity modulated laser is used to output modulated laser at a preset modulated laser power, and focus the intensity modulated laser on the surface of the metal material to be tested to generate modulated ultrasonic waves, so that the modulated ultrasonic waves can propagate and act on the inside of the metal material.

[0052] The detection laser emits a detection laser and focuses the detection laser on the surface to detect the ultrasonic signal generated by the modulated ultrasonic wave.

[0053] The function generator is used to adjust the laser energy of the intensity modulated laser so that the energy of the intensity modulated laser changes according to the function law set by the function generator. In addition, the synchronization signal generated by the function generator is input into the lock-in amplifier as a reference signal.

[0054] The lock-in amplifier is used to receive the modulated ultrasonic signal captured by the detection laser as an input signal, and receive the synchronization signal output by the function generator as a reference signal.

[0055] The FPGA is used to generate a pulse signal to control the three-axis mobile drive module to drive the three-axis mobile platform, and to generate an external trigger signal for the phase-locked amplifier to collect the amplitude and phase of the single-frequency modulated signal.

[0056] The PC computer obtains the modulated ultrasonic amplitude and phase according to the phase-locked amplifier to obtain the rigidity information of the detection point position, and performs two-dimensional scanning and real-time imaging based on the modulated ultrasonic amplitude and phase obtained by scanning the sample on the three-axis mobile platform to obtain the rigidity distribution of the metal material sample.

[0057] More specifically, the function generator 1 sets a designated modulation signal to the intensity modulated laser 2 to generate a modulated laser, which is incident on the spectroscope 4 after adjusting the optical path through the reflector 3, and then incident on the convex lens 5 to act on the sample 6 after adjusting the optical path through the spectroscope 4, and the sample 6 is fixed on the XYZ moving platform 7. The detection laser 8 generates a detection laser to detect the modulated ultrasonic signal. The modulated ultrasonic signal obtained by the detection laser is input to the phase-locked amplifier 9 and the amplitude and phase information of the modulated ultrasonic signal are obtained with the reference signal input by the function generator 1. The signal output by the phase-locked amplifier 9 is collected and stored in the computer 10, and the rigidity information of the metal material is obtained according to the amplitude and phase information of the modulated ultrasonic signal.

[0058] Furthermore, an optical path device is provided between the intensity modulated laser and the metal to be detected;

[0059] The optical path device is used to limit the excitation point where the modulated laser acts on the surface of the material of the metal to be detected.

[0060] Furthermore, the optical path device includes: a beam splitter, a reflector and a convex lens;

[0061] The modulated laser is incident on the beam splitter after the optical path is adjusted by the reflector, and then incident on the convex lens to act on the metal to be detected.

[0062] Specifically, the optical path device is arranged on the light output path of the intensity modulated laser, the beam splitter is arranged on the reflected light path of the reflector, and the convex lens is arranged on the beam splitter light path.

[0063] Furthermore, the metal to be detected is arranged on a three-axis mobile platform, and the three-axis mobile platform includes: an X-axis mobile platform, a Y-axis mobile platform and a Z-axis mobile platform;

[0064] X-axis moving platform, used to drive the metal to be detected to move along the X-axis direction;

[0065] The Y-axis moving platform is used to drive the metal to be detected to move along the Y-axis direction;

[0066] The Z-axis moving platform is used to drive the metal to be detected to move along the Z-axis direction.

[0067] like Figure 2 As shown, the present invention also provides a method for measuring the rigidity of metal materials based on intensity modulated laser ultrasound, comprising:

[0068] S1. Input the modulation signal to the intensity modulated laser through the function generator to obtain the current modulated laser and the current synchronization signal;

[0069] S2, applying the current modulated laser to the surface of the metal material to be detected to generate the current modulated ultrasonic wave;

[0070] S3, based on the current modulated ultrasonic wave, using a detection laser to detect the current modulated ultrasonic wave signal;

[0071] S4, inputting the current modulated ultrasonic signal into the input end of the phase-locked amplifier, and performing phase-locked analysis with the synchronization signal to obtain the amplitude and phase of the current modulated ultrasonic signal;

[0072] S5. Based on the amplitude and phase of the current modulated ultrasonic signal, a classical spring model is introduced to obtain the resonance response of the metal material to the modulated ultrasonic wave, and the current rigidity characteristics of the metal material are obtained according to the resonance response;

[0073] S6. Repeat steps S1-S5 to obtain the rigidity distribution state of the metal surface to be detected.

[0074] Furthermore, obtaining the amplitude and phase of the current modulated ultrasonic signal includes:

[0075] Perform Fourier transform on the current modulated ultrasonic signal to obtain the amplitude and phase of the current modulated ultrasonic signal.

[0076] Further, S5, based on the amplitude and phase of the current modulated ultrasonic signal, a classical spring model is introduced to obtain the resonance response of the metal material to the modulated ultrasonic wave, and according to the resonance response, the current rigidity characteristics of the metal material are obtained, including:

[0077] S501: Based on the heat conduction equation:

[0078]

[0079] Among them, ρ is the density of the metal material, c is the specific heat capacity, k is the thermal conductivity, T is the temperature, and Q(x,t) is the heat source term.

[0080] S502: Wave equation caused by thermal stress:

[0081]

[0082] Among them, σ ij is the stress tensor, u i is the displacement component.

[0083] S503: Stress and strain relationship

[0084] In the theory of thermoelasticity, the stress tensor σ ij The relationship between and strain tensor can be expressed as:

[0085] σ ij =λδ ij ∈ kk +2μ∈ ij -β(T-T0)δ ij

[0086] Where λ and μ are Lame constants, β is the thermal expansion coefficient, T is the temperature, T0 is the reference temperature, δ ij is the Kronecker symbol, the strain tensor

[0087] Substituting the strain tensor into the strain relation and the wave equation, we obtain:

[0088]

[0089] For homogeneous isotropic materials, the one-dimensional form of the intensity modulated laser source is approximated as:

[0090] T=T0+I0cos(ωt)

[0091] Where I0 is the intensity modulated laser source power and ω is the modulation frequency.

