CN104807698B - A kind of method of testing of continuous fiber reinforced composites Poisson's ratio - Google Patents

Abstract

The invention discloses a method for testing the Poisson's ratio of a continuous fiber-reinforced resin-based composite material. New FBG test method for Poisson's ratio of composite materials; (2) Solve the problems of poor surface quality, uneven thickness, uneven width, and poor parallelism caused by traditional composite material specimen vacuum bag and autoclave manufacturing techniques The problem is to provide a continuous fiber-reinforced resin-based composite material standard specimen manufacturing technology based on closed hot molding technology, focusing on solving the problem of separation between the composite material standard specimen and the rigid closed mold with embedded fiber Bragg grating strings, and realizing composite materials. Convenient, accurate and effective test of Poisson's ratio.

Description

A Test Method for Poisson's Ratio of Continuous Fiber Reinforced Resin Matrix Composites

technical field

The invention relates to a method for testing the Poisson ratio of a material, in particular to a method for testing the Poisson ratio of a continuous fiber reinforced resin matrix composite material.

Background technique

Fiber-reinforced resin-based composites are widely used in aerospace, automobiles, ships, construction and other fields due to their high specific strength and specific modulus, good chemical corrosion resistance, and strong designability. Among them, carbon fiber reinforced resin-based composite materials have a density of only about 1.6g/cm ³ and superior performance, and are expected to become one of the main materials for new energy vehicles and aircraft.

To carry out the research on structural mechanics of composite materials, the first problem to be solved is the accurate measurement of engineering elastic constants such as Poisson's ratio and modulus of composite materials; when using classical laminate theory to analyze and evaluate structural mechanics of composite materials, the first problem to be solved is Accurate characterization of Poisson's ratio, because Poisson's ratio is an important material parameter in structural design and analysis, which directly affects the calculated value of internal force and deformation of the structure. With the deepening of material research and application, modern methods for accurately determining Poisson's ratio have attracted more and more researchers' attention. The Poisson's ratio test itself has high precision requirements for equipment and standard specimens. For example, the surface quality requirements of continuous fiber-reinforced resin matrix composite standard specimens are high, and the surface and edges should be free of scratches, voids, depressions and burrs; the specimens should be free of distortion, and adjacent planes should be perpendicular to each other; There should be no delamination failure and fiber breakage. This requires test piece preparation equipment and molds to produce high-quality standard test pieces.

At present, the most widely used method for determining Poisson's ratio of composite materials is to use various extensometers and secondary instruments to collect data to obtain longitudinal and transverse strain data, thereby measuring Poisson's ratio. However, the large self-weight and clamping force of the extensometer will cause additional deformation of the soft sample, resulting in low test accuracy and unstable measurement values; moreover, if it is necessary to use this method to measure the Poisson's ratio of composite materials at higher temperatures, It is required that the displacement measuring element must be resistant to high temperature, which is a difficult technical problem to solve at present. In recent years, the micro-indentation method with higher testing accuracy has begun to emerge, but no matter how small the indentation amount is, it will cause plastic deformation, and the stress and strain of the material are quite complicated during the indenter pressing process. Regarding the test method of pasting moiré sheets or resistance sheets on the surface of the specimen, the area of the strain gauge, the quality of the pasting, and the position and direction of the patch are likely to increase the measurement error, and the measurement range is limited, the cost is high, and it is difficult to apply under high temperature conditions. . Acoustic methods can basically achieve non-destructive testing, but because of the large acoustic resistance and internal damping of non-metallic materials, it is difficult to test sound velocity and vibration, and this method cannot guarantee that the test is carried out within the elastic limit. Optical interferometry generally requires the specimen to be optically smooth, which requires precise surface polishing, which increases the workload and difficulty of the experiment.

