Flexible conductivity monitoring system and method for curing performance of composite material

Abstract

The invention discloses a flexible conductivity monitoring system for curing performance of a composite material, and relates to the field of marine composite material performance monitoring, and the flexible conductivity monitoring system comprises a DSC measuring device, a flexible sensor, a flexible data processor, a data transmission device and a display device; the DSC measuring device is used for obtaining the corresponding relation between the curing degree and the glass transition temperature; the flexible sensor comprises a flexible substrate and a flexible induction electrode, the flexible induction electrode can deform along with the flexible substrate, and the flexible induction electrode is used for acquiring a conductance signal generated in the curing process in real time; the flexible data processor obtains a curing degree change curve and a glass transition temperature change curve; and the data transmission device transmits the data to the display device. The system can be tightly attached to a three-dimensional curved surface in any shape, real-time nondestructive monitoring of conductivity is achieved, the curing degree and the glass-transition temperature are obtained online in situ, and the curing performance monitoring accuracy and reliability are improved. The flexible conductivity monitoring method disclosed by the invention has the same advantages.

Description

Technical Field

[0001] The invention belongs to the technical field of marine composite material performance monitoring, and in particular relates to a flexible conductivity monitoring system and method for composite material curing performance. Background Art

[0002] Composite materials have great potential for application in the marine field, and their excellent performance has brought significant advantages to marine engineering. First of all, the high strength characteristics of composite materials are one of their core advantages. In the marine environment, equipment and structures often need to bear huge loads, such as the impact of waves and the pressure of seawater. Composite materials, with their excellent strength characteristics, ensure that they can remain stable under extreme conditions, meeting the extremely high requirements of marine engineering for material strength and safety; secondly, composite materials have a low density, which makes them lightweight, so that the overall weight of marine vehicles can be significantly reduced, which not only improves the fuel efficiency of vehicles and reduces energy consumption, but also enhances their maneuverability and controllability, further improving performance. At the same time, the lightweight characteristics also reduce transportation and installation costs, bringing economic benefits to marine engineering. In the high-salt environment of the ocean, corrosion is a major challenge facing equipment. Composite materials have super corrosion resistance, can operate stably for a long time, and effectively resist the erosion of seawater, so they can significantly extend the service life of equipment and reduce maintenance costs. In addition, composite materials also have excellent fatigue resistance. In the marine environment, since equipment is often subjected to repeated impact and stress, the material is required to have fatigue resistance. Composite materials, with their unique structure and properties, can maintain stable performance under repeated impact and stress, thereby reducing maintenance costs and failure rates, and improving the reliability and economy of equipment.

[0003] In order to ensure that marine composite materials perform well in the marine environment, it is crucial to monitor the key parameters of the curing process in real time. Among them, the degree of curing and the glass transition temperature are the core indicators for measuring the curing performance of marine composite materials. This degree of curing reflects the degree of transformation of the resin matrix from liquid or viscous state to solid state, which can directly affect the mechanical properties and chemical stability of the composite material. With the increase of the degree of curing, the strength and stability of the composite material are also enhanced, which can better cope with the challenges of the marine environment. The glass transition temperature (T g) is the critical temperature at which the resin matrix changes from a highly elastic state to a glassy state. Below this temperature, the resin matrix maintains high elasticity and flexibility and can adapt to the fluctuations and changes of the marine environment. However, once this temperature is exceeded, the resin matrix will become hard and brittle, and the performance of the composite material will drop sharply. Therefore, real-time monitoring of the curing process to ensure that the resin matrix reaches an appropriate degree of curing and glass transition temperature is crucial to ensure the excellent performance of marine composite materials. In an existing monitoring scheme, a flexible dielectric sensor is prepared using a polyimide (PI) substrate and a copper electrode material, and is integrated on a PI circuit board to form a flexible dielectric monitoring system, which is embedded in the composite material and can effectively monitor its curing process. However, due to the poor flexibility of the PI substrate and the lack of good tensile properties, after it is embedded in the composite material, it will damage the mechanical properties of the composite material to a certain extent, thereby reducing the overall reliability. In addition, since the flexible dielectric sensor and other processing chips are integrated on the same PI substrate, they need to be embedded in the composite material together during the monitoring process, which greatly increases the volume when embedded, which further increases the negative impact on the mechanical properties of the composite material. Summary of the invention

[0004] To solve the above problems, the present invention provides a flexible conductivity monitoring system and method for the curing performance of composite materials. The system can be tightly attached to a three-dimensional curved surface of any shape, thereby realizing real-time monitoring of the conductivity signal of a marine composite material with any surface shape, thereby obtaining the degree of curing and glass transition temperature in situ online, thereby improving the accuracy and reliability of curing performance monitoring in a complex marine environment, and there is no need to embed in the marine composite material, so as not to damage its internal mechanical properties, thereby improving the overall reliability and realizing non-destructive testing.

[0005] The present invention provides a flexible conductivity monitoring system for composite material curing performance, comprising a DSC measuring device, a flexible sensor, a flexible data processor, a data transmission device and a display device which are electrically connected in sequence;

[0006] The DSC measuring device is used to obtain the corresponding relationship between the degree of solidification and the glass transition temperature of the monitored object;

[0007] The flexible sensor comprises a flexible substrate and a flexible sensing electrode wrapped by the flexible substrate on five sides, wherein the flexible sensing electrode can deform along with the flexible substrate so that an exposed side thereof is completely attached to the surface of the monitored object, and the flexible sensing electrode is used to obtain in real time a conductivity signal generated by the monitored object during the curing process;

[0008] The flexible data processor is used to obtain a curing degree change curve of the monitored object according to the conductivity signal, and to obtain a glass transition temperature change curve of the monitored object according to the curing degree and the corresponding relationship;

[0009] The data transmission device is used to transmit the curing degree variation curve and the glass transition temperature variation curve to the display device for display.

[0010] Preferably, the flexible conductivity monitoring system for the curing properties of the composite material described above further includes a flexible circuit board for carrying the flexible data processor and the data transmission device, and the flexible circuit board and the flexible sensor are electrically connected together and packaged into a flexible whole.

[0011] Preferably, in the above-mentioned flexible conductivity monitoring system for the curing properties of the composite material, the flexible circuit board includes a polyimide substrate, a circuit pattern arranged on the polyimide substrate, and electronic components electrically connected to and fixed on the polyimide substrate using the circuit pattern, and the electronic components and the circuit pattern constitute the flexible data processor and the data transmission device.

[0012] Preferably, in the above-mentioned flexible conductivity monitoring system for the curing properties of composite materials, the flexible circuit board and the flexible sensor are electrically connected by silver nanowires.

[0013] Preferably, in the above-mentioned flexible conductivity monitoring system for composite material curing performance, the flexible circuit board, the flexible sensor and the silver nanowires are cured by polydimethylsiloxane solution to package them into a flexible whole, so that the exposed side of the flexible sensing electrode is still exposed to the outside.

[0014] Preferably, in the above-mentioned flexible conductivity monitoring system for the curing performance of composite materials, the flexible data processor is used to obtain the curing degree change curve of the monitored object according to the conductivity signal, including:

[0015] According to the formula

[0016] ,

[0017] Obtaining the curing degree α of the monitored object at time t, and obtaining a curing degree variation curve according to the corresponding relationship between α and t;

[0018] Among them, log(G s ) is the logarithm of the conductivity value of the monitored object detected at the beginning of curing;

[0019] log(G(t)) is the logarithm of the conductivity value of the monitored object detected at the solidification time t;

[0020] log(G e ) is the logarithm of the conductivity value of the monitored object detected when the degree of curing finally stops changing.

