Method for detecting stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy

Abstract

The invention relates to a terahertz time-domain spectroscopy-based unidirectional glass fiber reinforced polymer stress optical coefficient detection method, which comprises the following steps: S1, preparing unidirectional glass fiber reinforced polymers at different curing temperatures, and respectively embedding fiber bragg gratings in a fiber direction and a direction vertical to the fiber direction in the preparation process; obtaining residual strain epsilon x and epsilon y of the unidirectional glass fiber reinforced polymer along the fiber direction and the direction vertical to the fiber direction, and further calculating residual stress sigma x and sigma y along the fiber direction and the direction vertical to the fiber direction; s2, based on a transmission-type terahertz time-domain spectroscopy system, obtaining refractive indexes nx and ny of the unidirectional glass fiber reinforced polymer in the fiber direction and the direction perpendicular to the fiber direction; s3, establishing a propagation model of terahertz waves in different stress states of the unidirectional glass fiber reinforced polymer; and calculating the stress optical coefficient of the unidirectional glass fiber reinforced polymer by combining sigma x, sigma y, nx and ny. The method is beneficial to accurately detecting the stress optical coefficient of the unidirectional glass fiber reinforced polymer.

Description

Technical Field

[0001] The invention belongs to the technical field of nondestructive testing, and in particular relates to a method for detecting stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy. Background Art

[0002] Glass fiber reinforced polymer matrix composites are widely used in the field of high-end equipment manufacturing due to their advantages such as light material, high strength and corrosion resistance. Since the residual stress generated during the curing process of unidirectional glass fiber reinforced polymer will affect its performance and life, it is crucial to characterize the residual stress of unidirectional glass fiber reinforced polymer. Although terahertz time-domain spectroscopy has been widely studied and reported in stress measurement of materials such as ceramics and rubber, its application in residual stress of unidirectional glass fiber reinforced polymer is rarely reported. In addition, the stress optical coefficient is the core parameter connecting terahertz time-domain spectroscopy with residual stress. There is currently a lack of research on the stress optical coefficient of unidirectional glass fiber reinforced polymer, which leads to certain difficulties in using terahertz time-domain spectroscopy to characterize the residual stress of unidirectional glass fiber reinforced polymer. As a result, the terahertz time-domain spectroscopy evaluation system of residual stress of unidirectional glass fiber reinforced polymer is not accurate enough and has low reliability. It can only be used as a qualitative analysis and has a low reference degree in quantitative analysis. Therefore, it is necessary to calibrate the stress optical coefficient of unidirectional glass fiber reinforced polymer by experimental means. Summary of the invention

[0003] The object of the present invention is to provide a method for detecting the stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy, which is conducive to accurately detecting the stress optical coefficient of unidirectional glass fiber reinforced polymer.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: a method for detecting the stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy, comprising the following steps:

[0005] S1. Prepreg compression molding technology is used to prepare unidirectional glass fiber reinforced polymers at different curing temperatures. During the preparation process, fiber Bragg grating sensors are embedded in the unidirectional glass fiber reinforced polymers along the fiber direction and perpendicular to the fiber direction respectively; the residual strain ε of the unidirectional glass fiber reinforced polymer along the fiber direction is obtained by a fiber Bragg grating demodulator. x and the residual strain ε perpendicular to the fiber direction y , and then calculate the residual stress σ of unidirectional glass fiber reinforced polymer along the fiber direction x and the residual stress σ perpendicular to the fiber direction y ;

[0006] S2. Use a transmission terahertz time-domain spectroscopy system, use the transmission signal of the non-unidirectional glass fiber reinforced polymer as the reference signal, rotate the unidirectional glass fiber reinforced polymer so that the polarization directions of the terahertz wave are along the fiber direction and perpendicular to the fiber direction, respectively, use the transmission signal of air-unidirectional glass fiber reinforced polymer-air as the sample signal, perform Fourier transform on the reference signal and the sample signal to obtain the frequency domain signals of the two, thereby obtaining the phase change of the reference signal and the sample signal, and then calculate the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction. x and the refractive index n perpendicular to the fiber direction y ;

[0007] S3, establish a terahertz wave propagation model under different stress states of unidirectional glass fiber reinforced polymer; combine the residual stress σ of the unidirectional glass fiber reinforced polymer along the fiber direction obtained in step S1 x and the residual stress σ perpendicular to the fiber direction y , the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction obtained in step S2 x and the refractive index n perpendicular to the fiber direction y , calculate the stress optical coefficient of unidirectional glass fiber reinforced polymer.

