Method for testing interfacial shear strength of fiber and resin

Abstract

The invention relates to a method for testing interfacial shear strength of fiber and resin, and belongs to the technical field of carbon fiber detection. The method comprises the following steps: preparing a micro-droplet debonding sample, fixing the micro-droplet debonding sample, vertically placing fibers into a fiber rail, ensuring verticality, fixing the fibers by using an adhesive tape, connecting a clamp with a bracket, testing the size of the micro-droplet, placing the micro-droplet debonding sample on an objective table, opening a three-dimensional optical contourgraph, finding interference fringes on the surface of the sample, and constructing the three-dimensional shape of the surface of the sample. Data analysis and processing are carried out through a software algorithm to obtain accurate values of the fiber embedding length and the fiber diameter, an interfacial shear strength test is carried out, a DCAT25 fiber microdroplet debonding measuring instrument is turned on, scraper accessories are placed on a base, fibers are located between scrapers, the distance between the two scrapers is adjusted to be closest, and the fiber microdroplet debonding measuring instrument is obtained. The fiber can move but the microdroplet cannot pass through a scraper gap, testing is started after the fiber embedding length and the fiber diameter are input into software, the full-direct-acting measurement process is completed, and the interfacial shear strength tau is determined according to a formula.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber detection, and more specifically, to a method for testing the interfacial shear strength between fibers and resin. Background Art

[0002] As is well known, the interface between fibers and the resin matrix is one of the key components of fiber-reinforced composites and plays an important role in the mechanical properties of the composites. Accurately characterizing the bonding situation at the fiber-matrix interface is the key to fabricating high-performance composites. Among them, micro-droplet debonding is a rapid, simple, and effective means of testing the interfacial strength of fiber-reinforced composites. Its basic principle is to apply a matrix solution or sol on a single fiber filament, form a micro-droplet after curing, apply a pair of scrapers on both sides of the micro-droplet, apply a load along the fiber axis, generate a shear force to detach the micro-droplet from the fiber filament, record the maximum load during the process, combine the micro-droplet length and fiber diameter, and use a formula to obtain the interfacial shear strength.

[0003] At present, the composite material interface mechanical testing instruments developed based on the micro-droplet debonding method at home and abroad mainly include interfacial shear strength measuring instruments, universal material testing machines using special fixtures, etc. These devices are not only expensive but also complex to operate and selective in fiber measurement. Recently, the DCAT25 fiber micro-droplet debonding measuring instrument produced by DataPhysics Company in Germany is a comprehensive device suitable for composite material interface characterization. Although this device is applicable to almost all types of fiber measurements, there are still certain limitations. At present, all devices used for micro-droplet debonding tests require the input of the micro-droplet area and cannot directly measure the size of the micro-droplet with the device, which is likely to cause test errors and affect the accuracy of fiber interface strength testing. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a method for testing the interfacial shear strength between fibers and resin, which solves the problems that the micro-droplet size cannot be measured and double-sided tape is required to fix the sample in the traditional testing process.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a method for testing the interfacial shear strength between fibers and resin, characterized by including the following steps:

[0006] S1. Prepare a micro-droplet debonding sample

[0007] Fiber separation: Separate single fiber filaments from a bundle of fibers;

[0008] Determine the bonding method between the micro-droplet and the fiber according to the resin properties and fiber diameter, so as to prepare a sample with symmetric micro-droplets and uniform resin;

[0009] S2. Fix the micro-droplet debonding sample

[0010] Design a fixture. The fixture is in the shape of a hollow rectangle, with fiber tracks symmetrically arranged on the upper and lower sides. Fibers can be vertically inserted to ensure perpendicularity. Then, the exposed fibers are folded to the back of the fixture and fixed with tape. Next, the fixture is connected to the bracket and ready for use;

[0011] S3. Precisely measure the microdroplet size

[0012] Place the microdroplet debonding sample on the stage, turn on the three-dimensional optical profiler. By adjusting the focal length and light source intensity, find the interference fringes on the sample surface, construct the three-dimensional topography of the sample surface, and finally perform data analysis and processing through software algorithms to obtain the accurate values of the fiber embedding length and fiber diameter;

