A multi-elastic modulus measurement system based on self-mixing interference

Abstract

The present invention discloses a multi-elastic modulus measurement system based on self-mixing interference. The optical unit includes two optical groups, and each optical group includes a semiconductor laser, a collimating lens, and a photoelectric receiver. The semiconductor laser is used to emit an initial optical signal to a sample, so that the initial optical signal is reflected or scattered by the sample excited by an external excitation signal to form a feedback optical signal. The feedback optical signal returns to the laser resonator of the photoelectric receiver and undergoes a self-mixing interference effect with the initial optical signal. The excitation unit is used to excite the sample with an external excitation signal to cause the sample to generate bending vibration and shear vibration. The calculation module is used to perform a fast Fourier analysis on the electrical signal to obtain the bending resonance frequency and shear resonance frequency of the sample, so as to calculate the Poisson's ratio and bulk modulus of the sample. The present invention realizes the simultaneous and high-precision measurement of the bending resonance frequency and shear resonance frequency of the specimen in one measurement, and further achieves the goal of obtaining multiple elastic moduli.

Description

Technical Field

[0001] The invention relates to the technical field of optical measurement, and in particular to a multi-elastic modulus measurement system based on self-mixing interference. Background Art

[0002] Elastic modulus includes shear modulus, Young's modulus, Poisson's ratio and bulk modulus. It is an important performance parameter in engineering materials, a measure of the ability of an object to resist elastic deformation, and a reflection of the bond strength between atoms, ions or molecules. Traditional elastic modulus testing methods are mainly achieved through static measurement methods such as stretching, bending and torsion of samples. Static methods cannot accurately reflect the structural changes inside the material because of the large load when the sample is stretched, the slow loading speed, the relaxation process, material fatigue or damage, low efficiency and accuracy. Especially for brittle materials, it is impossible to use static methods to measure different elastic moduli. Different measurement methods are required to determine, and multiple tests are required. The repeatability of the experiment is not high, but the material properties of the sample are prone to change in the static method measurement. More experimental equipment is required, which is costly and time-consuming.

[0003] The existing elastic modulus measurement system based on optical interferometry can generally only measure one parameter in the elastic modulus, and cannot measure multiple elastic moduli at the same time. The Chinese patent application with application number CN2021229560238 discloses an all-fiber material parameter measurement system based on self-mixing interference, which obtains the vibration frequency of the sample through the optical fiber adhered to the surface of the material sample and then determines the Young's modulus. Since the sensing optical fiber has a certain length, this method may cause inconsistent strains at various locations of the optical fiber, affecting the extraction of the vibration frequency. At the same time, the device and method can only measure one elastic modulus such as Young's modulus, and cannot simultaneously measure multiple elastic moduli of materials including shear modulus, Young's modulus, Poisson's ratio and bulk modulus. Different elastic moduli need to be measured multiple times using different methods. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a multi-elastic modulus measurement system based on self-mixing interference, which can achieve simultaneous synchronous, contactless, non-destructive and high-precision measurement of the bending resonance frequency and shear resonance frequency of the sample in one measurement, thereby obtaining the goal of multiple elastic moduli.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A multi-elastic modulus measurement system based on self-mixing interference, comprising an optical unit, an excitation unit and a signal processing unit. The optical unit includes two optical groups, and each optical group includes a semiconductor laser, a collimating lens and a photoelectric receiver. The semiconductor laser is used to emit an initial optical signal to a sample, so that the initial optical signal is reflected or scattered by the sample excited by an external excitation signal to form a feedback optical signal. The feedback optical signal returns to the laser resonator of the photoelectric receiver and undergoes a self-mixing interference effect with the initial optical signal. The collimating lens is located in the optical path of self-mixing interference between the semiconductor laser and the sample to form a self-collimating optical path for this optical path. The photoelectric receiver is used to receive the optical signal of self-mixing interference and convert the optical signal into an electrical signal. The excitation unit is used to excite the sample with an external excitation signal to cause the sample to generate bending vibration and shear vibration. The signal processing unit includes a conversion and amplification module and a calculation module. The conversion and amplification module is connected to the photoelectric receiver and is used to convert the electrical signal into a digital signal. The calculation module is connected to the conversion and amplification module and is used to perform a fast Fourier analysis on the electrical signal to obtain the bending resonance frequency and the shear resonance frequency of the sample, and then determine the Young's modulus and the shear modulus of the sample based on the bending resonance frequency, the shear resonance frequency and the material parameters of the sample, so as to calculate the Poisson's ratio and the bulk modulus of the sample.

