Device and method for measuring hot-press forming resistance change of conductive composite material

Abstract

The invention relates to the technical field of conductive composite materials, in particular to a conductive composite material hot press forming resistance change measuring device and method, and the method comprises the steps: measuring and recording initial resistance values of a plurality of conductive composite material samples; placing the plurality of conductive composite material samples in an autoclave, and obtaining the resistance value of each conductive composite material sample before curing; collecting resistance change data of the conductive thin layer of one conductive composite material sample in real time in the curing process; calculating the resistance change rate of the conductive composite material sample before and after curing; measuring the resistance value of the residual conductive composite material sample after curing, and calculating the average value of the resistance change rate; and when the error between the resistance change rate and the resistance change rate average value is smaller than a second preset value, determining the resistance change data as effective data. The device and the method for measuring the hot-press forming resistance change of the conductive composite material aim at solving the problem that the real-time measurement difficulty of the resistance is relatively high in the hot-press curing forming process of the conductive composite material.

Description

Technical Field

[0001] The invention relates to the technical field of conductive composite materials, and in particular to a device and method for measuring resistance changes of conductive composite materials during hot pressing molding. Background Art

[0002] Structural conductive composite materials are mainly used in the field of aviation for lightning protection, electromagnetic shielding, electromagnetic wave reflection, deicing and surface wave suppression. Structural conductive composite materials are a new type of aviation material that integrates structural load-bearing and conductive functions. Its application in the field of aviation and aerospace is gaining increasing attention. Or by laying a conductive film layer on the surface of the composite material or between layers, a certain layer of the composite material has a conductive function to meet the relevant conductive function requirements, which is called a thin-layer conductive composite material.

[0003] The resistance of the conductive thin layer often changes after the composite material is introduced, thus affecting its performance. Composite materials are generally cured in an autoclave, and their surface is covered with a vacuum bag through a combination of processes. During the curing process, they are in the high temperature and high pressure environment of the autoclave, and it is impossible to measure the vacuum curing process in real time.

[0004] In the prior art, the performance of the conductive thin layer is usually evaluated by measuring the change in resistance before and after curing, but it is impossible to measure the change in resistance in real time during the curing process, and it is currently impossible to understand the mechanism of resistance change and its influencing factors. Therefore, this limits the way to reduce the resistance change through process optimization and adjustment.

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

[0006] (1) Technical issues to be solved

[0007] The embodiment of the present invention provides a device and method for measuring resistance change of a conductive composite material during hot pressing and curing, which solves the technical problem of how to measure resistance change in real time during hot pressing and curing of a conductive composite material.

[0008] (2) Technical solution

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

[0010] measuring and recording initial resistance values ​​of a plurality of conductive composite material samples;

[0011] Placing a plurality of the conductive composite material samples in an autoclave, and connecting the electrode end of each conductive composite material sample to an external data measurement and acquisition unit to obtain a measured resistance value of each conductive composite material sample, and determining that the measured resistance value is a resistance value before curing when the difference between the measured resistance value and the initial resistance value is less than a first preset value;

[0012] During the curing process, real-time data on the resistance change of the conductive thin layer of one of the conductive composite material samples is collected, and a curve of the resistance value changing over time is recorded;

[0013] Calculating the resistance change rate of the conductive composite material sample before and after curing according to the resistance value before curing and the resistance change data;

[0014] Measuring the resistance values ​​of the remaining conductive composite material samples after curing, calculating the resistance change rates before and after curing, and obtaining an average value of the resistance change rates;

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

[0016] Furthermore, the 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.

[0017] Further, it is ensured that the electrodes extend out of the prepreg layup to access the electrode connection system.

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

[0019] Furthermore, before the curing starts, the method further 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 the conductive composite material samples is at least 6.

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

[0022] The second aspect of the present invention provides a device for measuring resistance change of a conductive composite material 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 collect the resistance data of the conductive composite material in the curing process in real time, and 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 collection 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 at a reserved lead outlet of the autoclave, and the lead-out position is sealed with a high-temperature resistant sealant to ensure that the autoclave maintains high temperature and high pressure operation.