As a sensor element with excellent performance, fiber Bragg grating (FBG) senses the change of external temperature or stress through the movement of reflection wavelength, and the movement of reflection wavelength has a good linear relationship with strain; in addition, it has high sensitivity, Excellent corrosion resistance, high and low temperature resistance, strong anti-interference ability, small size and light weight, almost no impact on the structure, stable and reliable test data and flexible optical path, etc., can be pre-embedded in the preparation process of composite materials It can penetrate into the interior of the composite material structure and accurately measure the longitudinal and transverse strain inside the structure at the same time, which has advantages and broad application prospects that cannot be achieved by other methods.

According to a series of advantages of the FBG sensor, the researchers embedded a single longitudinal and transverse FBG sensor in the central position of the composite material specimen in the length, width, and thickness directions; The Poisson's ratio measurement experiment is carried out on the material testing machine, and the longitudinal strain and transverse strain of the composite material standard specimen are measured by using the corresponding relationship between the FBG central wavelength change and the strain, and then the Poisson's ratio test result of the composite material specimen is obtained. However, there are a series of key core problems in the method of using a single longitudinal and transverse FBG sensor to test the Poisson's ratio of composite materials. Take the "Fiber Bragg Grating of Composite Laminate Engineering Constants" paper by Wang Kaige and Mei Zhiyuan "Test and Analysis" as an example is as follows: (1) The distance between the bending position of the fiber in the transverse direction (90° direction of the fiber) and the grating area is too close, which may easily cause the deformation of the grating area to generate chirp signals, and the optical signal intensity attenuation is serious, resulting in lateral The accuracy of the strain test is greatly reduced; (2) The position of the lead wire conflicts with the position of the fixture of the universal material testing machine. When the optical fiber is led out from the fixture of the testing machine, it needs to be bent significantly, resulting in attenuation of the optical signal intensity and a decrease in test accuracy; (3) Transverse grating No protective measures are added during laying, which will easily cause the grating to be sheared and damaged by the uneven reinforcing fibers perpendicular to it; (4) only one grating area is used to measure the micro-strain of the composite material standard specimen in the horizontal and vertical directions, so that it cannot Averaging the uneven spatial distribution of the material Poisson's ratio in the same sample will bring large errors to the experimental results.

Fiber Bragg grating string technology is to write multiple Bragg gratings with different central wavelengths at intervals on a single fiber to form a grating string to meet the needs of long-distance measurement or multi-point measurement. Errors caused by multiple layouts during a single grating test improve the reliability and stability of the measurement system, and the number and spacing of grating areas can be set according to actual needs. At the same time, multiple grating strings can form a sensor network to realize quasi-distributed measurement. In addition, the use of fiber Bragg grating series can also make the handling of lead wires easier and more convenient.

In order to ensure that the FBG sensor can effectively, accurately and conveniently detect the Poisson's ratio of continuous fiber-reinforced resin matrix composites (that is, transversely isotropic composites), enabling researchers to reliably design, analyze, and evaluate composite structures , it is of great significance to develop the fiber Bragg grating string testing method for Poisson's ratio of composite materials.

Contents of the invention

The purpose of the invention is: (1) overcome the deficiency of existing composite material Poisson's ratio test technology, provide a kind of FBG test method of new composite material Poisson's ratio based on fiber Bragg grating series technology; (2) solve traditional Composite material specimen vacuum bag, autoclave manufacturing technology caused poor surface quality, uneven thickness, uneven width, poor parallelism and other problems, based on closed hot molding technology to provide a continuous fiber reinforced resin matrix composite material Specimen manufacturing technology focuses on solving the problem of detachment of composite material specimens with embedded fiber Bragg grating strings and rigid closed molds, and realizes convenient, accurate and effective testing of Poisson's ratio of composite materials.