[0021] Preferably, in the above-mentioned flexible conductivity monitoring system for the curing performance of composite materials, the corresponding relationship between the curing degree and the glass transition temperature of the monitored object is obtained by using the DSC measuring device using the following formula:

[0022] ,

[0023] in,

[0024] T gu is the glass transition temperature of the monitored object in a liquid state;

[0025] T gcmax The maximum glass transition temperature of the monitored object when the degree of solidification finally stops changing;

[0026] T g is the glass transition temperature of the monitored object at the solidification time t;

[0027] ΔC pu is the heat capacity difference between the glass state and the rubber state of the monitored object in the liquid state at the glass transition temperature;

[0028] ΔC pc It is the thermal tolerance difference between the glass state and the rubber state of the monitored object at the glass transition temperature when the degree of cure finally stops changing.

[0029] Preferably, in the above-mentioned flexible conductivity monitoring system for the curing performance of composite materials, obtaining the glass transition temperature change curve of the monitored object according to the curing degree and the corresponding relationship comprises:

[0030] Using the following formula:

[0031] ,

[0032] Obtain the glass transition temperature T of the monitored object at time t g , and according to T g The corresponding relationship between and t is used to obtain the glass transition temperature change curve of the monitored object.

[0033] Preferably, in the above-mentioned flexible conductivity monitoring system for the curing properties of composite materials, the data transmission device is a Bluetooth transmission device, and the display device is a remote terminal display.

[0034] In a flexible conductivity monitoring method for the curing performance of a composite material provided by the present invention, a system as described in any one of the above items is used, comprising:

[0035] Taking out a portion of the sample of the monitored object and placing it in the DSC measuring device to obtain the corresponding relationship between the degree of curing and the glass transition temperature of the monitored object;

[0036] Placing the flexible sensor on the surface of the monitored object so that the exposed side of the flexible sensing electrode is completely attached to the surface of the monitored object to obtain the conductivity signal in real time;

[0037] During the curing process of the monitored object, the curing degree α of the monitored object at time t is obtained according to the conductivity signal, and a curing degree variation curve is obtained according to the corresponding relationship between α and t;

[0038] According to the curing degree and the corresponding relationship, the glass transition temperature T of the monitored object at time t is obtained. g , and according to T g The corresponding relationship between t and glass transition temperature curve is obtained;

[0039] transmitting the curing degree variation curve and the glass transition temperature variation curve to the display device in real time;

[0040] The curing degree change curve and the glass transition temperature change curve are shown.

[0041] It can be known from the above description that the flexible conductivity monitoring system for the curing performance of the composite material provided by the present invention includes a DSC measuring device, a flexible sensor electrically connected in sequence, a flexible data processor, a data transmission device and a display device, and the DSC measuring device is used to obtain the corresponding relationship between the curing degree and the glass transition temperature of the monitored object, the flexible sensor includes a flexible substrate and a flexible sensing electrode wrapped by the flexible substrate on five sides, the flexible sensing electrode can deform along with the flexible substrate so that the exposed side thereof is completely attached to the surface of the monitored object, and the flexible sensing electrode is used to obtain the conductivity signal generated by the monitored object during the curing process in real time, so it can be tightly attached to a three-dimensional curved surface of any shape, thereby realizing the monitoring of marine composite materials with any surface shape. Real-time monitoring of the conductivity signal, and because the flexible data processor is used to obtain the curing degree change curve of the monitored object according to the conductivity signal, and obtain the glass transition temperature change curve of the monitored object according to the curing degree and the corresponding relationship, the data transmission device is used to transmit the curing degree change curve and the glass transition temperature change curve to the display device for display, so the curing degree and glass transition temperature can be obtained in situ online, improving the accuracy and reliability of curing performance monitoring in complex marine environments, and there is no need to embed in marine composite materials, so as not to damage their internal mechanical properties, improve overall reliability, and realize non-destructive testing. After the detection is completed, the system can be taken down to continue monitoring the next monitored object, and the monitoring efficiency is higher. The flexible conductivity monitoring method for the curing performance of composite materials provided by the present invention has the same advantages as the above-mentioned system. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0043] Figure 1 An overall schematic diagram of an embodiment of a flexible conductivity monitoring system for composite material curing performance provided by the present invention;

[0044] Figure 2 A schematic diagram of an embodiment of a flexible conductivity monitoring method for curing properties of a composite material provided by the present invention;

[0045] Figure 3 The figure is a schematic diagram of the preparation process of a flexible circuit board;

[0046] Figure 4A schematic diagram of the connection and packaging between the flexible circuit board and the flexible sensor;

[0047] Figure 5 It is the principle block diagram of the sensor integration system;

[0048] Figure 6 It is the flow chart of the measurement scheme;

[0049] Figure 7 is the measured curing degree variation curve of the composite material;

[0050] Figure 8 The glass transition temperature curve of the composite material is measured. DETAILED DESCRIPTION

[0051] The core of the present invention is to provide a flexible conductivity monitoring system and method for the curing performance of composite materials. The system can be tightly attached to a three-dimensional curved surface of any shape, thereby realizing real-time monitoring of the conductivity signal of marine composite materials with any surface shape, thereby obtaining the degree of curing and glass transition temperature in situ online, improving the accuracy and reliability of curing performance monitoring in complex marine environments, and there is no need to embed in marine composite materials, so as not to damage their internal mechanical properties, thereby improving overall reliability and realizing non-destructive testing.

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] The implementation example of the flexible conductivity monitoring system for composite material curing performance provided by the present invention is as follows: Figure 1 As shown, Figure 1 The overall schematic diagram of an embodiment of a flexible conductivity monitoring system for composite material curing performance provided by the present invention, the system may include a DSC measuring device 1, a flexible sensor 2, a flexible data processor 3, a data transmission device 4 and a display device 5 which are electrically connected in sequence;

[0054] The above-mentioned DSC (differential scanning calorimetry) measuring device 1 is used to obtain the corresponding relationship between the degree of solidification and the glass transition temperature of the monitored object, so that the glass transition temperature can be directly obtained according to the degree of solidification at each time point, thereby assisting in obtaining the change curve of the glass transition temperature. It should be noted that the DSC measuring device is a separate device and is not connected to other devices in the system;

[0055] The flexible sensor 2 comprises a flexible substrate 21 and a flexible sensing electrode 22 wrapped on five sides of the flexible substrate 21. The flexible sensing electrode 22 can deform along with the flexible substrate 21 so that the exposed side thereof is completely attached to the surface of the monitored object. The flexible sensing electrode 22 is used to obtain the conductivity signal generated by the monitored object during the curing process in real time. Figure 1 It can be seen that the three-dimensional shape of the flexible sensing electrode 22 can be similar to a cuboid. The upper surface and the four surrounding surfaces of the flexible sensing electrode 22 can be completely wrapped by the flexible substrate 21, leaving only the bottom surface exposed to the outside to contact the monitored object to obtain the conductivity signal. The flexible sensor 2, as the sensing front end of the entire system, has strong flexibility and stretchability, ensuring that it can be closely attached to various curved structures for conductivity measurement without affecting the monitoring accuracy. One side of the flexible sensor can be a low-potential electrode and the other side can be a high-potential electrode. Through this design, the conductivity signal changes generated during the curing process of the composite material can be effectively captured and transmitted, which not only simplifies the signal acquisition path, but also significantly improves the sensitivity and stability of the system. The object can be, but is not limited to, marine composite materials;