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

[0027] (3) Beneficial effects

[0028] In summary, the present invention uses an external measuring device to measure the real-time change of the resistance of the conductive composite material in the autoclave during the hot pressing curing molding process, thereby realizing online monitoring of the resistance during the curing process of the conductive composite material, understanding the factors affecting the resistance change during the curing process, and providing a reference for process adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 It is a schematic flow chart of a method for measuring resistance change of a conductive composite material during hot pressing molding provided by an embodiment of the present invention;

[0031] Figure 2 It is a schematic structural diagram of electrical connection of a prepreg preform containing a conductive thin layer provided by an embodiment of the present invention;

[0032] Figure 3 It is a schematic diagram of the curing process and laying of a conductive composite material sample provided by an embodiment of the present invention;

[0033] Figure 4 This is a diagram showing the effect of pressure on the resistance change of monolein fabric provided in Example 1 of the present invention;

[0034] Figure 5 This is a resistance change diagram of a monene fabric during curing provided by Example 2 of the present invention;

[0035] Figure 6This is a resistance change diagram of a conductive non-woven fabric during curing provided by Example 3 of the present invention.

[0036] In the figure:

[0037] 1-vacuum bag film; 2-breathable felt; 3-first polytetrafluoroethylene cloth; 4-porous film; 5-prepreg preform containing a conductive thin layer; 6-high temperature resistant wire; 7-non-porous film; 8-second polytetrafluoroethylene cloth; 9-sealing tape; 10-flat mold; 11-conductive thin layer electrode. DETAILED DESCRIPTION

[0038] The following is a further detailed description of the embodiments of the present invention in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to exemplarily illustrate the principles of the present invention, but cannot be used to limit the scope of the present invention, that is, the present invention is not limited to the described embodiments, and covers any modification, replacement and improvement of parts, components and connection modes without departing from the spirit of the present invention.

[0039] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0040] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "rear", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the products of the present invention are conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art. These are merely for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0041] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "setting" and "installation" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] Conductive thin layers are divided into metal mesh foil, conductive fabric, carbon nanotube film and graphene film, etc. The conductive fabric, carbon nanotube film and graphene film prepared by different methods often change their resistance when introduced into composite materials for curing. For fields such as anti-icing and traveling wave suppression, it is often necessary to control the resistance change to ensure that the conductive thin layer can still maintain the corresponding resistance and resistance uniformity after curing. Conductive thin layers (such as metal mesh foil, conductive fabric, carbon nanotube film and graphene film) are widely used in composite materials for anti-icing, traveling wave suppression and other functional requirements. However, after these conductive thin layers are introduced into composite materials and undergo a curing process, their resistance often changes. This change can significantly affect the electrical properties and functional performance of the composite material.

[0043] Figure 1 is a flow chart of a method for measuring resistance change of a conductive composite material by hot pressing molding provided by an embodiment of the present invention, see Figure 1 , the method may include the following steps:

[0044] S100, measuring and recording initial resistance values ​​of a plurality of conductive composite material samples.

[0045] Specifically, six identical samples can be prepared at the same time, and their initial resistance values ​​can be measured and recorded. Five of the samples only record the initial and post-curing resistance data, without monitoring the changes during the curing process. The average value is used as the comparison value of the resistance change to verify the validity of the changes before and after the test data. Figure 2 As shown, the preparation process of the conductive composite material sample is: introducing the conductive thin layer into the electrode by copper spraying or conductive glue, introducing the conductive thin layer electrode 11 with the electrode into the ply of the prepreg preform 5, ensuring that the electrode is exposed from the ply so as to be connected to the electrode connection system, and the electrode extension position is separated by a non-porous isolation membrane to ensure that the glue during the curing process will not flow onto the electrode, causing the electrode to no longer be conductive.

[0046] S200, placing a plurality of conductive composite material samples in an autoclave, and connecting the electrode end of each conductive composite material sample to an external data measurement and acquisition unit to obtain a measured resistance value of each conductive composite material sample, and when the difference between the measured resistance value and the initial resistance value is less than a first preset value, determining that the measured resistance value is the resistance value before curing.

