In-situ characterization method of tensile strain-structure-fracture mechanism of graphene film

Abstract

The invention relates to an in-situ characterization method of a tensile strain-structure-fracture mechanism of a graphene film, and belongs to the technical field of mechanical measurement and material characterization, and the in-situ characterization method comprises the following steps: (1) assembling a stretching device matched with a microscope; (2) preparing a graphene film for a tensile test; (3) in-situ Raman characterization: clamping the prepared graphene film at two ends of a stretching device, and acquiring continuous change of the D peak position of the graphene nanosheet in the whole process of stretching the sample to be close to fracture through a Raman spectrum to obtain structure change information of the graphene nanosheet in the stretching process; (4) testing the change characteristics of the D peak position of the graphene nanosheet in the process that the graphene film is unloaded from an initial non-stress state to before fracture and then is unloaded to an initial state; and (5) analyzing a tensile strain-nanosheet layer structure-macroscopic fracture mechanism of the graphene film. The method is simple to operate, and the macroscopic tensile property and real-time changing microstructure information of the graphene nanosheet can be tested at the same time.

Description

Technical Field

[0001] The present invention belongs to the fields of mechanical measurement and material characterization, and relates to the mechanical property testing and microstructural analysis of graphene films. In particular, it relates to an in-situ characterization method for the tensile strain-structure-fracture mechanism of graphene films, which is used to monitor in real time the microstructural changes of graphene films before stretching to fracture through Raman spectroscopy technology. Combining with the design of a biaxial stretching device, the in-situ characterization of microstructures and macroscopic mechanical properties is realized. Background Art

[0002] Graphene films have excellent properties such as high strength, high conductivity, and good flexibility due to their unique micro-nano layered structure, and show great application potential in many fields. Graphene films are composed of graphene nanosheets and other materials, and their internal microstructures are complex, and it is this complex structure that plays a decisive role in their mechanical properties. With the continuous progress of technology, the requirements for material properties are becoming increasingly stringent, and graphene films face severe challenges in some special application scenarios. For example, in flexible electronic devices, graphene films need to maintain good performance under repeated stretching. Therefore, in-depth understanding of the performance change mechanism of graphene films in the actual use environment is of crucial significance for further optimizing material properties and expanding the application scope.

[0003] Traditional mechanical property testing methods can obtain the macroscopic mechanical properties of materials, such as stress-strain curves, tensile strength, elongation at break, etc. However, these testing methods usually can only provide information at the macroscopic level and cannot reveal the microstructural evolution and fracture mechanism of materials during the stretching process. For example, a tensile device for graphene film manufacturing and testing disclosed in Chinese invention patent CN112146979A realizes more uniform stress through a biaxial synchronous stretching method, solving the problem of uneven stress in traditional uniaxial tensile testing. However, this device only focuses on macroscopic tensile property testing and lacks in-situ real-time observation means for the microstructural changes of materials, and cannot establish the connection between macroscopic mechanical properties and microstructures.

[0004] As a powerful microstructural analysis tool, Raman spectroscopy can accurately characterize the nano-sheet layer structure. For example, through information such as the position, intensity, and width of characteristic peaks in Raman spectroscopy, the orientation, defect degree, orientation, and binding state with other materials of graphene nano-sheets can be intuitively reflected, etc. In addition, Raman spectroscopy can capture the subtle changes in the microstructure in real time during the stretching process. By continuously monitoring the evolution law of Raman spectroscopy during the stretching process, the influence mechanism of different interfacial actions between nano-sheets on the macroscopic properties of materials can be analyzed, thus establishing a dynamic connection between microstructures and macroscopic mechanical properties.

[0005] However, most existing Raman testing methods use static testing modes, which cannot achieve continuous monitoring during the stretching process, and it is difficult to capture the microstructural changes at different strain stages in real time. In addition, the traditional graphene film tensile performance test mainly uses mechanical testing equipment to measure the material's tensile strength, elongation at break and other mechanical performance indicators separately, and cannot be placed under a microscope for in-situ observation. The commercially available microscopic stretching tables are generally unidirectional stretching, and the observed point in the microscope continues to change during the stretching process, which affects the accuracy of the Raman data and has a high procurement cost. In addition, the mechanism of the influence of the chemical bonds in the graphene film and the interface between the nanosheets on its mechanical properties is mainly established through computational simulation methods.

