CN119164917A - Detection method of stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy - Google Patents
Detection method of stress optical coefficient of unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy Download PDFInfo
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- 229920002430 Fibre-reinforced plastic Polymers 0.000 title claims abstract description 128
- 239000003365 glass fiber Substances 0.000 title claims abstract description 128
- 230000003287 optical effect Effects 0.000 title claims abstract description 32
- 238000001328 terahertz time-domain spectroscopy Methods 0.000 title claims abstract description 24
- 238000001514 detection method Methods 0.000 title abstract description 8
- 239000000835 fiber Substances 0.000 claims abstract description 132
- 238000000034 method Methods 0.000 claims abstract description 19
- 239000013307 optical fiber Substances 0.000 claims abstract description 11
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- 230000005540 biological transmission Effects 0.000 claims description 18
- 230000010287 polarization Effects 0.000 claims description 9
- 230000008859 change Effects 0.000 claims description 8
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- 230000035945 sensitivity Effects 0.000 claims description 6
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- 238000001228 spectrum Methods 0.000 description 9
- 238000010586 diagram Methods 0.000 description 6
- 238000005259 measurement Methods 0.000 description 4
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- 238000004519 manufacturing process Methods 0.000 description 1
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- 238000009659 non-destructive testing Methods 0.000 description 1
- 239000011160 polymer matrix composite Substances 0.000 description 1
- 238000004451 qualitative analysis Methods 0.000 description 1
- 238000004445 quantitative analysis Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
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- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
- G01N21/3586—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation by Terahertz time domain spectroscopy [THz-TDS]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/0047—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes measuring forces due to residual stresses
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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Abstract
The invention relates to a terahertz time-domain spectroscopy-based unidirectional glass fiber reinforced polymer stress optical coefficient detection method which comprises the steps of S1, preparing unidirectional glass fiber reinforced polymers at different curing temperatures, embedding optical fiber Bragg gratings in the fiber direction and the vertical fiber direction in the preparation process, obtaining residual strain epsilon x、εy of the unidirectional glass fiber reinforced polymers in the fiber direction and the vertical fiber direction, further calculating residual stress sigma x、σy in the fiber direction and the vertical fiber direction, S2, obtaining refractive indexes n x、ny of the unidirectional glass fiber reinforced polymers in the fiber direction and the vertical fiber direction based on a transmission-type terahertz time-domain spectroscopy system, S3, establishing a propagation model of terahertz waves in different stress states of the unidirectional glass fiber reinforced polymers, and calculating the stress optical coefficient of the unidirectional glass fiber reinforced polymers by combining sigma x、σy、nx、ny. The method is favorable for accurately detecting the stress optical coefficient of the unidirectional glass fiber reinforced polymer.
Description
Technical Field
The invention belongs to the technical field of nondestructive testing, and particularly relates to a unidirectional glass fiber reinforced polymer stress optical coefficient detection method based on terahertz time-domain spectroscopy.
Background
The glass fiber reinforced polymer matrix composite material has wide application in the field of high-end equipment manufacturing by virtue of the advantages of light material, high strength, corrosion resistance and the like. Characterization of the residual stress of unidirectional glass fiber reinforced polymers is critical because the residual stress generated during curing and molding of unidirectional glass fiber reinforced polymers affects their performance and lifetime. Although the terahertz time-domain spectrum is widely researched and reported in stress measurement of materials such as ceramics and rubber, the application of the terahertz time-domain spectrum in the aspect of the residual stress of unidirectional glass fiber reinforced polymers is still fresh, and the stress optical coefficient is used as a core parameter for connecting the terahertz time-domain spectrum with the residual stress, and the research on the stress optical coefficient of the unidirectional glass fiber reinforced polymers is lacking at present, so that certain difficulty exists in using the terahertz time-domain spectrum to characterize the residual stress of the unidirectional glass fiber reinforced polymers, so that the terahertz time-domain spectrum evaluation system of the residual stress of the unidirectional glass fiber reinforced polymers is inaccurate, has lower reliability, can only be used as qualitative analysis, has lower referent degree in quantitative analysis, and therefore, the stress optical coefficient of the unidirectional glass fiber reinforced polymers needs to be calibrated through experimental means.
Disclosure of Invention
The invention aims to provide a method for detecting the stress optical coefficient of a unidirectional glass fiber reinforced polymer based on terahertz time-domain spectroscopy, which is favorable for accurately detecting the stress optical coefficient of the unidirectional glass fiber reinforced polymer.