[0047] Specifically, the assembled composite material sample to be tested is placed in an autoclave, ensuring that the electrode end of the conductive thin layer is reliably connected to the electrode fixture of the resistance measurement unit, and the resistance is measured using the data measurement and acquisition unit to determine whether it is close to the initial resistance value of step S100. If the data is significantly different, check the connection of the entire system, and when its resistance value is close to the initial resistance value of the previous step, record the resistance measurement value before curing.

[0048] S300, collecting resistance change data of the conductive thin layer of one of the conductive composite material samples in real time during the curing process, and recording a curve of resistance value change over time.

[0049] Specifically, the time of the data measurement and collection 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 collection unit is started, and 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 ended.

[0050] like Figure 3 As shown, before the prepreg preform 5 containing the conductive thin layer is placed in the autoclave for hot pressing curing treatment, it is also necessary to lay the vacuum bag film 1, the breathable felt 2, the first polytetrafluoroethylene cloth 3 and the porous film 4 on the upper surface of the prepreg preform 5 containing the conductive thin layer from top to bottom, and lay the non-porous film 7 and the second polytetrafluoroethylene cloth 8 on the lower surface of the prepreg preform 5 containing the conductive thin layer from top to bottom, and then put the above-laid overall structure on the flat mold 10, and then cover the overall structure with the vacuum bag film 1, and seal the contact position between the flat mold 10 and the vacuum bag film 1 with a sealing strip 9, and the high temperature resistant wire 6 is passed through the sealing strip 9 and connected to the prepreg preform 5 containing the conductive thin layer. Among them, the material of the first polytetrafluoroethylene cloth 3 and the second polytetrafluoroethylene cloth 8 is the same, and their thickness and area can be the same or different, which is determined according to the actual situation.

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

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

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

[0054]

[0055] Wherein, 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, measuring the resistance values ​​of the remaining conductive composite material samples after curing, calculating the resistance change rates before and after curing, and obtaining an average resistance change rate.

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

[0058] S600: When the error between the resistance change rate and the average resistance change rate is less than a second preset value, determine that the resistance change data is valid data.

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

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

[0061]

[0062] In summary, the measurement method of the present invention realizes online monitoring of resistance during the curing process of conductive composite materials, which makes up for the defect that the existing technology cannot measure in real time; at the same time, it provides a complete resistance change curve and data support, which can reveal the mechanism of resistance change, provide a scientific basis for the adjustment of process parameters, and significantly improve the uniformity and reliability of the conductive performance of composite materials. It also has a wide range of applicability and can be used for the research of multiple conductive composite materials such as lightning protection, electromagnetic shielding, and deicing.

[0063] The embodiment of the present invention also provides a device for measuring the resistance change of a conductive composite material during hot pressing, including a data measurement and collection unit and an electrode connection system; wherein:

[0064] The data measurement and acquisition unit is used to collect the resistance data of the conductive composite material in the curing process in real time, and 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 fixture, and two ends of the high temperature resistant wire are respectively connected to the data measurement and acquisition unit and the detachable electrode fixture.

[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 by high temperature resistant tape. The electrode connection system is fixed to the conductive composite material by high temperature resistant insulating tape to prevent it from loosening during the high temperature and high pressure process, which reduces the accuracy of the recorded data.

[0068] Example 1

[0069] The graphene fabric (conductive fabric with graphene CVD deposited on the surface of quartz fiber) is introduced into the epoxy resin-based composite material as a conductive thin layer, and the measuring device of the present invention is used to measure the resistance change under different temperatures and pressures online. The measured data obtained are as follows: Figure 4 shown.

[0070] from Figure 4 It can be found that as the pressure increases, its resistance decreases, indicating that it is beneficial to increase the contact points of the conductive fibers. When the pressure is removed, the resistance of the monene fabric returns to its original level. This process is reversible.

[0071] Example 2

[0072] The graphene fabric (conductive fabric with graphene CVD deposited on the surface of quartz fiber) was introduced into the epoxy resin-based composite material as a conductive thin layer, and the measuring device of the present invention was used to measure the online resistance of the autoclave curing process. The measured data obtained are as follows: Figure 5 shown.