[0006] In summary, the existing graphene film tensile performance testing technology has problems such as being unable to capture microstructural changes in real time, insufficient test data accuracy, and complex and costly tensile device design. Therefore, it is urgent to develop a new in-situ characterization technology that can take into account both mechanical properties and real-time changes in microstructural information in a fixed area. The in-situ characterization method of graphene film fracture mechanism obtained by experimental methods is a technical problem that needs to be solved in the field of graphene mechanical characterization and material optimization design. Summary of the invention

[0007] 1. Purpose of the invention In view of the above defects and deficiencies of the prior art, in order to solve at least one of the above and other technical problems, the present invention aims to provide an in-situ characterization method for the tensile strain-structure-fracture mechanism of a graphene film, by assembling a biaxial stretching device adapted to a microscope, combined with in-situ Raman spectroscopy technology, to achieve synchronous real-time observation of the macroscopic mechanical properties and microstructural changes of the graphene film during the stretching process. Through the above technical solution, the present invention realizes the dynamic correlation analysis between the microstructure and macroscopic mechanical properties of the graphene film, which can provide an important experimental basis for the performance optimization and application expansion of the graphene film.

[0008] (II) Technical solution In order to achieve the purpose of the invention and solve the technical problems, the present invention adopts the following technical solutions: An in-situ characterization method for tensile strain-structure-fracture mechanism of a graphene film is used to monitor the microstructure evolution of the graphene film in real time during the stretching process to analyze its fracture mechanism, comprising the following steps: SS1. Assemble the biaxial stretching device suitable for the microscope: A clamping block is processed on two oppositely arranged sliders of the biaxial stretching device to clamp the two ends of the graphene film sample, and insulating rubber pads are pasted on the clamping surfaces of the slider and the clamping block to prevent the ends of the sample from slipping or being clamped off during the clamping process; SS2. Preparation of graphene film specimens for tensile testing: Cut the graphene film into long strips as tensile test specimens, and paste reinforcing sheets with matching sizes at both ends of the graphene film specimens to prevent the graphene film specimens from slipping or tearing at the edges during the tensile process; SS3. In-situ Raman characterization of the graphene film specimen during the tensile process: Clamp the prepared long-strip graphene film specimen at both ends of a biaxial tensile device, and continuously collect the change in the position of the D peak of the graphene nanosheets during the entire process of the specimen being stretched until near fracture through Raman spectroscopy, so as to obtain the structural change information of the graphene nanosheets during the tensile process; SS4. Test the Raman spectral evolution of the graphene film specimen during the loading and unloading process: Test the continuous change in the position of the D peak of the graphene nanosheets during the process of the graphene film specimen from the initial unloaded state to near fracture and then unloaded back to the initial unloaded state, so as to obtain the structural change characteristics of the graphene nanosheets during the entire loading and unloading process; SS5. In-situ characterization of the tensile strain-structure-fracture mechanism: Based on the continuous change data of the D peak position of the graphene film specimen during the loading and stretching and unloading processes, by analyzing the relationship between the change in the D peak position of the graphene nanosheets and the tensile strain, determine the tensile strain-nanosheet layer structure-macroscopic fracture mechanism of the graphene film.

[0009] (III) Technical effects Compared with the prior art, the in-situ characterization method for the tensile strain-structure-fracture mechanism of the graphene film of the present invention has the following beneficial and remarkable technical effects: (1) The present invention assembles a tensile device with precisely controllable displacement that can cooperate with Raman spectroscopy testing, enabling the graphene film to in-situ capture the subtle changes in the microstructure through Raman spectroscopy during the tensile process. By continuously monitoring the evolution law of the Raman spectrum during the tensile process, analyze the influence mechanism of different interfacial actions between the nanosheet layers on the macroscopic properties of the graphene film, so as to comprehensively understand the dynamic relationship between the microstructure and the macroscopic mechanical properties through experimental methods, making up for the deficiencies of traditional macroscopic tensile property testing.