In order to achieve the aim, the technical scheme adopted by the invention is that the unidirectional glass fiber reinforced polymer stress optical coefficient detection method based on terahertz time-domain spectroscopy comprises the following steps:
S1, preparing unidirectional glass fiber reinforced polymers at different curing temperatures by adopting a prepreg compression molding technology, and embedding an optical fiber Bragg grating sensor into the unidirectional glass fiber reinforced polymers along the fiber direction and the vertical fiber direction in the preparation process respectively, wherein the residual strain epsilon x of the unidirectional glass fiber reinforced polymers along the fiber direction and the residual strain epsilon y of the unidirectional glass fiber reinforced polymers along the vertical fiber direction are obtained through an optical fiber grating demodulator, and further the residual stress sigma x of the unidirectional glass fiber reinforced polymers along the fiber direction and the residual stress sigma y of the unidirectional glass fiber reinforced polymers along the vertical fiber direction are calculated;
S2, adopting a transmission type terahertz time-domain spectrum system, using a transmission signal without unidirectional glass fiber reinforced polymer as a reference signal, rotating the unidirectional glass fiber reinforced polymer to enable the polarization direction of terahertz waves to be along the fiber direction and the vertical fiber direction respectively, using the transmission signal of air-unidirectional glass fiber reinforced polymer-air as a sample signal, carrying out Fourier transformation on the reference signal and the sample signal to obtain frequency domain signals of the reference signal and the sample signal, thereby obtaining the phase change of the reference signal and the sample signal, and further calculating the refractive index n x of the unidirectional glass fiber reinforced polymer along the fiber direction and the refractive index n y of the unidirectional glass fiber reinforced polymer along the vertical fiber direction;
And S3, establishing a propagation model of the terahertz waves under 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 the residual stress sigma x of the unidirectional glass fiber reinforced polymer along the fiber direction and the residual stress sigma y of the unidirectional glass fiber reinforced polymer vertical to the fiber direction, the refractive index n x of the unidirectional glass fiber reinforced polymer along the fiber direction and the refractive index n y of the unidirectional glass fiber reinforced polymer vertical to the fiber direction, which are obtained in the step S2.
Further, in the step S1, the residual strain epsilon x of the unidirectional glass fiber reinforced polymer along the fiber direction and the residual strain epsilon y perpendicular to the fiber direction are regulated and controlled by changing the curing temperature.
Further, in the step S1, only the grating portion of the fiber bragg grating sensor is embedded in the unidirectional glass fiber reinforced polymer.
Further, in the step S1, the method for calculating the residual strain epsilon x of the unidirectional glass fiber reinforced polymer along the fiber direction and the residual strain epsilon y perpendicular to the fiber direction includes:
Wherein Deltalambda x is the central wavelength variation value of the reflected light of the fiber Bragg grating embedded along the fiber direction, deltalambda y is the central wavelength variation value of the reflected light of the fiber Bragg grating embedded along the vertical fiber direction, K ε is the strain sensitivity coefficient, K T is the temperature sensitivity coefficient, and DeltaT is the temperature variation.
Further, in the step S1, the calculation method of the residual stress σ x of the unidirectional glass fiber reinforced polymer along the fiber direction and the residual stress σ y perpendicular to the fiber direction is as follows:
σx＝Ex·εx
σy＝Ey·εy
Wherein E x is the elastic modulus of the unidirectional glass fiber reinforced polymer along the fiber direction, and E y is the elastic modulus of the unidirectional glass fiber reinforced polymer perpendicular to the fiber direction.
Further, the elastic modulus E x of the unidirectional glass fiber-reinforced polymer in the fiber direction and the elastic modulus E y in the perpendicular fiber direction were measured using a universal tester.
Further, in the step S2, the calculation method of the refractive index n x of the unidirectional glass fiber reinforced polymer along the fiber direction and the refractive index n y perpendicular to the fiber direction is as follows:
Where c is the speed of light in vacuum, f is the frequency, d is the thickness of the unidirectional glass fiber reinforced polymer, 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 δ 0 is the phase of the reference signal.
Further, in the step S3, a propagation model of the terahertz wave in different stress states of the unidirectional glass fiber reinforced polymer is as follows:
ΔNx＝q11Δσx+q12Δσy
ΔNy＝q21Δσx+q22Δσy
Wherein q 11、q12、q21、q22 are stress optical coefficients.
