A measuring device and method for measuring the resistance change of a hot-press formed conductive composite material

Abstract

The present application relates to the technical field of conductive composite material, and particularly relates to a measuring device and method for resistance change of conductive composite material hot-press forming, which comprises the following steps: measuring and recording initial resistance values of a plurality of conductive composite material samples; placing the plurality of conductive composite material samples in a hot-pressing tank to obtain pre-solidification resistance values of each conductive composite material sample; collecting resistance change data of a conductive thin layer of one of the conductive composite material samples in real time during the solidification process; calculating resistance change rates of the conductive composite material samples before and after solidification; measuring post-solidification resistance values of the remaining conductive composite material samples and obtaining an average value of the resistance change rates; and determining the resistance change data as valid data when an error between the resistance change rate and the average value of the resistance change rates is less than a second preset value. The purpose of the measuring device and method for resistance change of conductive composite material hot-press forming is to solve the problem of greater difficulty in real-time resistance measurement during the hot-press solidification forming process of the conductive composite material.

Description

A device and method for measuring the resistance change of conductive composite materials during hot pressing. Technical Field

[0001] This invention relates to the field of conductive composite materials technology, and specifically to a measuring device and method for measuring the resistance change of conductive composite materials during hot pressing. Background Technology

[0002] Structural conductive composite materials are mainly used in the aerospace field for lightning protection, electromagnetic shielding, electromagnetic wave reflection, de-icing, and surface traveling wave suppression. These materials are a new type of aerospace material that integrates structural load-bearing and conductive functions, and their application in the aerospace industry is receiving increasing attention. Alternatively, by laying conductive thin film layers on the surface or between layers of the composite material, a particular layer can possess conductive properties to meet relevant conductivity requirements; this type is called thin-layer conductive composite material.

[0003] The resistance of conductive thin layers often changes after being introduced into composite materials, thus affecting their performance. Composite materials are generally cured in autoclaves, and their surfaces are covered with vacuum bags through a combination of processes. During the curing process, they are in the high-temperature and high-pressure environment of the autoclave, making it impossible to measure the vacuum curing process in real time.

[0004] In existing technologies, the performance of conductive thin layers is typically evaluated by measuring the change in resistance before and after curing. However, it is impossible to measure the resistance change during the curing process in real time, and the mechanism of this resistance change and its influencing factors are currently unknown. Therefore, this limits the ways to reduce resistance changes through process optimization and adjustment.

[0005] Therefore, the inventors provide a device and method for measuring the resistance change of conductive composite materials during hot pressing. Summary of the Invention

[0006] (1) Technical problems to be solved

[0007] This invention provides a device and method for measuring the resistance change of conductive composite materials during hot pressing, solving the technical problem of how to measure the resistance change of conductive composite materials in real time during the hot pressing curing process.

[0008] (2) Technical solution

[0009] The first aspect of the present invention provides a method for measuring the resistance change of a conductive composite material during hot pressing, comprising the following steps:

[0010] The initial resistance values ​​of multiple conductive composite material samples were measured and recorded;

[0011] Multiple conductive composite material samples are placed in an autoclave, and the electrode of each conductive composite material sample is connected to an external data measurement and acquisition unit to obtain the measured resistance value of each conductive composite material sample. When the difference between the measured resistance value and the initial resistance value is less than a first preset value, the measured resistance value is determined to be the resistance value before curing.

[0012] During the curing process, the resistance change data of the conductive thin layer of one of the conductive composite material samples is collected in real time, and the resistance value changes over time.

[0013] Based on the resistance value before curing and the resistance change data, the resistance change rate of the conductive composite material sample before and after curing is calculated.

[0014] Measure the resistance value of the remaining conductive composite material samples after curing, calculate the resistance change rate before and after curing for each sample, and obtain the average resistance change rate.

[0015] When the error between the resistance change rate and the average resistance change rate is less than a second preset value, the resistance change data is determined to be valid data.