[0008] Furthermore, in step S1, the residual strain ε of the unidirectional glass fiber reinforced polymer along the fiber direction is regulated by changing the curing temperature. x and the residual strain ε perpendicular to the fiber direction y .

[0009] Furthermore, in the step S1, only the grating part of the fiber Bragg grating sensor is embedded in the unidirectional glass fiber reinforced polymer.

[0010] Furthermore, in step S1, the residual strain ε of the unidirectional glass fiber reinforced polymer along the fiber direction is x and the residual strain ε perpendicular to the fiber direction y The calculation method is:

[0011]

[0012] Among them, Δλ x is the change in the central wavelength of the reflected light from the fiber Bragg grating embedded along the fiber direction; Δλ y K is the change in the center wavelength of the reflected light from the fiber Bragg grating embedded in the vertical fiber direction; ε is the strain sensitivity coefficient; K T is the temperature sensitivity coefficient; ΔT is the temperature change.

[0013] Furthermore, in step S1, the residual stress σ of the unidirectional glass fiber reinforced polymer along the fiber direction is x and the residual stress σ perpendicular to the fiber direction y The calculation method is:

[0014] σ x =E x ·ε x

[0015] σ y =E y ·ε y

[0016] Among them, E x is the elastic modulus of unidirectional glass fiber reinforced polymer along the fiber direction, E y It is the elastic modulus of unidirectional glass fiber reinforced polymer perpendicular to the fiber direction.

[0017] Furthermore, the elastic modulus E of unidirectional glass fiber reinforced polymer along the fiber direction was measured using a universal testing machine. x and the elastic modulus E perpendicular to the fiber direction y .

[0018] Furthermore, in step S2, the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction is x and the refractive index n perpendicular to the fiber direction y The calculation method is:

[0019]

[0020] Where c is the speed of light in vacuum, f is the frequency, d is the thickness of the unidirectional glass fiber reinforced polymer, and δ x is the phase received by the receiving antenna when the polarization direction is along the fiber direction, δ y is the phase received by the receiving antenna when the polarization direction is perpendicular to the fiber direction, and δ0 is the phase of the reference signal.

[0021] Furthermore, in step S3, the propagation model of the terahertz wave in the unidirectional glass fiber reinforced polymer under different stress states is:

[0022] ΔN x =q 11 Δσ x +q 12 Δσ y

[0023] ΔN y =q 21 Δσ x +q 22 Δσ y

[0024] Among them, q 11 ,q 12 ,q 21 ,q 22 are stress optical coefficients.

[0025] Furthermore, the transmission-type terahertz time-domain spectroscopy system includes a femtosecond laser, an optical fiber attenuator, a terahertz transmitter, a unidirectional glass fiber reinforced polymer, a terahertz receiver and a delay line; the laser light emitted by the femtosecond laser is divided into two paths via the optical fiber, one path is emitted to the terahertz transmitter, and the other path is emitted to the terahertz receiver as a delay line; the terahertz wave emitted by the terahertz transmitter is emitted to the terahertz receiver through the unidirectional glass fiber reinforced polymer.

[0026] Furthermore, the transmission-type terahertz time-domain spectroscopy system adopts an all-fiber transmission mode.

[0027] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for detecting the optical stress coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy. The method calculates the residual stress σ of the unidirectional glass fiber reinforced polymer along the fiber direction. x and the residual stress σ perpendicular to the fiber direction y , the refractive index n of unidirectional glass fiber reinforced polymer along the fiber direction x and the refractive index n perpendicular to the fiber direction y , and establish a terahertz wave propagation model under different stress states of unidirectional glass fiber reinforced polymer, and then calculate the stress optical coefficient of unidirectional glass fiber reinforced polymer. This method can effectively realize the detection of the stress optical coefficient of unidirectional glass fiber reinforced polymer, and then realize the high-precision non-destructive detection of residual stress of unidirectional glass fiber reinforced polymer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of a fiber Bragg grating demodulator system according to an embodiment of the present invention;

