Metal material mechanical property multi-parameter nondestructive evaluation method based on grating laser ultrasonic sound spectrum

Abstract

The invention discloses a multi-parameter nondestructive evaluation method for mechanical properties of a metal material based on a grating laser ultrasonic sound spectrum, which comprises the following steps of: irradiating a high-energy pulse laser beam on the surface of the metal material to be detected through a micro-lens array to form a periodically distributed transient grating, and exciting a monochromatic ultrasonic Rayleigh wave with a fixed wavelength in the material; and meanwhile, detecting laser is adopted to receive Rayleigh wave signals near the to-be-detected area in a non-contact manner. And performing fast Fourier transform on the received Rayleigh wave signal to obtain a narrow-band frequency spectrum, and calculating acoustic parameters such as sound velocity and acoustic nonlinear parameters through the narrow-band frequency spectrum. And according to a theoretical formula, an experimental relationship calibration curve and the like, respectively establishing calibration relationships between the elastic modulus and the sound velocity, between the hardness and the sound nonlinear parameter, between the yield strength and the sound nonlinear parameter and between the ultimate tensile strength and the sound nonlinear parameter of the metal material, thereby realizing multi-parameter quantitative evaluation on the mechanical properties of the metal material.

Description

Technical Field

[0001] The present invention relates to a method for evaluating the mechanical properties of metal materials, and in particular to a multi-parameter evaluation method for the mechanical properties of metal materials based on grating laser ultrasonic sound spectrum, which can realize non-contact, non-destructive quantitative evaluation of multiple mechanical property parameters. Background Art

[0002] Metal materials are widely used in the industrial field. They will age during long-term service, causing degradation of mechanical properties. At the same time, the evaluation of mechanical properties can determine the stress-strain behavior of materials under specific conditions, as well as their performance under different loads, which is undoubtedly of great significance. Traditional methods for testing the mechanical properties of metal materials mainly rely on destructive methods such as destructive testing. Therefore, it is necessary to study and develop non-destructive evaluation methods for the mechanical properties of metal materials.

[0003] Ultrasonic testing is one of the most widely used non-destructive testing methods, and has made many achievements in the field of mechanical properties testing. Traditional ultrasonic testing methods mainly use piezoelectric transducers to achieve the excitation and reception of ultrasonic waves. However, piezoelectric transducers rely on coupling agents and need to contact the surface of the material. They cannot survive in harsh environments such as high temperatures and have many limitations. Therefore, it is imperative to develop new mechanical properties testing technologies. Laser ultrasonic technology is an emerging ultrasonic testing technology that uses lasers to excite and receive ultrasonic signals. It has many advantages such as non-contact, high spatial resolution, good accessibility, and adaptability to harsh environments such as high temperatures. In particular, the spatially modulated laser ultrasonic technology developed in recent years can excite narrow-band monochromatic Rayleigh waves by using certain beam shaping technologies to arrange the excitation laser source in space and periodically, thereby realizing multi-parameter extraction of ultrasonic spectral signals. However, there is currently a lack of research and development on mechanical properties evaluation methods based on spatially modulated laser ultrasonic technology. Summary of the invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to propose a multi-parameter non-destructive evaluation method of the mechanical properties of metal materials based on grating laser ultrasonic spectrum. This method uses a spatially modulated pulsed laser beam to excite a single-frequency narrowband ultrasonic Rayleigh wave inside the metal material, and detects the ultrasonic signal by an all-optical method. Multiple acoustic parameters are extracted synchronously from the detected ultrasonic signal spectrum, and multiple mechanical parameters are evaluated simultaneously based on theoretical formulas or calibration curves. This method can realize synchronous, non-contact, non-destructive quantitative evaluation of multiple mechanical performance parameters of metal materials, and has high application potential.

[0005] In order to achieve the above purpose, the present invention adopts the following technical scheme:

[0006] A multi-parameter nondestructive evaluation method for mechanical properties of metal materials based on grating laser ultrasonic spectroscopy, firstly, a microlens array 2 with a constant period d is used to make a high-energy pulsed laser beam 1 irradiated on the surface of a material to be tested 5 form a transient grating 3 with a period d; the material to be tested 5 is stimulated by the periodic thermal expansion of the transient grating 3 to stimulate an ultrasonic Rayleigh wave 4 with a fixed wavelength λ, and the wavelength λ is the transient grating period d; near the area to be tested, a detection laser beam 6 is used to receive the stimulated ultrasonic Rayleigh wave 4 in a non-contact manner;

[0007] The ultrasonic Rayleigh wave time domain signal 7 received by the detection laser beam 6 can be used to obtain its narrowband spectrum 8 by fast Fourier transform. In its narrowband spectrum 8, according to formula 9: c = λ × f and The ultrasonic Rayleigh wave speed c and the acoustic nonlinear parameter β can be easily calculated, where f is the center frequency of the ultrasonic Rayleigh wave spectrum, A1 and A2 are the amplitude of the fundamental frequency signal and the amplitude of the second harmonic signal of the ultrasonic Rayleigh wave spectrum respectively;

[0008] Acoustic parameters such as the sound velocity c and the acoustic nonlinear parameter β can be respectively calculated according to formula 10: By means of calibration of the relationship between hardness, strength and acoustic nonlinear parameters, we can obtain the calibration curve 11 of the relationship between the material elastic modulus E and the sound velocity c, the calibration curve 12 of the relationship between the hardness H and the acoustic nonlinear parameter β, and the yield strength σ s Calibration curve of the relationship between acoustic nonlinear parameter β 13. Ultimate tensile strength σ b The relationship between the acoustic nonlinear parameter β and the calibration curve 14 is used to achieve multi-parameter quantitative evaluation of the mechanical properties of the material.

