Detection method of stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy

Abstract

The present application relates to a kind of unidirectional glass fiber reinforced polymer stress optical coefficient detection methods based on terahertz time-domain spectroscopy, comprising: S1, preparation of unidirectional glass fiber reinforced polymer under different curing temperature, in preparation process, respectively along fiber direction and perpendicular fiber direction embedding fiber Bragg grating;Obtain the residual strain of unidirectional glass fiber reinforced polymer along fiber direction and perpendicular fiber direction e x 、 e y , and then calculate the residual stress of along fiber direction and perpendicular fiber direction s x 、 s y ;S2, based on transmission terahertz time-domain spectroscopy system, obtain the refractive index of unidirectional glass fiber reinforced polymer along fiber direction and perpendicular fiber direction n x 、 n y ;S3, establish the propagation model of terahertz wave in different stress state of unidirectional glass fiber reinforced polymer;Combined s x 、 s s y 、 n x 、 n y , calculate the stress optical coefficient of unidirectional glass fiber reinforced polymer.This method is conducive to accurately detecting the stress optical coefficient of unidirectional glass fiber reinforced polymer.

Description

Technical Field

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

[0002] Glass fiber reinforced polymer (GFR) composites are widely used in high-end equipment manufacturing due to their advantages such as light weight, high strength, and corrosion resistance. Since the residual stress generated during the curing and molding of unidirectional GFR polymers can affect their performance and lifespan, characterizing the residual stress in GFR polymers is crucial. Although terahertz time-domain spectroscopy (THz) has been widely studied and reported for stress measurement in materials such as ceramics and rubber, its application in residual stress in GFR polymers is rarely reported. Furthermore, the stress optical coefficient (SOC), a key parameter linking THz time-domain spectroscopy with residual stress, is currently lacking research. This leads to difficulties in using THz time-domain spectroscopy to characterize the residual stress in GFR polymers. Consequently, the THz time-domain spectroscopy evaluation system for residual stress in GFR polymers is inaccurate and unreliable, and can only be used for qualitative analysis, with a low degree of reference for quantitative analysis. Therefore, experimental calibration of the SOC is necessary. 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 optical stress coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy, comprising the following steps:

[0005] S1. Unidirectional glass fiber reinforced polymers (UGRPs) at different curing temperatures were prepared using prepreg compression molding technology. Fiber Bragg grating sensors were embedded into the UGRPs along the fiber direction and perpendicular to the fiber direction during the preparation process. The residual strain ε of the UGRPs along the fiber direction was obtained using a fiber Bragg grating interrogator. 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. Using a transmission terahertz time-domain spectroscopy system, the transmission signal of the non-unidirectional glass fiber reinforced polymer is used as a reference signal. The unidirectional glass fiber reinforced polymer is rotated so that the polarization directions of the terahertz wave are along the fiber direction and perpendicular to the fiber direction, respectively. The transmission signal of air-unidirectional glass fiber reinforced polymer-air is used as a sample signal. The reference signal and the sample signal are Fourier transformed to obtain their frequency domain signals. The phase change of the reference signal and the sample signal is obtained, and then the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction is calculated. x and the refractive index n perpendicular to the fiber direction y ;

[0007] S3, establish the propagation model of terahertz wave under different stress states of unidirectional glass fiber reinforced polymer; combine the residual stress σ of unidirectional glass fiber reinforced polymer along the fiber direction obtained in step S1 x and the residual stress perpendicular to the fiber direction σ 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 portion 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] Where 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 perpendicular to the fiber direction σ 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, a universal testing machine was used to measure the elastic modulus E of unidirectional glass fiber reinforced polymer along the fiber direction. 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 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.

[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 advantages: The present invention provides a method for detecting the optical stress coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy, which calculates the residual stress σ of unidirectional glass fiber reinforced polymer along the fiber direction. x and the residual stress perpendicular to the fiber direction σ 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 A terahertz wave propagation model was established for unidirectional glass fiber reinforced polymers under different stress states, and the stress optical coefficient of the unidirectional glass fiber reinforced polymers was calculated. This method can effectively detect the stress optical coefficient of unidirectional glass fiber reinforced polymers, thereby achieving high-precision nondestructive testing of residual stress in unidirectional glass fiber reinforced polymers. 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 Schematic diagram of the working principle of the fiber Bragg grating in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the structure of a transmission terahertz time-domain spectroscopy system according to 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 perpendicular to the fiber direction σ 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 embodiment 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 with reference to 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 meaning as 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, they indicate 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. Unidirectional glass fiber reinforced polymers (UGRPs) at different curing temperatures were prepared using prepreg compression molding technology. Fiber Bragg grating sensors were embedded into the UGRPs along the fiber direction and perpendicular to the fiber direction during the preparation process. The residual strain ε of the UGRPs along the fiber direction was obtained using a fiber Bragg grating interrogator. 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 perpendicular to the fiber direction σ 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 only reflects light with a wavelength corresponding to the effective refractive index. Based on this, 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] Where 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 perpendicular to the fiber direction σ 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 is measured using a universal testing machine. x and the elastic modulus E perpendicular to the fiber direction y .