[0016] Furthermore, a conductive thin layer is introduced into the electrode, and the conductive thin layer with the electrode is placed into the prepreg layup to form the conductive composite material sample.

[0017] Furthermore, ensure that the electrode extends beyond the prepreg layup to connect to the electrode connection system.

[0018] Furthermore, the protruding portion of the electrode is separated by a non-porous insulating membrane.

[0019] Furthermore, before curing begins, the process includes: synchronizing the time of the data acquisition unit with the time of the autoclave, and setting the temperature, pressure, and curing time of the autoclave.

[0020] Furthermore, the number of conductive composite material samples is at least six.

[0021] Furthermore, the second preset value is 15%.

[0022] A second aspect of the present invention provides a measuring device for the resistance change of conductive composite materials during hot pressing, comprising a data measurement and acquisition unit and an electrode connection system; wherein,

[0023] The data measurement and acquisition unit is used to acquire the resistance data of the conductive composite material in real time during the curing process, and to record and analyze the real-time resistance change data to obtain the resistance change trend.

[0024] The two ends of the electrode connection system are respectively connected to the data measurement and acquisition unit and the conductive composite material in the autoclave.

[0025] Furthermore, the electrode connection system includes a high-temperature resistant wire and a detachable electrode clamp. The two ends of the high-temperature resistant wire are respectively connected to the data measurement and acquisition unit and the detachable electrode clamp. The high-temperature resistant wire is led out from the reserved lead outlet of the autoclave, and the lead-out position is sealed with high-temperature resistant sealant to ensure that the autoclave maintains high temperature and high pressure operation.

[0026] Furthermore, the two ends of the electrode connection system are fixed to the data measurement and acquisition unit and the conductive composite material in the autoclave respectively by high-temperature resistant tape.

[0027] (3) Beneficial effects

[0028] In summary, this invention uses an external measuring device to monitor the real-time resistance changes of conductive composite materials in an autoclave during the hot-press curing process. This enables online monitoring of the resistance of conductive composite materials during curing, helps to understand the factors affecting resistance changes during curing, and provides a reference for process adjustment. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 is a flowchart illustrating a method for measuring the resistance change of a conductive composite material during hot pressing, according to an embodiment of the present invention.

[0031] Figure 2 is a schematic diagram of the electrical connection of a prepreg containing a conductive thin layer according to an embodiment of the present invention.

[0032] Figure 3 is a schematic diagram of the curing process of a conductive composite material sample provided in an embodiment of the present invention.

[0033] Figure 4 is a graph showing the effect of pressure on the resistance of montmorillonite fabric according to Embodiment 1 of the present invention.

[0034] Figure 5 is a graph showing the change in electrical resistance during the curing process of a montmorillonite fabric provided in Embodiment 2 of the present invention.

[0035] Figure 6 is a graph showing the resistance change during the curing process of a conductive nonwoven fabric provided in Embodiment 3 of the present invention.

[0036] In the picture:

[0037] 1-Vacuum bag film; 2-Breathable felt; 3-First PTFE cloth; 4-Porous membrane; 5-Prepreg preform with conductive thin layer; 6-High temperature resistant wire; 7-Non-porous membrane; 8-Second PTFE cloth; 9-Sealing strip; 10-Plate mold; 11-Conductive thin layer electrode. Detailed Implementation

[0038] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention by way of example, but should not be used to limit the scope of the present invention. That is, the present invention is not limited to the described embodiments, and any modifications, substitutions and improvements to the parts, components and connection methods are covered without departing from the spirit of the present invention.

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0040] In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0041] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set" and "install" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0042] Conductive thin layers, including metal mesh foils, conductive fabrics, carbon nanotube films, and graphene films, often exhibit changes in resistance during the curing process after being introduced into composite materials. For applications such as de-icing and traveling wave suppression, it is crucial to control these resistance changes to ensure the conductive thin layer maintains its resistance and uniformity after curing. Conductive thin layers (such as metal mesh foils, conductive fabrics, carbon nanotube films, and graphene films) are widely used in composite materials for de-icing, traveling wave suppression, and other functional requirements. However, the resistance of these conductive thin layers often changes after being introduced into composite materials and undergoing the curing process. This change significantly affects the electrical properties and functional performance of the composite material.