[0007] Further, the photoelectric receiver is a photodiode, and the output wavelength of the semiconductor laser is 780 nm and the rated power is 30 mW.

[0008] Further, the semiconductor laser is connected with a temperature controller. The temperature controller is used to monitor the working temperature of the semiconductor laser in real time and adjust the input current of the semiconductor laser according to its working temperature, so that the semiconductor laser works stably in a suitable temperature environment.

[0009] Further, the input current of the temperature controller is 55 mA, and the working temperature of the semiconductor laser is controlled at 25 ± 0.1 °C.

[0010] Further, when the excitation source of the excitation unit acts on the midpoint of the end of the sample, the sample mainly generates bending vibration along the direction of both ends of the sample. The length of both ends of the sample is set as 1L, then the position 0.224L away from both ends on the sample is the node of the first-order mode of the bending vibration of the sample, that is, the irradiation point of the semiconductor laser of one of the optical groups. The midpoint between 0.5L of the two ends of the sample is the antinode of the bending oscillation of the sample. When the excitation source of the excitation unit acts on a point on one side of the end of the sample, the sample will generate shear vibration, then the midpoint at 0.5L of the sample is the node of the first-order mode of the shear vibration of the sample, that is, the irradiation point of the semiconductor laser of the other optical group. The two sides of the sample perpendicular to the direction of both ends are the antinodes of the shear oscillation.

[0011] Further, one side point at 0.224L of one end of the sample and the midpoint at 0.5L of the sample are used as measurement points to interact with the optical signal of the semiconductor laser, and the excitation unit acts on the midpoint of the other end of the sample and one side point of the other end of the sample.

[0012] Further, the sample is connected with a support frame, and the support frame supports the sample at 0.224L so that the sample can vibrate freely without affecting the vibration frequency of the sample.

[0013] Further, the sample is in the shape of a rectangular strip.

[0014] Further, the ratio of the length of the sample to its thickness or width is not less than 20.

[0015] Further, the excitation unit is the free fall impact of a steel ball or the tapping of a rubber hammer.

[0016] Compared with the prior art, the advantages of the present invention are as follows:

[0017] After the present invention applies an external excitation signal to the sample through the excitation unit, the sample can simultaneously generate a composite vibration of bending vibration and shear vibration. The semiconductor laser can simultaneously collect the bending vibration signal and the shear vibration signal when the sample undergoes the composite vibration. The feedback optical signal carrying the vibration information of the sample is emitted or scattered back into the laser resonator of the photoelectric receiver to generate a self-mixing interference effect with the initial optical signal, and a self-mixing interference optical signal is generated. The optical signal is converted and amplified into an electrical signal by the conversion and amplification module. After the Fourier analysis of the electrical signal by the calculation module, the bending resonance frequency and the shear resonance frequency of the sample are obtained. Then, the Young's modulus and shear modulus of the sample are determined through the resonance frequency and the material parameters of the sample itself, and further the Poisson's ratio and bulk modulus of the sample are calculated, thereby realizing the simultaneous, non-contact, non-destructive, and high-precision measurement of the bending resonance frequency and shear resonance frequency of the specimen in one measurement, and further achieving the goal of obtaining multiple elastic moduli. Compared with other elastic modulus measurement methods, the present invention is convenient to operate, can simultaneously measure multiple elastic moduli of the sample, and is non-destructive testing, effectively improving the measurement efficiency. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of a multi-elastic modulus measurement system based on self-mixing interference.

[0019] Figure 2 It is a working flow chart of a multi-elastic modulus measurement system based on self-mixing interference.