The transmission type terahertz time-domain spectrum 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, wherein laser emitted by the femtosecond laser is divided into two paths through the optical fiber, one path of the laser is emitted to the terahertz transmitter, the other path of the laser is emitted to the terahertz receiver as the delay line, and terahertz waves emitted by the terahertz transmitter are emitted to the terahertz receiver through the unidirectional glass fiber reinforced polymer.
Further, the transmission type terahertz time-domain spectroscopy system adopts an all-fiber transmission mode.
Compared with the prior art, the method has the beneficial effects that the method for detecting the stress optical coefficient of the unidirectional glass fiber reinforced polymer based on the terahertz time-domain spectrum has the advantages that the residual stress sigma x of the unidirectional glass fiber reinforced polymer along the fiber direction and the residual stress sigma y of the unidirectional glass fiber reinforced polymer perpendicular to the fiber direction are calculated, the refractive index n x of the unidirectional glass fiber reinforced polymer along the fiber direction and the refractive index n y of the unidirectional glass fiber reinforced polymer perpendicular to the fiber direction are calculated, a propagation model of terahertz waves under different stress states of the unidirectional glass fiber reinforced polymer is built, and then the stress optical coefficient of the unidirectional glass fiber reinforced polymer is calculated. The method can effectively realize the detection of the stress optical coefficient of the unidirectional glass fiber reinforced polymer, and further realize the high-precision nondestructive detection of the residual stress of the unidirectional glass fiber reinforced polymer.
Drawings
FIG. 1 is a schematic diagram of a fiber grating demodulator according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the operation of a fiber Bragg grating according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a transmission terahertz time-domain spectroscopy system in an embodiment of the invention;
FIG. 4 is a schematic diagram of the residual stress σ x of the unidirectional glass fiber-reinforced polymer along the fiber direction and the residual stress σ y perpendicular to the fiber direction at different curing temperatures in the embodiment of the invention;
Fig. 5 is a schematic view of refractive index n x of unidirectional glass fiber reinforced polymer along fiber direction and refractive index n y perpendicular to fiber direction at different curing temperatures in the embodiment of the present invention.
Detailed Description
The invention will be further described with reference to the accompanying drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
The embodiment provides a 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 by adopting a prepreg compression molding technology, embedding optical fiber Bragg grating sensors into the unidirectional glass fiber reinforced polymers along the fiber direction and the vertical fiber direction in the preparation process, obtaining residual strain epsilon x of the unidirectional glass fiber reinforced polymers along the fiber direction and residual strain epsilon y of the unidirectional glass fiber reinforced polymers along the vertical fiber direction by using an optical fiber Bragg grating demodulator, and further calculating residual stress sigma x of the unidirectional glass fiber reinforced polymers along the fiber direction and residual stress sigma y of the unidirectional glass fiber reinforced polymers along the vertical fiber direction.
In this embodiment, as shown in fig. 1, 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, and the residual strain epsilon x of the unidirectional glass fiber reinforced polymer along the fiber direction and the residual strain epsilon y perpendicular to the fiber direction are regulated by changing the curing temperature. As shown in fig. 2, the fiber bragg grating has wavelength selectivity, so the grating reflects only light of a wavelength corresponding to the effective refractive index, and the amount of change in the center wavelength of the reflected light is analyzed based on this.
Specifically, the method for calculating the residual strain epsilon x of the unidirectional glass fiber reinforced polymer along the fiber direction and the residual strain epsilon y perpendicular to the fiber direction comprises the following steps:
The method comprises the steps of setting delta lambda x as a central wavelength change value of reflected light of the fiber Bragg grating embedded in the fiber direction, setting delta lambda y as a central wavelength change value of reflected light of the fiber Bragg grating embedded in the vertical fiber direction, setting K ε as a strain sensitivity coefficient, setting K ε＝-0.0012MPa/℃;KT as a temperature sensitivity coefficient, setting K T = -0.0095MPa/°C, and setting delta T as a temperature change amount.