The technical scheme that the present invention takes is:

A method for testing the Poisson's ratio of a continuous fiber reinforced resin matrix composite, comprising the following steps:

1) Fabrication of composite material standard test piece: wrap PTFE tape and PTFE cloth on the mold side wall frame plate and its lead groove in sequence; lay N layers (N≥20 ) resin-based composite material prepreg, and laying a plurality of optical fiber Bragg grating strings along the fiber direction and perpendicular to the fiber direction on different prepreg layers; then, curing molding;

2) Demoulding: Clean up the resin around the fiber grating lead wire, keep the lead wire straight, and pull the exposed part of the PTFE cloth to demould the composite material part;

3) Test: Under the condition of constant temperature, place the demolded composite material standard specimen in the universal material testing machine to measure Poisson’s ratio, and act on the normal stress σ _j in the j direction (fiber 0° direction) alone, without other external force;

4) Data processing: process the central wavelength data of the grating area collected in real time, obtain the time-varying curve of the central wavelength of each grating area of the fiber Bragg grating string, and obtain the composite material according to the corresponding relationship between the grating central wavelength variation and micro-strain The longitudinal micro-strain and transverse micro-strain of the standard specimen are then calculated to obtain Poisson's ratio ν.

Preferably, in step 1), the specific step of laying a plurality of fiber Bragg grating strings along the fiber direction and perpendicular to the fiber direction on different prepreg layers is that the nth layer (N-10>n> 5) Lay multiple fiber Bragg grating strings in the longitudinal direction (fiber 0° direction), and lay multiple Fiber Bragg grating strings protected by dipping materials.

Preferably, in step 1), the curing molding method is a composite material thermal compression molding method.

Preferably, in step 1), the grating region of the fiber Bragg grating string cannot be set at the intersection point of the fiber Bragg grating string in the 0° and 90° directions.

Preferably, in step 1), 2 to 6 grating regions are distributed on the fiber Bragg grating string.

Preferably, in step 1), the thickness of the narrow strip-shaped and homodirectional prepreg is the same as that of the whole prepreg.

Preferably, in step 1), the laying position of the fiber Bragg grating string is at the center of the specimen, but it should be noted that there are at least 5 layers of prepreg between the fiber Bragg grating strings in the 0° and 90° directions.

Preferably, in step 1), the lead wires of the fiber Bragg grating series parallel to the fiber direction are bent in a region close to the end of the test piece, and are uniformly led out from one side.

Preferably, the pigtail of the fiber Bragg grating string is protected by a Teflon tube.

Preferably, in step 3), during the test, the tensile loading speed does not exceed 5mm/min.

The grating area of the fiber Bragg grating string described in step 1) of the above test method cannot be set at the cross point of the fiber Bragg grating string in the 0° and 90° directions. 2 to 6 grating areas are distributed on the optical fiber Bragg grating string for strain detection. The pigtail is protected by a Teflon tube, so that the fiber Bragg grating string can be used for a long time in the range of -80°C to 280°C. The thickness of the narrow strip-shaped prepreg used to protect the transverse grating area is the same as that of the whole prepreg, which is 0.1-0.2mm, rectangular in shape, 35-40mm in length and 5-10mm in width. The laying position of the fiber Bragg grating string is in the center of the specimen, but it should be noted that there are at least 5 layers of prepreg between the fiber Bragg grating strings in the 0° and 90° directions to avoid mutual interference between the two. The lead wires of the longitudinal fiber Bragg grating strings are bent near the end of the specimen, with a bending radius of 2cm, and are uniformly drawn out from one side to avoid conflict with the fixture of the universal material testing machine, so that the lead wires can be connected to the optical fiber in an orderly and convenient manner Grating demodulator, while ensuring the optical signal strength. The reason for wrapping a layer of polytetrafluoroethylene tape on the entire mold frame and its lead groove is that the melting point of polytetrafluoroethylene is as high as 327 ° C, so it will not melt during the high-temperature curing of the composite material; polytetrafluoroethylene has many advantages Performance, such as chemical stability, solvent resistance, oxidation resistance, long-term use at 260 ° C, etc.; especially its poor bonding performance, it does not adhere to epoxy resin or metal mold frame, which makes demoulding easy to operate. Coating a layer of polytetrafluoroethylene cloth can increase the sliding ability between the composite material and the metal frame, and facilitate demoulding. The hot molding process is set according to the needs, for example: firstly, the temperature is raised from room temperature to 80°C, and the temperature is kept for 30 minutes, and then the temperature is raised to 130°C, and the temperature is kept for 60 minutes; the pressure of the two stages is 0.5Mpa.