[0056] The flexible data processor 3 is used to obtain the curing degree change curve of the monitored object according to the conductivity signal, and obtain the glass transition temperature change curve of the monitored object according to the corresponding relationship between the curing degree and the curing degree and the glass transition temperature obtained by the DSC measuring device. Specifically, each curing degree corresponds to a glass transition temperature, and then the obtained glass transition temperatures and time are plotted in a coordinate system to obtain the glass transition temperature change curve;

[0057] The data transmission device 4 is used to transmit the curing degree change curve and the glass transition temperature change curve to the display device 5 for display. Figure 1 The dotted line in the figure indicates that there is no need for a physical connection between the data transmission device 4 and the display device 5, but they are connected via wireless communication. This eliminates the need for wiring and makes on-site measurement more convenient. In addition, the flexible data processor 3 can also utilize the data transmission device 4 to communicate with the DSC measuring device to obtain data including the above-mentioned corresponding relationship from the DSC measuring device. In this case, after the DSC measuring device measures various parameters of the monitored object, it can obtain the corresponding relationship between the degree of solidification and the glass transition temperature of the monitored object, and then transmit this corresponding relationship to the flexible data processor 3. The flexible data processor 3 can then use this corresponding relationship to perform subsequent calculations.

[0058] In summary, the system effectively avoids the problems of existing technologies such as reliance on external desktop instruments, cumbersome operation and high cost. The system has the advantages of low cost and convenient carrying. The flexible data processor therein not only has powerful data processing capabilities, but also can receive and process signals from flexible sensors in real time, and can transmit the processed signals to a display device in real time through a data transmission device. This display device can be a display located in a remote monitoring center or a mobile terminal to achieve remote access and real-time monitoring of data.

[0059] It can be seen from the above description that in the embodiment of the flexible conductivity monitoring system for the curing performance of the composite material provided by the present invention, since it includes a DSC measuring device, a flexible sensor electrically connected in sequence, a flexible data processor, a data transmission device and a display device, and the DSC measuring device is used to obtain the corresponding relationship between the curing degree and the glass transition temperature of the monitored object, the flexible sensor includes a flexible substrate and a flexible sensing electrode wrapped by the flexible substrate on five sides, the flexible sensing electrode can follow the deformation of the flexible substrate so that its exposed side is completely attached to the surface of the monitored object, and the flexible sensing electrode is used to obtain the conductivity signal generated by the monitored object during the curing process in real time, so it can be tightly attached to a three-dimensional curved surface of any shape, thereby realizing the monitoring of marine composite materials. Real-time monitoring of conductivity signals, and since the flexible data processor is used to obtain the curing degree change curve of the monitored object according to the conductivity signal, and obtain the glass transition temperature change curve of the monitored object according to the curing degree and the corresponding relationship, the data transmission device is used to transmit the curing degree change curve and the glass transition temperature change curve to the display device for display, so the curing degree and glass transition temperature can be obtained in situ online, thereby improving the accuracy and reliability of curing performance monitoring in complex marine environments, and there is no need to be embedded in marine composite materials, so as not to damage its internal mechanical properties, thereby improving the overall reliability and realizing non-destructive testing. After the detection, the system can be taken down to continue monitoring the next monitored object, and the monitoring efficiency is higher.

[0060] In a specific embodiment of the flexible conductivity monitoring system for the composite material curing performance, continue to refer to Figure 1, and may also include a flexible circuit board 6 for carrying the flexible data processor 3 and the data transmission device 4, and the flexible circuit board 6 and the flexible sensor 2 are electrically connected together and packaged into a flexible whole. After forming a flexible and lightweight whole, it is more convenient to carry, and there is no need to use large equipment like the prior art. Moreover, when it is necessary to monitor a certain monitoring object, the whole can be placed on it, which is more convenient to operate and does not require any on-site connection operation. Further, the flexible circuit board 6 may include a polyimide substrate, a circuit pattern arranged on the polyimide substrate, and electronic components (such as Figure 1As shown), the electronic components and circuit patterns constitute the flexible data processor 3 and the data transmission device 4. Specifically, a polyimide substrate with a thickness of 50 microns to 300 microns can be preferably used here, and a polyimide substrate with a thickness of 125 microns can be selected in a further embodiment, which can be selected according to actual needs. The manufacturing process can be as follows: On the polyimide (PI) substrate, a uniform copper layer of about 20 μm thick is deposited by a precision sputtering process as the basis of the conductive path, and then the copper layer is finely processed by wet etching technology to form the required circuit pattern. Before etching, the copper-clad polyimide substrate is thoroughly cleaned and dried to ensure that the substrate surface is clean and free of dirt, laying a good foundation for subsequent processes. During the etching process, a corrosion-resistant solvent is used to protect the surface of the copper layer to prevent the etching solution from corroding non-target areas. After etching, various electronic components (including chips, resistors, capacitors, etc.) are accurately welded to the polyimide substrate using reflow soldering technology to construct a complete flexible circuit board to integrate the data processing module and the data transmission module together, wherein the formed flexible data processor 3 can be specifically a microcontroller processor MCU. In this process, the uniform coating of solder paste, the precise positioning of electronic components, and the high-temperature melting effect of the reflow soldering furnace are all crucial to jointly ensure the firmness and reliability of the solder joint connection and the excellent electrical performance. It should also be noted that this microcontroller (MCU) may include a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), input / output (I / O) interface, reset and clock circuits, etc., and the MCU is small in size, light in weight, low in power consumption, and has powerful control functions and flexible expansion. There are many options for selecting MCU, such as STM32 series, ARM Cortex-M series, MSP430 series, etc. The STM32 series includes STM32F2, STM32F4, STM32F7, STM32H7, STM32F0, STM32F1, STM32F3 and the ultra-low power STM32L0, STM32L1, STM32L4, etc.; the ARM Cortex-M series includes Cortex-M0, Cortex-M0+, Cortex-M1, Cortex-M3, Cortex-M4, Cortex-M7, Cortex-M23, Cortex-M33, etc.; the MSP430 series includes MSP430F1132, MSP430F133, MSP430F149, MSP430F2003, MSP430F2011 and other models. You can choose any MCU model.

[0061] Another specific embodiment provided by the present application is based on the embodiment of the flexible conductivity monitoring system for the curing performance of the composite material described above, and further refers to Figure 1, the flexible circuit board 6 and the flexible sensor 2 are electrically connected by silver nanowires 7. The specific manufacturing process may include: fixing the flexible circuit board on a smooth glass plate by double-sided traceless tape, then pasting PI tape on the rest of the glass plate, and accurately outlining the outline of the sensor structure and the conductive path by laser cutting technology, removing the cut part of the PI tape, and then dripping the silver nanowire solution on the exposed glass substrate, and after the solution is completely dried, an electrode layer and a conductive path with excellent conductive performance are formed. It should also be noted that this silver nanowire can also be replaced by other conductive materials with high flexibility and excellent conductivity, such as carbon-based flexible conductive materials: graphene, carbon nanotubes, carbon fibers, graphene oxide, reduced graphene oxide, titanium carbide, MXenes, etc.; metal-based flexible conductive materials: gold nanowires, copper nanowires, metal foil (copper foil, aluminum foil); polymer-based flexible conductive materials: polystyrene sulfonic acid doped polystyrene (PEDOT:PSS), polystyrene sulfonic acid doped polyparaphenylene (PEDOT:PTS), poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS), polyacetylene, polyaniline, polypyrrole, polybenzimidazole, polythiophene, etc.; conductive gel, graphite composites, metal-organic frameworks (MOF), transition metal disulfides (such as molybdenum disulfide, tungsten disulfide), etc.; in terms of preparation technology, it can be processed by laser cutting, screen printing, inkjet printing, physical vapor deposition and other technologies.