[0009] 4. As a preferred embodiment of the present invention, the high-energy pulsed laser beam 1 should be a collimated laser beam with a pulse length of nanometers, and its light wavelength should be in the near-infrared band; the period of the microlens array 2 should be in the sub-millimeter or millimeter level, and its material should be UV-grade fused quartz; the distance between the microlens array 2 and the surface of the material to be tested 5 is preferably twice the focal length; the detection laser beam 6 should be a continuous wave laser, and the wavelength is preferably 532nm; the distance between the high-energy pulsed laser beam 1 and the continuous laser beam 6 is preferably not more than 10cm; the signal sampling frequency of the ultrasonic Rayleigh wave 4 is preferably not less than 100MHz.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] The multi-parameter nondestructive evaluation method for the mechanical properties of metal materials described in the present invention realizes the simultaneous evaluation of multiple mechanical parameters through all-optical means, and has many advantages such as non-destructive, completely non-contact, high accessibility, and adaptability to harsh environments, and has great potential in practical engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The figure is a schematic diagram of the process of multi-parameter non-destructive evaluation of mechanical properties of metal materials according to the present invention. DETAILED DESCRIPTION

[0013] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0014] The present invention proposes a multi-parameter evaluation method for the mechanical properties of metal materials based on grating laser ultrasonic spectroscopy. Figure 1 As shown. A high-energy pulsed laser beam 1 is spatially modulated by a microlens array 2 into a transient grating 3 with a period of d, and irradiated onto the surface of the material to be tested 5. Under the periodic thermoelastic excitation of the transient grating 3, a monochromatic ultrasonic Rayleigh wave 4 with a fixed wavelength is excited inside the material to be tested 5, and its wavelength λ is equal to the period d of the transient grating 3, that is, equal to the period d of the microlens array 2. Near the excitation area, a continuous detection laser beam 6 is used to detect the off-plane displacement of the surface of the material to be tested 5 and receive the ultrasonic Rayleigh wave 4. The received ultrasonic Rayleigh wave time domain signal 7 can be obtained by fast Fourier transform to obtain a narrowband spectrum 8. In its narrowband spectrum 8, according to formula 9: c = λ × f and The acoustic parameters such as the sound velocity c and the acoustic nonlinear parameter β can be calculated conveniently and quickly.

[0015] The basic principle of the present invention is that acoustic parameters such as the sound velocity c and the acoustic nonlinear parameter β can be mapped to corresponding material mechanical parameters in different ways, such as Figure 1 As shown. For the elastic modulus E of metal materials, its functional relationship with the Rayleigh wave speed c can be expressed by formula 10: Represents. It can be seen that the elastic modulus E of the material is related to the density ρ and Poisson's ratio ν of the material in addition to the ultrasonic Rayleigh wave speed c. However, the density of the material is usually easier to know and has no uncertainty; the Poisson's ratio v of the material has a smaller effect on the speed of sound than the elastic modulus of the material and can be ignored. Therefore, the density ρ and Poisson's ratio v of the material can be regarded as constant values, and the elastic modulus E is only a function of the ultrasonic Rayleigh wave speed c, that is, the relationship calibration curve (11). After obtaining the ultrasonic Rayleigh wave speed c, substitute it into formula 10: The elastic modulus E of the material can be calculated.

[0016] For the hardness H and strength σ of metal materials, it is necessary to establish a calibration curve with the Rayleigh wave acoustic nonlinear parameter β. Due to the dislocation strengthening mechanism of metal materials, the hardness and strength of the material are positively correlated with microscopic characteristic quantities such as dislocation density; at the same time, according to the classical nonlinear theory of metal materials, the acoustic nonlinear parameters are also positively correlated with microscopic characteristic quantities such as dislocation density in the material. Therefore, using the microscopic characteristic quantity of the material as an intermediate medium, the relationship calibration curves between the acoustic nonlinear parameter β and the hardness H can be established 12, and the acoustic nonlinear parameter β and the yield strength σ sCalibration curve of the relationship between acoustic nonlinear parameter β and ultimate tensile strength σ b The relationship calibration curve 14. After obtaining the Rayleigh wave acoustic nonlinear parameter β, the corresponding multiple mechanical property parameters of the material can be obtained according to the corresponding calibration curve.

[0017] Combine the following Figure 1 and specific implementation methods to further describe the proposed method in detail.