The tensile loading speed in the above step 3) is not more than 5mm/min; since the elongation at break of a single carbon fiber is about 1%, the strain range of the composite material in the tensile test is controlled to be 0.5% to 0.6%, so as to ensure that it is Poisson's ratio is determined within the elastic limit of the composite.

A kind of preparation method of the standard test piece of Poisson's ratio of continuous fiber reinforced resin matrix composite material, adopts following steps:

1) Fabrication of composite material standard test piece: wrap PTFE tape and PTFE cloth on the mold side wall frame plate and its lead groove in sequence; lay N layers (N≥20 ) resin-based composite material prepreg, and a plurality of fiber Bragg grating strings along the fiber direction and perpendicular to the fiber direction are respectively laid on different prepreg layers; the lead wires of the fiber Bragg grating strings parallel to the fiber direction are The area close to the end of the specimen is bent and uniformly drawn from one side; then, it is solidified and formed;

2) Demoulding: Clean up the resin around the fiber grating lead wire, keep the lead wire straight, pull the exposed part of the PTFE cloth, and demould the composite material, that is, the Poisson's ratio of the continuous fiber reinforced resin matrix composite material Standard test piece.

The beneficial effects of the present invention are:

(1) The present invention effectively solves the phenomenon of chirping optical signals and optical signal intensity attenuation caused by the deformation of the grating area easily caused by improper bending of optical fibers by rationally designing the way and position of the lead wires of the fiber Bragg grating strings drawn from the composite material specimen Serious problems, lower test accuracy, etc.; by rationally designing the embedding position of the fiber Bragg grating string in the composite material specimen, it effectively solves the problem of poor shear resistance of the grating area of the FBG sensor when detecting the Poisson’s ratio of the composite material, resulting in fragility and vulnerability. broken problem.

(2) By laying multiple fiber Bragg grating strings along the fiber direction and perpendicular to the fiber direction, the spatial multi-point synchronous measurement of the Poisson's ratio of continuous fiber-reinforced resin matrix composites is met. No welding is required, the position is accurate, and the test is improved. The reliability and stability of the system, and the number and spacing of the grating regions of each fiber Bragg grating string can be set according to actual needs.

(3) Before curing and forming, the side wall frame plate and its lead groove of the mold are covered with polytetrafluoroethylene tape and polytetrafluoroethylene cloth, which avoids the metal mold side wall frame plate and its lead groove and the composite material. Direct contact, and although the metal mold frame, PTFE tape and PTFE cloth are in contact but not bonded, they are easy to slip and are conducive to demoulding, effectively improving the surface quality and size of composite material standard test pieces Accuracy and survival of fiber Bragg grating strings embedded in composite materials.

(4) Use the same direction and narrow strip-shaped prepreg to embed the upper and lower sides of the fiber Bragg grating string in the transverse direction (90° direction of the fiber), which can protect the grating area and effectively prevent the fragile transverse grating area from being replaced by rigid and uneven gratings Longitudinal fiber shear failure.

The invention largely improves the problems of the traditional optical fiber Bragg grating lead wires are complex, difficult to lead out, and the grating area is easily deformed and easily damaged, making the FBG detection steps of the Poisson's ratio of the composite material simple and efficient; solving the problem of the traditional composite The surface quality of the material standard test piece is low, and the dimensional accuracy is poor; the grating area of the fiber Bragg grating string as a sensitive element is well protected, making the obtained data more comprehensive, accurate and reliable.

Description of drawings

Fig. 1 is the structure diagram of the device of the embodiment of the present invention (in order to show the composite material standard test piece and the optical fiber lead, the upper template is not drawn in the structure diagram of the device).

