A metal material rigidity measurement system and method based on intensity modulated laser ultrasound

Abstract

The application discloses a kind of metal material rigidity measurement system and method based on intensity-modulated laser ultrasonic, and the measurement system includes: function generator, intensity-modulated laser, probe laser, lock-in amplifier and PC computer;The function generator is used to generate modulation signal and synchronization signal;Intensity-modulated laser is used to output modulation laser according to the modulation signal, and acts on the metal to be detected;The probe laser is used to detect the modulation ultrasonic signal generated by the metal to be detected;The lock-in amplifier is used to obtain the amplitude and phase information of modulation ultrasonic signal according to the modulation ultrasonic signal and synchronization signal;The PC computer is used to obtain the rigidity information of metal material according to the amplitude and phase information of modulation ultrasonic signal.The application is used to solve the destructive measurement problem of traditional method, and proposes the resonance response characteristic frequency of modulation ultrasonic to obtain the mechanical parameter of sample.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of modulated laser ultrasonic testing, and particularly relates to a metal material rigidity measurement system and method based on intensity modulated laser ultrasonic. BACKGROUND

[0002] With the continuous progress of material science, new materials emerge in an endless stream, showing excellent mechanical properties. Therefore, accurately measuring the mechanical parameters of materials is the key to ensuring the effective application of these new materials. Among them, rigidity, as an extremely important parameter to characterize the mechanical properties of materials, is particularly important. At present, the commonly used rigidity measurement methods include tensile test method, nanoindentation method and ultrasonic method. However, the tensile test method and the nanoindentation method not only have a complicated process, but also need to process the sample into a standard size for measurement, and most importantly, they will cause damage to the sample. The pulsed laser ultrasonic method generates broadband ultrasonic waves by acting on the metal material with pulsed laser, and the mechanical properties of the metal material are obtained by measuring the sound velocities of different modal ultrasonic waves and combining the acoustic elasticity theory. However, the traditional sound velocity method needs to measure multiple sound velocities, and the operation is complicated. In addition, the signal-to-noise ratio of the pulsed laser is low under the thermal elastic condition; although the problem of weak signal can be improved under the ablation condition, the sample will be damaged. Moreover, the cost of the pulsed laser ultrasonic system is also relatively high. Therefore, it is urgent to develop a metal material rigidity measurement system and method based on intensity modulated laser ultrasonic to overcome the shortcomings of the prior art. SUMMARY

[0003] To solve the above technical problems, the application provides a metal material rigidity measurement system and method based on intensity modulated laser ultrasonic, which is used to solve the problems of complicated process and material damage measurement existing in the traditional method. The application can obtain the mechanical parameters of the sample by modulating the resonance response characteristic frequency of the ultrasonic wave, and the method also has the advantages of non-contact, non-destructive, low cost, high signal-to-noise ratio and the like.

[0004] The application provides a metal material rigidity measurement system based on intensity modulated laser ultrasonic, which comprises a function generator, an intensity modulated laser, a detection laser, a lock-in amplifier and a PC computer.

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

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

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

[0008] The phase-locked amplifier is used for obtaining amplitude and phase information of the modulated ultrasonic wave according to the modulated ultrasonic wave signal and the synchronous signal.

[0009] The PC computer is used for obtaining rigidity information of the metal material according to the amplitude and phase information of the modulated ultrasonic wave.

[0010] Optionally, the light path device is arranged between the intensity modulation laser and the metal to be detected.

[0011] The light path device is used for limiting the excitation point of the modulated laser acting on the material surface of the metal to be detected.

[0012] Optionally, the light path device comprises a beam splitter, a mirror and a convex lens.

[0013] The modulated laser is adjusted by the mirror and then enters the beam splitter, and the modulated laser is adjusted by the beam splitter and then enters the convex lens to act on the metal to be detected.

[0014] Optionally, the metal to be detected is arranged on a three-axis moving platform, and the three-axis moving platform comprises an X-axis moving platform, a Y-axis moving platform and a Z-axis moving platform.

[0015] The X-axis moving platform is used for driving the metal to be detected to move along the X-axis direction.

[0016] The Y-axis moving platform is used for driving the metal to be detected to move along the Y-axis direction.