[0046] S2. Using a transmission terahertz time-domain spectroscopy system, the transmission signal of the non-unidirectional glass fiber reinforced polymer is used as a reference signal. The unidirectional glass fiber reinforced polymer is rotated so that the polarization directions of the terahertz wave are along the fiber direction and perpendicular to the fiber direction, respectively. The transmission signal of air-unidirectional glass fiber reinforced polymer-air is used as a sample signal. The reference signal and the sample signal are Fourier transformed to obtain their frequency domain signals. The phase change of the reference signal and the sample signal is obtained, and then the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction is calculated. 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, a fiber attenuator, a terahertz transmitter, a unidirectional glass fiber reinforced polymer (GFRP), a terahertz receiver, and a delay line. The laser light emitted by the femtosecond laser is split into two paths via an optical fiber: one path is directed to the terahertz transmitter, and the other path, which serves as a delay line, is directed to the terahertz receiver. The terahertz waves emitted by the terahertz transmitter travel through the unidirectional glass fiber reinforced polymer to the terahertz receiver. The transmission-type terahertz time-domain spectroscopy system utilizes all-fiber transmission.

[0048] Specifically, the refractive index n of 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 the propagation model of terahertz wave under different stress states of unidirectional glass fiber reinforced polymer; combine the residual stress σ of unidirectional glass fiber reinforced polymer along the fiber direction obtained in step S1 x and the residual stress perpendicular to the fiber direction σ 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 perpendicular to the fiber direction σ 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 is x and the residual stress perpendicular to the fiber direction σ y Three measurements were performed and the average value was taken to determine the refractive index n along the fiber direction. x and the refractive index n perpendicular to the fiber direction y Measure five times and take the average value.

[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 experimental results prove that the method can effectively measure the stress-optical coefficient q of unidirectional glass fiber reinforced polymer, and has strong practicability and broad application prospect.

[0065] The above is only a preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any skilled person in the art can modify or change the above disclosed technical content to equivalent embodiments. However, any simple modification, equivalent change and modification made on the basis of the technical essence of the present application without departing from the technical solution of the present application still falls within the protection scope of the present application.

Claims

1. A method for detecting the optical stress coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy, characterized in that: The following steps are involved: S1. Unidirectional glass fiber reinforced polymers (UGRPs) at different curing temperatures were prepared using prepreg compression molding technology. Fiber Bragg grating sensors were embedded into the UGRPs along the fiber direction and perpendicular to the fiber direction during the preparation process. The residual strain ε of the UGRPs along the fiber direction was obtained using a fiber Bragg grating interrogator. 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. Using a transmission terahertz time-domain spectroscopy system, the transmission signal of the non-unidirectional glass fiber reinforced polymer is used as a reference signal. The unidirectional glass fiber reinforced polymer is rotated so that the polarization directions of the terahertz wave are along the fiber direction and perpendicular to the fiber direction, respectively. The transmission signal of air-unidirectional glass fiber reinforced polymer-air is used as a sample signal. The reference signal and the sample signal are Fourier transformed to obtain their frequency domain signals. The phase change of the reference signal and the sample signal is obtained, and then the refractive index n of the unidirectional glass fiber reinforced polymer along the fiber direction is calculated. x and the refractive index n perpendicular to the fiber direction y ; S3, establish the propagation model of terahertz wave under different stress states of unidirectional glass fiber reinforced polymer; combine the residual stress σ of 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; 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 All are stress optical coefficients; 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 split into two paths via an optical fiber, one path being directed to the terahertz transmitter, and the other path being directed to the terahertz receiver as a delay line. The terahertz wave emitted by the terahertz transmitter is directed to the terahertz receiver through the 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, 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 optical stress coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, characterized in that: In the step S1, only the grating portion of the fiber Bragg grating sensor is embedded in the unidirectional glass fiber reinforced polymer.

4. The method for detecting the optical stress coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, characterized in that: In the 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: Where 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 optical stress coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, 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 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 optical stress coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 5, 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 the optical stress coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, characterized in that: In the 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, and δ0 is the phase of the reference signal.

8. The method for detecting the optical stress coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy according to claim 1, characterized in that: The transmission-type terahertz time-domain spectroscopy system adopts an all-fiber transmission mode.

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