Method for nondestructive evaluation of mechanical properties of metal materials based on grating laser ultrasonic spectrum

Abstract

The application discloses a kind of metal material mechanics performance multi-parameter nondestructive evaluation method based on grating laser ultrasonic spectrum, the method utilizes high-energy pulsed laser beam to be irradiated on the surface of the metal material to be measured by micro-lens array and form periodic distribution transient grating, excite monochromatic ultrasonic Rayleigh wave of fixed wavelength in material interior, simultaneously, non-contact receive Rayleigh wave signal in the vicinity of the detection area by probe laser.The received Rayleigh wave signal is subjected to fast Fourier transform to obtain narrow-band spectrum, and the acoustic parameters such as sound velocity and acoustic nonlinear parameter can be calculated through the narrow-band spectrum.According to theoretical formula and experimental relationship calibration curve, the calibration relationship between the elastic modulus of metal material and sound velocity, hardness and acoustic nonlinear parameter, yield strength and acoustic nonlinear parameter, ultimate tensile strength and acoustic nonlinear parameter is established respectively, so as to realize the quantitative evaluation of the mechanical properties of metal material.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for evaluating the mechanical properties of a metal material, and in particular to a method for evaluating the mechanical properties of a metal material based on a grating laser ultrasonic acoustic spectrum, which can realize non-contact and non-destructive quantitative evaluation of multiple mechanical property parameters. BACKGROUND

[0002] Metal materials are widely used in the industrial field, and will exhibit aging phenomena during long-term service, leading to degradation of mechanical properties. At the same time, evaluation of the mechanical properties can determine the stress-strain behavior of the material under certain conditions, as well as its performance under different loads, which is undoubtedly of great significance. Traditional methods for detecting the mechanical properties of metal materials mainly rely on destructive tests and other destructive methods. Therefore, it is necessary to develop a non-destructive evaluation method for the mechanical properties of metal materials.

[0003] Ultrasonic testing is one of the most widely used non-destructive testing methods, and has made great contributions in the field of mechanical property testing. Traditional ultrasonic testing methods mainly use piezoelectric transducers to excite and receive ultrasonic waves. However, piezoelectric transducers rely on coupling agents and need to be in contact with the material surface, which cannot survive in harsh environments such as high temperatures, and have many limitations. Therefore, it is imperative to develop new mechanical property testing techniques. Laser ultrasonic technology is a new ultrasonic testing technology that uses laser to excite and receive ultrasonic signals, with the advantages of non-contact, high spatial resolution, good accessibility, and the ability to adapt to harsh environments such as high temperatures. In particular, the spatial modulation laser ultrasonic technology developed in recent years arranges the excitation laser source in a spatial periodic manner through certain beam shaping techniques, which can excite narrow-band monochromatic Rayleigh waves, thereby realizing the extraction of multiple parameters of the ultrasonic acoustic spectrum. However, there is currently a lack of research and development of mechanical property evaluation methods based on spatial modulation laser ultrasonic technology. SUMMARY

[0004] In order to solve the problems existing in the prior art, the present application aims to provide a method for non-destructive evaluation of multiple mechanical properties of metal materials based on a grating laser ultrasonic acoustic spectrum. This method uses spatially modulated pulsed laser beams to excite single-frequency narrow-band ultrasonic Rayleigh waves inside the metal material, and detects the ultrasonic signals through an all-optical method. Multiple acoustic parameters are extracted simultaneously from the detected ultrasonic signal spectrum, and multiple mechanical parameters are evaluated simultaneously using theoretical formulas or calibration curves. This method can realize simultaneous, non-contact, and non-destructive quantitative evaluation of multiple mechanical property parameters of metal materials, and has high application potential.