[0073] from Figure 5 It can be found that the monene fabric exhibits a negative temperature coefficient (NTC) characteristic, and the resistance decreases as the temperature rises. When the temperature rises to 130°C and the pressure reaches 0.7MPa, it is observed that the resistance value of the fabric introduced into the composite material increases rapidly compared to the fabric introduced into the composite material. Analysis shows that this change is related to the resin flowing and infiltrating the conductive network, which leads to a decrease in contact between the monene fibers. As the resin solidifies, this increase is retained until after solidification. Compared with the monene fabric not introduced into the composite material, its resistance increases by 4% after the composite material is introduced, which is closely related to the flow and curing reaction of the resin.

[0074] Example 3

[0075] An ion electrodeposited conductive nonwoven fabric is used as a conductive thin layer and introduced into an epoxy resin-based composite material. The measuring device of the present invention is used to measure the online resistance of the autoclave curing process. The obtained measurement data are as follows: Figure 6 shown.

[0076] from Figure 6 It can be found that the conductive non-woven fabric has a positive temperature coefficient (PTC) characteristic. Its resistance does not increase with the change of resin viscosity during the curing process. Its resistance change is mainly caused by temperature change. After curing, its resistance change returns to the same level as before curing. This characteristic is related to its conductive network.

[0077] It should be clear 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 each other, and each embodiment focuses on the differences from other embodiments. The present invention is not limited to the specific steps and structures described above and shown in the figures. In addition, for the sake of brevity, a detailed description of known methods and technologies is omitted here.

[0078] The above are only embodiments of the present application and are not limited to the present application. For those skilled in the art, the present application may have various changes and variations without departing from the scope of the present invention. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A method for measuring the resistance change of a conductive composite material during hot pressing molding, characterized in that: The method comprises the following steps: measuring and recording initial resistance values ​​of a plurality of conductive composite material samples; Placing a plurality of the conductive composite material samples in an autoclave, and connecting the electrode end of each of the conductive composite material samples to an external data measurement and acquisition unit through an electrode connection system to obtain a measured resistance value of each of the conductive composite material samples, and determining that the measured resistance value is a resistance value before curing when the difference between the measured resistance value and the initial resistance value is less than a first preset value; During the curing process, real-time data on the resistance change of the conductive thin layer of one of the conductive composite material samples is collected, and a curve of the resistance value changing over time is recorded; Calculating the resistance change rate of the conductive composite material sample before and after curing according to the resistance value before curing and the resistance change data; Measuring the resistance values ​​of the remaining conductive composite material samples after curing, calculating the resistance change rates before and after curing, and obtaining an average value of the resistance change rates; When the error between the resistance change rate and the average value of the resistance change rate is less than a second preset value, the resistance change data is determined to be valid data.

2. The method for measuring resistance change of conductive composite materials during hot pressing molding according to claim 1, characterized in that: The 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.

3. The method for measuring resistance change of conductive composite material during hot pressing molding according to claim 2, characterized in that: Ensure that the electrodes extend out of the prepreg layup to access the electrode connection system.

4. The method for measuring resistance change of conductive composite material during hot pressing molding according to claim 3, characterized in that: The extended portions of the electrodes are separated by a non-porous separator.

5. The method for measuring resistance change of conductive composite material during hot pressing molding according to claim 1, characterized in that: Before the curing starts, the method further 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.

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

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

8. A measuring device using the method for measuring resistance change of a conductive composite material subjected to hot pressing molding as claimed in any one of claims 1 to 7, 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 collect the resistance data of the conductive composite material in the curing process in real time, 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 collection unit and the conductive composite material in the autoclave.

9. The measuring device according to claim 8, characterized in that The electrode connection system includes a high-temperature resistant wire and a detachable electrode fixture. The two ends of the high-temperature resistant wire are respectively connected to the data measurement and acquisition unit and the detachable electrode fixture. The high-temperature resistant wire is led out at the reserved lead outlet of the autoclave, and the lead-out position is sealed with a high-temperature resistant sealant to ensure that the autoclave maintains high temperature and high pressure operation.

10. The measuring device according to claim 8 or 9, characterized in that The two ends of the electrode connection system are respectively fixed to the data measurement and acquisition unit and the conductive composite material in the autoclave through high temperature resistant tapes.

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