Method for detecting carbon fiber content of carbon fiber reinforced epoxy resin composite material

Abstract

The invention discloses a method for detecting the carbon fiber content of a carbon fiber reinforced epoxy resin composite material, which comprises the following steps of: removing a matrix part and reducing mass loss caused by carbon fiber oxidation by a method of combining high-temperature oxygen-free burning and low-temperature oxygen burning on a carbon fiber laminated plate and a control component carbon fiber tow; and calculating the mass ratio of the control component carbon fiber tows before and after firing to obtain a correction coefficient, thereby correcting the change mass of the carbon fibers in the carbon fiber laminated plate after two times of firing, and achieving the purpose that the test result of the mass content of the carbon fibers in the composite material is more accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material testing, and particularly relates to a method for detecting the carbon fiber content of a carbon fiber reinforced epoxy resin composite material. Background Art

[0002] A carbon fiber reinforced epoxy resin composite material is mainly a composite material formed by combining a carbon fiber reinforcement and an epoxy resin matrix. In terms of performance and structure, it has the advantages of high strength, high temperature resistance, wear resistance, corrosion resistance, long service life, etc., and is widely used in important fields such as aerospace, national defense, automotive, energy, and rail transit. In a carbon fiber reinforced epoxy resin composite material, the resin content and the carbon fiber content play a crucial role in the performance of the material, and the content of each component is also one of the important indicators for measuring the manufacturing quality of carbon fiber composites.

[0003] Currently, the main testing methods for the fiber content in carbon fiber composites are the acid etching method and the burning method. The acid etching method is to put a carbon fiber reinforced epoxy resin composite material specimen into concentrated sulfuric acid / hydrogen peroxide. After a period of oxidation reaction, the resin in the composite material is completely dissolved, and then the carbon fiber is retained. Then, the resin content and the fiber content are calculated according to the mass change. The concentrated sulfuric acid / hydrogen peroxide used in the acid etching method is a strong oxidant, and it is dangerous to dissolve the resin at high temperature, and it also takes a long time. The burning method usually burns the carbon fiber epoxy resin composite material at high temperature in an oxygen-containing state to remove the resin. The disadvantage of this method is that in the case of high temperature and oxygen, the carbon fiber will undergo an oxidation reaction, resulting in a mass loss of the carbon fiber. Although this method calculates the correction coefficient by increasing the burning comparison of single carbon fiber components of the same specification, and calculates the ratio of the original carbon fiber mass to the carbon fiber mass after burning to obtain the correction coefficient, and corrects the carbon fiber mass after burning the composite material through the correction coefficient to obtain the original carbon fiber mass, so as to calculate the carbon fiber mass content in the carbon fiber composite material. However, since the carbon fiber is severely oxidized and the mass loss is large in this case, and the calculated correction coefficient is also on the high side, the fiber mass content obtained by this method has a large error and cannot accurately measure the fiber mass content. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for detecting the carbon fiber content of a carbon fiber reinforced epoxy resin composite material, and its technical solution is as follows: A method for detecting the carbon fiber content of a carbon fiber reinforced epoxy resin composite material includes the following steps: Step S1, Sampling: Uniformly select a number of specimens with the same specifications on the carbon fiber reinforced epoxy resin composite material; Step S2, Weighing: Heat and clean a number of crucibles corresponding to the specimens, then dry and cool them to room temperature, and then weigh the masses of the a number of crucibles respectively, denoted as M1 , and then weigh the specimens selected in step S1 respectively, denoted as M 2 , and place one specimen in one crucible respectively; Step S3: Ignite; Step S31: Anaerobic ignition of the specimen: Place several crucibles containing the specimens in a muffle furnace, close the valve, evacuate the muffle furnace, and then continuously and evenly introduce an inert gas to maintain an anaerobic state in the furnace. Then start the muffle furnace, set the temperature at 600 ± 10 °C, and conduct anaerobic combustion of the specimen for 3 - 6H; Step S32: Aerobic combustion of the specimen: After anaerobic ignition is completed, close the inert gas source, then open the air source, introduce air, maintain an aerobic environment in the furnace, set the temperature at 500 ± 10 °C, and conduct aerobic combustion for 1.5 - 3H until the combustion is complete; Step S33: Weigh each crucible after ignition and the remaining fibers in the crucible one by one, denoted as M3; Step S4: Calculate the fiber correction coefficient. Select several carbon fiber specimens of the same specification batch as the carbon fiber raw material used in the laminate. The specific number of specimens is the same as the number of specimens in step S1. According to the same method as in steps S2 and S3, obtain the crucible mass m 1 , the mass of the fiber specimen m 2 , the total mass of the fiber and the crucible after ignition m 3 , and then calculate the fiber correction coefficient K according to the following calculation formula; K = m 2 / (m 3 - m 1 ); Step S5: Calculate the carbon fiber mass in the laminate according to the following formula: M 0 = (M 3 - M 1 ) * K; Step S6: Calculate the carbon fiber mass content in the laminate according to the following formula, M f = M 0 / M 2 * 100%.