[0043] Figure 1 is a flowchart illustrating a method for measuring the resistance change of a conductive composite material during hot pressing according to an embodiment of the present invention. Referring to Figure 1, the method may include the following steps:

[0044] S100. Measure and record the initial resistance values ​​of multiple conductive composite material samples.

[0045] Specifically, six identical samples can be prepared simultaneously, and their initial resistance values ​​can be measured and recorded. For five of these samples, only the initial and post-curing resistance data are recorded; changes during the curing process are not monitored. The average value is used as a comparison value for resistance changes to verify the validity of the changes before and after the test data. As shown in Figure 2, the preparation process of the conductive composite material sample is as follows: a conductive thin layer is introduced into the electrode by copper spraying or adhesive bonding. The conductive thin layer electrode 11 with electrodes is introduced into the layup of the prepreg preform 5, ensuring that the electrode is exposed in the layup for connection to the electrode connection system. The electrode protrusion position is separated by a non-porous insulating membrane to ensure that the adhesive during the curing process does not flow onto the electrode, causing it to lose conductivity.

[0046] S200. Place multiple conductive composite material samples in an autoclave and connect the electrode of each conductive composite material sample to an external data measurement and acquisition unit to obtain the measured resistance value of each conductive composite material sample. When the difference between the measured resistance value and the initial resistance value is less than a first preset value, the measured resistance value is determined to be the resistance value before curing.

[0047] Specifically, the assembled composite material sample to be tested is placed in an autoclave, ensuring a reliable connection between the electrode terminals of the conductive thin layer and the electrode clamps of the resistance measurement unit. The resistance is measured using a data measurement and acquisition unit to determine if it is close to the initial resistance value from step S100. If the data difference is significant, the connection of the entire system is checked. Once the resistance value is close to the initial resistance value from the previous step, the resistance measurement value before curing is recorded.

[0048] S300: During the curing process, the resistance change data of the conductive thin layer of one of the conductive composite material samples is collected in real time, and the resistance value changes over time.

[0049] Specifically, the time of the data measurement and acquisition unit is coordinated with the time of the autoclave. The temperature, pressure and curing time of the autoclave are set, and the curing program is started. At the same time, the data measurement and acquisition unit is started. During the curing process, the resistance change data of the conductive thin layer is collected in real time, and the resistance value change curve over time is recorded. After the curing process is completed, the resistance recording is stopped.

[0050] As shown in Figure 3, before placing the prepreg preform 5 containing the conductive thin layer into an autoclave for hot-press curing, a vacuum bag film 1, a breathable felt 2, a first PTFE cloth 3, and a porous film 4 are sequentially laid on the upper surface of the prepreg preform 5 from top to bottom. On the lower surface of the prepreg preform 5, a non-porous film 7 and a second PTFE cloth 8 are sequentially laid on from top to bottom. The assembled structure is then placed onto a flat mold 10, and the contact area between the flat mold 10 and the vacuum bag film 1 is sealed with a sealing strip 9. A high-temperature resistant wire 6 passes through the sealing strip 9 and connects to the prepreg preform 5 containing the conductive thin layer. The first PTFE cloth 3 and the second PTFE cloth 8 are made of the same material, but their thickness and area can be the same or different, depending on the specific circumstances.

[0051] S400. Based on the resistance value before curing and the resistance change data, calculate the resistance change rate of the conductive composite material sample before and after curing.

[0052] Specifically, time, temperature, and pressure data are exported from the recording system of the autoclave, and resistance data is exported from the resistance recorder. The resistance change rate Km before and after curing is calculated. The resistance change rate Km is calculated according to the following formula (1):

[0053] The rate of change of resistivity before and after curing is calculated according to the following formula:

[0054]

[0055] In the formula, ΔR represents the resistance difference before and after curing, R1 represents the resistance value after curing, and R0 represents the resistance value before curing.