[0018] The specific implementation of the present invention comprises the following steps:

[0019] Step 1: First, prepare a batch of n specimens with the same material and working conditions as the metal material to be tested and different mechanical properties, numbered as i=1, 2, ..., n. Figure 1 The batch of samples was tested using the spatially modulated laser ultrasonic method shown in the figure, and the acoustic parameters of the batch of samples were obtained in turn: sound velocity c i , acoustic nonlinear parameter β i .

[0020] Step 2: Perform destructive tests such as hardness test and strength test on the above n samples in turn to obtain their mechanical performance parameters: elastic modulus E i , Hardness H i , yield strength σ si , Ultimate tensile strength σ bi .

[0021] Step 3: According to the corresponding relationship between different mechanical performance parameters and the measured acoustic parameters, the elastic modulus E is established respectively. i The speed of sound c i , Hardness H i and acoustic nonlinear parameter β i , yield strength σ si and acoustic nonlinear parameter β i , Ultimate tensile strength σ bi and acoustic nonlinear parameter β i The fitting relationship curve between Figure 1 11, 12, 13, and 14 are shown as the detection calibration curve, such as Figure 1 shown.

[0022] Step 4: For samples with unknown mechanical properties, use Figure 1 The spatially modulated laser ultrasonic technology shown in the figure is used to detect the unknown sample and obtain its acoustic parameters: sound velocity c and acoustic nonlinear parameter β. According to the calibration curve established in step 3, the elastic modulus E, hardness H, yield strength σ of the unknown sample are measured respectively. s , Ultimate tensile strength σ b Make a quantitative assessment.

Claims

1. A multi-parameter nondestructive evaluation method for the mechanical properties of metal materials based on grating laser ultrasonic spectroscopy, characterized in that: First, a microlens array (2) with a constant period d is used to make a high-energy pulsed laser beam (1) irradiated on the surface of a material to be tested (5) form a transient grating (3) with a period d; the material to be tested (5) is stimulated by the periodic thermal expansion of the transient grating (3) to stimulate an ultrasonic Rayleigh wave (4) with a fixed wavelength λ, wherein the wavelength λ is the transient grating period d; near the area to be tested, a detection laser beam (6) is used to non-contactly receive the stimulated ultrasonic Rayleigh wave (4); The ultrasonic Rayleigh wave time domain signal (7) received by the detection laser beam (6) is used to obtain its narrowband spectrum (8) by fast Fourier transform; in its narrowband spectrum (8), according to formula (9): c = λ × f and That is, the ultrasonic Rayleigh wave speed c and the acoustic nonlinear parameter β are calculated, where f is the center frequency of the ultrasonic Rayleigh wave spectrum, A1 and A2 are the amplitude of the fundamental frequency signal and the amplitude of the second harmonic signal of the ultrasonic Rayleigh wave spectrum respectively; The ultrasonic Rayleigh wave velocity c and the acoustic nonlinear parameter β are respectively based on formula (10): And the relationship between hardness, strength and acoustic nonlinear parameters is calibrated, where ρ is the density of the material, v is the Poisson's ratio of the material, and ξ is the dimensionless coefficient of the Poisson's ratio of the material; the relationship calibration curve between the material elastic modulus E and the sound velocity c (11), the relationship calibration curve between the hardness H and the acoustic nonlinear parameter β (12), the yield strength σ s The relationship between the calibration curve (13) and the acoustic nonlinear parameter β, the ultimate tensile strength σ b The relationship between the acoustic nonlinear parameter β and the calibration curve (14) is obtained, thereby realizing multi-parameter quantitative evaluation of the mechanical properties of the material.

2. The method for nondestructive evaluation of mechanical properties of metal materials based on grating laser ultrasonic spectroscopy according to claim 1, characterized in that: The high-energy pulse laser beam (1) is a collimated laser beam with a pulse length in the nanometer range, and its light wavelength is in the near-infrared band.

3. The method for nondestructive evaluation of mechanical properties of metal materials based on grating laser ultrasonic spectroscopy according to claim 1, characterized in that: The period of the microlens array (2) is sub-millimeter or millimeter level, and its material is UV-level fused quartz.

4. The method for nondestructive evaluation of mechanical properties of metal materials based on grating laser ultrasonic spectroscopy according to claim 1, characterized in that: The distance between the microlens array (2) and the surface of the material to be measured (5) is twice the focal length.

5. The method for multi-parameter nondestructive evaluation of mechanical properties of metal materials based on grating laser ultrasonic spectroscopy according to claim 1, characterized in that: The detection laser beam (6) is a continuous wave laser.

6. The method for multi-parameter nondestructive evaluation of mechanical properties of metal materials based on grating laser ultrasonic spectroscopy according to claim 5, characterized in that: The continuous wave laser wavelength is 532nm.

7. The method for multi-parameter nondestructive evaluation of mechanical properties of metal materials based on grating laser ultrasonic spectroscopy according to claim 1, characterized in that: The distance between the high-energy pulse laser beam (1) and the detection laser beam (6) does not exceed 10 cm.

8. The method for multi-parameter nondestructive evaluation of mechanical properties of metal materials based on grating laser ultrasonic spectroscopy according to claim 1, characterized in that: The signal sampling frequency of the ultrasonic Rayleigh wave (4) is not less than 100 MHz.

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