[0062] The present application also provides another specific embodiment, which is based on another specific embodiment of the flexible conductivity monitoring system of the above composite material curing performance, and preferably uses polydimethylsiloxane solution to cure the flexible circuit board 6, the flexible sensor 2 and the silver nanowire 7 to encapsulate them into a flexible whole, so that the exposed side of the flexible sensing electrode 22 is still exposed to the outside. The specific manufacturing process can be as follows: the flexible circuit board and the flexible sensor and the conductive path (silver nanowire) between them are surrounded by tape, and the tape thickness is 1 cm (the thickness of 1 mm can be obtained by stacking 5 times of 2 mm thick tape), so as to ensure that the polydimethylsiloxane solution (PDMS) does not flow around, and the PDMS solution is poured, and it is left to level and cure at a constant temperature in a horizontal place to finally form a strong and durable packaging layer. After the packaging is completed, the excess PDMS material is removed by a cutting machine, so that the flexible sensor can be flexibly integrated on a complex three-dimensional surface to meet the needs of diversified monitoring. It can be seen that the use of this flexible overall packaging structure not only protects the internal circuit from environmental erosion, but also maintains the flexibility and durability of the system. Of course, in addition to polydimethylsiloxane, the packaging material here can also be other stretchable materials with small elastic modulus and excellent flexibility, such as silicone materials, hydrogel materials, etc., which can be selected according to actual needs.

[0063] It should also be noted that in one of the above-mentioned specific embodiments, polyimide (PI) is used as the base material for the preparation of the flexible circuit board 6, and copper is used as the conductive material. The polyimide substrate provides a reliable guarantee for the stable operation of the flexible circuit board in a complex deformation environment due to its excellent high temperature resistance and good flexibility, while the copper material plays a core role in the construction of the conductive path of the flexible circuit board 6 due to its excellent conductive properties. Moreover, the preparation of the above-mentioned flexible sensor 2 adopts a combination of silver nanowires and polydimethylsiloxane (PDMS) substrates. This silver nanowire not only has excellent conductivity, but its unique nanoscale size also gives the sensor higher sensitivity, and the PDMS substrate has good flexibility and shows significant advantages in multiple application fields. In the connection design of this flexible circuit board 6 and the flexible sensor 2, silver nanowires of the same material as the flexible sensor 2 are selected as the conductive path for electrode connection. However, there are still certain technical problems in achieving efficient and stable connection between the copper electrode of the flexible circuit board 6 and the silver nanowire material. To solve this connection problem, the present application provides a preparation process, which includes the following steps:

[0064] The specific preparation steps are as follows:

[0065] The first step is to construct a lower electrode layer on the PI substrate of the flexible circuit board 6. Specifically, magnetron sputtering technology can be used, which uses a magnetic field to constrain the movement of electrons in the plasma, significantly improving the sputtering efficiency and the uniformity of thin film deposition. Under strictly controlled process parameters (including sputtering power, sputtering time, vacuum degree, etc.), a uniform circular copper layer (thickness of about 20μm and diameter of about 0.5cm) is deposited on the PI substrate. This lower electrode layer serves as the basis for subsequent connection with the silver nanowire electrode material, and its quality and performance are crucial to the stability of the overall connection structure.

[0066] The second step is to prepare an intermediate electrode layer on the surface of the lower electrode layer. Specifically, a simple drip coating method can be used to evenly drip the silver nanowire dispersion on the surface of the lower electrode. By accurately controlling parameters such as the drip coating time and solution concentration, it is ensured that the silver nanowires can completely and evenly cover the surface of the lower electrode to form a continuous conductive network. After the silver nanowire solution is fully dried, the silver nanowire layer at this time constitutes the intermediate electrode layer, which plays a bridge role in the entire connection structure, realizing the conductive connection between the flexible circuit board 6 and the flexible sensor 2.

[0067] The third step is to prepare an upper electrode layer on the dried silver nanowire intermediate electrode layer. Specifically, magnetron sputtering technology can be used again to deposit a uniform copper layer (thickness of about 20μm and diameter of about 0.65cm). The function of this upper electrode layer is to completely wrap the intermediate layer and the lower electrode layer to form a sandwich-like three-layer structure. This structural design greatly enhances the conductivity and bonding tightness between the two different electrode materials. From a microscopic point of view, the copper of the upper electrode layer forms a strong metallurgical bond with the intermediate silver nanowire layer and the copper of the lower electrode layer through atomic interactions, which effectively reduces the contact resistance and improves the electron transmission efficiency; at the same time, the mechanical stability of the sandwich structure is significantly improved, which can better adapt to the bending, stretching and other mechanical deformations of flexible devices during actual use.

[0068] The present application also provides a preferred embodiment, based on the embodiment of the flexible conductivity monitoring system for the curing performance of the composite material, the flexible data processor 3 is used to obtain the curing degree change curve of the monitored object according to the conductivity signal, which may specifically include:

[0069] According to the formula

[0070] ,

[0071] Obtaining the curing degree α of the monitored object at time t, and obtaining a curing degree variation curve according to the corresponding relationship between α and t;

[0072] Among them, log(G s ) is the logarithm of the conductivity value of the monitored object detected at the beginning of curing;

[0073] log(G(t)) is the logarithm of the conductivity value of the monitored object detected at the solidification time t;

[0074] log(G e ) is the logarithm of the conductivity value of the monitored object detected when the degree of curing finally stops changing.

[0075] Specifically, since the viscosity of the monitored object is closely related to the degree of curing, that is, the greater the viscosity, the higher the degree of curing, and the viscosity is inversely proportional to the ionic conductivity, that is, the greater the viscosity, the smaller the ionic conductivity and the higher the degree of curing, based on this, the above formula can be used to accurately obtain the real-time degree of curing according to the conductivity. e), it should be noted here that it is the logarithm of the conductivity value detected when the degree of curing finally stops changing, and the degree of curing finally stops changing does not mean that the degree of curing reaches 100%, because at each temperature there is a corresponding degree of curing that finally stops changing. For example, at a certain temperature, the degree of curing when it finally stops changing is only 80%, that is, the maximum degree of curing when the monitored object at this temperature finally stops changing can reach 80%, but cannot reach 100%. At this time, the conductivity obtained is G e , while G s It is the conductivity value detected at the beginning of curing, and G(t) is the conductivity value detected after the curing time has passed t time. It should also be noted that when the above curing performance monitoring is performed on a certain monitoring object in this embodiment, a curing process from the beginning of curing to the curing degree no longer changes is required to obtain the conductivity value from G s , G e And G(t) corresponding to each moment in the curing process, and then the curing degree corresponding to each moment t can be obtained according to the above formula. However, these curing degree values ​​are not obtained in real time during the curing process. After all, G is needed in this formula. e Only after the solidification is completed can this G be obtained e .