[0005] To achieve the above purpose, the present application adopts the following technical solutions:

[0006] A method for non-destructive evaluation of mechanical properties of metal materials based on grating laser ultrasonic spectrum, which comprises the following steps: a high-energy pulsed laser beam 1 is irradiated on the surface of a material to be measured 5, and a micro-lens array 2 with equal period d is used to form a transient grating 3 with a period of d; the material to be measured 5 is excited to generate ultrasonic Rayleigh waves 4 with a fixed wavelength λ under the periodic thermal expansion of the transient grating 3, and the wavelength λ is equal to the period d of the transient grating; in the vicinity of the measured area, a probe laser beam 6 is used to non-contact receive the excited ultrasonic Rayleigh waves 4;

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

[0008] The acoustic parameters such as the speed c and the acoustic nonlinear parameter β can be obtained according to formula 10: respectively, and the relationship calibration curves 11 of the elastic modulus E and the speed c, the relationship calibration curves 12 of the hardness H and the acoustic nonlinear parameter β, the relationship calibration curves 13 of the yield strength σ s and the acoustic nonlinear parameter β, and the relationship calibration curves 14 of the ultimate tensile strength σ b and the acoustic nonlinear parameter β are obtained by means of calibration, so as to realize the quantitative evaluation of the mechanical properties of the material.

[0009] 4. As a preferred embodiment of the present application, the high-energy pulsed laser beam 1 should be a collimated laser beam with a pulse length of nanometer level, and the light wavelength should be in the near-infrared band; the period of the micro-lens array 2 should be in the sub-millimeter or millimeter level, and the material should be UV-grade fused quartz; the distance between the micro-lens array 2 and the surface of the material to be measured 5 is preferably twice the focal length; the probe 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 application has the following advantages:

[0011] The method for non-destructive evaluation of mechanical properties of metal materials according to the present application realizes the synchronous evaluation of multiple mechanical parameters by all-optical means, and has the advantages of non-destructive, complete non-contact, high accessibility, adaptability to harsh environments and the like, and has great potential in practical engineering applications. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 This is a schematic diagram of the process for non-destructive evaluation of multiple parameters of mechanical properties of metallic materials according to the present invention. Detailed Implementation

[0013] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0014] This invention proposes a multi-parameter evaluation method for the mechanical properties of metallic materials based on grating laser ultrasonic spectra, such as... 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 irradiates the surface of the material under test 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 under test 5. The wavelength λ is equal to the period d of the transient grating 3, which is also equal to the period d of the microlens array 2. Near the excitation region, a continuous probe laser beam 6 is used to detect the out-of-plane displacement of the surface of the material under test 5 and to receive the ultrasonic Rayleigh wave 4. The received ultrasonic Rayleigh wave time-domain signal 7 can be used to obtain a narrowband spectrum 8 through a fast Fourier transform. In its narrowband spectrum 8, according to formula 9: c = λ × f and It can conveniently and quickly calculate acoustic parameters such as the sound velocity c and the acoustic nonlinear parameter β.

[0015] The basic principle of this invention is that acoustic parameters such as sound velocity c and acoustic nonlinearity parameter β can establish mapping relationships with corresponding material mechanical parameters in different ways, such as... Figure 1 As shown. The elastic modulus E of a metallic material, and its functional relationship with the Rayleigh wave velocity c, can be expressed by Equation 10: This indicates that the elastic modulus E of a material, in addition to the ultrasonic Rayleigh wave velocity c, is also related to the material's density ρ and Poisson's ratio ν. However, the material's density is usually easy to obtain and has no uncertainty; the material's Poisson's ratio ν has a smaller impact on the sound velocity than the material's elastic modulus and can be ignored. Therefore, the material's density ρ and Poisson's ratio ν can be regarded as constant values, and the elastic modulus E is only a function of the ultrasonic Rayleigh wave velocity c, i.e., the relationship calibration curve (11). After obtaining the ultrasonic Rayleigh wave velocity c, substitute it into formula 10: The elastic modulus E of the material can then be calculated.

[0016] For the hardness H and strength σ of metallic materials, calibration curves must be established with respect to the Rayleigh wave acoustic nonlinear parameter β. Due to the dislocation strengthening mechanism of metallic materials, the hardness, strength, and microscopic characteristics such as dislocation density are positively correlated. Simultaneously, according to the classical nonlinear theory of metallic materials, the acoustic nonlinear parameter is also positively correlated with microscopic characteristics such as dislocation density. Therefore, using the microscopic characteristics of the material as an intermediate medium, calibration curves relating the acoustic nonlinear parameter β to hardness H and yield strength σ can be established respectively. sthe relationship calibration curve 13, the acoustic nonlinear parameter β and the ultimate tensile strength σ b the relationship calibration curve 14. After obtaining the Rayleigh wave acoustic nonlinear parameter β, the corresponding mechanical property parameters of the material can be obtained according to the corresponding calibration curve.