[0010] (2) The present invention uses a displacement stage with biaxial tensile function to ensure that the tested points on the graphene film during the tensile process are always within the microscope field of view, improving the accuracy of the test. The present invention obtains the fracture mechanism of the graphene film by comparing the Raman frequency shift-strain diagrams of two graphene films before and after chemical modification. In addition, adopting the method of the present invention, the assembly cost of the tensile device is low, the test method is simple, the tensile stroke is long, and it can also be widely used to study other materials with Raman signals, such as polymer composite films, organic / inorganic fibers, etc. Description of the drawings

[0011] The following further elaborates on the specific implementation manners of the present invention with reference to the accompanying drawings.

[0012] Figure 1 It is a flowchart of the implementation of the in-situ characterization method for the tensile strain-structure-fracture mechanism of the graphene film.

[0013] Figure 2 It is a schematic diagram of the tensile device assembled and adapted to the microscope in the present invention. The specimen is clamped on the fixtures at both ends of the biaxial tensile device, and the Raman light is perpendicular to the specimen surface to test the sample.

[0014] Figure 3 It is the stress-strain curve diagram (a) and Raman spectrum diagram (b) of the pure graphene film and graphene composite film in the present invention.

[0015] Figure 4 It is the continuous change of the D peak position of graphene nanosheets during the whole process of stretching the pure graphene film (a) and graphene composite film (b) in the present invention until near fracture, obtaining the structural change information of graphene nanosheets during the stretching process.

[0016] Figure 5 It is the change characteristic of the D peak position of graphene nanosheets in the pure graphene film (a) and graphene composite film (b) in the present invention from the initial unloaded state to before fracture, and then unloaded back to the initial state. Specific implementation manners

[0017] The present invention aims to provide an in-situ characterization method for the tensile strain-structure-fracture mechanism of a graphene film. To make the purpose, technical solution, and advantages of the implementation of the present invention clearer, the technical solutions in the embodiments of the present invention will be described in more detail below with reference to the accompanying drawings in the embodiments of the present invention. The described embodiments are part of the embodiments of the present invention, rather than all of the embodiments, and the described embodiments are exemplary and are intended to explain the present invention and should not be construed as a limitation to the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0018] Example 1: In-situ characterization method As a specific example, as Figure 1 shown, the in-situ characterization method for the tensile strain-structure-fracture mechanism of the graphene film provided in the embodiment of the present invention is used to monitor the microscopic structure evolution of the graphene film in real time during stretching to analyze its fracture mechanism, and it at least includes the following steps when implemented: (1) Assemble a tensile device adapted to the microscope, as Figure 2As shown, the overall height of the assembled biaxial stretching device is preferably designed to match the working distance of the microscope, so as to ensure that the Raman spectroscopy laser beam can be accurately focused on the measurement area of the graphene film specimen, while meeting the observation under the microscope and the requirements of Raman spectroscopy measurement. Among them: (a) One clamping block with the same length and width as the slider is machined on each of the two sliders on the horizontally placed uniaxial stretching displacement table for clamping both ends of the specimen; and among them, the sliders at both ends of the assembled biaxial stretching device are preferably designed to move synchronously in two directions, so that the observed specimen area can remain relatively stationary in the microscope field of view during the stretching process, ensuring that the Raman signals collected during the stretching process are always located at the same position to improve the accuracy of the test, and ensuring that the structural evolution information of the nanosheets during the stretching process is continuously and accurately collected; (b) Special glue is used to paste 1-mm-thick insulating rubber pads on the sliders on the stretching table and on the surface of the post-processed test block for clamping the specimen, to prevent the graphene film from slipping or being clamped and broken during the clamping process; among them, the insulating rubber pads are pasted to cover the entire clamping area of the clamping block, and the material thereof is preferably an elastic material with appropriate hardness and friction coefficient, ensuring that the graphene film specimen is evenly stressed and does not undergo local stress concentration during the clamping process, while preventing the film from slipping out of the clamping device during the stretching process.