[0076] The present application also provides another preferred embodiment, which is based on the preferred embodiment of the flexible conductivity monitoring system for the curing performance of the composite material, and the corresponding relationship between the curing degree and the glass transition temperature of the monitored object obtained by using a DSC measuring device can be obtained by using the following formula:

[0077] ,

[0078] in,

[0079] T gu is the glass transition temperature of the monitored object in a liquid state;

[0080] T gcmax The maximum glass transition temperature of the monitored object when the degree of solidification finally stops changing;

[0081] T g is the glass transition temperature of the monitored object at the solidification time t;

[0082] ΔC pu is the heat capacity difference between the glass state and the rubber state of the monitored object in the liquid state at the glass transition temperature;

[0083] ΔC pc It is the thermal tolerance difference between the glass state and the rubber state of the monitored object at the glass transition temperature when the degree of cure finally stops changing.

[0084] It should be noted that this is to associate the obtained conductivity signal with differential scanning calorimetry (DSC). A small piece of the monitored object can be selected and measured using this DSC to obtain multiple parameters in the formula. Specifically, through isothermal DSC testing, T at different curing temperatures can be obtained. g and α, and finally T is calculated by least squares regression model analysis. gu , T gc , ΔC pu , ΔC pc After all the parameters in the formula are measured, only T g and α are unknown, and the previous embodiment mentioned that the value of α of the monitored object at each moment can be obtained by using the conductivity signal, so T g The above nonlinear relationship with α is obtained by substituting the α value obtained above into the formula to obtain the corresponding T g That is to say, according to α at each moment, we can get T corresponding to each moment. g .

[0085] The present application also provides another preferred embodiment, which is based on another preferred embodiment of the flexible conductivity monitoring system for the curing performance of the composite material, and according to the curing degree and the corresponding relationship, obtaining the glass transition temperature change curve of the monitored object can specifically include:

[0086] Using the following formula:

[0087] ,

[0088] Get the glass transition temperature T of the monitored object at time t g , and according to T g The corresponding relationship between and t can be used to obtain the glass transition temperature change curve of the monitored object.

[0089] It can be seen that by using this formula, the corresponding curing degree α and glass transition temperature T of the composite material can be obtained according to the conductivity signal obtained at each moment. g According to the corresponding relationship between the value of and time, the flexible data processor can use this formula to quickly and accurately obtain the glass transition temperature change curve, thereby realizing a rapid and direct quantitative analysis of the curing process of the composite material.

[0090] Regarding the above formulas, it is necessary to further explain that temperature is one of the key factors that affect the conductivity value of a substance. Specifically, as the temperature increases, the conductivity value of a substance generally increases. The internal mechanism is that the increase in temperature will cause the atoms or molecules in the substance to obtain higher kinetic energy. In this case, the movement of electrons in the lattice becomes more intense. As the carrier of charge, the more intense movement of electrons will greatly promote the migration process of electrons, thereby enhancing the conductivity of the substance. Therefore, the effect of temperature on conductivity can be further considered to modify the above formula to a certain extent.

[0091] In the study of composite materials, it is crucial to accurately monitor their degree of cure. Since the conductivity values ​​at different temperatures will be significantly affected by temperature, accurately monitoring the temperature of the material while monitoring the cure of the composite material can help effectively solve the problems faced in the composite material cure monitoring process and can significantly improve the accuracy of monitoring. It is particularly noteworthy that compared with traditional constant temperature curing experiments, decoupling temperature and conductivity has obvious advantages. By decoupling temperature and conductivity, the limitations of constant temperature conditions can be broken through, and effective monitoring of variable temperature curing processes can be achieved, making this monitoring technology more suitable for practical applications (because in practical applications, the temperature of the material will continue to change with the environment and the heat release of its own curing process), so that it can adapt to more diverse actual working conditions. Based on this, the following formula is proposed:

[0092] ,

[0093] Where G(T) represents the conductivity value at temperature T, G0 represents the initial conductivity value at T0, T0 represents the initial temperature, T represents the temperature at any time, and K is the compensation coefficient. The calculation of K can be obtained by the following formula:

[0094] ,

[0095] Since the conductivity values ​​at different temperatures are significantly affected by temperature, in order to more accurately monitor the degree of cure of the composite material, it is necessary to convert the conductivity values ​​at different temperatures so that they all correspond to the conductivity values ​​at the same temperature. After theoretical derivation and decoupling the relationship between temperature and conductivity, the optimized degree of cure formula is obtained as follows:

[0096] ,

[0097] in, is the logarithm of the conductivity value of the monitored object detected at the beginning of curing at temperature T0; It is the logarithm of the conductivity value of the sample that has been cured at temperature T0; It represents the logarithm of the conductivity value of the monitored object detected at the temperature T0 and the curing time t;

[0098] The corresponding relationship between the degree of curing and the glass transition temperature is still:

[0099] ,

[0100] Substituting the above curing degree formula into the corresponding relationship between curing degree and glass transition temperature, the glass transition temperature formula can be obtained as follows:

[0101] ,

[0102] In order to determine the compensation coefficient K in the above formula, an experiment was designed and implemented. During the experiment, we first focused on the cured composite material and accurately measured the conductivity value of the cured composite material at temperature T0. This step provides an important basic data point for subsequent research. Then the conductivity value of the cured composite material at temperature T was measured. By comparing the conductivity data at different temperatures, we can preliminarily know the trend of the influence of temperature on conductivity. Finally, these different temperatures and their corresponding conductivity values ​​are substituted into the above expression, and after precise mathematical calculations, the compensation coefficient K can be calculated.

[0103] The specific steps are as follows:

[0104] Select a small piece of cured epoxy resin (composite material) and place it on a heating table at 30°C. Use a temperature sensor to measure the temperature first. When the surface temperature of the epoxy resin stabilizes at 30°C, use an LCR meter to measure it and read the value of the LCR meter at this time.

[0105] Select the same size of cured epoxy resin (composite material) and place it on a heating table at 60℃. Use the temperature sensor to measure the temperature. When the surface temperature of the epoxy resin is stable at 60℃, use the LCR meter to measure it and read the value of the LCR meter at this time.

[0106] According to the LCR reading, the conductivity value of epoxy resin at 30°C is G(30)=2.271pS; the conductivity value of epoxy resin at 60°C is G(60)=2.953pS. Substituting the obtained value into the compensation coefficient calculation formula, K is obtained to be 0.0089. In each embodiment of the flexible conductivity monitoring system for composite material curing performance, the data transmission device can be preferably a Bluetooth transmission device. Of course, other types of wireless transmission devices can also be selected, such as any one of wireless radio frequency identification (RFID) devices, ZigBee wireless communication devices, Wi-Fi communication devices, and 4G / 5G mobile communication devices. Moreover, the display device can be preferably a remote terminal display. The use of such a wireless communication device can realize long-distance transmission, and directly display intuitive curing information during the curing process of the composite material on the remote control terminal.