[0017] The proposed method will be further described in detail below in combination with Figure 1 and specific embodiments.

[0018] The specific embodiments of the present application include the following steps:

[0019] Step one: first prepare a batch of n samples with different mechanical properties which are the same as the material and working conditions of the metal material to be tested, numbered as i = 1, 2, …, n. The spatial modulation laser ultrasonic method as shown in Figure 1 is used to detect the batch of samples, and the acoustic parameters of the batch of samples are obtained in turn: the acoustic velocity c i , the acoustic nonlinear parameter β i .

[0020] Step two: destructive tests such as hardness test and strength test are performed on the above n samples in turn, and the mechanical property parameters are obtained in turn: the elastic modulus E i , the hardness H i , the yield strength σ si , the ultimate tensile strength σ bi .

[0021] Step three: according to the corresponding relationship between different mechanical property parameters and measured acoustic parameters, fitting relationship curves between the elastic modulus E i and the acoustic velocity c i , the hardness H i and the acoustic nonlinear parameter β i , the yield strength σ si and the acoustic nonlinear parameter β i , the ultimate tensile strength σ bi and the acoustic nonlinear parameter β i are established respectively, as shown in Figure 1 11, 12, 13 and 14, which are used as detection calibration curves, as shown in Figure 1 .

[0022] Step four: for the sample with unknown mechanical properties, the spatial modulation laser ultrasonic technology as shown in Figure 1 is used to detect the unknown sample, and the acoustic parameters of the unknown sample are obtained: the acoustic velocity c and the acoustic nonlinear parameter β. According to the calibration curves established in step three, the elastic modulus E, the hardness H, the yield strength σ s , the ultimate tensile strength σ b of the unknown sample are quantitatively evaluated respectively.

Claims

1. A multi-parameter non-destructive evaluation method for the mechanical properties of metallic materials based on grating laser ultrasonic spectra, characterized in that: First, a microlens array (2) with an equal period d is used to form a transient grating (3) with a period of d by a high-energy pulsed laser beam (1) irradiating the surface of the material under test (5). The material under test (5) is excited by the periodic thermal expansion of the transient grating (3) to generate 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 probe laser beam (6) is used to receive the excited ultrasonic Rayleigh wave (4) in a non-contact manner. The ultrasonic Rayleigh wave time-domain signal (7) received by the probe 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 velocity c and the acoustic nonlinear parameter β are calculated, where f is the center frequency of the ultrasonic Rayleigh wave spectrum, and 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 determined according to formula (10): The relationship between hardness, strength and acoustic nonlinear parameters was calibrated, where ρ is the density of the material, v is the Poisson's ratio of the material, and ξ is a dimensionless coefficient with respect to the Poisson's ratio of the material; the calibration curves of the relationship between the elastic modulus E of the material and the sound velocity c (11), the relationship between hardness H and the acoustic nonlinear parameter β (12), and the yield strength σ were obtained respectively. 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 obtained, thereby realizing the multi-parameter quantitative evaluation of the mechanical properties of the material.

2. The method for multi-parameter non-destructive evaluation of the mechanical properties of metallic materials based on grating laser ultrasonic spectrum according to claim 1, characterized in that: The high-energy pulsed laser beam (1) is a collimated laser beam with a pulse length in the nanometer range and a wavelength in the near-infrared band.

3. The method for multi-parameter non-destructive evaluation of the mechanical properties of metallic materials based on grating laser ultrasonic spectrum according to claim 1, characterized in that: The microlens array (2) has a period of sub-millimeter or millimeter and is made of UV-grade fused silica.

4. The method for multi-parameter non-destructive evaluation of the mechanical properties of metallic materials based on grating laser ultrasonic spectrum according to claim 1, characterized in that: The microlens array (2) is twice the focal length from the surface of the material to be tested (5).

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

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

7. The method for multi-parameter non-destructive evaluation of the mechanical properties of metallic materials based on grating laser ultrasonic spectrum according to claim 1, characterized in that: The distance between the high-energy pulsed laser beam (1) and the probe laser beam (6) does not exceed 10 cm.

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

Images