The calculation method of the residual stress sigma x of the unidirectional glass fiber reinforced polymer along the fiber direction and the residual stress sigma y perpendicular to the fiber direction comprises the following steps:
σx＝Ex·εx
σy＝Ey·εy
Wherein E x is the elastic modulus of the unidirectional glass fiber reinforced polymer along the fiber direction, and E y is the elastic modulus of the unidirectional glass fiber reinforced polymer perpendicular to the fiber direction. The elastic modulus E x of the unidirectional glass fiber-reinforced polymer in the fiber direction and the elastic modulus E y in the perpendicular fiber direction were measured using a universal tester.
S2, adopting a transmission type terahertz time-domain spectrum system, using a transmission signal without unidirectional glass fiber reinforced polymer as a reference signal, rotating the unidirectional glass fiber reinforced polymer to enable the polarization direction of terahertz waves to be along the fiber direction and the vertical fiber direction, using the transmission signal of air-unidirectional glass fiber reinforced polymer-air as a sample signal, carrying out Fourier transformation on the reference signal and the sample signal to obtain frequency domain signals of the reference signal and the sample signal, and further calculating the refractive index n x of the unidirectional glass fiber reinforced polymer along the fiber direction and the refractive index n y of the unidirectional glass fiber reinforced polymer along the vertical fiber direction.
As shown in fig. 3, the transmission 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 emitted by the femtosecond laser is divided into two paths through an optical fiber, one path of the laser is emitted to the terahertz transmitter, and the other path of the laser is emitted to the terahertz receiver as a delay line. Terahertz waves emitted by the terahertz transmitter are transmitted to the terahertz receiver through the unidirectional glass fiber reinforced polymer. The transmission type terahertz time-domain spectroscopy system adopts an all-fiber transmission mode.
Specifically, the calculation method of the refractive index n x of the unidirectional glass fiber reinforced polymer along the fiber direction and the refractive index n y perpendicular to the fiber direction is as follows:
Where c is the speed of light in vacuum, f is the frequency, d is the thickness of the unidirectional glass fiber reinforced polymer, 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 δ 0 is the phase of the reference signal.
And S3, establishing a propagation model of the terahertz waves under different stress states of the unidirectional glass fiber reinforced polymer, and calculating the stress optical coefficients of the unidirectional glass fiber reinforced polymer by a multiple linear regression method by combining the residual stress sigma x of the unidirectional glass fiber reinforced polymer along the fiber direction and the residual stress sigma y of the unidirectional glass fiber reinforced polymer vertical to the fiber direction, the refractive index n x of the unidirectional glass fiber reinforced polymer along the fiber direction and the refractive index n y of the unidirectional glass fiber reinforced polymer vertical to the fiber direction, which are obtained in the step S2.
Specifically, the propagation model of terahertz waves in different stress states of the unidirectional glass fiber reinforced polymer is as follows:
ΔNx＝q11Δσx+q12Δσy
ΔNy＝q21Δσx+q22Δσy
Wherein q 11、q12、q21、q22 are stress optical coefficients.
Fig. 4 is a schematic diagram of the residual stress σ x of the unidirectional glass fiber reinforced polymer along the fiber direction and the residual stress σ y perpendicular to the fiber direction at different curing temperatures in this example. Fig. 5 is a schematic diagram of refractive index n x of unidirectional glass fiber reinforced polymer along fiber direction and refractive index n y perpendicular to fiber direction at different curing temperatures in this example. The measurement results of the residual stress and refractive index are shown in table 1, and in each set of curing temperature experimental tests, the residual stress σ x in the fiber direction and the residual stress σ y in the perpendicular fiber direction were measured three times and averaged, and the refractive index n x in the fiber direction and the refractive index n y in the perpendicular fiber direction were measured five times and averaged.
TABLE 1 measurement of residual stress and refractive index of unidirectional glass fiber reinforced polymer
From the above data, the stress-optical coefficients of unidirectional glass fiber reinforced polymers can be calculated as shown in tables 2 and 3:
TABLE 2 calculation of the stress-optical coefficient q 11、q12 of unidirectional glass fiber reinforced polymer
TABLE 3 calculation of the stress-optical coefficients q 21、q22 for unidirectional glass fiber reinforced polymers
The experimental result proves that the method can effectively realize the measurement of the stress optical coefficient of the unidirectional glass fiber reinforced polymer, and has stronger practicability and wide application prospect.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the invention in any way, and any person skilled in the art may make modifications or alterations to the disclosed technical content to the equivalent embodiments. However, any simple modification, equivalent variation and variation of the above embodiments according to the technical substance of the present invention still fall within the protection scope of the technical solution of the present invention.
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