[0020] Figure 3 It is a schematic diagram of the sample measurement points of a multi-elastic modulus measurement system based on self-mixing interference. Description of the Drawings:

[0022] 1. Optical unit; 11. Optical group; 12. Temperature controller; 2. Excitation unit; 3. Signal processing unit; 31. Conversion and amplification module; 32. Calculation module; 4. Sample; 5. Support frame. Detailed implementation mode

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Such as Figure 1 And Figure 2As shown in the figure, a multi-elastic modulus measurement system based on self-mixing interference in this embodiment includes an optical unit 1, an excitation unit 2, and a signal processing unit 3. The optical unit 1 includes two optical groups 11. Each of the optical groups 11 includes a semiconductor laser, a collimating lens, and a photoelectric receiver. The semiconductor laser is used to emit an initial optical signal to a sample 4, so that the initial optical signal is reflected or scattered by the sample 4 excited by an external excitation signal to form a feedback optical signal. The feedback optical signal returns to the laser resonator of the photoelectric receiver and undergoes a self-mixing interference effect with the initial optical signal. The collimating lens is located in the optical path of self-mixing interference between the semiconductor laser and the sample 4 to make the optical path form a self-collimating optical path. The photoelectric receiver is used to receive the optical signal of self-mixing interference and convert the optical signal into an electrical signal. The excitation unit 2 is used to excite the sample 4 with an external excitation signal to make the sample 4 generate bending vibration and shear vibration. The signal processing unit 3 includes a conversion and amplification module 31 and a calculation module 32. The conversion and amplification module 31 is connected to the photoelectric receiver and is used to convert the electrical signal into a digital signal. The calculation module 32 is connected to the conversion and amplification module 31 and is used to perform a fast Fourier analysis on the electrical signal to obtain the bending resonance frequency and shear resonance frequency of the sample 4, and then determine the Young's modulus and shear modulus of the sample 4 through the bending resonance frequency, shear resonance frequency, and the material parameters of the sample 4, so as to calculate the Poisson's ratio and bulk modulus of the sample 4. After applying an external excitation signal to the sample 4 through the excitation unit 2, the sample 4 can simultaneously generate a composite vibration of bending vibration and shear vibration. The bending vibration signal and shear vibration signal when the sample 4 undergoes the composite vibration can be collected simultaneously through the semiconductor laser. The feedback optical signal carrying the vibration information of the sample 4 is reflected or scattered back into the laser resonator of the photoelectric receiver and undergoes a self-mixing interference effect with the initial optical signal, and generates an optical signal of self-mixing interference. The optical signal is converted and amplified into an electrical signal by the conversion and amplification module 31. After performing a Fourier analysis on the electrical signal by the calculation module 32, the bending resonance frequency and shear resonance frequency of the sample 4 are obtained. Then, the Young's modulus and shear modulus of the sample 4 are determined through the resonance frequency and the material parameters of the sample 4 itself, and further the Poisson's ratio and bulk modulus of the sample 4 are calculated, thus realizing the simultaneous, non-contact, non-destructive, and high-precision measurement of the bending resonance frequency and shear resonance frequency of the specimen in one measurement, and further achieving the goal of obtaining multiple elastic moduli. Compared with other elastic modulus measurement methods, the operation of the present invention is convenient, multiple elastic moduli of the sample 4 can be measured simultaneously, and non-destructive detection is carried out, effectively improving the measurement efficiency.

[0025] In this embodiment, the photoelectric receiver is a photodiode, and the output wavelength of the semiconductor laser is 780 nm and the rated power is 30 mW. The photodiode is convenient to purchase, has a low price, and is easy to install; the photodiode (Photo Diode, abbreviated as PD) can also be other similar photoelectric conversion components and lasers in other application examples, and the present invention does not limit this.

[0026] In this embodiment, the semiconductor laser is connected to a temperature controller 12, which is used to monitor the operating temperature of the semiconductor laser in real time and adjust the input current of the semiconductor laser according to its operating temperature, so that the semiconductor laser can operate stably in a suitable temperature environment. Through the temperature controller 12, it can be ensured that the semiconductor laser is always in an effective working state.

[0027] In this embodiment, the input current of the temperature controller 12 is 55 mA, and the operating temperature of the semiconductor laser is controlled at 25 ± 0.1 °C. In other application examples, other types of current temperature controllers 12 can also be selected according to the actually used semiconductor laser, and the present invention does not limit this.