Figure 2(a) is a top view of the mold with lead grooves (in order to facilitate the observation of lead grooves, the upper template is deleted in this figure);

Fig. 2 (b) is the A-A direction view of the mold that has lead groove;

Figure 2 (c) is a mold covered with one deck of polytetrafluoroethylene adhesive tape and one deck of polytetrafluoroethylene cloth;

Figure 2(d) is a mold with part of the prepreg laid inside;

Figure 2 (e) is the laying method of the longitudinal fiber Bragg grating string inside the specimen;

Figure 2(f) is the laying method of the transverse fiber Bragg grating string inside the specimen;

Figure 2(g) shows the laying method of the transverse fiber Bragg grating strings protected by narrow strips and co-directional prepreg inside the specimen.

Among them, 1 is the prepreg, 2 is the fiber Bragg grating string laid in the longitudinal direction (fiber 0° direction) (the pigtail is protected by a Teflon tube), and 3 is the fiber Bragg grating string laid in the transverse direction (fiber 90° direction) (The pigtails are protected by Teflon tubes), 4 is the lead groove of the mold side wall frame plate, 5 is the mold side wall frame plate, 6 is a layer of polytetrafluoroethylene tape and a layer of polytetrafluoroethylene cloth, 7 is the lower template, and 8 is the narrow strip-shaped and homodirectional prepreg used to protect the transverse (fiber 90° direction) grating area.

specific implementation

The present invention will be further elaborated below in conjunction with the accompanying drawings. It should be noted that the following descriptions are only for explaining the present invention, and do not limit the content thereof.

Example 1:

A fiber Bragg grating string test method for the Poisson's ratio of a continuous fiber reinforced resin matrix composite material.

(1) Fabrication of composite material standard test piece: uniformly wrap a layer of polytetrafluoroethylene tape on the entire mold frame 5 and its lead groove 4, and then wrap a layer of polytetrafluoroethylene cloth. Lay N layers (N≥20) of resin-based composite material prepreg 1 in the mold cavity, and lay fiber Bragg grating strings on the two prepreg layers respectively, that is, the nth layer (N-10> n>5) A fiber Bragg grating string 2 is laid longitudinally (fiber 0° direction), and a narrow strip shape, same The fiber Bragg grating string 3 protected by the prepreg 8, the fiber direction of these narrow strips and the same direction of the prepreg 8 is the same as the fiber Bragg grating string 3, and the thickness is the same as the thickness of the whole prepreg, which is 0.1~ 0.2 mm, rectangular in shape; 6 grating areas are distributed on the longitudinal fiber Bragg grating string 2, and the distance between the grating area and the edge of the specimen should be at least 40 mm; 2 grating areas are distributed on the transverse fiber Bragg grating string 3, and the grating area and the edge of the specimen The distance should be at least 5mm; the pigtails should be protected by Teflon tubes, so that the fiber Bragg grating series can be used for a long time in the range of -80°C to 280°C. The curing method is a composite thermal molding method.

Specific implementation steps:

a) Wrap a layer of polytetrafluoroethylene tape evenly on the entire mold frame 5 and its lead groove 4, and then completely cover it with a layer of polytetrafluoroethylene cloth so that they are tightly attached to the mold side wall frame .

b) Use a prepreg cutting machine to cut the prepreg layer by layer parallel to the fiber direction (fiber 0° direction), and cut out the prepreg with the in-plane size of 260mm*40mm and the in-plane size of 40mm*10mm Narrow strip prepreg used to protect the grating area.

c) Lay the cut prepreg with an in-plane size of 260mm*40mm layer by layer as required in the mold cavity surrounded by the lower template 7 pre-coated with the release agent and the prepared mold frame 5, The layer mode is [0°] ₂₂ . During the laying process, lay a group of fiber Bragg grating strings 2 in the longitudinal direction (fiber 0° direction) on the 8th layer, which is used as an axial strain sensor; 1. The fiber Bragg grating string 3 protected by the same direction prepreg 8 is used as a transverse strain sensor. The lead wires of the fiber Bragg grating series 2 used as axial strain sensors are bent in the area close to the end of the specimen, with a bending radius of 2 cm, and are uniformly drawn out from one side to avoid conflicts between the lead wires and the clamps of the universal material testing machine, so that the lead wires can be Orderly and convenient access to the fiber grating demodulator to ensure the strength of the optical signal while avoiding the chirp phenomenon of the optical signal.