[0013] S4. Conduct interface shear strength test

[0014] Turn on the DCAT25 fiber microdroplet debonding measuring instrument. Put the video system on the base as a whole and tighten the screws. Then connect the bracket on the fixture to the connector under the high-precision electronic balance. At the same time, place the scraper accessory on the base so that the fiber is between the scrapers. Adjust the distance between the two scrapers to the closest so that the fiber can move but the microdroplet cannot pass through the gap between the scrapers. Finally, input the fiber embedding length and fiber diameter into the software and start the test, and control the video system to start recording to complete the fully direct-acting measurement process. The interface shear strength τ can be determined according to the following formula:

[0015]

[0016] Among them, d is the fiber diameter, L is the fiber embedding length, F max is the maximum tensile force value when the sample undergoes microdroplet debonding under tensile action, and π is the pi.

[0017] As a further improvement of the present invention, the bonding method of the microdroplet and the fiber can use the solution method, the microsphere melting method, the knot melting method or the mold method.

[0018] As a further improvement of the present invention, the material of the fixture is a hard paper hollow frame body, and fiber tracks are symmetrically arranged on the upper and lower sides. The width of the fiber track should be slightly larger than the fiber diameter by 1 mm to 2 mm, and it is smooth and burr-free.

[0019] As a further improvement of the present invention, the fixture and the bracket are fixed by threads.

[0020] As a further improvement of the present invention, the front of the scraper is horizontal and the back is inclined, forming a certain angle with the tip of the knife, and the distance between the two scrapers can be precisely adjusted by a micrometer.

[0021] As a further improvement of the present invention, environmental vibration and light changes should be noted during the test with the three-dimensional optical profiler.

[0022] As a further improvement of the present invention, the DCAT25 fiber microdroplet debonding measuring instrument includes a high-precision electronic balance, a video system, and a base.

[0023] For a further improvement of the present invention, the resolution of the high-precision electronic balance is ≤10 μg, and a connector is provided below for convenient connection with a fixture.

[0024] The beneficial effects of the present invention are that the size of the microdroplets can be accurately measured, thereby improving the repeatability of the fiber interface strength test, reducing the test error, and improving the accuracy of the fiber interface strength test. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below with reference to the drawings and embodiments.

[0026] Figure 1 Schematic structural diagram of the present invention.

[0027] Figure 2 It is a schematic structural diagram of a carbon fiber microdroplet debonding sample described in an embodiment of the present invention.

[0028] In the figure, 1 - high-precision electronic balance, 2 - base, 3 - video system, 4 - connector, 5 - bracket, 6 - fixture, 7 - fiber rail, 8 - scraper. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The following is a detailed description of the present invention. The described embodiments are part of the embodiments of the present application, rather than all of the embodiments. The following described embodiments are exemplary and are intended to explain the present application and should not be construed as limiting the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts fall within the protection scope of the present invention.

[0030] Embodiment 1:

[0031] As Figure 1 shown, a test method for the interfacial shear strength of a fiber and a resin includes the following steps:

[0032] S1. Prepare a microdroplet debonding sample

[0033] Select a bundle of T300 carbon fibers and ultrasonically separate the single-filament fibers through an ethanol aqueous solution;

[0034] Select the mold method to prepare 10 microdroplet debonding samples, and the prepared sample epoxy resin is uniformly and symmetrically coated around the carbon fibers;

[0035] S2. Fix the microdroplet debonding sample

[0036] Design a fixture. The fixture is in the shape of a hollow rectangle, and fiber tracks are symmetrically arranged on the upper and lower sides. Prepare a white paper and lay it flat on the table, and place the fixture 6 on it. Take a micro-droplet debonding sample and put it into the fiber track 7 in the fixture 6. Then gently lift one end of the fixture 6, place the extra carbon fiber behind the fixture 6, and fix it with a small amount of tape. At the same time, lift the other end of the fixture 6 and fix the sample in the same way. The sample prepared with this fixture 6 can ensure the perpendicularity of the sample. Then connect the fixture 6 to the bracket 5 and set it aside for use;