[0107] In summary, the above system provided by the present invention has a relatively simple and portable overall structure, does not require complex external measuring instruments, greatly simplifies the overall equipment for composite material monitoring, and can effectively improve the mechanical properties of marine composite materials after curing by real-time online monitoring of two important parameters in the composite material curing process, namely, degree of curing and glass transition temperature, so that its application range is wider, its stability and reliability are more excellent, and it can better cope with the challenges of the marine environment. The system is completely built on flexible materials, and its sensor part uses fully flexible materials. In terms of material selection, the base material has flexibility, corrosion resistance and high reliability, while the electrode material has both high flexibility and excellent electrical conductivity. This design enables the sensor to fit tightly to any three-dimensional complex surface, thereby breaking through the limitations of traditional plane monitoring and broadening the scope of application. The flexible circuit part of the system also uses flexible materials as its base, thereby reducing the weight of its own circuit, making it more miniaturized and lightweight.

[0108] The implementation example of the flexible conductivity monitoring method for the curing performance of a composite material provided by the present invention is as follows: Figure 2 As shown, Figure 2 A schematic diagram of an embodiment of a flexible conductivity monitoring method for composite material curing performance provided by the present invention, using any of the above systems, may include the following steps:

[0109] S1: taking out a portion of the sample of the monitored object and placing it in a DSC measuring device to obtain the corresponding relationship between the degree of solidification and the glass transition temperature of the monitored object;

[0110] The specific steps can be as follows:

[0111] 1. Place a small sample of the composite material into a test tube;

[0112] 2. Place the test tube containing the sample on the heater of the differential scanning calorimeter (DSC equipment);

[0113] 3. Set the cavity environment inside the differential scanning calorimeter to air, and use the heat flow sensor of the differential scanning calorimeter to detect the reaction enthalpy of the sample;

[0114] 4. The degree of curing α can be inferred from the reaction enthalpy obtained from the isothermal DSC test, and its expression is: , where H(t) represents the reaction enthalpy of the composite material when it reacts to time t, and H∞ represents the reaction enthalpy of the composite material when it reacts to infinite time;

[0115] 5. Perform a non-isothermal test on the test sample, with the temperature rising from -50°C to 275°C at a heating rate of 5°C / min. By observing the temperature turning point of the isothermal DSC curve obtained, the glass transition temperature of the test sample can be obtained;

[0116] 6. The ΔC is finally obtained by fitting the degree of cure and glass transition obtained at different curing temperatures using the least squares method. pu and ΔC pc , where ΔC pu is the thermal capacity difference between the glass state and the rubber state of the monitored object in the liquid state at the glass transition temperature, ΔC pc It is the heat capacity difference between the glass state and the rubber state of the monitored object at the glass transition temperature when the degree of cure finally stops changing;

[0117] 7. Get T directly from non-isothermal DSC test gu and T gcmax , where T gu is the glass transition temperature of the monitored object in liquid state, T gcmax It is the maximum glass transition temperature of the monitored object when the degree of solidification finally stops changing.

[0118] Substituting the above parameters into the formula,

[0119] ,

[0120] The curing degree α and glass transition temperature T of the monitored object can be obtained g The corresponding relationship between them.

[0121] S2: placing the flexible sensor on the surface of the monitored object so that the exposed side of the flexible sensing electrode is completely attached to the surface of the monitored object to obtain the conductivity signal in real time;

[0122] It should be noted that this flexible sensing electrode can fit the surface of any shape of the monitored object to ensure comprehensive acquisition of the conductivity signal of the contact part. It can be seen that this can test the conductivity signal of marine composite materials of various shapes to achieve the monitoring of curing performance.

[0123] S3: during the curing process of the monitored object, the curing degree α of the monitored object at time t is obtained according to the conductivity signal, and a curing degree variation curve is obtained according to the corresponding relationship between α and t;

[0124] It can be seen that the conductivity signals at various time points are obtained until the final curing is completed, and then the curing degree can be calculated based on these conductivity signals, so that the curing degree change curve can be drawn using t as the horizontal axis and the curing degree α as the vertical axis.

[0125] S4: According to the curing degree and the corresponding relationship, the glass transition temperature T of the monitored object at time t is obtained. g , and according to T g The corresponding relationship between t and glass transition temperature curve is obtained;

[0126] This correspondence is obtained from the previous step S1. Combined with the data of the degree of solidification α at each moment obtained in step S3, the glass transition temperature T at each moment can be obtained. g The data is then taken as t on the horizontal axis and T g The glass transition temperature change curve can be drawn with θ as the vertical axis.

[0127] S5: transmitting the curing degree change curve and the glass transition temperature change curve to a display device in real time;

[0128] Specifically, wireless communication may be used to transmit the display device at the remote control end to achieve remote monitoring.

[0129] S6: Displays the curing degree change curve and glass transition temperature change curve.

[0130] It should be noted that this allows the remote control end to see the changes in these curves in real time, so as to understand these curing properties in a timely manner.

[0131] The following is a detailed description of the manufacturing process and measurement process of the flexible conductivity monitoring system for the curing performance of the composite material using a preferred example:

[0132] The composite material used in this example is an epoxy resin-based composite material. For the flexible conductivity monitoring system of the curing performance of the composite material, the sensor part uses silver nanowire electrode material and PDMS substrate material, which is prepared by laser etching patterning and drip coating. For the flexible circuit design part, PI-Cu substrate is used as the substrate material, which is prepared by wet etching process, reflow soldering and other processes. For the microcontroller processor, the low-power STM32L0 model chip was selected. In terms of wireless communication, a Bluetooth communication transmission module with lower cost, more stable data transmission and security was selected.

[0133] refer to Figure 3 , Figure 3 The present invention is a schematic diagram of the preparation process of a flexible circuit board. The flexible circuit board uses a 125 μm thick PI film as a substrate 101. A 20 μm thick copper layer is plated on the surface of the PI film by sputtering technology as the conductive layer 102 of the circuit board. The copper-plated PI film is cleaned to remove surface dirt and wet-etched. A corrosion-resistant solvent is evenly coated on the surface of the copper layer. After the solution dries, a protective thin layer can be formed on the surface of the copper layer. The desired conductive path pattern is obtained by exposing and developing it. Finally, the developed PI copper-clad substrate is placed in a copper wet etcher to obtain an etched copper conductive path. After the conductive path is etched, the STM32L0 chip, Bluetooth communication chip and other electronic components are integrated on the etched PI copper-clad substrate by using reflow soldering technology. First, the solder paste is evenly coated on the solder joints of the substrate, and the required electronic components are installed on the solder joints. The assembled circuit board is then placed in a reflow oven, where the high temperature melts the solder paste again and forms a reliable solder joint connection. After the reflow is completed, the soldered circuit board is taken out of the reflow oven and cooled to form the final flexible circuit board.