d) Cover the upper formwork pre-coated with release agent, close the mold, and put it into a vulcanizer; heat and pressurize, so that the prepreg is hot-pressed in a fully rigid closed mold to realize the curing of the composite material. The hot pressing process adopted is to continuously raise the temperature from room temperature to 80°C and keep it warm for 30 minutes, then continuously raise the temperature to 130°C and keep it warm for 60 minutes; the pressure in both stages is 0.5Mpa, and finally cool to room temperature to obtain solidified molded resin-based composites.

(2) Demoulding: Open the vulcanizing machine and clean the resin around the lead wires of the fiber Bragg grating string to prevent the fiber grating from being damaged due to the adhesion of the resin; keep the lead wires straight to avoid bending and affecting signal acquisition. The exposed part of the PTFE cloth is pulled to release the composite part from the mold.

(3) Test: Place the successfully demoulded composite material standard specimen in a universal testing machine to measure Poisson's ratio, and apply the tensile stress σ in the longitudinal direction alone without other external forces. The test loading speed is 2mm/min; since the elongation at break of a single carbon fiber is about 1%, the tensile ratio of the standard specimen in the tensile test is controlled to be 0.5% to 0.6%, so as to ensure that it is within the elastic limit range Determine Poisson's ratio.

Specific implementation steps:

a) Control the ambient temperature to ensure that the test is carried out under constant temperature conditions.

b) Put the standard test piece in the fixture, make sure that the long axis of the standard test piece is in line with the axis of the testing machine, apply prestress to the standard test piece, and slightly tighten the standard test piece; pre-strain ε≤0.05%.

c) Connect the FBG lead wires that were bent in the standard test piece in advance and led out from one side to the fiber Bragg grating demodulator.

d) Stretch the standard specimen at a loading speed of 2 mm/min until the strain reaches 0.5% to 0.6%; at the same time, dynamically collect the central wavelength data of the grating area in real time.

(4) Data processing: process the central wavelength data of the grating area collected in real time, and obtain the curve of the central wavelength of each grating area of the fiber Bragg grating string as a function of time; take the longitudinal reflection wavelength as the abscissa, and the transverse reflection wavelength as the ordinate , to get a relationship curve, the slope of this curve is the Poisson's ratio ν of the composite standard specimen.

Example 2:

A fiber Bragg grating string test method for the Poisson's ratio of a continuous fiber reinforced resin matrix composite material.

(1) Fabrication of composite material standard test piece: uniformly wrap a layer of polytetrafluoroethylene tape on the entire mold frame 5 and its lead groove 4, and then wrap a layer of polytetrafluoroethylene cloth. Lay N layers (N≥20) of resin-based composite material prepreg 1 in the mold cavity, and lay fiber Bragg grating strings on the two prepreg layers respectively, that is, the nth layer (N-10> n>5) Lay a fiber Bragg grating string 2 longitudinally (fiber 0° direction), and lay a narrow strip shape in the same direction on the n+i layer (N-14≥i>5) transversely (fiber 90° direction) Fiber Bragg grating strings 3 protected by prepregs 8. The fiber direction of these narrow strips and co-directional prepregs 8 is the same as that of fiber Bragg grating strings 3, and the thickness is the same as that of the entire prepreg, which is 0.1 to 0.2 mm, the shape is rectangular; 4 grating areas are distributed on the longitudinal fiber Bragg grating string 2, and the distance between the grating area and the edge of the specimen should be at least 40 mm; 2 grating areas are distributed on the transverse fiber Bragg grating string 3, and the grating area and the edge of the specimen should be at least 40 mm apart. At least 5mm apart; the pigtails are protected by Teflon tubes, so that the fiber Bragg grating series can be used for a long time in the range of -80°C to 280°C. The curing method is a composite thermal molding method.