[0037] S3. Accurately measure the size of the micro-droplet

[0038] Place the micro-droplet debonding sample on the stage, turn on the Zygo NewView 9000 three-dimensional optical profiler, adjust the focal length and light source intensity, and use the white light interference mode to scan the surface of the sample to obtain three-dimensional topography data. In the MetroPro software, select Analysis to enter the analysis mode, select the Distance Measurement tool to measure the fiber embedding length and fiber diameter. Find the starting point of the fiber on the three-dimensional topography map and record it as Ax1, y1, z1, then select the end point and record it as Bx2, y2, z2. The software automatically records the coordinates. At this time, the fiber diameter is The calculation results will be displayed on the screen and marked on the topography map. Select the starting point C and the end point D of the fiber embedding length according to the same method and calculate the fiber embedding length L. Repeat the test on 10 samples according to the above steps;

[0039] S4. Conduct interface shear strength test

[0040] Turn on the DCAT25 fiber micro-droplet debonding measuring instrument, put the entire video system 3 on the base 2, tighten the screws, then install the bracket 5 on the fixture 6 so that it can be connected to the connector 4 below the high-precision electronic balance 1 of the equipment. At the same time, place the scraper attachment on the base 2 so that the fiber is between the scrapers 8. Adjust the distance between the two scrapers 8 to the closest so that the fiber can move but the micro-droplet cannot pass through the gap between the scrapers 8. Enter the fiber embedding length L and fiber diameter d obtained in S3 into the software, then start the test and control the video system 3 to start recording to complete the full direct-acting measurement process. The interface shear strength τ can be determined according to the following formula:

[0041]

[0042] where d is the fiber diameter, L is the fiber embedding length, F max is the maximum tensile force value at which the micro-droplet debonds under the tensile action of the sample, and π is the pi.

[0043] Repeat the test on 10 samples according to the above steps.

[0044] Comparative Example 1:

[0045] Select a bundle of T300 carbon fibers, ultrasonically separate the monofilament fibers with an ethanol aqueous solution, dip a small amount of epoxy resin and gently coat it on the carbon fibers, and prepare 10 micro-droplet debonding samples. Then, stick both ends of the fibers of the micro-droplet debonding samples on both sides of the hollow rectangular fixture with double-sided tape. Use a scanning electron microscope to calculate the average diameter of a bundle of carbon fibers as the fiber diameter d, and measure the fiber embedding length L with a ruler. Finally, turn on the DCAT25 fiber micro-droplet debonding measuring instrument, put the entire video system 3 on the base 2, tighten the screws, then install the bracket 5 on the fixture so that it can be connected to the joint 4 below the high-precision electronic balance 1 of the device. At the same time, place the scraper attachment on the base 2 so that the fibers are between the scrapers 8. Adjust the distance between the two scrapers 8 to the closest so that the fibers can move but the micro-droplets cannot pass through the gap between the scrapers 8. After entering the fiber embedding length L and the fiber diameter d into the software, start the test and control the video system 3 to start recording to complete the measurement process. Repeat the test on 10 samples according to the above steps.

[0046] Compare the test results of the carbon fiber interface shear strength of Example 1 and Comparative Example 1 of the present invention. The obtained results are as follows in the table:

[0047] Table 1 Comparison table of interface shear strength test results

[0048]

[0049] By observing the test results of the examples and comparative examples, it is found that when only using the DCAT25 fiber micro-droplet debonding measuring instrument for testing, the interface shear strength between the carbon fiber and the epoxy resin is low, the repeatability is poor, and the authenticity of the test results cannot be reflected. By using the three-dimensional optical profiler and the DCAT25 fiber micro-droplet debonding measuring instrument in combination, the fiber embedding length and the fiber diameter can be automatically measured. The size test accuracy is high, and the interface shear strength test data is stable. At the same time, special fixtures are used to clamp the samples, which is not only simple to operate, but also can ensure the perpendicularity of the samples, and can ensure good consistency of the test results, greatly reducing the operation requirements of the test personnel.

[0050] As can be seen from the above technical solutions, the advantages of a test method for the interfacial shear strength of fibers and resins provided by the present invention are as follows: It provides a test method with controllable and reliable processes. This method proposes a special test fixture. By designing a fiber track, the perpendicularity of the sample can be ensured, laying a foundation for the reliability of the test results. At the same time, through the combined use of a three-dimensional optical profiler and a DCAT25 fiber micro-droplet debonding measuring instrument, the fiber embedding length and fiber diameter can be accurately measured, providing data support for the subsequent interfacial shear strength test. By using this method to test the interfacial shear strength, not only is the operation simple and convenient, with high repeatability, greatly reducing the operation requirements for testers and improving the test efficiency, but also the test stability is improved, and the precision of the test results is optimized. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention.