[0005] In step S1, the number of specimens selected should be no less than 4, preferably 5. When 5 specimens are selected, randomly select a rectangular or square sample plate, then determine the midpoint of the diagonal as the central sampling point on the sample plate, and then select four points equidistant from the central sampling point on the diagonal as the sample points. Take 5 squares of 25 × 25 mm with the sample points as the centers as the test specimens.

[0006] In step S31, the inert gas introduced is nitrogen, and the gas flow rate is 2.8 L / min to keep the inside of the muffle furnace in an anaerobic state.

[0007] In step S32, the gas flow rate of the air introduced is 2.8 L / min to maintain a sufficient aerobic environment inside the muffle furnace.

[0008] In step S4, the combustion of the carbon fiber includes anaerobic combustion and aerobic combustion. The anaerobic combustion temperature is set at 600 ± 10 °C, and the combustion time is 180 ± 5 min. The aerobic combustion temperature is set at 500 ± 10 °C, and the combustion time is 90 ± 5 min.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: For the fiber content test method of the carbon fiber reinforced epoxy resin composite material adopting the above technical solution, the inorganic components difficult to remove in the epoxy resin are first removed by high-temperature anaerobic burning in a gas-extractable muffle furnace, and this process can protect the carbon fiber from being oxidized; then, by reducing the temperature and introducing oxygen, the organic chemical components of the resin are burned in a relatively low-temperature aerobic muffle furnace. At the same time, the low temperature and shortening the burning time while ensuring sufficient burning of the organic chemical components can maximize the oxidation rate of the carbon fiber, thereby controlling the mass loss rate of the carbon fiber. At this time, the correction coefficient of the carbon fiber mass loss is calculated by the mass ratio of the carbon fiber tow of the same specification in the control group before and after burning, and the mass of the carbon fiber in the original composite material is calculated through the correction coefficient, so as to calculate the fiber mass content and the resin content. This method has a small error and the calculation result is more accurate. Description of the Drawings

[0010] Appendix Figure 1 is a sampling schematic diagram of the carbon fiber reinforced epoxy resin composite material; Appendix Figure 2 is a photo of the unburned sufficiently carbon fiber epoxy resin composite material laminate; Appendix Figure 3 is a photo of the sufficiently burned carbon fiber epoxy resin composite material laminate. Embodiment

[0011] Next, the technical solution of the present invention will be described clearly and completely with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present invention. Example

[0012] In this embodiment, the carbon fiber reinforced epoxy resin composite material is a carbon fiber fabric laminate prepared from 12K carbon fiber tows, and the designed value of the resin mass content in its theoretical process parameters is 34%, and the designed value of the carbon fiber mass content is 66%.

[0013] The present invention provides a method for detecting the carbon fiber content of a carbon fiber reinforced epoxy resin composite material, including: Step S1, sampling: Uniformly select 5 specimens of 25×25 mm at the positions shown in the appendix on the carbon fiber reinforced epoxy resin composite material, and mark the specimens with serial numbers 1, 2, 3, 4, and 5; Figure 1 Step S2, weighing: Take 5 crucibles, mark them with serial numbers 1, 2, 3, 4, and 5, then heat and clean the crucibles, and then dry and cool them to room temperature. Then, respectively weigh the masses of the 5 crucibles, denoted as M , and then weigh the 5 specimens selected in step S1 respectively, denoted as M 1 according to the serial numbers, and place the specimens corresponding to the serial numbers in the crucibles with the same serial numbers; 2 Step S3, burning; Step S31, anaerobic burning of the specimen: Place the 5 crucibles containing the specimens in a muffle furnace, close the valve, evacuate the muffle furnace, and then continuously and uniformly introduce an inert gas to maintain an anaerobic state in the furnace. Then start the muffle furnace, set the temperature at 600±10°C, and carry out anaerobic combustion of the specimens for 3-6H; Step S32, aerobic burning of the specimen: After the anaerobic burning is completed, close the inert gas gas source, then open the air gas source, introduce air, maintain an aerobic environment in the furnace, set the temperature at 500±10°C, and carry out aerobic combustion for 1.5-3H until the combustion is complete; Specifically, whether the sample block is burned completely can be judged by whether the sample block is easily dispersed into filaments. For example, in the appendix is not burned completely and is in a hard block shape; in the appendix Figure 2 is easily dispersed into filaments; Figure 3 Step S33, weigh each of the crucibles after burning and the remaining fibers in the crucibles one by one, denoted as M3; Step S4, calculate the fiber correction coefficient K. Select 5 specimens of 12K carbon fiber with the same specification batch as the carbon fiber raw material used in the laminate, each with a mass of 4-5 g. According to the same method as in steps S2 and S3, obtain the crucible mass m , the fiber specimen mass m 1 , and the total mass of the fiber and the crucible after burning m 2 , 3, then calculate the fiber correction coefficient K according to the following calculation formula; specifically, the anaerobic combustion temperature of carbon fiber is set at 600 ± 10 °C, the combustion time is set at 180 ± 5 min, the aerobic combustion temperature is set at 500 ± 10 °C, and the combustion time is set at 90 ± 5 min. The calculation formula of K is as follows: K = m 2 / (m 3 - m 1 ); Step S5: Calculate the carbon fiber mass in the laminate according to the following formula: M 0 = (M 3 - M 1 ) * K; Step S6: Calculate the carbon fiber mass content in the laminate according to the following formula, M f = M 0 / M 2 * 100%.