[0029] Figure 2 A diagram showing the working principle of a fiber Bragg grating in an embodiment of the present invention;

[0030] Figure 3 This is a structural principle diagram of a transmission terahertz time-domain spectroscopy system in an embodiment of the present invention;

[0031] Figure 4 is the residual stress σ along the fiber direction of the unidirectional glass fiber reinforced polymer at different curing temperatures in the embodiment of the present invention x and the residual stress σ perpendicular to the fiber direction y Schematic diagram;

[0032] Figure 5 is the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction at different curing temperatures in the embodiments of the present invention x and the refractive index n perpendicular to the fiber direction y Schematic diagram. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0034] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0035] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0036] This embodiment provides a method for detecting the stress optical coefficient of a unidirectional glass fiber reinforced polymer, comprising the following steps:

[0037] S1. Prepreg compression molding technology is used to prepare unidirectional glass fiber reinforced polymers at different curing temperatures. During the preparation process, fiber Bragg grating sensors are embedded in the unidirectional glass fiber reinforced polymers along the fiber direction and perpendicular to the fiber direction respectively; the residual strain ε of the unidirectional glass fiber reinforced polymer along the fiber direction is obtained by a fiber Bragg grating demodulator. x and the residual strain ε perpendicular to the fiber direction y , and then calculate the residual stress σ of unidirectional glass fiber reinforced polymer along the fiber direction x and the residual stress σ perpendicular to the fiber direction y .

[0038] In this embodiment, if Figure 1 As shown in the figure, in order to reduce the influence of the embedded fiber Bragg grating sensor on the unidirectional glass fiber reinforced polymer, the fiber Bragg grating sensor only embeds the grating part into the unidirectional glass fiber reinforced polymer; the residual strain ε of the unidirectional glass fiber reinforced polymer along the fiber direction is regulated by changing the curing temperature. x and the residual strain ε perpendicular to the fiber direction y .like Figure 2As shown, the fiber Bragg grating has wavelength selectivity, so the grating will only reflect light with a wavelength corresponding to the effective refractive index, based on which the change in the central wavelength of the reflected light is analyzed.

[0039] Specifically, the residual strain ε of unidirectional glass fiber reinforced polymer along the fiber direction is x and the residual strain ε perpendicular to the fiber direction y The calculation method is:

[0040]

[0041] Among them, Δλ x is the change in the central wavelength of the reflected light from the fiber Bragg grating embedded along the fiber direction; Δλ y K is the change in the center wavelength of the reflected light from the fiber Bragg grating embedded in the vertical fiber direction; ε is the strain sensitivity coefficient, K ε =-0.0012MPa / ℃; K T is the temperature sensitivity coefficient, K T =-0.0095MPa / ℃; ΔT is the temperature change.

[0042] Residual stress σ along the fiber direction of unidirectional glass fiber reinforced polymer x and the residual stress σ perpendicular to the fiber direction y The calculation method is:

[0043] σ x =E x ·ε x

[0044] σ y =E y ·ε y

[0045] Among them, E x is the elastic modulus of unidirectional glass fiber reinforced polymer along the fiber direction, E y The elastic modulus E of unidirectional glass fiber reinforced polymer in the direction perpendicular to the fiber. The elastic modulus E of unidirectional glass fiber reinforced polymer along the fiber direction is measured using a universal testing machine. x and the elastic modulus E perpendicular to the fiber direction y .

[0046] S2. Use a transmission terahertz time-domain spectroscopy system, use the transmission signal of the non-unidirectional glass fiber reinforced polymer as the reference signal, rotate the unidirectional glass fiber reinforced polymer so that the polarization directions of the terahertz wave are along the fiber direction and perpendicular to the fiber direction, respectively, use the transmission signal of air-unidirectional glass fiber reinforced polymer-air as the sample signal, perform Fourier transform on the reference signal and the sample signal to obtain the frequency domain signals of the two, thereby obtaining the phase change of the reference signal and the sample signal, and then calculate the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction. x and the refractive index n perpendicular to the fiber direction y .