[0056] S500. Measure the resistance value of the remaining conductive composite material samples after curing, calculate the resistance change rate before and after curing for each sample, and obtain the average resistance change rate.

[0057] Specifically, the rate of change of resistance before and after curing of all remaining samples was measured, and the average value was taken. As its rate of change of resistance.

[0058] S600. When the error between the resistance change rate and the average resistance change rate is less than the second preset value, the resistance change data is determined to be valid data.

[0059] Specifically, if the error ΔE between the two is less than 15%, the monitoring data is considered valid.

[0060] The error between the monitored rate of change of resistance and the rate of change of the comparison sample is calculated according to the following formula (2):

[0061]

[0062] In summary, the measurement method of this invention enables online monitoring of resistance during the curing process of conductive composite materials, overcoming the shortcomings of existing technologies that cannot measure resistance in real time. It also provides complete resistance change curves and data support, revealing the mechanism of resistance change and providing a scientific basis for adjusting process parameters. This significantly improves the uniformity and reliability of the conductive properties of the composite material, and has wide applicability, enabling research on multiple conductive composite materials such as those for lightning protection, electromagnetic shielding, and de-icing.

[0063] This invention also provides a measuring device for the resistance change of conductive composite materials during hot pressing, including a data measurement and acquisition unit and an electrode connection system; wherein,

[0064] The data measurement and acquisition unit is used to acquire the resistance data of conductive composite materials in real time during the curing process, and to record and analyze the real-time resistance change data to obtain the resistance change trend.

[0065] The two ends of the electrode connection system are respectively connected to the data measurement and acquisition unit and the conductive composite material in the autoclave.

[0066] Specifically, the electrode connection system includes a high-temperature resistant wire and a detachable electrode clamp, with the two ends of the high-temperature resistant wire connected to the data measurement and acquisition unit and the detachable electrode clamp, respectively.

[0067] As an optional implementation, the two ends of the electrode connection system are fixed to the data measurement and acquisition unit and the conductive composite material in the autoclave using high-temperature resistant tape. Using high-temperature resistant insulating tape to fix the electrode connection system to the conductive composite material prevents it from loosening during the high-temperature, high-pressure process, which could reduce the accuracy of the recorded data.

[0068] Example 1

[0069] Graphene fabric (conductive fabric with graphene CVD deposited on the surface of quartz fiber) was introduced as a conductive thin layer into epoxy resin-based composite material. The resistance change under different temperatures and pressures was measured online using the measuring device of this invention. The measurement data obtained are shown in Figure 4.

[0070] As can be seen from Figure 4, the resistance decreases with increasing pressure, indicating that it is beneficial to increase the contact points of conductive fibers. When the pressure is removed, the resistance of the montmorillonite fabric returns to its original level. This process is reversible.

[0071] Example 2

[0072] A graphene fabric (a conductive fabric with graphene CVD deposited on the surface of quartz fibers) was introduced as a conductive thin layer into an epoxy resin-based composite material. The online resistance was measured during the autoclave curing process using the measuring device of this invention, and the measurement data obtained are shown in Figure 5.

[0073] As shown in Figure 5, the montmorillonite fabric exhibits a negative temperature coefficient (NTC) characteristic, with its resistance decreasing as the temperature increases. When the temperature reaches 130℃ and the pressure reaches 0.7MPa, compared to the fabric without the composite material, the resistance of the fabric with the composite material is observed to increase rapidly. Analysis shows that this change is related to the reduced contact between the montmorillonite fibers caused by the resin flowing and wetting the conductive network. This increase persists until after the resin cures. Compared to the montmorillonite fabric without the composite material, the resistance of the fabric with the composite material increased by 4%, which is closely related to the resin flow and curing reaction.

[0074] Example 3

[0075] Ion electrodeposited conductive nonwoven fabric was used as a conductive thin layer and introduced into epoxy resin-based composite material. The measuring device of this invention was used to perform online resistance measurement during the autoclave curing process. The measurement data obtained are shown in Figure 6.