[0028] In this embodiment, when the excitation source of the excitation unit 2 acts on the midpoint of the end of the sample 4, the sample 4 mainly generates bending vibration along the direction of both ends of the sample 4. The length of both ends of the sample 4 is set to 1L, then the position 0.224L away from both ends on the sample 4 is the node of the first-order mode of the bending vibration of the sample 4, that is, the irradiation point of the semiconductor laser of one of the optical groups 11. The midpoint between 0.5L of the two ends of the sample 4 is the antinode of the bending oscillation of the sample 4; when the excitation source of the excitation unit 2 acts on a side point at the end of the sample 4, the sample 4 will generate shear vibration, then the midpoint at 0.5L of the sample 4 is the node of the first-order mode of the shear vibration of the sample 4, that is, the irradiation point of the semiconductor laser of the other optical group 11. The two sides of the sample 4 perpendicular to the direction of both ends are the antinodes of the shear oscillation. By continuously exciting the midpoint and the edge of one end of the sample 4 to make the sample 4 vibrate, and simultaneously irradiating two initial optical signals onto the intersection point of the first-order bending vibration node and the first-order shear vibration antinode of the sample 4 and the intersection point of the first-order bending vibration and the first-order shear vibration node of the sample 4 through the semiconductor laser, the feedback optical signal brings the vibration information of the sample 4 back to the optical resonator to generate a self-mixing interference effect with the initial optical signal, and the self-mixing interference effect can be effectively obtained, so that the material parameters of the sample 4 itself can be accurately obtained to determine the Young's modulus and shear modulus of the sample 4, and then the Poisson's ratio and bulk modulus of the sample 4 can be calculated more effectively. As Figure 3 shown, where point A is the measurement point of the shear resonance frequency, point B is the measurement point of the bending resonance frequency, and points C and D are the excitation points of the external excitation on the material sample.

[0029] In this embodiment, a side point at 0.224L of one end of the sample 4 and the midpoint at 0.5L of the sample 4 are both used as measurement points to interact with the optical signal of the semiconductor laser, and the excitation unit 2 acts on the midpoint of the other end of the sample 4 and a side point at the other end of the sample 4. Each measurement point and excitation point are key points for bending oscillation and shear oscillation. Measuring or exciting at the key points can more effectively obtain the self-mixing interference effect.

[0030] In this embodiment, the sample 4 is connected to a support frame 5, and the support frame 5 is supported at 0.224L of the sample 4 so that the sample 4 can vibrate freely without affecting the vibration frequency of the sample 4. The support frame 5 supports the sample 4 at key points, which can not only support the sample 4 well, but also minimize the influence of the external environment on the sample 4 during bending oscillation and shear oscillation.

[0031] In this embodiment, the sample 4 is in the shape of a rectangular strip, which is more conducive to generating vibration.

[0032] In this embodiment, the ratio of the length to the thickness or width of the sample 4 is not less than 20. The sample 4 of specific specifications can reduce the volume of the sample 4 while obtaining the vibration effect, thereby saving the amount of the sample 4 and facilitating the measurement operation.

[0033] In this embodiment, the excitation unit 2 is a free-fall impact of a steel ball or a knock of a rubber hammer.

[0034] In this embodiment, the conversion and amplification unit is a combination of a dedicated A / D conversion module (Analog to Digital) and a mutual resistance amplifier circuit, which are integrated and packaged on a printed circuit board (PCB). The computing unit is a personal computer (PC), or other electronic systems that can perform signal processing, such as a single-chip microcomputer (MCU) or a minimum system composed of a digital signal processing chip, and the present invention is not limited to this.

[0035] The bending resonance frequency and shear resonance frequency of sample 4 are expressed as f b and f t Indicates that the mass, length, width and thickness of sample 4 are represented as m, L, b and t respectively, and the Young's modulus E of sample 4 is: Shear modulus G of sample 4: Among them, the shape factor B is: Empirical correction factor A: Where, χ is the ratio of the thickness to the width of sample 4: χ = t / b, and the Poisson's ratio μ of sample 4 is: Bulk modulus K of sample 4: The corresponding material parameters are calculated according to the above mathematical expressions.

[0036] The above mathematical expression is easy to operate and simple to calculate. By collecting and analyzing data at specific measuring points of sample 4, the bending resonance frequency f of the sample is obtained at the same time. band the shear resonance frequency f t , and then determine the Young's modulus E and shear modulus G of the specimen through the resonance frequency and the material parameters of the sample 4, and further calculate the Poisson's ratio μ and bulk modulus K of the sample 4.