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

[0018] The application further provides a metal material rigidity measurement method based on intensity modulation laser ultrasonic wave, comprising:

[0019] S1, inputting a modulated signal to an intensity modulation laser through a function generator to obtain current modulated laser and current synchronous signal;

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

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

[0022] S4, inputting the current modulated ultrasonic wave signal to the input end of a phase-locked amplifier, and performing phase-locked analysis on the current modulated ultrasonic wave signal and the synchronous signal to obtain the amplitude and phase of the current modulated ultrasonic wave signal.

[0023] S5, introducing a classical spring model based on the amplitude and phase of the current modulated ultrasonic wave signal, obtaining resonance response of the metal material to the modulated ultrasonic wave, and obtaining current rigidity characteristics of the metal material according to the resonance response;

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

[0025] Optionally, the amplitude and phase of the current modulated ultrasonic wave signal include:

[0026] The amplitude and phase of the current modulated ultrasonic wave signal are obtained by phase-locked analysis of the current modulated ultrasonic wave signal.

[0027] Optionally, the classical spring model is:

[0028]

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

[0030] Optionally, the current rigidity characteristics of the metal material are obtained according to the resonance response, including:

[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 wave u(t)=Acos(ωt-θ), wherein A is the amplitude, θ is the phase, and the amplitude A is solved as:

[0032]

[0033] The resonance frequency is obtained based on the amplitude:

[0034]

[0035] wherein k is the spring rigidity, the rigidity is enhanced, and the resonance frequency is also increased.

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

[0037] Based on the theory of multi-physics coupling of light, heat, and sound, this invention introduces a classic spring model and establishes a relationship between the rigidity characteristics of metal materials and the characteristic frequency of their resonant response. By irradiating the metal surface with an intensity-modulated laser, modulated ultrasonic waves are generated. A detection laser is used to acquire the ultrasonic signal, and a lock-in amplifier is used to perform time-domain signal analysis to accurately determine the characteristic frequency of the ultrasonic resonance response. This invention proposes a new method for measuring the rigidity of metal materials. Using a C-scan format, the rigidity distribution of the metal material can be determined, achieving non-contact, non-destructive measurement at low cost and with a high signal-to-noise ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

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

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

[0046] The intensity modulation laser is used for outputting modulated laser according to a modulation signal and acting on the metal to be detected.

[0047] The detection laser is used for detecting the modulated ultrasonic signal generated by the metal to be detected.

[0048] The phase-locked amplifier is used for obtaining the amplitude and phase information of the modulated ultrasonic signal according to the modulated ultrasonic signal and a synchronization signal.

[0049] The PC computer is used for obtaining the rigidity information of the metal material according to the amplitude and phase information of the modulated ultrasonic signal.

[0050] Specifically, the function generator, the detection laser, the FPGA module and the phase-locked amplifier are electrically connected, and the phase-locked amplifier is electrically connected with the PC computer. The function generator is electrically connected with the intensity modulation laser and the phase-locked amplifier, and the FPGA module 11 is electrically connected with the phase-locked amplifier and the three-axis moving driving module.

[0051] The intensity modulation laser is used for outputting modulated laser with a preset modulated laser power, and focusing the intensity modulation laser on the surface of the metal material to be detected, so as to generate modulated ultrasonic waves, thereby enabling the modulated ultrasonic waves to propagate and act on the inside of the metal material.

[0052] The detection laser emits detection laser and focuses the detection laser on the surface, and is used for detecting the ultrasonic signal generated by the modulated ultrasonic wave.

[0053] The function generator is used for adjusting the laser energy of the intensity modulation laser, so that the energy of the intensity modulation laser changes according to the function set by the function generator. In addition, the synchronization signal generated by the function generator is input into the phase-locked amplifier as a reference signal.

[0054] The phase-locked amplifier is used for receiving the modulated ultrasonic signal captured by the detection laser as an input signal, and receiving the synchronization signal output by the function generator as a reference signal.

[0055] The FPGA is used for generating a pulse signal for controlling the three-axis moving driving module, so as to drive the three-axis moving platform, and generating an external trigger signal for the phase-locked amplifier, so as to collect the amplitude and phase of the single-frequency modulated signal.