[0134] refer to Figure 4 , Figure 4The figure is a schematic diagram of the connection and packaging between the flexible circuit board and the flexible sensor. After the flexible circuit board is prepared, the packaging and connection between the flexible circuit board and the flexible sensor are carried out. First, the prepared flexible circuit 103 is fixed on the smooth glass plate 104 with double-sided traceless tape, and the rest of the glass plate is pasted with a PI tape 105 with a thickness of 55 μm and patterned. The patterned PI tape is realized by a laser cutting machine. Subsequently, the silver nanowire electrode solution is dripped on the cut part of the PI tape. After the silver nanowire solution is dried, the PI tape is torn off to form a conductive path 106 between the flexible sensor and the flexible circuit board and an electrode structure 107 of the flexible sensor. Next, a circle of 1 cm thick traceless tape is wrapped around the glass plate to ensure that the flexible circuit board, the flexible sensor and the conductive path between them are all enclosed. The prepared PDMS solution 108 is poured on the glass plate, and then the glass plate is moved to a horizontal place and left to stand for 5 minutes to allow the PDMS solution to be completely leveled. After being completely leveled, the whole thing is placed in a thermostatic box, the curing temperature is set to 60°C, and it is taken out after curing for 4 hours, the surrounding tapes are torn off, and then the bottom glass plate is removed, and the encapsulated flexible circuit board and flexible sensor and the conductive path 109 connecting them can be obtained. Finally, the PDMS encapsulation layer other than the conductive path between the flexible sensor and the flexible circuit board is removed by a cutting machine to obtain the main part 110 of the flexible conductivity monitoring system for the curing performance of the composite material.

[0135] The flexible sensor is attached to the surface of the composite material on the three-dimensional curved surface so that the electrode structure 107 directly contacts the surface of the composite material to monitor the signal during the curing process, and the data is transmitted to the computer for processing through the wireless Bluetooth communication module. Figure 5 As shown, Figure 5 The schematic diagram of the sensor integration system is shown in Figure 1. The power module supplies power to the system, which includes a battery module, a power management chip and an overcurrent protection device. The microcontroller unit (MCU) can be embedded with a real-time algorithm program, and is connected with a filter circuit, a temperature sensor, a flexible sensor, an I / O interface, a data storage module, a clock module, a crystal oscillator module, an AD conversion module, an antenna, an antenna communication module, a drive module and a signal generation unit. In the internal processing, the flexible sensor is connected to the I / O interface, so that the data collected by the flexible sensor is transmitted to the MCU, and stored through the data storage module (ROM / RAM) in the MCU. After being processed by the real-time algorithm program embedded in the MCU, the processed data is converted into digital quantity through the AD conversion module for output, and finally the output data is filtered and transmitted to the remote computer through the communication module.

[0136] refer to Figure 6 , Figure 6The flow chart of the measurement scheme is as follows. First, the program is initialized, and an excitation signal (i.e., the conductivity signal obtained by the sensor) is applied to the input. After the data is processed by the algorithm, ADC conversion is performed. A delay of 1-2s is performed and the ADC value is read and stored. After that, the software loop is repeated until the delay time ends. Finally, the excitation signal is removed from the input, and a delay is added before the next measurement to ensure that the circuit can operate stably. Finally, the monitored data is uploaded to the PC via Bluetooth, and the final curing degree data and glass transition temperature data are displayed on the PC. For reference, Figure 7 and Figure 8 , Figure 7 is the measured curing degree change curve of the above composite material, Figure 8 The glass transition temperature curve of the composite material is measured.

[0137] It should also be noted that the edge computing algorithm can be further integrated into the chip part of the above-mentioned flexible circuit board. The conductivity temperature expression, curing degree expression and glass transition temperature expression derived above are accurately written into the chip. In this way, the chip can display the curing degree and glass transition temperature of the composite material in real time.

[0138] However, there is an important problem in actual monitoring practice: in low temperature environment, the curing time of composite materials will be significantly prolonged. This characteristic causes the power consumption of the curing monitoring device to be rapid during long-term continuous monitoring. To solve this problem, the program design was optimized, and the monitoring functions of the flexible sensor and temperature sensor in the hardware part were fully combined with the function of real-time calculation of the conductivity, curing degree and glass transition temperature of the composite material in the software part. Three different working modes were designed, namely sleep mode (low-frequency monitoring), normal mode (medium-frequency monitoring) and fast mode (high-frequency monitoring).

[0139] Specifically, by comparing the curing degree values ​​at different times in real time, the system can automatically and dynamically adjust to the most suitable operating mode in real time according to the changes in the curing degree. The curing degree numerical comparison is chosen here because the curing degree can intuitively represent the curing status of the composite material. This method can effectively reduce the energy consumption of the system while ensuring that the monitoring accuracy is not affected, and achieve a balance between performance and efficiency.

[0140] Program initialization and startup: After the program is started, a comprehensive initialization operation is first performed. During the initialization phase, the system will perform self-tests on each hardware module to ensure that the temperature sensor, flexible dielectric sensor, communication module, and the computing unit inside the chip are in normal working condition. After the self-test is completed, the system applies an excitation signal and enters the normal working state mode (default mode). In this mode, the system begins to collect temperature values ​​and conductance values ​​of the temperature sensor and flexible dielectric sensor.

[0141] Sensor selection and calibration: The temperature sensor uses a high-precision thermistor sensor with a measurement accuracy of ±0.1°C, which can accurately sense the temperature change on the surface of the composite material. The dielectric sensor uses a capacitive dielectric sensor with a measurement resolution of 0.01pS for the conductivity value, ensuring the accuracy of the conductivity data collection. Before each experiment, the sensor needs to be calibrated by a standard temperature source and a standard sample with a known conductivity value to eliminate the sensor's systematic error.

[0142] Data acquisition and processing: After collecting the temperature and conductivity values ​​in real time, the conductivity value is converted using the relationship between temperature and conductivity, and converted into a value at a specific temperature. The reference temperature of the experimental environment is usually selected here, such as 25°C. In the data processing process, in order to improve the calculation accuracy, double-precision floating-point operations are used inside the chip. The converted data will be stored in the high-speed cache inside the chip, and then the curing degree at this time will be obtained based on the converted conductivity value and stored accordingly.

[0143] Working mode judgment and switching:

[0144] Data reading and comparison: Repeat the above data acquisition and processing operations, read the temperature and conductivity values ​​of the temperature sensor and dielectric sensor at the next moment, and convert and store the conductivity and curing degree again. Then, compare the curing degree values ​​recorded at the two moments. During the comparison process, high-precision subtraction and absolute value operation instructions are used inside the chip to ensure the accuracy of the comparison results.

[0145] Mode switching logic: For mode switching logic, the working mode of the system is determined based on the absolute value of the difference between the curing degree values ​​before and after. The conversion and comparison of the curing degree values ​​are uninterrupted. If the absolute value of the difference between the two is greater than 1%, it indicates that the curing process of the composite material is changing rapidly, and the system will immediately switch to fast mode. In fast mode, the data acquisition frequency will double, and its main purpose is to capture the dynamic information of the rapid changes in the curing process more timely and accurately, and provide users with high-resolution monitoring data. If the absolute value of the curing degree measured before and after is still greater than 1% after the data acquisition frequency is doubled, the acquisition frequency will continue to double on the previous basis. When the absolute value of the difference between the two is in the range of 0.1%-1%, it means that the curing process is in a relatively stable stage of change, and the system will continue to maintain normal mode. The monitoring frequency in this mode is moderate, which can ensure a certain monitoring accuracy while avoiding excessive energy consumption. When the absolute value of the difference between the two is less than 0.1%, it means that the curing process is nearing the end and its change speed is extremely slow. The system will switch to sleep mode to reduce unnecessary energy consumption.