[0037] The above are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. For those skilled in the art of this technology, the improvements and transformations obtained without departing from the technical concept of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A multi-elastic modulus measurement system based on self-mixing interference, characterized in that It includes an optical unit (1), an excitation unit (2) and a signal processing unit (3). The optical unit (1) includes two optical groups (11). Each optical group (11) includes a semiconductor laser, a collimating lens and a photoelectric receiver. The semiconductor laser is used to emit an initial optical signal to a sample (4) so that the initial optical signal is reflected or scattered by the sample (4) excited by an external excitation signal to form a feedback optical signal. The feedback optical signal returns to the laser resonator of the photoelectric receiver and generates a self-mixing interference effect with the initial optical signal. The collimating lens is located in the optical path of the self-mixing interference between the semiconductor laser and the sample (4) so that the optical path forms a self-collimating optical path. The photoelectric receiver is used to receive the optical signal of the self-mixing interference and convert the optical signal into an electrical signal. The excitation unit (2) is used to excite the sample (4) with an external excitation signal so that the sample (4) generates bending vibration and shear vibration. The signal processing unit (3) includes a conversion and amplification module (31) and a calculation module (32). The conversion and amplification module (31) is connected to the photoelectric receiver and is used to convert the electrical signal into a digital signal. The calculation module (32) is connected to the conversion and amplification module (31) and is used to perform a fast Fourier analysis on the electrical signal to obtain the bending resonance frequency and the shear resonance frequency of the sample (4). Then, through the bending resonance frequency and the shear resonance frequency and the material parameters of the sample (4), the Young's modulus and the shear modulus of the sample (4) are determined, and thus the Poisson's ratio and the bulk modulus of the sample (4) are calculated; When the excitation source of the excitation unit (2) acts on the midpoint of the end of the sample (4), the sample (4) mainly generates bending vibration along the direction of both ends of the sample (4). The length between both ends of the sample (4) is set as 1L. Then, the point 0.224L away from both ends on the sample (4) is the node of the first-order mode of the bending vibration of the sample (4), that is, the irradiation point of the semiconductor laser of one of the optical groups (11). The midpoint between both ends of the sample (4) and the midpoint at 0.5L between both ends is the antinode of the bending oscillation of the sample (4). When the excitation source of the excitation unit (2) acts on a side point at the end of the sample (4), the sample (4) will generate shear vibration. Then, the midpoint at 0.5L of the sample (4) is the node of the first-order mode of the shear vibration of the sample (4), that is, the irradiation point of the semiconductor laser of the other optical group (11). The two sides of the sample (4) perpendicular to the direction of both ends are the antinodes of the shear oscillation; One side point at 0.224L of one end of the sample (4) and the midpoint at 0.5L of the sample (4) are both used as measurement points to interact with the optical signal of the semiconductor laser. The excitation unit (2) acts on the midpoint of the other end of the sample (4) and a side point at the other end of the sample (4).

2. The multi-elastic modulus measurement system based on self-mixing interference according to claim 1, wherein The photoelectric receiver is a photodiode. The output wavelength of the semiconductor laser is 780 nm and the rated power is 30 mW.

3. The multi-elastic modulus measurement system based on self-mixing interference according to claim 1, characterized in that, The semiconductor laser is connected to a temperature controller (12), and the temperature controller (12) is used to monitor the operating temperature of the semiconductor laser in real time and adjust the input current of the semiconductor laser according to its operating temperature so that the semiconductor laser can operate stably in a suitable temperature environment.

4. The multi-elastic modulus measurement system based on self-mixing interference according to claim 3, wherein The input current of the temperature controller (12) is 55 mA, and the operating temperature of the semiconductor laser is controlled at 25 ± 0.1 °C.

5. The multi-elastic modulus measurement system based on self-mixing interference according to claim 1, characterized in that The sample (4) is connected to a support frame (5), and the support frame (5) is supported at 0.224L of the sample (4) so that the sample (4) can vibrate freely without affecting the vibration frequency of the sample (4).

6. The multi-elastic modulus measurement system based on self-mixing interference according to claim 1, characterized in that, The sample (4) is rectangular strip-shaped.

7. The multi-elastic modulus measurement system based on self-mixing interference according to claim 6, characterized in that The ratio of the length of the sample (4) to its thickness or width is not less than 20.

8. The multi-elastic modulus measurement system based on self-mixing interference according to claim 1, wherein The excitation unit (2) is the free fall impact of a steel ball or the percussion of a rubber hammer.

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