[0092] Under one-dimensional conditions, the spatial partial differential does not affect the time form of the intensity modulated heat source, so the one-dimensional form of the wave equation is:

[0093]

[0094] S504: Among them, the equation of a typical spring-mass-damper system in the forced vibration equation can be expressed as:

[0095]

[0096] Since the modulated laser acts on the solid surface, the friction or resistance between the hypothetical vibration system and the outside world is 0, so the damping coefficient b can be assumed to be 0. Then the equation can be matched with the one-dimensional form of the wave equation, and we have:

[0097]

[0098] in, is the inertia term in the spring system, is the spring term in the spring system. The external force term βI0cos(ωt) is the external force term of the spring system.

[0099] S505: Since the external force term is in the form of resonance, it is assumed that the steady-state solution of the system is also in the form of harmonic u(t)=Acos(ωt-θ), where A is the amplitude and θ is the phase. The amplitude A is solved as:

[0100]

[0101] At the resonant frequency, its amplitude A is the largest, which means Get the minimum. Then we have:

[0102]

[0103] k is the spring stiffness, which is related to the Young's modulus E and geometric dimensions L of the metal material. Young's modulus affects the resonant frequency. As the rigidity increases, the resonant frequency also increases (ω0∝E).

[0104] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A metal material rigidity measurement system based on intensity modulated laser ultrasound, characterized in that: include: Function generator, intensity modulated laser, detection laser, lock-in amplifier and PC computer; The function generator is used to generate a modulation signal and a synchronization signal; The intensity modulated laser is used to output modulated laser according to the modulation signal to act on the metal to be detected; The detection laser is used to detect the modulated ultrasonic signal generated by the metal to be detected; The lock-in amplifier is used to obtain the amplitude and phase information of the modulated ultrasonic signal according to the modulated ultrasonic signal and the synchronization signal; The PC is used to obtain the rigidity information of the metal material according to the amplitude and phase information of the modulated ultrasonic signal.

2. The metal material rigidity measurement system based on intensity modulated laser ultrasound according to claim 1 is characterized in that: An optical path device is provided between the intensity modulated laser and the metal to be detected; The optical path device is used to limit the excitation point where the modulated laser acts on the material surface of the metal to be detected.

3. The metal material rigidity measurement system based on intensity modulated laser ultrasound according to claim 2 is characterized in that: The optical path device comprises: a beam splitter, a reflector and a convex lens; The modulated laser is incident on the beam splitter after the optical path is adjusted by the reflector, and then incident on the convex lens after the optical path is adjusted by the beam splitter to act on the metal to be detected.

4. The metal material rigidity measurement system based on intensity modulated laser ultrasound according to claim 1, characterized in that: The metal to be detected is arranged on a three-axis mobile platform, and the three-axis mobile platform comprises: an X-axis mobile platform, a Y-axis mobile platform and a Z-axis mobile platform; The X-axis moving platform is used to drive the metal to be detected to move along the X-axis direction; The Y-axis moving platform is used to drive the metal to be detected to move along the Y-axis direction; The Z-axis moving platform is used to drive the metal to be detected to move along the Z-axis direction.

5. A method for measuring the rigidity of metal materials based on intensity modulated laser ultrasound, characterized in that: include: S1. Input the modulation signal to the intensity modulated laser through the function generator to obtain the current modulated laser and the current synchronization signal; S2, applying the current modulated laser to the surface of the metal material to be detected to generate the current modulated ultrasonic wave; S3, based on the current modulated ultrasonic wave, using a detection laser to detect the current modulated ultrasonic wave signal; S4, inputting the current modulated ultrasonic signal into the input end of the phase-locked amplifier, and performing phase-locked analysis with the synchronization signal to obtain the amplitude and phase of the current modulated ultrasonic signal; S5. Based on the amplitude and phase of the current modulated ultrasonic signal, a classical spring model is introduced to obtain the resonance response of the metal material to the modulated ultrasonic wave, and according to the resonance response, the current rigidity characteristics of the metal material are obtained; S6. Repeat steps S1-S5 to obtain the rigidity distribution state of the metal surface to be detected.

6. The method for measuring the rigidity of metal materials based on intensity modulated laser ultrasound according to claim 5, characterized in that: Obtaining the amplitude and phase of the current modulated ultrasonic signal includes: The current modulated ultrasonic signal is subjected to phase-locked analysis to obtain the amplitude and phase of the current modulated ultrasonic signal.

7. The method for measuring the rigidity of metal materials based on intensity modulated laser ultrasound according to claim 5, characterized in that: The classical spring model is: in, is the inertia term in the spring system, is the spring term in the spring system, the external force term βI0cos(ωt) is the external force term of the spring system, λ and μ are Lame constants, β is the thermal expansion coefficient, I0 is the power of the intensity modulated laser source, ω is the modulation frequency, t is the time, u is the displacement, ρ material is the density, and x is the deformation of u in the x direction.

8. The method for measuring the rigidity of metal materials based on intensity modulated laser ultrasound according to claim 7, characterized in that: According to the resonance response, obtaining the current rigidity characteristics of the metal material includes: Since the external force term is in the form of resonance, it is assumed that the steady-state solution of the spring system is also in the form of harmonic u(t)=Acos(ωt-θ), where A is the amplitude and θ is the phase. The amplitude A is solved as: Based on the amplitude, the resonant frequency is obtained: Among them, k is the spring stiffness. As the stiffness increases, the resonant frequency also increases.

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