[0019] (2) Preparation of graphene film specimens for tensile testing: The graphene film is cut into a strip with a length of 30 mm and a width of 5 mm as the tensile test specimen. The cutting method preferably adopts vertical downward cutting with the film laid flat on the desktop to reduce edge defects and avoid stress concentration and premature fracture caused by edge defects in the subsequent tensile test; and 4 small pieces of paper with a length of 10 mm and a width of 5 mm are used as reinforcement pieces for the graphene film specimen, and are respectively pasted at both ends of the strip-shaped specimen to prevent the specimen from slipping or edge tearing during the stretching process; in addition, the graphene film is a pure graphene film and / or a graphene composite film with a graphene content of 80 wt% or more. The graphene composite film contains a composite structure of chemically modified graphene and other materials. By comparing the tensile strain - structural evolution relationships of different types of graphene films, the effects of chemical modification and composite structure on the mechanical properties and fracture mechanism of graphene films are analyzed.

[0020] (3) Characterization of specimen structure and properties: Raman spectroscopy is used to characterize the graphene film to test its preliminary structure before stretching, as shown in Figure 3 Figure a in. The stress - strain curve of the graphene film is tested by a tensile testing machine, as shown in Figure 3 Figure b in, to obtain its maximum fracture tensile strain, providing a reference for subsequent in-situ Raman testing.

[0021] (4)In-situ Raman characterization of the graphene film specimen during the tensile loading process: As Figure 2 shown, the strip-shaped specimen of the prepared graphene film is clamped at both ends of the biaxial stretching device. The tensile displacement is adjusted by turning the corrugated knob. At the same time, the continuous change of the D peak position of the graphene nanosheets in the specimen during the whole process from the initial unloaded state to near fracture is collected by Raman spectroscopy. The D peak position is recorded every 0.1 mm of tensile displacement (corresponding to a 0.5% increase in tensile strain), and a Raman shift-strain diagram is established to obtain the structural change information of the graphene nanosheets during the tensile loading process, as Figure 4 shown.

[0022] Preferably, the original gauge length clamped at both ends of the biaxial stretching device is set to a fixed value to ensure the accuracy of tensile strain calculation and the comparability of test results for different specimens. Moreover, the tensile loading process applies the load in step increments, and the strain corresponding to each increment is calculated through the gauge length. The acquisition position of the Raman spectroscopy is fixed at the center of the specimen gauge section to ensure the dynamic correlation between the microstructure and the macroscopic strain.

[0023] (5)The tensile displacement is adjusted by turning the corrugated knob. At the same time, the continuous change of the D peak position of the graphene nanosheets in the specimen during the whole process from the initial unloaded state to near fracture is collected by Raman spectroscopy. The D peak position is recorded every 0.1 mm of tensile displacement (corresponding to a 0.5% increase in tensile strain), and then the change characteristics of the D peak position of the graphene nanosheets during the process of unloading back to the initial state are recorded. A Raman shift-strain diagram is established, as Figure 5 shown. Preferably, the unloading process adopts a step-by-step displacement withdrawal method, and the tensile displacement is gradually reduced step by step according to the same step size as the tensile loading, and the D peak position is recorded at each unloading step to analyze the reversible deformation behavior and irreversible damage characteristics of the graphene film. In addition, the analysis of the relationship between the change of the D peak position and the tensile strain includes the drawing of the Raman shift-strain curve and the calculation of the slope to determine the influence mechanism of the interlayer interface interaction of the graphene nanosheets on the macroscopic fracture behavior. By comparing the differences in the change characteristics of the D peak position of different types of graphene film specimens under the same tensile strain conditions, the influence mechanism of different interface interactions between graphene nanosheets on the mechanical properties of the graphene film is analyzed, providing an experimental basis for material property optimization.

[0024] The present invention obtains the Raman shift-strain diagram of the graphene film by recording the D peak position of the graphene film in the Raman spectroscopy at different tensile displacements. By using the method of the present invention, the fracture mechanism of the graphene film is obtained by comparing the Raman shift-strain diagrams of two graphene films before and after chemical modification.

[0025] Example 2: Characterization of the tensile strain-structure-fracture mechanism of the pure graphene film

[0026] On the basis of Example 1, in order to explore the tensile strain-structure-fracture mechanism of different types of graphene films, Example 2 takes pure graphene film as the research object. By preparing pure graphene film and conducting in-situ stretching-Raman spectroscopy test, its microstructure evolution characteristics and fracture mechanism during the stretching process are analyzed to reveal the influence of interlayer interaction of pure graphene film on its mechanical properties.