[0146] Sampling frequency setting: In sleep mode, the system records data every 3 minutes by default, and adjusts the frequency range up and down according to the speed of the curing process. This lower sampling frequency can effectively reduce the energy consumption of the system during the slow stage of the curing process; in normal mode, the system records data every 1 minute by default, and adjusts the frequency range up and down according to the speed of the curing process. This frequency can ensure the data collection density in the general curing stage, which not only meets the monitoring needs of the curing process, but also avoids excessive collection; in fast mode, the system records data every 15 seconds by default, and still adjusts the frequency range up and down according to the speed of the curing process. This high-frequency sampling frequency can ensure that no key information is missed during the fast curing stage. These sampling frequencies have been verified by experiments. By comprehensively considering the curing characteristics of different stages, while meeting the data collection frequency requirements at different stages, they can effectively balance the energy consumption and monitoring accuracy of the system, providing the best monitoring solution for composite material curing.

[0147] Glass transition temperature calculation: After the real-time mode switch is completed, the glass transition temperature will be deeply calculated. Substitute the above-recorded conductivity values ​​and curing values ​​into the glass transition temperature formula. This process uses the powerful complex mathematical operation unit inside the chip for calculation. During the calculation process, in order to improve the calculation efficiency, optimized algorithms and parallel computing technology are used to quickly obtain the glass transition temperature of the composite material at this moment. The calculation results will also be stored in the cache inside the chip for subsequent transmission and analysis.

[0148] Data transmission and display: The communication module is started, which uses low-power Bluetooth technology to wirelessly transmit the recorded values ​​to the PC. On the PC, a special data analysis and display system is designed, which can receive and analyze the transmitted data in real time, and display the change curve of the curing degree and glass transition temperature of the composite material over time in an intuitive chart form. The operator can clearly observe the progress of the curing process through the software interface.

[0149] Monitoring end judgment: The system will repeat the above steps in sequence and continue monitoring and calculation. When the recorded curing degree value is basically stable, it indicates that the curing process of the composite material has been basically completed. When judging whether the curing degree value is stable, the standard deviation method in statistics is used to calculate the standard deviation of the curing degree value over a period of time and compare it with the set threshold (0.01%). If the standard deviation is less than the set threshold, the system considers that the curing degree value is basically stable. Compare the final stable curing value with 1. If the curing value is close to 1, it means that the curing has been completed. At this time, the system will automatically remove the excitation signal and complete the entire curing monitoring process; if the final stable curing value is much less than 1, it means that the curing is not complete, which may be due to unreasonable curing conditions. At this time, a signal will be sent to inform the operator to adjust the curing conditions. At the same time, monitoring will continue until the curing process is completely completed.

[0150] Through the careful optimization of the program details and experimental details, the above system can work more efficiently and accurately, providing more reliable data support for the study of the curing process of composite materials.

[0151] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A flexible conductivity monitoring system for composite material curing performance, characterized in that: It includes a DSC measuring device, a flexible sensor, a flexible data processor, a data transmission device and a display device which are electrically connected in sequence; The DSC measuring device is used to obtain the corresponding relationship between the degree of solidification and the glass transition temperature of the monitored object; The flexible sensor comprises a flexible substrate and a flexible sensing electrode wrapped by the flexible substrate on five sides, wherein the flexible sensing electrode can deform along with the flexible substrate so that an exposed side thereof is completely attached to the surface of the monitored object, and the flexible sensing electrode is used to obtain in real time a conductivity signal generated by the monitored object during the curing process; The flexible data processor is used to obtain a curing degree change curve of the monitored object according to the conductivity signal, and to obtain a glass transition temperature change curve of the monitored object according to the curing degree and the corresponding relationship; The data transmission device is used to transmit the curing degree variation curve and the glass transition temperature variation curve to the display device for display.

2. The flexible conductivity monitoring system for composite material curing performance according to claim 1, characterized in that: It also includes a flexible circuit board for carrying the flexible data processor and the data transmission device, and the flexible circuit board and the flexible sensor are electrically connected together and packaged into a flexible whole.

3. The flexible conductivity monitoring system for composite material curing performance according to claim 2, characterized in that: The flexible circuit board includes a polyimide substrate, a circuit pattern disposed on the polyimide substrate, and electronic components electrically connected by the circuit pattern and fixed on the polyimide substrate. The electronic components and the circuit pattern constitute the flexible data processor and the data transmission device.

4. The flexible conductivity monitoring system for composite material curing performance according to claim 3, characterized in that: The flexible circuit board and the flexible sensor are electrically connected by using silver nanowires.

5. The flexible conductivity monitoring system for composite material curing performance according to claim 4, characterized in that: The flexible circuit board, the flexible sensor and the silver nanowire are cured by using a polydimethylsiloxane solution to package them into a flexible whole, so that the exposed side of the flexible sensing electrode is still exposed to the outside.

6. The flexible conductivity monitoring system for composite material curing performance according to claim 1, characterized in that: The flexible data processor is used to obtain a curing degree change curve of the monitored object according to the conductivity signal, including: According to the formula ， Obtaining the curing degree α of the monitored object at time t, and obtaining a curing degree variation curve according to the corresponding relationship between α and t; Among them, log(G s ) is the logarithm of the conductivity value of the monitored object detected at the beginning of curing; log(G(t)) is the logarithm of the conductivity value of the monitored object detected at the solidification time t; log(G e ) is the logarithm of the conductivity value of the monitored object detected when the degree of curing finally stops changing.

7. The flexible conductivity monitoring system for composite material curing performance according to claim 6, characterized in that: The corresponding relationship between the degree of solidification and the glass transition temperature of the monitored object is obtained by using the DSC measuring device using the following formula: ， in, T gu is the glass transition temperature of the monitored object in a liquid state; T gcmax The maximum glass transition temperature of the monitored object when the degree of solidification finally stops changing; T g is the glass transition temperature of the monitored object at the solidification time t; ΔC pu is the heat capacity difference between the glass state and the rubber state of the monitored object in the liquid state at the glass transition temperature; ΔC pc It is the thermal tolerance difference between the glass state and the rubber state of the monitored object at the glass transition temperature when the degree of cure finally stops changing.

8. The flexible conductivity monitoring system for composite material curing performance according to claim 7, characterized in that: The obtaining of the glass transition temperature change curve of the monitored object according to the curing degree and the corresponding relationship comprises: Using the following formula: ， Obtain the glass transition temperature T of the monitored object at time t g , and according to T g The corresponding relationship between and t is used to obtain the glass transition temperature change curve of the monitored object.

9. The flexible conductivity monitoring system for composite material curing performance according to any one of claims 1 to 8, characterized in that: The data transmission device is a Bluetooth transmission device, and the display device is a remote terminal display.

10. A flexible conductivity monitoring method for composite material curing performance, characterized in that: Utilizing the system according to any one of claims 1 to 9, comprising: Taking out a portion of the sample of the monitored object and placing it in the DSC measuring device to obtain the corresponding relationship between the degree of curing and the glass transition temperature of the monitored object; Placing the flexible sensor on the surface of the monitored object so that the exposed side of the flexible sensing electrode is completely attached to the surface of the monitored object to obtain the conductivity signal in real time; During the curing process of the monitored object, the curing degree α of the monitored object at time t is obtained according to the conductivity signal, and a curing degree variation curve is obtained according to the corresponding relationship between α and t; According to the curing degree and the corresponding relationship, the glass transition temperature T of the monitored object at time t is obtained. g , and according to T g The corresponding relationship between t and glass transition temperature curve is obtained; transmitting the curing degree variation curve and the glass transition temperature variation curve to the display device in real time; The curing degree change curve and the glass transition temperature change curve are shown.

Images