[0051] The fiber track on the fixture of the present invention can ensure the vertical arrangement of the fibers, effectively ensuring that the alignment center lines of the fibers, the left and right scrapers are consistent, and improving the test accuracy. The combined use of a three-dimensional optical profiler and a DCAT25 fiber micro-droplet debonding measuring instrument can automatically measure the fiber embedding length and fiber diameter, ensuring accurate test data and simple operation at the same time. The test has strong repeatability. This method clearly describes the key steps that can affect the final test results, stipulates the specific operation steps, and when the testers master this method proficiently, the repeated test results are basically the same.

Claims

1. A test method for the interfacial shear strength of fiber and resin, characterized in that, It includes the following steps: S1. Prepare a microdroplet debonding sample Fiber separation: Separate single-filament fibers from a bundle of fibers; Determine the bonding method between the microdroplets and the fibers according to the resin properties and fiber diameter, so as to prepare a sample with symmetric microdroplets and uniform resin; S2. Fix the microdroplet debonding sample Design a fixture. The fixture is in the shape of a hollow rectangle, with fiber tracks symmetrically arranged on the upper and lower sides. The fibers can be vertically placed into it to ensure perpendicularity. Then fold the exposed fibers to the back of the fixture and fix them with tape. Then connect the fixture to the bracket for later use; S3. Accurately measure the microdroplet size Place the microdroplet debonding sample on the stage, turn on the three-dimensional optical profiler, find the interference fringes on the sample surface by adjusting the focal length and light source intensity, construct the three-dimensional topography of the sample surface, and finally perform data analysis and processing through software algorithms to obtain the accurate values of the fiber embedding length and fiber diameter; S4. Perform interface shear strength test Turn on the DCAT25 fiber microdroplet debonding measuring instrument, put the video system on the base as a whole, tighten the screws, then connect the bracket on the fixture to the connector under the high-precision electronic balance. At the same time, place the scraper attachment on the base so that the fibers are between the scrapers. Adjust the distance between the two scrapers to the closest so that the fibers can move but the microdroplets cannot pass through the gap between the scrapers. Finally, input the fiber embedding length and fiber diameter into the software and start the test, and control the video system to start recording to complete the full direct-acting measurement process. The interface shear strength τ can be determined according to the following formula: where d is the fiber diameter, L is the fiber embedding length, and F max is the maximum tensile force value at which droplet debonding occurs in the sample under tensile action, and π is the ratio of the circumference of a circle to its diameter.

2. The test method for the interfacial shear strength of the fiber and the resin according to claim 1, characterized in that The bonding method between the microdroplets and the fibers can use the solution method, the microsphere melting method, the knot melting method or the mold method.

3. The test method for the interfacial shear strength of the fiber and resin according to claim 1, wherein The material of the fixture is a hard paper hollow frame body, and fiber tracks are symmetrically arranged on the upper and lower sides. The width of the fiber track should be slightly larger than the fiber diameter by 1 mm to 2 mm, and it is smooth and free of burrs.

4. The test method for the interfacial shear strength of the fiber and the resin according to claim 1, characterized in that The fixture and the bracket are fixed by threads.

5. The test method for the interfacial shear strength of the fiber and the resin according to claim 1, characterized in that The front of the scraper is horizontal and the back is inclined, forming a certain angle with the tip of the knife, and the distance between the two scrapers can be accurately adjusted by a micrometer.

6. The test method for the interfacial shear strength of the fiber and the resin according to claim 1, wherein Attention should be paid to environmental vibration and light changes during the test with the three-dimensional optical profiler.

7. The test method for the interfacial shear strength of the fiber and the resin according to claim 1, characterized in that The DCAT25 fiber microdroplet debonding measuring instrument includes a high-precision electronic balance, a video system, and a base.

8. The test method for the interfacial shear strength of the fiber and the resin according to claim 1, characterized in that The resolution of the high-precision electronic balance is ≤10 μg, and a connector is provided below for easy connection to the fixture.

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