[0027] (1) Preparation of pure graphene film: After fully stirring 20 mL of 1 mg / mL graphene oxide aqueous solution, a graphene oxide film was obtained by vacuum filtration. After being placed in a vacuum drying oven at 80 °C for 1 hour, the film was demolded to obtain a pure graphene film. Its chemical structure was tested using Raman spectroscopy. Figure 3 As shown in Figure a.

[0028] (2) Pure graphene film tensile property test: The pure graphene film was cut into strips with a length of 30 mm and a width of 5 mm, and its stress-strain curve was tested using a tensile testing machine. Figure 3 As shown in Figure b, the maximum tensile strain is obtained as the reference critical strain value for in-situ tensile strain / Raman spectroscopy testing.

[0029] (3) In-situ tensile strain / Raman spectroscopy test: Figure 2 As shown in the figure, the prepared long strip sample of pure graphene film is clamped at both ends of the stretching device, and the stretching displacement is adjusted by turning the corrugated knob. At the same time, the continuous change of the D peak position of the graphene nanosheet during the whole process of stretching the sample to the point of fracture is collected by Raman spectroscopy. The D peak position is recorded at each stretch of 0.1 mm (corresponding to a 0.5% increase in tensile strain), and a Raman frequency shift-strain diagram is established, as shown in FIG. Figure 4 As shown in Figure a. Then, the change characteristics of the D peak position of the graphene nanosheet during the unloading process to the initial state. The Raman frequency shift-strain diagram is established, as shown in Figure 5 As shown in Figure a.

[0030] (4) Data analysis: Figure 4 As shown in Figure a, before the pure graphene film is stretched to 1%, the position of the D peak changes continuously; after the 1% stretching strain and before the fracture, the position of the D peak hardly changes, that is, the nanosheet structure hardly changes, indicating that before the pure graphene film is about to be broken, there is only interface sliding between the nanosheet layers, and there is no interaction force, so it is easy to be broken. Figure 5 As shown in Figure a, from the Raman frequency shift-strain diagram of the pure graphene film after being stretched to near fracture and then unloaded to the initial state, it can be seen that when unloaded to the same strain, the D peak displacement of the graphene nanosheet changes, indicating that the graphene nanosheet structure has undergone irreversible changes during the stretching process and the nanosheet structure has been squeezed and deformed.

[0031] In summary, Example 2 revealed the tensile strain-structure-fracture mechanism of the pure graphene film through in-situ Raman spectroscopy testing, indicating that the main dependence between its layers is on interfacial slip and the lack of strong interactions, resulting in easy fracture. This study provides an experimental basis for optimizing the mechanical properties of graphene films and enhancing their structural stability.

[0032] Example 3: Characterization of the Tensile Strain-Structure-Fracture Mechanism of Graphene Composite Films

[0033] To further explore the effects of chemical modification and composite structure on the tensile properties of graphene films, Example 3 took graphene composite films as the research object and analyzed the effects of different interaction mechanisms between nanosheets on their mechanical properties and fracture behavior by comparing the Raman frequency shift-strain relationships of pure graphene films and composite films.

[0034] (1) Preparation of graphene composite films: After adding 300 mg of sulfosalicylic acid aqueous solution (mass fraction 70 wt%) to 20 mL of graphene oxide aqueous solution with a concentration of 1 mg / mL and stirring well, a graphene oxide composite film was obtained by vacuum filtration. 1 mL of hydrochloric acid with a concentration of 5 mol / L was dropped onto the surface of the film, and vacuum filtration was continued until it was completely dried to fully acidify the graphene oxide composite film. It was placed in a vacuum drying oven and dried at 80 °C for 1 hour and then demolded to obtain a graphene composite film. Its chemical structure was tested using Raman spectroscopy, as shown in Figure 3 Figure a below.

[0035] (2) Tensile property testing of graphene composite films: The graphene film was cut into strips with a length of 30 mm and a width of 5 mm, and its stress-strain curve was tested using a tensile test, as shown in Figure 3 Figure b below, and its maximum tensile strain was obtained as the reference fracture tensile strain value for in-situ tensile strain / Raman spectroscopy testing.