[0076] As can be seen from Figure 6, the conductive nonwoven fabric has a positive temperature coefficient (PTC) characteristic. It does not exhibit an increase in resistance as the resin viscosity changes during the curing process. The resistance change is mainly caused by temperature changes. After curing, the resistance change returns to the level before curing. This characteristic is related to its conductive network.

[0077] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. The present invention is not limited to the specific steps and structures described above and shown in the figures. Furthermore, for the sake of brevity, detailed descriptions of known methods and techniques are omitted here.

[0078] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art without departing from the scope of the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A method for measuring the resistance change of conductive composite materials during hot pressing, characterized in that, The method includes the following steps: measuring and recording the initial resistance values ​​of multiple conductive composite material samples; placing the multiple conductive composite material samples in an autoclave, and connecting the electrode terminals of each conductive composite material sample to an external data measurement and acquisition unit through an electrode connection system to obtain the measured resistance value of each conductive composite material sample; when the difference between the measured resistance value and the initial resistance value is less than a first preset value, the measured resistance value is determined to be the resistance value before curing; during the curing process, the resistance change data of the conductive thin layer of one of the conductive composite material samples is collected in real time, and the resistance value change curve over time is recorded; based on the resistance value before curing and the resistance change data, the resistance change rate of the conductive composite material sample before and after curing is calculated; and the post-curing resistance value of the remaining conductive composite material samples is measured. The resistance change rate before and after curing is calculated separately, and the average resistance change rate is obtained. When the error between the resistance change rate and the average resistance change rate is less than a second preset value, the resistance change data is determined to be valid data. A conductive thin layer is introduced into the electrode, and the conductive thin layer with the electrode is placed into the prepreg layer to form the conductive composite material sample. A vacuum bag film, a breathable felt, a first PTFE cloth, and a porous film are sequentially laid on the upper surface of the conductive composite material sample from top to bottom. A non-porous film and a second PTFE cloth are sequentially laid on the lower surface of the conductive composite material sample from top to bottom. The above-laid overall structure is placed on a flat mold, and then the overall structure is covered with the vacuum bag film. Ensure that the electrode extends out of the prepreg layer to connect to the electrode connection system, and the protruding part of the electrode is separated by a non-porous isolation film.

2. The method for measuring the resistance change of conductive composite materials during hot pressing according to claim 1, characterized in that, Before curing begins, the process also includes: synchronizing the time of the data acquisition unit with the time of the autoclave, and setting the temperature, pressure, and curing time of the autoclave.

3. The method for measuring the resistance change of conductive composite materials during hot pressing according to claim 1, characterized in that, The number of conductive composite material samples is at least 6.

4. The method for measuring the resistance change of conductive composite materials during hot pressing according to claim 1, characterized in that, The second preset value is 15%.

5. A measuring device employing the method for measuring the resistance change of conductive composite materials during hot pressing as described in any one of claims 1-4, characterized in that, It includes a data measurement and acquisition unit and an electrode connection system; wherein, the data measurement and acquisition unit is used to acquire the resistance data of the conductive composite material in real time during the curing process, and record and analyze the real-time resistance change data to obtain the resistance change trend; the two ends of the electrode connection system are respectively connected to the data measurement and acquisition unit and the conductive composite material in the autoclave.

6. The measuring device according to claim 5, characterized in that, The electrode connection system includes a high-temperature resistant wire and a detachable electrode clamp. The two ends of the high-temperature resistant wire are connected to the data measurement and acquisition unit and the detachable electrode clamp, respectively. The high-temperature resistant wire is led out from the reserved lead outlet of the autoclave, and the lead-out position is sealed with high-temperature resistant sealant to ensure that the autoclave maintains high temperature and high pressure operation.

7. The measuring device according to claim 5 or 6, characterized in that, The two ends of the electrode connection system are fixed to the data measurement and acquisition unit and the conductive composite material in the autoclave by high-temperature resistant tape.

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