[0047] like Figure 3 As shown, the transmission type terahertz time domain spectroscopy system includes a femtosecond laser, an optical fiber attenuator, a terahertz transmitter, a unidirectional glass fiber reinforced polymer, a terahertz receiver and a delay line. The laser light emitted by the femtosecond laser is divided into two paths through the optical fiber, one path is emitted to the terahertz transmitter, and the other path is emitted to the terahertz receiver as a delay line. The terahertz wave emitted by the terahertz transmitter is emitted to the terahertz receiver through the unidirectional glass fiber reinforced polymer. The transmission type terahertz time domain spectroscopy system adopts an all-optical fiber transmission method.

[0048] Specifically, the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction is x and the refractive index n perpendicular to the fiber direction y The calculation method is:

[0049]

[0050] Where c is the speed of light in vacuum, f is the frequency, d is the thickness of the unidirectional glass fiber reinforced polymer, and δ x is the phase received by the receiving antenna when the polarization direction is along the fiber direction, δ y is the phase received by the receiving antenna when the polarization direction is perpendicular to the fiber direction, and δ0 is the phase of the reference signal.

[0051] S3, establish a terahertz wave propagation model under different stress states of unidirectional glass fiber reinforced polymer; combine the residual stress σ of the unidirectional glass fiber reinforced polymer along the fiber direction obtained in step S1 x and the residual stress σ perpendicular to the fiber direction y , the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction obtained in step S2 x and the refractive index n perpendicular to the fiber direction y The stress-optical coefficient of unidirectional glass fiber reinforced polymer was calculated by the multivariate linear regression method.

[0052] Specifically, the propagation model of terahertz waves in unidirectional glass fiber reinforced polymer under different stress states is:

[0053] ΔN x =q 11 Δσ x +q 12 Δσ y

[0054] ΔN y =q 21 Δσ x +q 22 Δσ y

[0055] Among them, q 11 ,q 12 ,q 21 ,q 22 are stress optical coefficients.

[0056] Figure 4 is the residual stress σ along the fiber direction of the unidirectional glass fiber reinforced polymer at different curing temperatures in this embodiment x and the residual stress σ perpendicular to the fiber direction y Schematic diagram. Figure 5 is the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction at different curing temperatures in this embodiment x and the refractive index n perpendicular to the fiber direction y Schematic diagram. The measurement results of residual stress and refractive index are shown in Table 1. In each set of curing temperature experimental tests, the residual stress σ along the fiber direction x and the residual stress σ perpendicular to the fiber direction y Three measurements were performed and the average value was taken to obtain the refractive index n along the fiber direction. x and the refractive index n perpendicular to the fiber direction y The measurements were taken five times and the average value was taken.

[0057] Table 1 Measurement results of residual stress and refractive index of unidirectional glass fiber reinforced polymer

[0058]

[0059] The stress optical coefficient of unidirectional glass fiber reinforced polymer can be calculated from the above data, as shown in Table 2 and Table 3:

[0060] Table 2 Stress optical coefficient q of unidirectional glass fiber reinforced polymer 11 ,q 12 The calculation results

[0061]

[0062] Table 3 Stress optical coefficient q of unidirectional glass fiber reinforced polymer 21 ,q 22 The calculation results

[0063]

[0064] The above experimental results prove that this method can effectively measure the stress-optical coefficient of unidirectional glass fiber reinforced polymer, and has strong practicality and broad application prospects.