[0036] (3) In-situ tensile strain / Raman spectroscopy testing: As shown in Figure 2 below, the strip-shaped specimen of the prepared graphene composite film was clamped at both ends of the tensile device, and the tensile displacement was adjusted by turning the corrugated knob. At the same time, the continuous change in the position of the D peak of graphene nanosheets in the specimen during the entire process before approaching fracture was collected by Raman spectroscopy, and the position of the D peak was recorded at every 0.1 mm of stretching (corresponding to a 0.5% increase in tensile strain) to establish a Raman frequency shift-strain diagram, as shown in Figure 4 Figure b below. Then, the change characteristics of the position of the D peak of graphene nanosheets during the process of unloading to the initial state were also observed. A Raman frequency shift-strain diagram was established, as shown in Figure 5 Figure b below.

[0037] (4) Data analysis: As shown in Figure 4As shown in Figure b, before the graphene composite film reaches 1% tensile strain, the position of the D peak continuously changes, similar to that of the pure graphene film, indicating that there are interaction forces between the graphene nanosheets (hydrogen bond interaction between graphene oxide nanosheets) during the initial stretching stage; after reaching 1% tensile strain until fracture, the position of the D peak continuously changes, and the slope of the trend line becomes larger, indicating that there are stronger interaction forces between the nanosheets during stretching (modified covalent bond cross-linking between the nanosheet layers). Therefore, the graphene composite film has better tensile properties than the pure graphene film. As Figure 5 As shown in Figure b, for the graphene composite film, the strain continuously changes with the Raman frequency shift from being stretched to near fracture and then unloaded to the initial state. This indicates that during the stretching process, the covalent bond cross-linking between the graphene nanosheets offsets part of the energy, improving the toughness of the graphene composite film.

[0038] In summary, Example 3 reveals the tensile strain-structure-fracture mechanism of the graphene composite film through in-situ Raman spectroscopy testing, indicating that there are hydrogen bonds and covalent bond cross-linking between its layers, effectively enhancing the interaction between the nanosheets and improving the tensile strength and toughness. This research provides an experimental basis for the performance optimization of graphene-based composites.

[0039] Through the above embodiments, the object of the present invention is completely and effectively achieved. Those skilled in the art can understand that the present invention includes but is not limited to the content described in the drawings and the above specific embodiments. Although the present invention has been described with respect to the currently considered most practical and preferred embodiments, it should be understood that the present invention is not limited to the disclosed embodiments, and any modification that does not deviate from the functional and structural principles of the present invention will be included in the scope of the claims.

Claims

1. An in-situ characterization method for tensile strain-structure-fracture mechanism of graphene film, characterized in that: The method comprises at least the following steps when implemented: SS1. Assemble a biaxial stretching device adapted to a microscope: process a clamping block on each of the two oppositely disposed sliders of the biaxial stretching device to clamp the two ends of the graphene film sample, and paste insulating rubber pads on the clamping surfaces of the slider and the clamping block to prevent the ends of the sample from slipping or being clamped off during the clamping process; SS2. Preparation of graphene film samples for tensile testing: Cut the graphene film into long strips as tensile test samples, and paste reinforcing sheets of matching size at both ends of the graphene film samples to prevent the graphene film samples from slipping or tearing at the edges during the stretching process; SS3. In-situ Raman characterization of graphene film sample loading and stretching process: The prepared long strip of graphene film sample is clamped at both ends of the biaxial stretching device, and the continuous change of the D peak position of the sample from the initial unstressed state to the near fracture process is collected by Raman spectroscopy to obtain the structural change information of the graphene nanosheet during the loading and stretching process; SS4. Raman spectrum evolution of graphene film sample during loading and unloading process: The continuous change of the D peak position of the graphene nanosheet during the test of the graphene film sample from the initial unstressed state to the point of fracture and then unloading to the initial unstressed state was obtained to obtain the structural change characteristics of the graphene nanosheet during the entire loading and unloading process; SS5. In situ characterization of tensile strain-structure-fracture mechanism: Based on the continuous change data of the D peak position of the sample during loading, stretching and unloading, the tensile strain-nanosheet structure-macroscopic fracture mechanism of the graphene film is determined by analyzing the relationship between the change of the D peak position of the graphene nanosheet and the tensile strain.