Specific implementation steps:

a) Evenly wrap a layer of polytetrafluoroethylene tape on the entire mold side wall frame plate 5 and its lead groove 4, and then completely cover it with a single layer of polytetrafluoroethylene cloth, so that they are in contact with the mold side wall frame plate 5 Snug fit.

b) Use a prepreg cutting machine to cut the prepreg layer by layer parallel to the fiber direction (fiber 0° direction), and cut out the prepreg with an in-plane size of 260mm*40mm and the in-plane size of 40mm*10mm Narrow strip prepreg used to protect the grating area.

c) Lay the cut prepreg with an in-plane size of 260mm*40mm layer by layer according to the requirements, into the mold cavity surrounded by the lower template 7 pre-coated with the release agent and the prepared mold side wall frame plate 5 Inside, the layering method is [0°] ₂₀ . During the laying process, a group of fiber Bragg grating strings 2 is laid longitudinally on the sixth layer (fiber 0° direction) as an axial strain sensor; on the 12th layer transversely (fiber 90° direction) a set of 1. Fiber Bragg grating string 3 protected by prepreg material 8 in the same direction. Bend the lead wires of the longitudinal fiber Bragg grating string 2 with a bending radius of 2 cm, and uniformly lead them out from one side to avoid the conflict between the lead wires and the fixture of the universal material testing machine, so that the lead wires can be connected to the fiber grating demodulator in an orderly and convenient manner, ensuring Optical signal strength, while avoiding optical signal chirp phenomenon.

d) Cover the upper formwork pre-coated with release agent, close the mold, and put it into a vulcanizer; heat and pressurize, so that the prepreg is hot-pressed in a fully rigid closed mold to realize the curing of the composite material. The hot pressing process adopted is to continuously raise the temperature from room temperature to 80°C and keep it warm for 30 minutes, then continuously raise the temperature to 130°C and keep it warm for 60 minutes; the pressure in both stages is 0.5Mpa, and finally cool to room temperature to obtain solidified molded resin-based composites.

(2) Demolding: Open the vulcanizer, clean the resin around the lead wires of the fiber Bragg grating string to prevent it from damaging the fiber grating; keep the lead wires straight to avoid bending and affecting signal acquisition. Pull the exposed part of the PTFE cloth to release the composite part from the mold.

(3) Test: Place the successfully demoulded composite material standard specimen in a universal testing machine to measure Poisson's ratio, and apply the tensile stress σ in the longitudinal direction alone without other external forces. The test loading speed is 1mm/min; since the elongation at break of a single carbon fiber is about 1%, the tensile ratio of the standard specimen in the tensile test is controlled to be 0.5% to 0.6%, so as to ensure that it is within the elastic limit range Determine Poisson's ratio.

Specific implementation steps:

a) Control the ambient temperature to ensure that the test is carried out under constant temperature conditions.

b) Put the standard test piece in the fixture, make sure that the long axis of the standard test piece is in line with the axis of the testing machine, apply prestress to the standard test piece, and slightly tighten the standard test piece; pre-strain ε≤0.05%.

c) Connect the leads to the fiber grating demodulator.

d) Stretch the standard specimen at a loading speed of 1 mm/min until the strain reaches 0.5% to 0.6%; at the same time, dynamically collect the central wavelength data of the grating area in real time.

(4) Data processing: process the central wavelength data of the grating area collected in real time, obtain the curve of the central wavelength of each grating area of the fiber Bragg grating string changing with time, and obtain the compound according to the corresponding relationship between the grating central wavelength variation and micro-strain Longitudinal micro-strain and transverse micro-strain of material standard specimen, with longitudinal micro-strain as abscissa and transverse micro-strain as ordinate, a relationship curve is obtained, and the slope of this curve is Poisson’s ratio ν of composite material standard specimen.

Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (9)

1. a method for testing the Poisson's ratio of continuous fiber reinforced resin-based composite material, is characterized in that, comprises steps as follows: 1) Fabrication of composite material standard test pieces: Cover the polytetrafluoroethylene tape and polytetrafluoroethylene cloth on the mold side wall frame plate and its lead groove in turn; lay N layers of N≥20 resin in the mold cavity Base composite material prepreg, and lay a plurality of optical fiber Bragg grating strings along the fiber direction and perpendicular to the fiber direction on different prepreg layers; then, curing molding; 2) Demoulding: Clean up the resin around the fiber grating lead wire, keep the lead wire straight, and pull the exposed part of the PTFE cloth to demould the composite material part; 3) Test: Under constant temperature conditions, place the demoulded composite material standard specimen in a universal testing machine to measure Poisson's ratio, and act on the normal stress σ _j in the j direction alone, that is, the fiber 0° direction, while No other external force; 4) Data processing: process the central wavelength data of the grating area collected in real time, obtain the time-varying curve of the central wavelength of each grating area of the fiber Bragg grating string, and obtain the composite material according to the corresponding relationship between the grating central wavelength variation and micro-strain The longitudinal micro-strain and transverse micro-strain of the standard specimen are calculated to obtain Poisson's ratio; In step 1), the specific steps of laying a plurality of fiber Bragg grating strings along the fiber direction and perpendicular to the fiber direction on different prepreg layers are N-10>n>5 longitudinal direction of the nth layer, that is, the fiber In the 0° direction, multiple fiber Bragg grating strings are laid, and in the n+i layer N-14≥i>5 transverse direction, that is, in the 90° direction of the fiber, multiple fiber Bragg gratings protected by narrow strips and homodirectional prepregs are laid raster string. 2. The method according to claim 1, characterized in that, in step 1), the curing molding method is a composite material thermal compression molding method. 3. The method according to claim 1, characterized in that, in step 1), the grating region of the fiber Bragg grating string cannot be arranged at the intersection of the fiber Bragg grating string in 0° and 90° directions. 4. The method according to claim 1, characterized in that, in step 1), 2 to 6 grating regions are distributed on the fiber Bragg grating string. 5. The method according to claim 1, characterized in that, in step 1), the thickness of the narrow strip and homodirectional prepreg is the same as that of the whole prepreg. 6. the method for claim 1 is characterized in that, step 1) in, the laying position of fiber Bragg grating string is at the central position of standard specimen, wherein, at least between 0 ° and 90 ° direction fiber Bragg grating string Interval 5 layers of prepreg. 7. The method according to claim 1, characterized in that, in step 1), the lead wires of the fiber Bragg grating series parallel to the fiber direction are bent in the area near the end of the standard test piece, and are uniformly drawn from one side. 8. The method according to claim 1, wherein the pigtail of the fiber Bragg grating string is protected by a Teflon tube. 9. A method for preparing a standard test piece of continuous fiber reinforced resin-based composite material Poisson's ratio, characterized in that, the following steps are adopted: 1) Fabrication of composite material standard test pieces: Cover the polytetrafluoroethylene tape and polytetrafluoroethylene cloth on the mold side wall frame plate and its lead groove in turn; lay N layers of N≥20 resin in the mold cavity Based on the composite material prepreg, and lay a plurality of fiber Bragg grating strings along the fiber direction and perpendicular to the fiber direction on different prepreg layers; the lead wires of the fiber Bragg grating strings parallel to the fiber direction are near the The area at the end of the piece is bent and uniformly drawn from one side; then, it is solidified and formed; 2) Demoulding: Clean up the resin around the fiber grating lead wire, keep the lead wire straight, pull the exposed part of the PTFE cloth, and demould the composite material, that is, the Poisson's ratio of the continuous fiber reinforced resin matrix composite material Standard test piece.