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

[0057] More specifically, the function generator 1 sets the specified modulation signal to the intensity modulation laser 2 to generate the modulation laser, the modulation laser is adjusted by the mirror 3 to enter the beam splitter 4, the modulation laser is adjusted by the beam splitter 4 to enter the convex lens 5 to act on the sample 6, and the sample 6 is fixed on the XYZ moving platform 7. The probe laser 8 generates the probe laser for detecting the modulation ultrasonic wave signal. The modulation ultrasonic wave signal obtained by the probe laser is input to the lock-in amplifier 9 and the reference signal input by the function generator 1 to obtain the amplitude and phase information of the modulation ultrasonic wave signal, and the signal output by the lock-in 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 modulation ultrasonic wave signal.

[0058] Further, the intensity modulation laser and the metal to be detected are provided with a light path device.

[0059] The light path device is used to limit the excitation point of the modulation laser acting on the material surface of the metal to be detected.

[0060] Further, the light path device comprises a beam splitter, a mirror and a convex lens.

[0061] The modulation laser is adjusted by the mirror to enter the beam splitter, and the modulation laser is adjusted by the beam splitter to enter the convex lens to act on the metal to be detected.

[0062] Specifically, the light path device is arranged on the light path of the intensity modulation laser, the beam splitter is arranged on the reflected light path of the mirror, and the convex lens is arranged on the light path of the beam splitter.

[0063] Further, the metal to be detected is arranged on a three-axis moving platform, and the three-axis moving platform comprises an X-axis moving platform, a Y-axis moving platform and a Z-axis moving platform.

[0064] The X-axis moving platform is 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] As shown in Figure 2 The application also provides a metal material rigidity measurement method based on intensity modulation laser ultrasonic wave, which comprises:

[0068] S1, inputting a modulation signal to an intensity modulation laser through a function generator to obtain a current modulation laser and a current synchronization signal;

[0069] S2, the current modulation laser acts on the surface of the metal material to be detected to generate a current modulation 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 terminal 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] Furthermore, in 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. Based on the resonance response, the current rigidity characteristics of the metal material are obtained, including:

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

[0078]

[0079] Where 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 thermoelastic theory, the stress tensor σ ij The relationship between the strain tensor and the 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's 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 wave equation, we get:

[0088]

[0089] For homogeneous isotropic material, 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, ω is the modulation frequency.

[0092] Under one-dimensional condition, its 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: Where the typical spring-mass-damper system, in the forced vibration equation of the equation can be expressed as:

[0095]

[0096] Since the modulated laser acts on the surface of the solid, the friction or resistance of the vibration system in contact with the outside world under this assumption is 0, so the damping coefficient b = 0 can be assumed. Then this equation can be corresponded to the one-dimensional form of the wave equation, so we have:

[0097]

[0098] where, 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 harmonic vibration, then assume that the steady-state solution of the system is also in the form of harmonic vibration u(t) = Acos(ωt-θ), where A is the amplitude and θ is the phase. The amplitude A is then:

[0100]

[0101] At the resonance frequency, the amplitude A is maximum, which means gets the minimum. Then we have:

[0102]

[0103] k is the spring stiffness, which is related to the Young's modulus E of the metal material and the geometric dimension L, The Young's modulus influences the resonance frequency, and the stiffness increases, so does the resonance frequency (ω0∝E).

[0104] The above merely provides the preferred embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of the changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. 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 currently modulated laser to the surface of the metal material to be detected to generate currently modulated ultrasonic waves; 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 a lock-in 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 a resonance response of the metal material to the modulated ultrasonic signal, and based on the resonance response, a current rigidity characteristic of the metal material is obtained; Obtaining the current rigidity characteristics of the metal material according to the resonance response includes: Since the external force term is in the form of resonance, assuming 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. S6. Repeat steps S1-S5 to obtain the rigidity distribution state of the metal surface to be detected.

2. The method for measuring the rigidity of metal materials based on intensity modulated laser ultrasound according to claim 1, characterized in that: Obtaining the amplitude and phase of the current modulated ultrasonic signal includes: Perform phase-locked analysis on the current modulated ultrasonic signal to obtain the amplitude and phase of the current modulated ultrasonic signal.

3. The method for measuring the rigidity of metal materials based on intensity modulated laser ultrasound according to claim 1, 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 time, u is the displacement, ρ material is the density, and x is the deformation of u in the x direction.

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