2. The in-situ characterization method of tensile strain-structure-fracture mechanism of a graphene film according to claim 1, characterized in that: Before implementing step SS3, the method also includes the step of preliminary structural and performance characterization of the graphene film sample, in which Raman spectroscopy is used to perform preliminary structural characterization on the graphene film sample before stretching, and the stress-strain curve of the graphene film is obtained by a tensile testing machine, and the maximum tensile strain at break is extracted as the critical reference value for subsequent in-situ Raman testing.

3. The in-situ characterization method of tensile strain-structure-fracture mechanism of a graphene film according to claim 1, characterized in that: In the above step SS1, the overall height of the biaxial stretching device is designed to match the working distance of the microscope, ensuring that the Raman spectroscopy laser beam can be accurately focused on the measurement area of ​​the graphene film sample, while meeting the requirements of observation under the microscope and Raman spectroscopy measurement.

4. The in-situ characterization method of tensile strain-structure-fracture mechanism of a graphene film according to claim 1, characterized in that: In the above step SS1, the sliders at both ends of the biaxial stretching device adopt a biaxial synchronous movement design, so that the observed sample area can remain relatively still in the field of view of the microscope during the stretching process, ensuring that the Raman signal collected during the stretching process is always located at the same position, and ensuring that the structural evolution information of the nanosheet layer during the stretching process is continuously and accurately collected.

5. The in-situ characterization method of tensile strain-structure-fracture mechanism of a graphene film according to claim 1, characterized in that: In the above step SS1, the insulating rubber pad is pasted to cover the entire clamping area of ​​the clamp block, and its material is selected to be an elastic material with appropriate hardness and friction coefficient to ensure that the graphene film sample is subjected to uniform force during the clamping process and no local stress concentration occurs, while preventing the film from slipping out of the clamping device during the stretching process.

6. The in-situ characterization method of tensile strain-structure-fracture mechanism of a graphene film according to claim 1, characterized in that: In the above step SS2, the method for cutting the long strip sample of the graphene film is to lay the film flat on the table and press it down vertically to reduce edge defects and avoid stress concentration and premature fracture caused by edge defects in subsequent tensile tests.

7. The in-situ characterization method of tensile strain-structure-fracture mechanism of a graphene film according to claim 1, characterized in that: In the above step SS2, the graphene film is a pure graphene film and / or a graphene composite film with a graphene content of 80 wt% or more, and the graphene composite film includes a composite structure of chemically modified graphene and other materials. By comparing the tensile strain-structural evolution relationship of different types of graphene films, the influence of chemical modification and composite structure on the mechanical properties and fracture mechanism of the graphene film is analyzed.

8. The in-situ characterization method of tensile strain-structure-fracture mechanism of a graphene film according to claim 1, characterized in that: In the above step SS3, the original gauge length of the long strip sample of graphene film clamped at both ends of the biaxial stretching device is set to a fixed value to ensure the accuracy of the tensile strain calculation and the comparability of the test results of different samples, and the load is applied in step increments during the loading and stretching process, and the strain corresponding to each increment is calculated by the gauge length; the collection position of the Raman spectrum is fixed at the center of the sample gauge section to ensure the dynamic correlation between the microstructure and the macro strain.

9. The in-situ characterization method of tensile strain-structure-fracture mechanism of a graphene film according to claim 1, characterized in that: In the above step SS4, the unloading process adopts a stepwise displacement withdrawal method, gradually reducing the tensile displacement according to the same step length as the loading stretching, and recording the D peak position at each unloading step length to analyze the reversible deformation behavior and irreversible damage characteristics of the graphene film.

10. The in-situ characterization method of tensile strain-structure-fracture mechanism of a graphene film according to claim 1, characterized in that: In the above step SS5, the analysis of the relationship between the change in the D peak position and the tensile strain includes the drawing of the Raman frequency shift-strain curve and the calculation of the slope to determine the influence mechanism of the interface effect between graphene nanosheets on the macroscopic fracture behavior; by comparing the differences in the D peak position change characteristics of different types of graphene film samples under the same tensile strain conditions, the influence mechanism of different interface effects between graphene nanosheets on the mechanical properties of graphene films is analyzed to provide an experimental basis for material performance optimization.

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