[0014] In this embodiment, the burning test data of carbon fiber of the same specification batch as the carbon fiber raw material used in the laminate are shown in Table 1. Table 1

[0015] In this embodiment, the burning test data of the carbon fiber laminate and the calculated values after obtaining the correction coefficient by combining with Table 1 are shown in Table 2. Table 2

[0016] Comparative example As a comparative example of Example 1, the inventor used the prior art to test the carbon fiber mass content of carbon fiber reinforced epoxy resin composites, that is, the same carbon fiber laminate and the same carbon fiber as in the example were selected, but the difference was that both the carbon fiber laminate and the carbon fiber were subjected to aerobic combustion at 600 °C for 180 min in the S3 combustion step. The fiber burning data are shown in Table 3, and the burning data and calculated values of the carbon fiber laminate are shown in Table 4. Table 3

[0017] Table 4

[0018] By comparing the test results of Example 1 and the comparative example, it can be seen that there is a significant difference in the test results of the carbon fiber laminate made of materials of one specification when burned in a pure aerobic environment and when burned in an environment combining anaerobic (600°C for 180 minutes) and aerobic (500°C for 90 minutes) environments. Among them, the test results of burning in the environment combining anaerobic (600°C for 180 minutes) and aerobic (500°C for 90 minutes) are close to the true value, while the test results of burning in a pure aerobic environment have a large error compared with the true value. Thus, it can be seen that the burning test method combining high-temperature anaerobic and relatively low-temperature aerobic can more accurately test the fibrous content in the carbon fiber laminate.

Claims

1. A method for detecting the carbon fiber content of a carbon fiber reinforced epoxy resin composite material, characterized in that, it includes the following steps: Step S1, sampling: Take a carbon fiber reinforced epoxy resin composite laminate, and select several specimens with the same specifications on the laminate; Step S2, weighing: Heat and clean a number of crucibles corresponding to the number of specimens, then dry and cool them to room temperature, and then weigh the masses of the number of crucibles respectively, denoted as M 1 , and then weigh the specimens selected in step S1 respectively, denoted as M 2 , and place one specimen in one crucible respectively; Step S3, burning; Step S31, anaerobic burning of the specimen: Place several crucibles containing the specimens in a vacuum-pumpable muffle furnace, close the valve, evacuate the muffle furnace, and continuously and evenly introduce an inert gas to maintain an anaerobic state in the furnace. Then start the muffle furnace, set the temperature at 600±10°C, and conduct anaerobic combustion of the specimen for 3 - 6H; Step S32, aerobic combustion of the specimen: After anaerobic burning is completed, close the inert gas source, then open the air source, maintain an aerobic environment in the furnace, set the temperature at 500±10°C, and conduct aerobic combustion for 1.5 - 3H; Step S33: Weigh each crucible and the remaining fibers in the crucible after burning, and record it as M 3 ; Step S4: Calculate the fiber correction coefficient. Select several carbon fiber specimens with the same specification batch as the carbon fiber raw material used in the laminate. The specific number of specimens is the same as that in Step S1. Obtain the crucible mass m in the same manner as in Steps S2 and S3. 1 , the fiber specimen mass m 2 , the total mass m of the fiber and the crucible after burning 3 , and then calculate the fiber correction coefficient K according to the following calculation formula; K = m 2 / (m 3 -m 1 ); Step S5, calculate the mass of carbon fiber in the laminate according to the following formula: M 0 = (M 3 - M 1 ) * K; Step S6, calculate the mass content of carbon fiber in the laminate according to the following formula, M f = M 0 / M 2 * 100%.

2. The method for detecting the carbon fiber content of a carbon fiber reinforced epoxy resin composite material according to claim 1, characterized in that, in the step S1, the number of the specimens is not less than 5.

3. The method for detecting the carbon fiber content of a carbon fiber reinforced epoxy resin composite material according to claim 2, characterized in that, the number of the specimens is 5, and sampling is carried out according to the five-point method.

4. The method for detecting the carbon fiber content of a carbon fiber reinforced epoxy resin composite material according to claim 1, characterized in that, in the step S4, the anaerobic combustion temperature of carbon fiber is set at 600±10°C, the combustion time is 180±5 min, the aerobic combustion temperature is set at 500±10°C, and the combustion time is 90±5 min.

Images