[0065] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for detecting the optical coefficient of stress in unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy. It is characterized in that The following steps are involved: S1. Prepreg compression molding technology is used to prepare unidirectional glass fiber reinforced polymers at different curing temperatures. During the preparation process, fiber Bragg grating sensors are embedded in the unidirectional glass fiber reinforced polymers along the fiber direction and perpendicular to the fiber direction respectively; the residual strain ε of the unidirectional glass fiber reinforced polymer along the fiber direction is obtained by a fiber Bragg grating demodulator. x and the residual strain ε perpendicular to the fiber direction y , and then calculate the residual stress σ of unidirectional glass fiber reinforced polymer along the fiber direction x and the residual stress σ perpendicular to the fiber direction y ; S2. Use a transmission terahertz time-domain spectroscopy system, use the transmission signal of the non-unidirectional glass fiber reinforced polymer as the reference signal, rotate the unidirectional glass fiber reinforced polymer so that the polarization directions of the terahertz wave are along the fiber direction and perpendicular to the fiber direction, respectively, use the transmission signal of air-unidirectional glass fiber reinforced polymer-air as the sample signal, perform Fourier transform on the reference signal and the sample signal to obtain the frequency domain signals of the two, thereby obtaining the phase change of the reference signal and the sample signal, and then calculate the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction. x and the refractive index n perpendicular to the fiber direction y ; S3, establish a terahertz wave propagation model under different stress states of unidirectional glass fiber reinforced polymer; combine the residual stress σ of the unidirectional glass fiber reinforced polymer along the fiber direction obtained in step S1 x and the residual stress σ perpendicular to the fiber direction y , the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction obtained in step S2 x and the refractive index n perpendicular to the fiber direction y , calculate the stress optical coefficient of unidirectional glass fiber reinforced polymer.

2. The method for detecting the optical stress coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, It is characterized in that In step S1, the residual strain ε of the unidirectional glass fiber reinforced polymer along the fiber direction is regulated by changing the curing temperature. x and the residual strain ε perpendicular to the fiber direction y .

3. The method for detecting the stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, It is characterized in that In the step S1, only the grating part of the fiber Bragg grating sensor is embedded in the unidirectional glass fiber reinforced polymer.

4. The method for detecting the stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, It is characterized in that In step S1, the residual strain ε of the unidirectional glass fiber reinforced polymer along the fiber direction x and the residual strain ε perpendicular to the fiber direction y The calculation method is: Among them, Δλ x is the change in the central wavelength of the reflected light from the fiber Bragg grating embedded along the fiber direction; Δλ y K is the change in the center wavelength of the reflected light from the fiber Bragg grating embedded in the vertical fiber direction; ε is the strain sensitivity coefficient; K T is the temperature sensitivity coefficient; ΔT is the temperature change.

5. The method for detecting the stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, It is characterized in that In the step S1, the residual stress σ of the unidirectional glass fiber reinforced polymer along the fiber direction x and the residual stress σ perpendicular to the fiber direction y The calculation method is: s x =E x ·e x σ=E·ε s y =E y ·e y Among them, E x is the elastic modulus of unidirectional glass fiber reinforced polymer along the fiber direction, E y It is the elastic modulus of unidirectional glass fiber reinforced polymer perpendicular to the fiber direction.

6. The method for detecting the stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 5, It is characterized in that The elastic modulus E of unidirectional glass fiber reinforced polymer along the fiber direction was measured using a universal testing machine. x and the elastic modulus E perpendicular to the fiber direction y .

7. The method for detecting stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, It is characterized in that In step S2, the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction is x and the refractive index n perpendicular to the fiber direction y The calculation method is: Where c is the speed of light in vacuum, f is the frequency, d is the thickness of the unidirectional glass fiber reinforced polymer, and δ x is the phase received by the receiving antenna when the polarization direction is along the fiber direction, δ y is the phase received by the receiving antenna when the polarization direction is perpendicular to the fiber direction, δ 0 is the phase of the reference signal.

8. The method for detecting the stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, It is characterized in that In step S3, the propagation model of the terahertz wave in the unidirectional glass fiber reinforced polymer under different stress states is: ΔN x =q 11 Board x +q 12 Board y ΔN y =q 21 Board x +q 22 Board y Among them, q 11 ,q 12 ,q 21 ,q 22 are stress optical coefficients.

9. The method for detecting stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, It is characterized in that The transmission-type terahertz time-domain spectroscopy system comprises a femtosecond laser, an optical fiber attenuator, a terahertz transmitter, a unidirectional glass fiber reinforced polymer, a terahertz receiver and a delay line; the laser light emitted by the femtosecond laser is divided into two paths via the optical fiber, one path is emitted to the terahertz transmitter, and the other path is emitted to the terahertz receiver as a delay line; the terahertz wave emitted by the terahertz transmitter is emitted to the terahertz receiver through the unidirectional glass fiber reinforced polymer.

10. The method for detecting the stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 9, It is characterized in that The transmission-type terahertz time-domain spectroscopy system adopts an all-optical fiber transmission mode.

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